i
h
a
p
H y d rogr
S u rvey i ng
c
.
a
bl
ad
Meth ods T
es
Form s
Notes
,
of
n
.
.
S A M U E L H I L L L EA ,
M A m S oc c E
.
.
.
.
.
NE W Y O R K
T H E E NGI NE E R I N G N E W S PU B L I S H I N G C O
1 905
.
.
zo ?
TA B LE O F C O N TEN TS
PA R T
H YD R O G R A PHI C
I
.
S UR V E YI N G
.
—
—
—
Obj ect O utline S urveys Traverse S urveys Con
l la
a
.
a
3
.
CH A P TE R I
—
—
—
duct of S urvey Topographic S urvey Other M eth od s C
—
ing Capacity S urvey of S ubmerged A rea
C HAP T ER
a?
II
a
—
oundings
Th e
S
M k i ng
.
t
cu
7
—
S oundi n g Party S hore
a
ent
Th e S ext n t
S o unding M achines
—
—
—
S ounding Ranges Range S ignals Bu o ys Locating S oundings
’
—
—
Coo per s M ethod B a
con s M ethod R eductio n of S oundings
25
A ssi st
Equipm
n ts
’
.
C
H A PTER
III
.
—
Book S ounding
Book
Platting
M aps and
r ts
Ch a
Notes
ad
n
—
Offi ce W ork S ounding
—
Bo ok A ngl e
—
—
Notes Co mplete Notes Tid e
—
Three A rm
Protractor H ydrograph ic
—
Notes S extant
Note s
.
-
70
—
C H A PTER I V M easurement of Dredged M aterial M easurement
—
t
i
c
a
in Place M easurement in S co w s— S urvey to Determine C a
y
p
.
a
—
of a L ke M ethod
by
—
Contour s M ethod by Cross S ecti ons
91
-
PA R T
ME A S UR E M E N T
OF
II
.
.
S T R E A M FLO W
-
.
a
—
—
CHAP T R I I ntroduction D ischarge S tati o n V el o city M e s
—
Float s— Current M eters—U se of Current M eters— M u l
u r em en ts
—
tiple M easurements M eth o d of I ntegration
1 03
E
C HAPT E R
.
II
.
M ethods of Field W ork—R ating Current M eters
R ating Table
Formula for D is
of Observations
—
M
charge
ethods and Computa
tion of Discharge W eir M easure
—
—
—
M
a
ments
easurement of H e d Conditions for A ccuracy D ischarge
Table and Conditio n s— Th e W etted Perimeter—Coefli c i len t of
Roughness— I rrigation Canals—Fl o w o f Water in Open Channels
—
—
n
R
Velocity Curves Coeffi c i e t o f eduction S ediment Obse rv
tion s
1 24
R eduction
,
'
a
P R EFA CE
In
.
thi s M anua l to the public the auth o r ventures to h ope
tha
t th e in formati on c o ntai n ed herei n may be useful to e n gi n eeri ng
s
s tude n ts and to the y o unger members of the pr o fessio n
s w ell
t o those en gi n eers of larger e x perie n ce wh o are n ot th or o ughly
familiar w ith the mi n or details o f H y d rograp hic S urv eying
Th e auth o r is conscious of the fact that much of the m tter con
ta
i n ed in the manual is elementary and that the hydraulic fo rmulas
a
re stated as nearly as practicable in their si m plest forms
While
t his is true
it is believe d tha
t the subj ect un d er c onsiderati on
hydrographic surveying does n ot require profo und discussi on nd
that plai n direct treatment of the subj ect matter will be pro ductive
o f the best results
No attempt has been made to introduce co mplicated mathematical
formulas int o the text si n ce it is believed that ultra re fin em e n t i n a
hydraulic fo rmul fo r discharge w o uld be out of place in view o f
t h e imp o ssibility o f making ordinary field m easurements with micro
s cO i c exactness
o
It
has
not
been
th
ught
necessary
to
g
o
deeply
p
i nt o theo retical or scienti fi c derivations of cause s and e ffect s
of phen om ena connected with the flow o f water S uch m tters are
fully covered in works on hydraulics of w hich there are a number
o f ex cellen t examples
’
I t is the auth o r s purpose to explain the pra
ctical fea
tures o f hydro
raphic
surveying
such
as
are
likely
to
be
encountered
by
the
g
t present to be learned
ctual practice and such as are a
s urveyor in a
M uch of the
o nly by actual fi eld exp erience in this class of work
i nfo rmation c o ntained in this manual was acquired by the author
l work and c on s equently has the
i n th e course of his profe s sion a
m erit of practicality
vored to limit the scope of th is manual to
s ende a
Th e author h a
s uch ordinary method s of hydrographic sur v eying as are likely to
It is desired
c o m e within the practice of the hydrographic surv ey o r
t this little b o ok will c on si tute a practical pape r on surveying s
th a
pplied t o hydrographic work and to embo dy therein ac oncise
a
explanation of modern methods of pract i ce
S A M U EL H LEA
New Y ork O ctober 1 90 4
ofi eri n g
'
,
a
a
a
.
.
a
,
,
,
,
,
.
a
.
a
.
,
.
,
.
.
.
a
.
,
.
.
,
,
.
.
PAR T
I
.
H YDROG RAPH IC S URVEYING
C H A PTE R
S u RVEY
—
S U RVEY TOPOGRAPH I C
A TI
—
RA V E R S E
S U RV EY S CO N D U CT OF
—
—
S URVEY OT H ER METH ODs CA Lé U
—
CAPA CIT Y S URVEY
NG
.
—
T
s
—
OB J ECT O U T LI N E
L
I
.
oP
S U B M ERGED
A REA
.
H y drographic S urveyi ng is applied to sur
ls a
n d o the r b o dies of water
ve ys of ri v ers lakes c a
na
Un der this
n d drai n age ar ea
head sh o uld be included surveys of water she ds a
s;
als o sttrvey s of basi ns or res ervoi rs for the stor age of water on a
Defini ti on
Th e term
.
‘
,
.
,
.
’
‘
large scale
.
Objec t
.
H ydrographic surveys are usually ma
de for one or more
of the fo ll o wing purposes
I To determine the outline of a body of water or of a w ater
s he d b si n or storage r eservoir
in o rder to obtain su fficien t i n for
rea surveyed
m ati o n from which to prepare an outline map of the a
an d to calculate the extent of the area c overed
2
To determine the dimensi o ns a n d the physical char cteristics
of a storage basin or reservoir in order to calculate its storage
c apacity
T
i
n
o
determi
e
the
ele
ations
of
a
su
cient
number
o
f
p
o
ints
n
v
f
fi
3
a submerged area to defin e the sub aque o us c o ntours o f th econtai n
ing valley or basin
i re
T
determine
the
discharge
of
a
river
or
stream
an
d
to
acqu
o
4
such i n formation as may be required concerning its physical charac
.
,
a
,
,
,
a
.
.
.
'
.
-
.
.
ter i sti c s
.
I t is evident from the foregoing that much of the field work con
with hydrographic surv eying is identical with that requ i red
i n m king o rdi n ary land or topo graphic surveys and is co nsequently
m o re or less familiar t o e ngineers and surv eyors in ge n eral I t is
not the obj ect of this manual to describe such w ork i n detail ; the
obj ect is rather to describe and explain such details o f h ydrographic
surveying as are not so generally familiar but which re necessary
for the proper execution of the work
n ec ted
a
,
.
,
.
a
HYDROGRAPH I C S U RVEY I N G
8
i
ai fi a
a
The v rious o peratio n s connected with hyd ro
graphic surveying may for conve n ien ce be classi fie d u nd er th e
fo ll ow ing h eads : I Outli n e S urveys ; 2 Topographic S urveys ;
S
urveys
o
f
ubmerged
A
reas
easurement
of
tream
F
S
M
l
o
w
S
;
3
4
These operations will be discussed i n order
Cl
ss
t on
c
.
,
,
.
.
.
.
.
.
O UT LI N E S URV EY S
.
a
a
re several kinds of outline surveys
There a
which may be cl ssi
fied according to the obj ect for which m de in three divisi ons s
foll o ws
aTo determin e the outline of a body of water of moderate size
a
s a small lake a river or a ca n al
b To determi n e the bo u n d ry o f a large bo dy of water s a b y
agreat lake or a large river
c
T o define the limits of a drainage area or of a
sto rage reser
voir a valley o r a basi n
Th e kind of surveys that are best adapted for the purp o ses m en
ti on ed will be discussed and their details explai n ed
a
,
,
,
,
,
a
,
,
a
,
.
,
,
,
a
.
.
.
TRA VE RS E S U RVEY
.
A n outline survey of a body of water of moderate size may be
co nducted as an o rdinary traverse using such field methods as are
best suited to the case ; such su rveys are usually made with transit
a
n d chain
W hen making a survey of this kind in order to obtain good re
s u l ts the transit points should be marked with hubs accurately cen
tered careful fore a n d back sights should be taken a n d the angles
The c ourses
should be rea d on the ver n ier to the nearest minute
sh o ul d be run at a
con venient di sta
nce from the water an d the po si
tion of the water line determined by measure m ents from the line of
the survey Th e position of the high water line when required
The details of the local t op o g
should also be deter m ined and noted
should
be
noted
with
more
or
less
minute
n
ess
depen
d
ing
upon
ra
h
p y
the importance of the work Pr o minent obj ects on s h ore that are
within conve n ient reach may be locate d by direct meas u rement
Obj ect s that are inaccessible or at a considerable distance from the
survey may be locate d by trian gulation as in the case of land sur
t two o r m ore tra n sit
veys sights being taken to each such obj ect a
stations f rom which the obj ect i s visible
Th e n o tes for a survey of this ki n d are kept in the s ame
N otes
ma n ner as for an ordinary traverse survey on la n d In Fo rm I i s
,
.
,
,
,
,
,
.
.
,
,
.
,
.
,
.
,
,
,
,
.
.
.
O
B J ECT
9
h o wn the fo rm of field note s o f an outline survey o f a lake m ade
’
u nd er the author s supervision In this survey a tra n sit an d l oo ft
st eel tape were used The a ngles were read on the vern ier a n d th e
magn etic bearings o f t h e courses were n o ted The survey w s a
little over 1 2 mi les i n length ; the n umber o f courses was large as
the shore li n e was very irregular requiri n g numer ous angles The
s urvey w s closed at the p o i n t o f begin n i n g ; the tra n sit was then
set up o ver this p o int a backsight was taken to the last tra n sit p o i n t
a
n d th e a n gu lar measurement betwee n the first and last c o urses was
ma d e in order to re determine the bearing of the first co urse This
was c o mpared with the first observ ati on made at t h e beginni n g o f
This di ffer
the surv ey and the di fference was f ou n d t o be 0
ence is within th e limit o f allowable erro r f o r a survey of this kind
and extent ; such error should n o t usually exceed 0
P r ty
Th e field party f o r a survey of this kind sh o uld be abo ut
the same as that required for an ordinary traverse on lan d or for a
railroad survey It is usually a good pla n to pr o vide i n ad d iti on
to th e regular sized party tw o tapeme n fo r maki n g si d e measure
ments t o l ocate the shore li n e a n d the local topography When such
additi o n is made the full party will co nsist o f a tra n si tman a fr on t
chainman a r ear chain m an tw o tapemen one o r m o re axe m en and
aback fl gm n On important surveys an en gineer i n charge will
be required in a d dition t o the fu l l party menti o ned On small sur
veys o r in cases where local condition s wi ll permi t the e ngi n eer i n
charge freque n tly acts a
s transitman
s
,
-
.
.
.
a
,
.
a
.
,
,
,
,
-
.
,
,
°
,
°
a
.
.
,
,
.
,
aa
,
,
,
,
.
,
.
,
.
O U T LI N E
OF
S TORA GE B A S I N
.
A transit traverse to determine the outline of a storage basin or
reserv o ir is c o nducted in a so mew h at di fferent manner to that j ust
described I n making a survey of this kind it is first necessary to
deter m ine the locati on of the flood li n e so metimes desi gnated as
the flow line Thi s is a
contour li n e at the height of th e proposed
surface of the impo unded or sto red wat er ; it is fixed by the height
of the storage dam being at the same elevation as the spillway or
overflow of th e dam W hen the dam is d esigned for overfl ow over
its entire l ength the elevation of the crest of the dam is taken as the
elevation of the fl o w line The location of this line on the gr o und
a
round the peri m eter of the proposed basin or re servoir fixes the
limits of the bas in and is the obj ect o f the survey I n order t o c
co m plish this obj ect it is necessary to have a level party to design ate
the po sition of the flow li n e on th e ground in addition to a tran sit
party to determine its l oc ation
.
,
.
,
.
.
.
,
.
a
H YDROGRAPH I C S URVEY I N G
ID
CO NDU CT
OF
S URVEY
.
aki n g a su rvey o f this ki nd th e lev el party s ho ul d keep
bre st o f o r slightly ah e d of th e tran sit party i n o r d en to i nd i
t
h
e
t
positi
on
o
f
the
li
n
on
t
h
e
gr
o
u
nd
T
h
e
li
n
t
h
e
e
fl
o
f
O
w
e
e
c ,
s u rv ey i s ru n as cl o se as practicabl e toth e flow li n e s i d e m easure
m ents being m ade t h eret o when necessary
P rty
The tra n sit party sh o ul d be abo ut the same as fo r a lake
surv ey
I f care is ex erci sed i n fitti n g t h e surv ey line to th e flo w l in e
the si d e measureme nt s wi ll be s ho rt ; t h ey c n then be estimated or
m d e by the level party o r by th e chai n m n and in such cases n o
tapem en w ill be req uired I n m any cases ho wever i t will be th e
f
o
art
ec
o
n
o
my
t
o
pr
v
ide
tw
o
tapemen
f
o
r
making
side
measure
O
p
m e n ts t o the fl o w l i ne as i n the case O f a lake survey for determ i n
i n g th e shore line
W h en this is don e th e w ork will be fac i litated
n d the general pro gr es s O f th e party accelerated
T h e level party s ho ul d con si st of level l er n d a rodman S i nce
i n s urv ey Of this ki nd there are n o v ari ti on s in elevation to over
c o me the wo rk c on sisti n g in foll o wi ng
c o ntour line the l evel
p rty shoul d experience but l i ttle difficulty i n keep i ng up with the
t r n sit p rty
I n a w ooded or brushy country it is goo d practice to provide a
‘
xemen to facilit te the pro gress of the survey
sufli ci en t n u m ber of
It is econo my always t o h ve pl enty o f help especially o f the
cheaper grade o n a surv ey party since b y this means it i s practicable
t o accelerate the general progress O f the s urvey and thus lessen the
total c o st Of the work
S T ADI A S URV EY S
It is frequently the case that ou tline hydrog r phic surve y s c n be
In such
m ade wi th the t ransit a n d stadia with satisfact o ry results
cases the method O f procedure is entirely similar to that foll o we d in
maki n g o rdi n ary stadia surveys The stadia sta tions are est b lished
at suit ble p o ints al on g the bo u n dary o f the area to be surve yed
Det i l S Of t op ography a n d the configu r ti bn of the shore li n e l i n the
case Of a bo dy of water o r of the fl o w li n e i n the case of a rese r
Vo ir are determi n e d by si d e sh o ts
Ot h er than stadia meth o ds re frequently employed for making
s those in u se for
sur veys o f this kind ; suc h methods are the same a
I n many cases the
l nd surv eys where the conditions are similar
t
e
o advant a
fi
l
n
able
can
be
used
e
esp
cially
i
n
lling
i
n
t
o
t
e
g
w
p
graph i c details ; this in strument has been much used by the en gi n eers
Of t h e U S C o ast a nd Ge o detic S urvey f o r w o r k o f this n tur e
In
aa
a
m
a
.
.
-
a
,
,
.
.
.
a
a
.
a
,
.
.
,
,
,
,
a
.
.
a
a
a
a
”
a
a
a
,
a
.
J
,
.
,
.
.
a
a
a
.
,
,
,
.
a
a
.
.
a
a
a
.
a
'
.
,
,
a
.
,
a
a
.
,
.
.
a
.
OB ECT
a
J
II
Wh ere great accuracy is n ot required
c ompass travers e w il l
O ften prove en ti r ely satisfact o ry i 9 r maki ng o u tli n e s u rv ey s Of
bod i es of w ate r
I n survey s o f this n ature the di st n ces re Inc s
ured w ith a l oo ft chai n nd t h e be ri n gs are read wit h the need l e
as i n th e case o f a n o rdi n ary c o mpass l n d survey
,
a a a
,
.
,
a
a
a
.
-
.
,
.
4
TR I A N GU LA TI O N S URVEY S
.
a
t o determine the o ut l ine o f a large body of w ater as
3
r
e
at
lake
large
river
a
b
etc
genera
ly
b
st
ma
d
by
e
e
e
l
gr
y
I n such cases the methods usually em pl o yed fo r
tri n gu lati on
u
ri
n
g
lati
on
w
o
rk
are
f
o
llowe
d
those
b
est
adapted
f
o
r
the
w
rk
i
n
o
;
t
h an d sh o uld be used
A good metho d of tri
angu lati ng a river O f Con
si d er bl e size is illustrated
in Figure I A base lin e
as 1 2 is fi rst carefully
measured with a steel t pe
the extremities Of the b se
being marked with sto ut
p
or
hu
b
s
carefully
osts
Fi g l Tr i n g u l t i on of Ri v e r
ce n tered
A ll the othe r
e
oints
a
n
d
distances
o
n
b
o
th
sides
the
river
are
determi
n
d
by
f
O
p
ngu l r measureme n ts the tra n sit occupying successively the dif
feren t trian gu lation statio n s ; the di stances betwee n stati on s are cal
Cu l ted by trigonom etry W he n such a survey is of con sid erable
-6
ex te n t it is usually
good plan to measu re the fin al c o urse as 5
with a steel tape as a check upon the accuracy o f the instr um e n tal
In order to Obtain good results each observed an gl e sh o ul d
w o rk
be m easured not less tha n three times the mean Of t h e several
rea d ings being taken as the true readi n g
S tud i o Wor k
In a survey o f a river where th e dist nce between
d
opposite ba
nks is not too great st d i m eth od s C n be used to a
va n tage i n connection with trian gulati on or traverse surveys I n
such a case a goo d m ethod to foll ow for such work is to ru n a
transit l i n e do wn on e bank of the river the distances be tw een
stations b eing carefully measure d with a steel tape a n d the angles
at all deflection p o ints being repeated i n o rder t o guar d against
possibl e erro r Poi n ts o n the oppo site b n k c n be l oc ted by i n ter
secti o n the dist nces being determined by stadia I n this way fairly
ccurate re s ult s can be obtained at mo derate expe n se
'
S urveys
a
a
,
,
a
,
.
a
,
,
.
.
.
a
,
.
-
a
,
a
,
‘
a a
.
.
aa
‘
,
.
.
,
a
a
.
,
,
.
‘
,
a
a
.
.
aa
,
0
'
,
.
,
,
a
.
,
a
aa
a
.
.
'
HYDROGRA PH I C
12
S
TOPOGRA PH I C
URVEY I NG
S U RV EY S
.
aa
made t o determi n e the topographic featu res o f w ter
shed or drai n age area
o r o f a reserv o ir site are esse ntially topo
graphic surveys an d as such require n o extended treatmen t i n this
m n ual
I n modern practice stadia methods are exte n sively used i n s urvevs
of this nature ; many Of the United S tates D eep W aterways surveys
were made with tra n sit and stadia I n the Un ited S tates Deep
Waterway s topographic surveys on the Blac k a n d S l mon rivers
co nducted by M r W B Landreth M em ber A merican S o ciety Civil
Engineers and descri b ed b y him in th e Tra n saction s O f the A merican
S ociety O f Civil Engineers the meth o ds used were both simple a n d
e ffective Th e fo ll o wing account of these surveys is taken from
the description above referred to ; it i s cited as a go od example O f
m odern pr ctice f o r such w o rk
S u rveys
,
a
,
,
,
.
a
.
.
.
.
,
,
,
,
.
a
Pa
a
d
O
y
.
party co nsisted O f the en gineer in charge
a transitman a rec o rder three o r more stadia ro dmen a draftsman
a com puter and two o r more axemen W hen running levels th e
head stadi arodman was deta
ched from the mai n party for that
pu rpose
The out fit consisted o f a transit fitted with stadia wires i ts h o ri
zont l limb reading to 2 0 sec o nds and its vertical re t o single mi n
utes ; a stadia rod for each ro dman a wye level a n d level rod a large
canvas umbrella a tin megaphone a I OO ft steel tape and the
n ecessary out fi t of d rawing table instrum e
n ts etc This equipme nt
is the same as that o rdi n arily used f o r a survey Of this nature with
the addition o f the umbrella and the megapho ne Th e former i s
quite useful fo r pro tecting the observer and his instrument from
the weather ; it is no t c ommonl y used however in ordinary surveys
A meg aphone is serviceable in trans m itting directions from the
observer to other member of the party ; it is a moder n innovati on
n d h s not come int o general use
a
Th e fi eld wo rk w s conducted in the m nner usually
Fi el d Wor k
dopted on surv eys where distances are determi n ed by stadia The
a
engineer in charge selected the base li n e p oi n ts t o be occupied and
located the stadia po ints on circuits so arranged as to cover the
E ach stadia
territory fully ; the party followed closely behind
rodman was assigned a particular class of Obj ects to l ocate ; on e
followed the streams an o ther selected c o ntour p o i n ts another locat ed
roads buildings woo ds etc Th e rodmen all wo rked i n depen d
ently O f each other ; when convenient all were kept on the same
rt
Th e
u tfit
n
.
,
,
,
,
,
.
.
a
a
,
,
,
,
,
‘
-
,
,
,
.
,
.
,
,
.
'
,
a
.
,
a
a
.
.
.
,
,
.
,
,
,
,
,
.
B J ECT
I
O
3
sid e O f the transit in orde r to facilitate th e r eading and platti n g of
th e a z imuths
When working on stream s of considerable size a circuit w s run
al on g o n e bank and the to p ography on bo th sides Of the stream was
t k en therefrom
In d o i n g this the corps Of ro dmen was divided
i n to two parties on e part y being kept on each side Of the stream
during the Observati on s
I n surveying a large stream that w s
fro zen over a circuit was run on the ice a n d the to po graphy on
both sides was located therefro m
The topography of cr ooked streams that were no t frozen w s
l o cated by means Of a circuit which was run so as to cro ss th e
stream at the bends and t o include as much o f the adj acent t opo
graphy as possible In such a case part of the ro dmen w o rked on
each bank and the remainder o f the party crossed the stream fr o m
y
i
n
t
to
point
as
the
surve
pro
ressed
o
g
p
Thi s m ethod i s
i llustrated in Fig
in which the
2
full li n e A B C
D rep rese n ts the
base line an d the
dotted li n e I 2 3
~
represents
a
cir
4
cuit
r eas
W oo ded
were surv eyed by
ow
n
s
t
i
d
F
i
S
2
methods suited t o
g
the local topo graphical c o nd i tions For deep h oll o ws or gorges a
circuit was run al o ng the to p of each blu ff the sl ope on either side
being take n from the line o n the opposite bluff Fo r l ong gentle
l p es a circuit was run al on g the top n d the fo ot o f each slope a n d
sho rt circuits were ru n co nnecting them so spaced as fully to cover
the territory surveyed
All streams roads buildings outlines O f woods to wn and c ou nty
lines were located Tw o corners Of each building were generally
l o cated by the Observer the rodman measuring the di m ensions with
his ro d and gi vin g the data to the recorder when passing him
’
A t the close Of each day s field work the field
Office Wor k
party reduced an d checked the st a
di a
readings made during the day
l s o the vertical angle elevations The ofli ce fo rce calculated the
latitudes and departures Of the stadia circuits Tw o o r more field
books were in u se at o ne time the recorder changing bo ok s each
a
.
a
.
a
,
.
,
a
.
,
,
.
.
.
,
,
,
.
,
,
,
,
a
.
.
v
i
o
u
.
,
a
.
,
,
.
,
,
,
,
.
,
.
.
a
,
.
.
.
H YDROGRA PH I C S URVEY I NG
14
d l a
vi ng
aa
a
boo k u sed i n the field on the previo us d y to r
’g
use Of the Ofli ce fo rce
In the i n s ta nce that has been cited the si z e o f th e party was
i
h
s
r
ter
t
n
o
rdinarily
used
for
making
survey
o
f
this
k
i
n
e
s
g
d
When r pid w o rk is req uired and the office w o rk is t o be ke pt u
p
with the field wo rk it is adva ntag eo us to have a large party
Usually h o wever in s urveys of this nature a sta d ia party cons ist
i ng o f five m en will be o f sufli ci en t size
S uch a party shoul d
con sist o f a n i n strument man a reco rder and three rod m en Wh en
req ui red o ne o r m o re axemen or labo rers sh o ul d be a dd e d to the
p rty for cutting brush rowing a bo at etc A party of this siz e
w it h no Ofli ce force wi l l n ot be able t o keep the fi eld n o tes written
up nd th e reductions made by evening work I t is therefo re
nd
d v is ble t o take a d va n tage of stormy days to do Ofli ce work a
whe n n ecessary to keep the entire party in the Ofli ce for a d a
to
y
catch up with the Office work
d y,
n
e
th e
.
a a
a
’
.
,
,
,
,
.
,
a
a
.
,
,
,
.
,
,
,
aa
.
,
,
,
,
.
,
.
OT H E R M ET HODS
.
are other methods in comm o n use for making topo graphic
surveys The meth od which is perhaps most c om m only employed
for this purpo se is that which is som etimes called the railroad
meth o d fro m the fact that it is generally used in topographic ra i l
road surveys This metho d req uires the use O i base lines c refu l l)
ru n with tra n sit and ch in with secon dary lines at right a ngles
the ret o all elevation s being taken with a level I n o pe n country
the pla n e table can be used to advantage to loca te the topog raphy
in which cas e the e levations are taken with a l evel as when an
o r d i n ary tr nsit is used
For close wo rk in a w ooded country the transit and level I s
s
nerally
referable
For
an
open
country
the
stadia
method
i
e
g
p
bo th ra p id and econ o m i cal n d is su ffi ciently accurate for ordinary
There
.
,
a
,
a
.
,
'
r
,
”
.
,
,
a
.
.
,
.
S URV E Y
.
a
OF
S TORAGE R ES ERVO I R
.
A survey to determine the capacity of a valley o r basin for water
stora
ge is usually a topogra
phic survey which can be made accor d
ing to one of the methods th at h a
ve bee n described ; care sho uld b
,
e
a
taken to u se such m ethods as re best suited to local condition s
I
I n practice there are tw o general methods suitable for d eterm i n
i ng the cubical capacity O f a stora g e reservoir ; these fo r
Conv enience m y be respectively designated as follows
S
M
by
Contours
thod
by
Cr
ecti
ns
2
h
o
t
e
s
e
o
d
s
o
;
LAM
d
m et hody i s d pted to its own s pecial pur pos e ; su ch m etho
a
,
aa
.
f
,
,
.
”
.
HYDROGRA PH I C S URVEY I N G
16
t r it is impo r ant that the m o st advantageous location for build
a
d maintai n i n g the dam sh ld be sele ted
in g a
Consideratio n
w
t
e
n
ou
c
s
.
a ffecti n g the v olume of water to be impo u n ded the cost of the d am
i ts safety mai n tenan ce etc will d ecide the ch o ice of locati o n
In
n y i n stances there is usu ally one site that is preeminently adapted
m
abo ve all others for a d m a n d in such a case the survey is made
with respect t o a dam to be built at this site In some cases h o w
eve r o ne Or m o re sites o ffer pparently equal advantages as l o ca
ti on s for a d am a n d in such ca s es a thorou gh examination should
be made t o d etermi n e th e best site
It will n o t be ttempted in this ma n ual to discuss the variou s
’ i
facto rs fl ect n g th e ch o ice o f a dam site since s uch c o nsideration s
are withi n th e province of the engineer rather than that of the
hydro graphic surveyo r Th e function of the surveyor for whom
this manual is written is to co nduct i n the best man n er such hydro
graph ic surveys as are intrusted to him ; and the scope of thi s
man ual will be con fined t o such work
Th e site for the dam having been s elected the
Fl ow Li ne
elev ti on o f the overflo w or spillway is fixed ; this determines the
height o f th e water su rface The el evation of the overflow is often
decide d by th e safe height to which the dam may be built S ome
times it is fixe d by th e permissible he i ght to which water may be
all o we d t o rise in the basin ; or by the elevation of the surrounding
high gro u nd ; o r by other factors dependin g upon loc l conditions
I n some cases the elevati on of the surrounding high gro und above
c tor i n fi xing the elevation of the
the dam site is the deciding fa
s pillway
The survey having been made atopog raphical m a
i
drawn
s
p
upo n which the position of the flow line is platted accur a
tely to
scale ; as are also th e positions of the severa
l contour lines whose
vertical distances apart are d etermi ne d by the h eight o f th e contour
interval
The o utline of the proposed dam is also platted showing the
crest and the to e o f sl o pe on either side The resulting figure will
resemble t h at shown at
Fi gure 3 in which the fl o w line an d the
successiv e co nt o urs are sh o wn by the irregular full l ines and the
outline o f the d am is design ate d by the full line across them Th e
intersection of each conto ur line with the face of the da
will form
m
straight line from side t o side of the valley as S hown
ti ng th e A r e
The nex t step is to carefully calculate
C l cu l a
separately th e area enclosed by the flow line and by each contour
l i n e Th e m o st convenient and expeditiou s meth od o f calcul ting
,
a
.
,
,
,
,
.
a
a
,
a
a
.
,
.
.
,
,
.
a
.
,
.
.
a
.
.
,
.
,
.
,
a
,
.
,
.
a
a
a
.
,
.
.
.
a
OB J E C
T
l
7
platted areas with irregular bo und a
ries is by means of the plan i
m e ter
By carefully usi n g this instrument upon an area draw n
ccu ratel y t o scale very close and accurate results can be obtained
a
A planimeter is not always available h o wever and where such is
t h e case areas can be quickly c o mputed by platting them t o scal e on
,
,
.
.
,
,
,
.
,
()
c
Cr
M p
n
os s
a ad
S
a
t S if
ec t i on
e of
‘
a
D
m
.
a
R
i
g
cro
ti on paper as shown in Figure 4 Th area
included within
each co n to ur li n e is then determined by c o unting th m a
ll squares
ad fracti ons o f squares enclosed therein ; the aggrega
te w ill be the
total area o f the surfa
ce considere d This is a pr a
ctical and satis
facto y metho d i determining ar a
s of irregular figures where
F1 3 3
.
C on t
ss sec
-
ou r
S
e ct
i on
of
-
,
S t or
e
e s erv o r
.
e
.
e s
n
.
r
o
mathematical exactness is
e
no t required
Cross secti o n paper
-
.
is
18
H
YDROG RAPH I C S URV EY I N G
cheap and easily obtainable and irregu lar figures can be rapidly
platted thereon
Another meth o d of determini ng such areas is to plat them care
fully to as large a scale as possible on drawing paper ; then d ivide
th e figure into triangles by me ns o f lines drawn between selected
po ints on the bo undary The area of each triangle is computed
sepa
rately an d the sum of the pa rtial areas added together fo r the
entire area W here the bo undary is very irregular that portion o f
the figu re between the boundary line and th e adj ace n t straight li n e
fo rming the side of a triangle ca n be cl o sely approximated by
dividing the included a
rea into small figu res approxi m ating trape
n d carefully computing these partial
a
zoi d s or trian gles in form
a
reas
,
.
a
.
.
,
,
,
,
aa
aa
.
C l cu l ti ng th e C p ci ty Th e r
reas encl o sed by th e several
a
‘
.
T
r
"
T
“
“
“
f
T
1 _ _L _
T
contours having been c om puted
I
L_
the reservo 1 r may be con s1d ered
a
s consisting of a series o f pris
m oi d s whose bases are the areas
encl o sed by the flow li n e n d by
the successive conto ur lines an d
whose altitudes are the c ont o ur
intervals A longitu d inal sec
tion from the upper en d o f the
reservoir t o the dam is show n at
A cr o ss secti on of
b Figure 3
th e valley at the dam site is
l
shown at c in the same figu re
The capacity o f the reservoir
can be calculated either by the
method or average end areas or
Th e r
by the p r i sm odi l formula
first method will give only p
prox imate values a nd sh oul d no t
1
be used when cl o se results are
req uired The sec ond method is
l
far m o re accurate a nd should be
1
L
4
1
L
u sed wh ere a close pp rox 1m
s
D
w
4
a
on t o
on
C
tion is req uired
t
h
G os s S
Pa
p
A n example will
Ex m pl e
be given sh o wing the results obt ine d by each method usi ng the
sa
ta in each case Th e capacity of the reservo ir ill ust r te d in
m e da
,
a
,
,
.
-
.
,
.
a
.
a
-
.
a
a
4
ur
.
a
n
r
,
r
a
.
,
.
-
e c
on
e r
,
a
OB J ECT
Fi gu re 4
n d the n
a
a
l9
th o d o f
w i ll be c l c ulated fi rst by th e
by th e p rismoi d al fo rm ula
m e
,
ge e n d ar a
aa
;
ver
e s
.
Let A o = th e
area enclosed by the flow line
Let A I = the area encl o sed by fi rst c o ntour
Let A , = th e area encl o se d by s ec on d c on to ur
Let A 3 = the area encl o se d by thi rd con to ur
Let A 4 = th e area enclose d by f o urth cont o ur
Let A , = the area enclosed by fi fth con t o ur
Let A, = the are encl o se d by sixth cont o ur
Th e c o ntour interval i s five feet
Then by the method of average end areas :
a
.
,
h (A1 + A22
h SA
2
2
2
V3
2
=
e tc
h
(1 )
.
I n thi s fo rmula v , v v3 v etc are the v o lumes o f the figure s
e nclosed by the fl o w line and by the successive con to urs a nd v i s
the volume of the entire reservoir S ubstituting the give n values i n
the abo ve formula and reducing we have discar d ing fractions
=71 5 5 c u b ft V z =5 323 cu b ft v 3 =40 25 c u b ft v4 =2860 cu b ft
=
=
vs
1 5 5 3 cub ft v . =5 5 8 cub ft
Th e r efor e v 2 1 474 c u b ft
Wh en the prismo idal formula is used tw o adj acen t prismo ids re
con sidered as o ne and every alternate area is use d as a middle area
I n such a case the height of each prism o i d is twice the c ontour
i n terval By the prism o idal fo rmula representi n g th e respecti ve
a
reas by A 0 A A 2 etc an d the respective partial vo lumes v , V,"
v s etc
and the tot l volu m e by v and the altitude of each prism oi d
by 2 h we have
.
,
2,
4,
,
,
.
,
.
.
.
.
.
.
.
.
,
,
.
.
.
.
,
.
a
.
.
.
,
,
.
,
,
a
,
.
,
,
,
,
=
v.
=
v.
h-
S ubstituting
fracti
ons :
( Ao+4A I + 2A z+4A 3+ 2A 4+4A 1 +A ol
(2
a
k no w n values and reducing we have disc r d i ng
,
,
=
2 I 40 2 cu
ft
v
I f the reservo ir is divided into an o dd number o f prism o i d s i n
clu d e d betw ee n a d j acen t c on to urs it is ev iden t that when the p ri s
p ri sm o i d fo r which th ere
m oi d l f o rmula is applie d there will b e
will be no known middle area I n such a case this fin l prism oi d
can be calculated separately by th e meth o d o f average en d are s ;
th is will usually i n volve no gr eat err o r when the prismoi d is at th e
,
.
.
,
a
,
,
.
a
,
a
a
HYDROGRAPH I C
20
S
URV EY I N G
bottom of the reservo i r sin ce in that cas e its volume is small co m
i
s
are
d
with
the
remaining
volume
A
more
exact
way
h
o
wever
p
to i n terp ol ate a middle area between the two final areas an d then to
c o mpute the v o lume o f the o dd prismoid by the prismoidal formul a
M eth od of I n terpol ti ng A re s Th e most practical and ex
n two adj acent
a
way
to
interpolate
middle
area
betwee
i
i
e
d
u
s
t
o
p
areas who se outlines are know n is by the graphic meth o d on cross
s ecti on paper I n order to do this draw the lines bo undi ng the two
adj acent areas accurately to scale in their relative positions on
cross section paper ; then draw a third line
midway between the two adj acent boun
da
ry lines Thi s third line will be th e
bou n dary of the middle area s ought ; thi s
s
rea is computed in the same manner a
a
that described for computin g the other
areas This method i s illustrated in Figure
in
which
the
dotted
line
is
the
boun
M
5
da ry of an interpolated area between the
nd
next larg er a
the next sm a
ller areas
l_ L 1
re spectively
_
1
I n the fore going calc ula
tions n o a
llow
F1 9 5 M t h o d of
a
nce has been made for the space in the
channel O f the stream w hich i s shown flowing through the valley
s ince the successive contours ha v e been taken simply to the surfac e
of th e water in the stream W hen close results are req uired it will
usually be nece ssary to take a
ccount of th e stream ch a
nnel below the
nd a
d d it to th e
water surface to calculate its volume corre c tl y a
vol ume a
lr ea
dy obtained for the ba sin
,
.
a
,
,
a
.
.
,
.
,
,
-
.
.
,
.
.
.
1 _1
L
.
L
.
J
_
.
.
e
,
.
,
.
.
M ET H OD
BY
CROS S S E C T I O N
-
.
ca
i n c l ose result s i n c o m p u t i ng
s e it i s not nec essary to obt a
volume s the method by cross sections i s by far th e cheaper n d
m ore ex p edit i o us of the two m ethod s for dete rmi n i n g the ca p ac i t y
of a storage r es ervoir W he n t h is me thod is u sed the flow line i s
loc ted on the gro und by on e of the meth o ds previously describe d
t
re t a
k en from side to si d e of the re serv o i r a
a
n d cross s ec ti ons a
Gen er a
l l y it i s a good plan to fi rst m a
ke th e o u t
s uita ble intervals
e
w i ng p a
l ine survey and then to plat it accurately to s c ale on d r a
p r
Th e plat having been made the best locatio n s for ta k i n g the cross
n
r e selected
In the case O f an extended survey around a
s ections a
rea of c onsiderable size selection s can frequently be made s the
a
survey p ro gresses and before i ts fin al completion The cro ss section s
In
a
-
a
.
.
-
.
.
,
.
a
,
,
-
.
J
OB EC
T
2 1
a
shoul d preferably be pa rallel i n o r d er to en cl o se between adj cen t
sectio ns figu r es resembli n g trapezoi ds s cl osely as p os sibl e Thi s
will result i n regular figures nd will ren der th e com put tions
l
r
e
tha
n
if
the
cross
secti
on
s
are
no
t
parallel
p
a
a
a
.
-
.
FI g 6
‘
.
.
Ou
a
M p
t lm e
of
S t or
a
g
e
Re s e r
v oi r .
ground within the flow line has a
fairly regular sl o pe the
sectio n s sh o uld be taken where the best results can be had in de
t erm i ni ng super ficial areas
I f however the ground is broken n d
i rre gu lar a s u fficient number o f sections should be taken to a fford
fa
irly well proportioned figures U sually the number o f secti on s
t aken i s govern ed by the clo seness O f result s required and by the
i m p o rt a
n c e of the s ur vey
I f th e
.
,
,
.
.
a
2
H YDROGRA P H I C
2
S
U RVEY I N G
p o i nts havi n g bee n selected lines are run acro ss the valley
c on necti ng the survey lines on either side These li n es sho uld be
sta k e d a n d the p o i n ts where their extremi ties i n tersect th e su rvey
li n es c refully n o te d ; als o the plus es and angular distances
Lev e ls
re then ru n o ve r the cro ss secti o n lines in o rder to determ i n e t h e
a
cro ss secti on pro files
In o rder to give a practical illustrati on of this method a plat of
reserv o ir is sh o w n i n Figure 6 i n which M N is the d am site a n d
th e li n es n umb ere d 1 2 3 4 etc represent the successive co urses
o f a n o utline survey followin g cl o sely the flow li n e which is rep re
s e n ted by the irregular do tted line
The parallel section s A B C D
E F etc divi d e t h e surface into trapezoids wh o se b ases are the
ho riz on tal proj ections o f the respective section s an d who se side s
are those portio ns o f the flow line included between adj acent sec
ti o ns The flow line is usually irregu lar but m y be co nsidered
straight bet w een adj acent secti o ns since when the survey li n e is
closely run i t will usually lie about as much within as without the
flow line The super ficial area enclose d within the flow line c n
be determin ed by computing the area of each trapezoid separately
It is not always n ecessary
( 1 adding the partial areas together
to determine the superficial area of a basin or reservoir but such
knowle d ge is Often d esirable and c a
n usually be acquired with but
little extra labo r In order to determine the capacity of the reser
vo ir it should be treated as a solid figure compose d of a series o f
figures cl o sely resembling pris m o ids whose bases are t h e cro ss
sections that have been taken and whose altitudes are the perp en
d i cul a
r distances between adj acent sections
This will be the case
when all the sections are parallel as they should preferably be for
convenience in calculation I f the outline of the reservoir i s very
irregular it m y be necessary to take the sections at di ff erent angles
instead o f p rallel I n such cases the resulting figures w ill not
usually be prismoids and their volumes should be calculated bv
s uch rules of mensuration as are applicable to them
Each instance
of this kind sh o uld be treated as a special case ; the example given
here is applicable to parallel sections Th e capacity of the reservoir
will be found by aggrega
ting the volumes of the several prismoid s
lly resemble wedges in form
a
n d of the two end figures which usu a
Th e volumes can be calculated by the m ethod of average end areas
or by the prism o idal form ula as previously explained A n example
will be given in t h e
s howing the applicati o n of the se two methods
ting th e contents of a lake ;
d escripti o n of the m ethod for calc u l a
this will apply t o
reservo ir since the two figures are similar in
shape
eneral
g
Th e
,
,
.
.
a
.
-
-
a
.
-
,
,
,
.
,
,
,
,
,
-
-
.
,
.
,
-
.
,
,
,
a
.
,
’
a
‘
.
.
,
.
,
,
.
,
a
a
.
.
.
.
.
.
,
,
a
.
,
.
2
HYDROGRAPH I C
4
S
U RV EY I NG
a
a
sh o re li n e a n d the necessary to pogr phy havi ng been l oc ted
t h e n ex t step i n a surv ey of this ki n d will be t o measure the d ep th s
bel o w the w ter surf ce o f a su ffi ci ent number o f p o i n t s t o sh o w
t h e con figurati o n o f the bott o m
This o perati on is anal ogo us to the
taki n g of levels in a t o pographic su rvey ; i t di ffers e ssentially in
de t il h o wever since in a to pographic survey the po ints where l evels
are taken are previ o usly l ocated while the measurem en ts bel ow the
w ter surface must be l o cated at the time they are made Th e
pr ocess o f making such measurem en ts is called M aki ng S ou nd i n gs ;
it will be d escribed in detail
Th e
a
a
,
.
a
a
,
,
,
.
.
,
CH A PTER
S ou N DI N Gs—TH
II
.
—
S OU N D I NG PA RT Y S HO RE A SS I S T
A N Ts
EQ UI P M EN T
S O U N D I N G M A C H I N ES
TH E S Ex
—
—
—
—
T A N T S O U N DI N G RA N GES RA N GE S I G N A LS B U OY S LO
’
’
—
—
CA TI N G S ou N DI N Gs
COOP ER S M ET H OD BA CO N S M ET H OD
R EDU C TI O N O F S OU N DI N GS
M A K I NG
E
.
are usually made either with a p o le or with a lead li n e
a
cco rd ing to th e depth of the water For depths o f about I 8 feet
or less a s o un d ing pole can be used to adva ntage ; fo r greater depths
it is custo mary to use a weighted line common ly called a lead line
S oundings are usually made from a bo at and s o u n di n g o perati o n s
g enerally req uire a party familiar with the w o rk to be don e an d an
equipment suitable for the w o rk in hand The S ize of the p rty
and the ki nd of eq uipment req uired in maki n g sou nd i n gs will vary
acco rding to the nature o f the lo cality where the s o un d i n gs re
made the exten t of the area to be sounded the meth o d used for
locating th e soundings and l ocal conditions of tide current etc
S oundings
,
.
.
,
a
a
,
.
,
,
ay
,
,
,
.
W hen s oundings are made i t is usually nec es
sa
ry to l ocate them in o rder that their positi o ns may be platted on a
map or chart A complete sounding party will therefo re include
in a
dditi o n to those req u ire d for mak ing and recordin g the sou n d
in gs the obse rvers who locat e the s oundings a
n d such assistants as
may be neces s ry accordi n g to the method of location used For
convenience the various members of the s o undin g party may be
classi fied as foll ow s : a
observers or instrument men ; b so undin g
c rew ; c boat cre w : d a
ssistan ts on sh o re
S ou n d i ng P
rt
.
,
.
a
,
,
.
,
,
.
ob s ervers wh o locate the positions o f the sou nd
i ng s a
r e stati o ned at selected points on sh o re except when the l o ca
tions are made from the boat in which case the obse rvers are
stati o ned in the s ounding boat
On e or more observers may b e
required depending upo n the method of location Th e duties of the
observer s will be ex p lai n ed in detail under the head of Lo cating
S o u ndin g s
O bs er v ers
.
Th e
.
,
.
.
,
“
”
.
sou nding crew usually co nsists of a t e
aleadsman and aS i gn a
co rder
lman In some c se s the recorde r
S
ou n d i n
,
r
ew
C
g
.
Th e
.
a
HYDROGRAPH I C S U RVEY I N G
26
at
as
c s
aig
al m an a nd i n special cases where great rapidity i s
the work tw o lea d smen are used who mak e sou n di n gs
n
S
req ui red i n
altern ately
,
,
,
,
.
The reco rd er is pro vided with a
n ote boo k in which
he reco rds the depths as they are ascertai n ed and called o ut bv th e
leadsman H e als o o bser ves a nd no tes the exact time when each
observed sounding is m ade an d perfo rms such other d uties as may
These duties will be ex plai n e d i n d etail in
be assigned to him
descri b i n g th e vari o us m ethod s of l ocating soundi n gs
R ecord er
.
,
.
.
.
.
aa
The lead s m a n is u sually an imp o rta n t m ember of the
s o u nd i n g crew si n ce upon his skill an d rapidity the progress of the
s o u nd i n g party is largely depen d e n t I n shall ow water where a
soundi n g po le is used fo r determining depths th e leadsma n st nds
up on a platfo rm in th e fo rward part of the b o at a little back of the
bo w a nd near one side In making a sou n ding h e plunges the po le
in t o the wate r h oldi n g it in such a man n er that it will beco me
vertical when the foo t o f th e po le reaches the b ottom I f the bo at
is in m oti o n as will usually be the case the foot of the pole is
thrust ahead at a sufli ci ent angl e to reach th e bo ttom at the sam e
time the boat pr ogresses far eno ugh for the pole to become vertical
i n the hand s of the leadsman A t the proper ti m e the leadsman
notes the depth o f the water on the po le and calls it out in feet and
ten ths to the rec o rder ; he the n draws up the pole a n d prepares for
the n ext s o unding In withdrawing the po le fro m th e water th e
leadsman pulls it up until the foo t is withi n a sho rt dista n ce of the
surface then he bre ks it d o wn over the side o f the bo w in fro nt
of him letting it rest there until the next sounding A good lead s
man will after a little practice bec ome q uite expert in withdrawing
the s o unding pole fro m the w ater i n the ma
nner described as well
as in casting it forward to co nform to the motion of the boat
Whe n a lead line i s used the leadsman should for each so u n ding
endeavo r to have th e line truly vertical and with o ut sag when th e
lead touches the botto m and the depth is read I f the s o u n ding boat
is i n m oti o n he should cast the lead ahead all o wi n g th e line to ru n
o ut freely until j ust befo re the bo ttom is reache d when the line is
a
ulled
taut
causing
it
to
assume
a
vertical
p
o
siti
o
n
as
the
le
d
p
to uches the bott o m When s o un d ing in a stream o r in water where
there is a current the l e dsman sh o uld be careful not to all o w his
li n e to sag o r belly under the a
ction o f the current befo re noting
th e d epth
A little practice will enable a skillful leadsman t o d eter
n d the
m i ne the ex act ti m e
t which th e lead t o uches the bo ttom
Le ds m
n
.
,
.
a
,
,
,
,
.
,
,
.
,
,
,
.
.
a
,
”
.
,
,
,
,
.
,
,
.
,
,
,
.
,
.
a
a
a
I
I
M A K N G S OU N D N GS
27
beco mes truly vertical at which tim e th e rea d i n g sh ou l d be
t ken Th e l e d sman sh o ul d b e tho ro ughly fam ili r w ith th e m rk
i ngs on th e l e d li n e d enoti n g depths a nd i n re d i n g the d epth o f
a s o u nd i n g h e sho ul d be ab le to q uickly estimate on a li n e gr du
ate d t o feet th e ne rest te nth o r half foot as may be re q uire d H e
observes th e t g n ex t abo ve the water i n o r d er t o d etermi ne th e
co rrect d ept h H e sh o ul d call out i n a clear d istinct v0 1ce th e
observ e d d epth o f e c h s o und in g to th e r ecor d er who repeats th e
call t o v o i d mista k e befo r e enteri n g it i n h is no te b oo k A t suit ble
intervals when req uire d the lea d sma n notes the character o f the bot
to m as sh o w n by the m terial adheri n g t o the bo ttom of the l e d
an d calls it o ut t o the recor d er I n with d rawing the lea d fr o m th e
wate r after a s o u nd i n g the l ea d sma n sh o ul d lay the li n e n eatly i n a
coil o n the platfo rm up on which he stan d s bei n g careful to have
successive co ils co me i n their pr o per places one ab o ve the o ther in
or der that th e li n e will n ot fo ul o r bec o me tangle d as it is pai d o ut
for the n ext s o un d ing With a little practice the lea d sma n w ill
usually learn to gage his spee d s o as to make each sounding at the
correct tim e This is impo rta nt when rapid w o rk is req uire d H e
sh o ul d carefully no te the co nditi on o f hi s line the appearance of the
tags marking the g raduati ons and the security o f the fastening o f
t h e line to the lead
H e should at all ti m es be careful to ma i ntain
h i s equipment in serviceable condition
l i ne
a
a
a
.
a
,
,
,
a
a
a
a
a
,
,
,
-
.
,
,
.
a
.
a
,
,
,
a
a
.
.
,
,
,
,
a
,
.
,
,
,
.
.
.
,
,
.
.
aa
In sounding operation s when the s o un d i ngs are
located by observers stationed on sh o re it is cust o mary to have a
n d o no ti fy t h e ob servers whe n to make observati ons
si gn l m
The
signalma n is usually prov i d e d with a small flag which he h o lds in
his ha n d rais i ng a nd l oweri n g it s d irected by the rec o r d er to
m ake th e si gn als
I n so me cases tw o flags on e re d a nd the ot h er
r e u s ed , ge n erally t h e white flag is use d fo r o rdi n ary
w h i te
soundi n gs an d the re d flag den o tes every fi fth o r every te n th s o un d
ing thus servi n g as a check upon the num beri n g of the observed
soundings S ometimes o ther forms o f s i gn a
ls t h an flags are u sed ;
in either case the s i gn a
lman sho u ld see th a
t th e si gn a
ls are properl y
displaye d
S i gn l m
n
.
,
aa
,
.
,
,
«
,
t,
a
.
a
,
,
,
,
,
.
.
aC
nd
composition a
size of the crew for the
s ou n ding bo at will d ep en d mainly up on the ki nd o f bo at use d ; als o
upon l o c l con diti ons o f wi n d current and ti de I f a ro w boat is
crew o f fro m tw o to six oarsmen will be required in ad d itio n
u s ed
to a st eersman I n sm ooth water where there is little o r n o current
Bo t
r ew
Th e
.
a
a
,
.
,
.
,
,
HYDROGRAPH xc
28
S U RVEY I N G
tw o oarsmen will usually be sufficie nt I n a stron g cur ren t f ro m
fo ur to six o arsmen will be neede d the latter n u m ber if th e boat i s
large n d i f a wind is b l o wi n g T h e auth o r in s o u nd i n g o per ti on s
on the M ississippi R iver where an ordi na ry row bo at w s u sed
fo und that four o rsm en fo rm ed a crew o f s ufficie nt size for o r d i
na ry serv ice
In s o u n ding upon a ra n ge or where it is necessary to
S teersm n
keep th e bo at on astr ight course a steersman is necessary In
so me insta n ces when few s o u n dings are to be m de or where rapid
work is not req uired the rec order or the signalman acts as steers
This arra ngement is n ot practicable however when rapid
n
m
progress is require d
Th e dutv o f a steersma n i s to keep the s o un d i n g bo at s cl o sel y
re
s p o ssib l e on the range o r c o urse upon whic h th e s o u nd i n gs
W hen traversi n g a ran ge he sights fro m th e front to t h e
m ad e
t all times as nearly as
bac k ra nge signal keepi n g both sign als a
possible in li n e as the bo at m oves W h en there is a strong curre nt
r e acro ss the stream
as in the case o f a river a nd when the ra nges a
as is freque n tly the case it is practically impossible to maintai n the
boat directly al o ng the range I n suc h cases a good plan is to start
th e bo at upstream and all o w it to d rift across th e range ma k i n g
the sounding j ust as the ra n ge is reac h ed
In cases where the cur
re n t is not t oo str on g a nd where th e range exte nd s acr o ss it t h e
boat m y be kept on r nge by holding its bo w q uartering upstream
a
s it m o ves al on g
Pow er L u nch
I f a steam or power launch is used for a s o u nd
i n g bo at a much s m aller crew will be re q uired tha n for a ro w bo at
I n such a case a full si z ed crew will consist o f an e n ginema n a
s to ker and a steers m an
In s ome instances only an engi n ema n a n d
a sto ker are used fo r ru nn ing a power la u nch ; the sto ker then acts
s steersman w h en required
a
.
a
a
,
a
a
,
.
,
a
,
.
'
a
.
,
a
,
.
,
,
a
,
.
,
,
a
.
a
a
.
,
,
.
,
,
,
.
,
.
a
a
,
a
,
.
.
.
,
.
I n so unding operati on s where ran ges a
nd
ra nge sign als are used it is usually n ecessary to h ave on e o r m o re
a
ssistants on s ho re to attend to th e signals In ca
ses w h ere m ov able
ign als are use d the sh o re assista nts after s o u nd ing work has been
finishe d on a given range take u p the sign als from th a
nd
t range a
m o ve th em o ver to place o n the nex t range to be s o un d e d Th e
sh o re assistants in addition t o placi n g the range p o les or si gna
ls
rran ge the pro per targets thereon to desi gn ate th e d i fferent ran ges
a
Sh
a
re
a
A ssi s t
n ts
.
.
,
,
.
s
,
,
,
.
,
,
and attend to such other details
amay be required
s
,
.
M A K I N G sov xnm c s
a
ay
a
Ti d e G ge R e der
i t is
sh ore
a
d r
re
a
ll y
t
a
y
p
n ecess r
us u
r
con si
e
to
st
in
a
a
a
d
g g
t
ve
e re
e
t
o
es
observ
i nter v l s th e
requi red
i
ai d ga
aa
g
a
d
a
b
a
i d ga
ha a
g
f ai d ga
i
g
i ng a
d
i ng a
di ng f h ti d
a
I n ti d l w ters , w here
.
Th e d u t
.
29
o
re
a
s
e
m em
e
s used .
er of
th e
e
e
t
n ot
n
er
t
t e
e
force nd di recti on o f th e
w i n d ; th i s i n fo rmati o n is rec o rd ed by hi m
in
note boo k p ro vided for th e pu rp o s e
By refer ri ng to this no te book t he stage
n y time duri n g t h e s ound
o f the water at
ing work can be determ ined
The regular equipment re
Equ i pm en t
quire d fo r m ki ng so u n di ngs c onsists of
apparatus and s o u n ding boat
so unding
The appa ratus o rd i na rily used c on sists o f
c
either a sou nd i ng po le or a lead lin e a
cording to the depth of the water to be
s o unded
S ou n di ng P ol e
A s o unding pole sh o uld
be of suitable length fo r the purpo se re
quired usually fro m 1 2 to 1 8 feet ; it sh o uld
be suffi ciently thick to a ffo rd the requisit e
s trength but not too large around for c on
v en i en ce in handling
S uch a p o le is usual
l y ma d e ro und in cross secti o n gradually i n
c reasing i n size from t o p t o bottom ; with
two plane faces diametrically o ppo site each
other upon which the graduations re
Fo r convenience of observation
mar k ed
bo th faces are usually graduate d the gra d u
The pol e
a
ti ons being in feet and tenths
should be m ade of t o ugh
durable w oo d
3m
referably
ash
or
hickory
the
lower
por
;
p
ti on sh o uld be snugly fitted into an iro n
sh o e o r s o cket which is pro vided with a
F13 7 S ou n d i n
g
flat d is k shaped base This base sh o uld
be large en o ugh to prevent the pole sink ing
in s o ft material when restin g u p on the bottom : it can he prov i ded
with a cup s h aped cavity o r h o llow fo r brin gi ng up sa m pl es o f th e
r e d es i red th e cavit y i s c o t ed w i th
W hen such sa m pl es a
bottom
n
e
th e
a
.
a
.
.
a
.
,
.
.
,
,
.
-
a
,
.
,
.
.
.
,
.
-
.
,
-
.
a
HYDR OGRAPH I C
0
3
S U RVEY I N G
a
tall o w o r with a prep ration of yellow s o ap and beeswax to wh ich
th e p rticles o f sand or mud adhere
A good form of s o unding pole is illustrated in Figure 7 which
sh o ws the shape of cross sectio n and the gra d uations ; th e zero o f
the gr d u ti on i s at the bo ttom of the iron shoe Th e rod sh o uld
be painted white with the figures design ating tenths in black an d
th o se denoting feet i n red as in the case o f a level rod
a
,
.
,
aa
-
'
.
,
,
a
.
A lead line for s o unding work co nsists of two parts
vi z the lead or weight and the line The lead i s made of s om e
dense h eavy material usually lead hence the name ; it sh o uld pre
fer bly be slen der in fo rm s o as to o ffer slight resistance i n passing
th ro ugh the w ter S ou n ding leads are ma d e in various patterns
that s ho wn at a
in Figure 8 bein g a comm on form This fo rm is
Le d Li n e
.
.
,
.
,
a
,
,
,
~
a
.
,
.
Ir on Rod
S
e c ri on
Pl
ai
n
Le
a
d
.
a
d
L a
h
d
i
t
w
L
b
e
( )
F39 8
.
S
o u n
d i
n
e
g
s
.
ma d e o f a si n gle piece o f lead slightly co nical in shape ; t h e upper
part is n arro w and flat with a h o le in it thro ugh which t o fast en th e
line A t b is sho wn another and m o re elaborate fo rm o f lead
which is sometimes used when especial care is required in obtai n ing
samples o f the b otto m A n iro n rod I has moulded arou n d it the
lead which gives the req uisite weight A t the l o wer en d is attached
th e cup 0 which is c o vered with a leather washer w that slides freely
on th e iro n ro d The cup sin ks in the material of the bottom and
fills ; when it is bei n g draw n to the surface the pressure o f the water
h o lds the w a
sher down on the cup and preve n ts the conten ts fr om
escaping W hen no t needed the cup ca n be rem o ve d i n w h ich
cas e t h e lead is used as a n o r d inary s o u n di n g lea d Th e w eigh t
o f a so u nd in g lead fo r o rd i nary so und ing w o rk varies fro m 5 t o 2 0
,
,
.
,
,
.
,
,
.
,
,
.
,
.
.
H YDROGRAPH I C
2
3
a An i
URVEY I N G
po rtant part of the eq uipment of a s o und
i ng party is a boat si n ce bo ats are req uire d in mo st s o u nd i n g
operati on s Fo r ord i n ary work where the area to be c overed i s
not large an ordinary row b o at p referably o f the cutter pattern W i ll
S uch a bo at s ho uld be as light as possible c on sistent
be ad eq uate
with safety to per
mit of be ing q uic kl y
m aneu vered ; also
to
a
llow being beach ed
as quickl y s possi
ble i f necessar y by
rty in
the s ou n d i n g p a
t
Pl a f S
di g B
Fi g 9
i n case a rough
weather It should have n ea r the bow on either S i d e a
p latfor m
up on which the lea d sman can sta n d when s o undin g ; also suffi cient
seati n g capacity for the re quisite number o f oars men a
n d other
m embers of the bo at party
Lockers or c o m partments should be
r locks
pro vided in th e b o w and the stern where spare lead lines o a
n d where sextants o r other i n stru m ents can be
etc ca n be kept a
laced
f
o
r
protection
fr
o
m
rain
or
for
other
purpos
s
I
n
Figure
e
p
9
is sho w n in plan a sketch o f a row boat suitable for sou n ding w ork
Wher e a large a
rea is to be sounded or where local c on diti o n s
w i ll permit it is usually advisable to use a s m all steam o r gasoline
launch fo r sounding w o rk S uch a
bo at is much m ore co n venient
for t h is purpos e than a ro w boat I t can be handled with a smaller
c rew
is capabl e of greater sp eed and can be more rapidly
man euvered than a
r ow boat I n modern practice the p o wer launch
has to a large extent superseded th e row boat for use in s o unding
work
S O U N DI N G M A C H I N ES
A lth o ugh the u s e of machine s in sounding work is not common
there are frequently occasion s when such devices may be a
dv n
t geousl y used
S uch apparatu s i s n o t part of the regular equip
ment o f a sounding party ; since however ma chines are s om etimes
u se d
fo r s o unding a de scription of s o me of the m o re mo d ern
mach ines will be given here a
lso an account of the meth o ds em
pl oye d i n using them
V arious forms o f machines h a
ve been u s ed in s ounding work ;
most of these were designed for the special conditions under which
they were to be used
i
A simple form of s o unding m achine consists o f a drum or wind
lass of go o d size m ounted upo n a
s u itable fram e or suppo rt and
S oundi ng B o t
.
S
.
m
,
.
,
,
,
,
.
,
,
a
,
.
ou n
o
n
.
oo
n
,
.
.
.
,
,
.
,
,
.
,
,
,
.
.
,
‘
,
.
.
,
,
.
.
.
a
,
a
.
,
,
,
,
.
.
,
,
M
A K I N G S OU N D I N GS
33
revolv ing on a
horiz o ntal axis The s o undi n g li n e is w o und aro un d
th e d ru m
and is pai d out o r w o und up acco rdi n g as the lea d i s
l ow ere d o r raised On the rim of th e drum is a registering device
which indicates the d epth o f the lead at any po int I t is so arra n ged
th at the registration is z er o wh en the bottom of the lead is at the
surface o f the water The principle upo n which the registratio n is
bas ed is that each revo lution of the dru m wi n ds or unwi n ds a
ce rtain len gt h of the s oun d i ng line ; this length of co urse c o rre
spon ds t o the circumference o f the drum
This fo rm of machi n e is
es peci ally adapted for use in s o unding thr o ugh ice In such cases
the machines are m o unted up o n wheels or ro llers i n o rder that they
can be re a
dily moved from po int to p oint as the sounding w o rk
progresses :
A fo rm of s o u nd in g machine similar in principle to that j ust
describ e d is illustrated n d described in Engi n eeri ng N ew s A u gu st
1 90 2
in an art icle w ritten by Ott o Gersbach The illustrati on
Figure 1 0 and the accom pa n ying description of the machine are
abstracted from this article The machi n e c on sists pri n cipally o f a
dru m 4 feet in circum fere n ce a nd I S in ches l o ng with a sm ller
d rum 4 i n ches in diameter and 6 inches l on g as sho wn in Figure
I O These are carried by a § é i nch axle pr o j ecti n g 3 i n che s beyo nd
the suppo rts at each en d T he who le machi n e is mo u n te d in a gas
pipe frame A round each pro j ecti n g e n d of the a x le is wou n d a
piece o f light picture wire which exte n ds around pulleys and
acro ss the face of the large drum and is attache d to a sli d ing
carriage which carries a p o inter fo r showi n g the rea d ings This
wire is w o und i n o p po site directi on s aro un d the axle at either end
in such a ma nn er that as the drum revolves to lower the lead th e
po inter m o ves fro m right to left A s the lead i s raised the po i nter
m oves to the right
The s o unding line co n sisting i n this case of a
Th e
wire is w o und aro u n d the e xtreme left of the larger dru m
mai n part o f this drum is graduated as sh o w n a n d from the se
A r o und the smaller
g raduati on s the recorder takes his rea d ings
drum is w o un d a
inch rope for revolving the larger drum i n
or d er to raise and lower the lead
s done after the machine had been fi tted up
The gr aduatin g w a
The drum w s first divided by four h o rizontal lines which were a
foot apart These d ivision s were subdivided into te nths by lighter
line s parallel to the o thers The spiral divisi on li n e extending
a
ro und the drum
was fi rst t raced by a pen cil po in t hel d fi rmly
on the pointer while the dr um was ma d e to revolve
.
,
.
.
.
,
,
.
.
,
a
,
,
,
,
,
.
,
a
.
,
,
,
,
,
~
.
,
.
.
,
,
,
.
.
,
.
.
,
,
.
,
.
-
,
.
a
.
,
.
.
,
,
,
.
HYDROGRAPH I C S U RV EY I N G
The machine is place d
o n a base which rests and
is fasten e d fi rmly in the
back end of the sounding
boat but the cut sh o ws it
m o unted o n a pile o f logs
for convenience in ph o to
graphing In use one man
operates the machine by
the ro pe which works v ery
easily ; a second man does
the rec o rding while a
third rows the boa
t T h is
machine was desi gned by
E
R
B
en
C
ich
C
r
M
c h i ne
Fi g 1 0
S ou n d i n g M a
for sounding work in Lake
M ichi gan at I ndiana H arbor I nd Th e machine shown in Figu re
exclusive of wooden base
1 0 was made by a tin s mith and cost
,
.
,
,
,
.
.
.
.
.
.
,
.
,
.
.
,
,
.
,
,
A noth er form of soundin g mach ine
Fi g
.
11
.
is
S ou n d i n g M
s
hown in
ah i
c
ne
II
Fi g ure
.
Thi s
.
s
e
r
N
w
e
i
n
e
i
n
E
n
mach ine which w a
il
str
ted
and
described
in
lu
a
s
g
g
J une 1 8 1 90 3 was invented by M r R M Pardessu s of N ew
e
o
ndon
onn
I
t
con
i
t
of
a
transverse
sweep
bar
attach
d to
s
s
s
C
L
the outer ends of two arms which are pivoted one on each si de o f
abarge or float and which extend backward down into th e water
l
n
t
fl
i
i
c
su
e
o
r
sweep
mad
of
a
piece
of
railr
ad
ail
e
i
s
The
y heavy to
give th e necess a
ry w eight for keepi n g it on the bott om A t the
w
h
ich
s
t
u
r
i
n
a
r
d
o
c
en d of the pi voted arm s is a re
u pper f
pp
g
m arks th e p ro file of the bottom on a strip of paper move d by
cl o ckwork ; the vertical m otion of the pen is t ake n by levers from
th e pivoted s weep arm w h ich evidently varies i n i n clinati on with
positio
t
h
e
sweep
speed
o
f
the
bar
e
an
d
the
m
o
tio
n
T
h
e
o
f
g
n
th e
,
,
,
,
.
,
.
.
.
.
,
,
.
,
,
aa
.
,
.
,
M
A KI NG
SO
U N D I N GS
35
of the paper being adj usted to a kn o wn rati o the cu rve trace d on th e
paper is a scale pro file of the botto m alon g the ra n ge o ver w h ich
the s o un d ing barge moves
Fo r c o nvenience in reading depths directly there are two vertical
gage rods one on each side which are hi n ged t o the e n ds o f th e
sweep and pass vertically along the side o f the barge ; these r od s
are graduated to sh o w the depth s o unded Th e gage rod s are
utilized als o to throw o verboard a marki n g buoy at every poi n t
where the b ott om forms a rid ge o r hillock risi n g abo ve the pro per
l evel ; the manner in which this is accomplishe d is clearly sh o wn i n
the figure Wh enever either e n d of the sweep with th e co rrespond
s a fo ot or more a proj ecti n g pi n o n the
ing gage rod rises as much a
rod lifts up a marking bu o y previ o usly laid in pro per po siti on on
deck an d throws it overbo ard
This fo r m o f soun d ing m achine was desi gn ed for use i n s o un di ng
dredged waters ; it h s been used by government en gi n eers in
examining harbo r and channel dredging at New H ave n Conn
S till an o ther fo rm o f sou n di n g machine was d escribe d in E ngi
1 90 4 from which the illustrati o n i n Figure
n eeri ng N ew s J u n e 1 6
12
n d the acc o mpa n ying descripti on have bee n abstracte d
It con
,
.
,
,
,
.
.
,
,
,
,
.
,
a
,
a
,
,
.
,
.
Fi g
.
12
.
S ou n d i ng
M
ah i
c
ne
.
sists o f a
raft s upporting a s o unding batten provided with a piv o t
where it passes th rough the raft There is a
weight at the l o wer
end of the batte n t o keep that en d submerged Th e upper en d act s
as a finger and i n d icates on a circular re the depth o f the water
on which the apparatus is fl o ating
This so under is t o we d al on g
si d e a
steam launch over the course or range to be s o un d ed The
observ er sit s at a table in the launch an d is pro vided with a s h eet
.
,
.
a
.
.
.
H YDROGRAPH I C
6
3
S
URV EY I N G
cro ss secti o n paper on which the vertical lines refer to po sition s
l ong the sh o re which are indicated by co rrespond i n g numbers in
pla n lying befo re the observer Th e horizontal rulings refer to
d epths belo w the datum used o r to heights abo ve it
A s th e laun ch proceed s al ong a river at a kn o wn spe ed th e ob
s e rver marks the depths indicate d by the sounder at the pr o per
po ints on the section t o correspon d with his positi o n al o ng the river ;
these depths are belo w the water line at the instant o f taki n g the
ob servations without reference to the height o f water relatively to
th e datum used
A t suitable intervals say ab o ut two miles water
ges
are
xed
on
t
h
river
banks
the
zero
of
each
gage
bei
n
g
fi
e
g
referred to the datum ; as the launch passes each gage the water
le v el an d the time are no te d
the
water
W hen the obser ver has finished so unding for the da
y
level as rea d from the gages is drawn on the ruled diagram fo rm
as indicated o n the sect i o n use d on the
n d the s o u nd ed depths
lau n ch are transferred from depths bel o w the water li n e at the
i n stant of taking the observations to depths bel o w corrected water
l ev el relatively to th e d atum This system of observing a n d t e
co rding s o undings admits of ver y rap id executi on It is h o wever
d apted for use i n comparatively sh ll o w water say for depths o f
abo ut 1 5 feet or less
H aving d escribed the methods use d a n d the equipment req uired
i n ma k ing s o undi n gs it is next in o rder to describe the vari o us
meth od s empl oyed in locating s oun d ings The l ocati on o f s o u nd
ings is usually e ff ected by instrumental o bservatio n in c o nnecti on
with base li n es and sounding ranges o r suitable obj ects on sh o re
wh o se po siti ons are know n The instruments used i n making the
observations are respectively transit c ompa
ss p lan e table a nd
En gineers and surveyors in general are m o re or les s
s extant
familiar with all of the instruments mentioned with the exception
this instrument being generally used for nautical
o f the sextant ;
observations fo r which it is ad a
pted S ince it is o ften use d in
lo cati n g soundings it is thought advisable to give a descripti on o f
this instrumen t together with an explanati o n of its principles a
nd
th e method of usin g it
TH E S EX T A N T
The sextant is a hand instrument for measuring angles ; it i s
especially a d apted fo r u se in a bo a
t where the m otion o f the w ater
re nd ers the use of a fixed instrument impossible The sextant d e
rives its n ame fro m the exten t of i ts g raduated re which is abo ut
the sixth part of a
circle
of
-
a
a
,
,
.
.
,
,
a
,
,
.
,
.
a
,
,
.
,
,
,
.
a
a
.
,
,
,
.
,
.
,
.
,
.
,
,
,
.
,
.
,
,
.
.
,
a
.
,
.
I
I
M A K N G S O U N D N GS
is a cut of a sextant sh o wing i ts
c on st ructi o n It co nsists o f a metal frame C D E t o which is
attache d the tw o mirrors B an d C the telescope F a n d the index
The arc D E which is called the limb is gra d uated into
b r C S
1 2 0 or 1 60 e q ual parts ; each part is equal to half a degree of arc
Descri pti on
In
37
.
Figure
13
,
.
a
,
,
.
,
,
Fi g
.
13
.
S ext
a
nt
.
but is marked as a who le degree in acco rdance with a principl e
that will be explained Th e gr duati o ns are su bdivided i n to pa rt s
1 5 or
correspo nding t o
according to the size and perfecti on
of the instrument A t C and B are shown two glass mirrors whose
planes are perpendicul a
r to the plane of the frame B is called th e
h ori z on g la
i ts lower half is silvered while the upper half i s
ss ;
transparent ; it is ri gidly attached to the frame o f th e in strume nt
C is called the i ndex gl s s or i nd ex m i rr or It is attache d t o the
index bar C S which is m o vable on the limb D E ar ound an xis
which is centered under the index mirror The planes o f the t w o
m irro rs are parallel whe n the zer o mark o n the index bar coincides
with the zero mark o n the limb F is the telesc o pe which is screwe d
i n to the collar 0
a
,
.
'
.
.
,
a
.
.
,
.
.
.
a
HYDROGRAPH I C
SU
RV EY I N G
a
T h e v e rn ier plate V is attached to the i n dex b r imme d iately
bel o w the gra d uati on s on the limb ; the i nd e x bar is fasten ed t o the
lim b by m eans o f a cl amp screw T is a tangent scre w b y which a
s l ight m oti o n ca n be gi ve n t o the i nd ex b r after i t h as been
M is a magn ifying glass fo r reading th e gr a d uati on s on
cl ampe d
N an d L are col o re d shades t o pro tect the
th e l im b and vern ier
eye w h en making observati o ns towar d the sun ; they ca n b e turn ed
back o ut o f the way w h en n ot needed
Theory of th e S ext nt The d esign o f th e sextant i s base d up o n
ray of ligh t i s refl ecte d fr o m a pl n e
the p ri n ciple t h t w hen
Th
su rf ce th e a n gles o f incidence a nd o f reflecti on are e q ual
followi ng dem o nstra ti on o f theory is o ff ere d : I n Figure 1 4 let S C
,
a
.
.
.
a
a
a
.
.
a
a
.
-
a
Fi gJ A i l l u s t r t i n
g
.
P ri n c i
l
e
p
of
S
ad at
i
-
n
.
i n cident ray and C B the reflected ray ; S and S are the t wo
obj ects betwee n which it is required to determine the an gle S O S
The i n strument is hel d i n such a po siti on that its pl an e passes
thro ugh bot h o bj ects while the inde x bar is clampe d at th e zero A
s o th at th e tw o mirro rs are parallel with each othe r Th e in d ex
be th e
'
-
'
.
,
,
.
,
HYDROGRAPH I C
S
URV EY I N G
a
a
who se to p is ho riz on tal and sight t o some obj ec t s th e
w ll o f
roo m abo ut 2 0 feet d ista nt ; an d mark on the w ll th e
place where the li n e o f sight over th e h o rizon tal wire strikes Tak e
tw o small pieces of woo d each o f a le ngth e q ual t o the height o f
the center of a telesc o pe above the plane o f the re ; set the pieces of
wood o n the re as far apart as possible a n d sight o ver their t op s
to ward the point marked on the wall I f the tw o lines o f sight
c o rrespo n d the adj ustment is correct ; i f they d o n ot c o rrespo nd
adj ust the telesc ope by means of the small adj usting screws in its
collar so as t o correct the error S ome instruments are provided
with a pair o f small peep sights for use in makin g this test
box
or
a a
,
,
.
a
,
a
,
,
.
,
.
,
.
in perfect a d j u stment the in d ex
reading will be zero when the reflected and direct images o f a
s a star coincide
dista n t obj ect a
In many cases h o wever it wil l
be found that when tw o such image s are made to co i n cide the zero
point of the index arm will be either to the right o r to the left of
the zero point on th e limb Th e reading o f the inde x is then calle d
the index error U sually this error i s small and i s n ot co rrected by
a
dj ustment sinc e s uch adj ustm ent would disturb any other adj ust
ment o f the sextant The index error is usually a
pplied as a cor
rection t o the observed angular readings I f when the tw o images
the zero o f the index is to the right o f the
a
re ma d e t o coincide
zero of t h e limb the index erro r is said to be off the arc a n d is
d d itive I f the zero p o int o f th e i n dex is t o the left of the zero
a
on the re a n d is subtractive from th e
o f the limb the error i s
observ ed readin g
I nd ex E rr or
I f a sextant
.
,
,
is
,
.
,
,
.
.
,
.
.
,
,
“
”
,
.
“
a
”
,
.
a
W
hen
us
d
f
o
r
m
easuri
n
g
the
a
n
gular
distance
e
f
between two obj ects the sextant is held in th e hand as previ o usly
d escribed so as to bring the direct and reflected images o f the two
when the angle is read on the limb Th e
obj ects into coincidence
n g le is then noted a
pplied as in the manner
a
n d the index erro r is a
I n su rvev
d escrib ed ; the res u lt will be the true angle required
w ork the sextant is usually held in a horizontal position or n early
an d the telescope is directed t o ward the fainter of the two
so
obj ect s the more distinct obj ect being observed by reflection I n
in o rder to accom p lish this it will be n ecess a
ry to hold
s ome cases
c y of the
ff ec t th e a
nt upsid e do w n bu t th i s w ill n ot a
c c u ra
th e se x t a
w o rk
S O U N D I N G R A N G ES
Us e
o
th e
S ex t
nt
.
,
,
,
.
,
.
,
,
.
,
,
,
.
.
it
de o ver a
co n s iderable expanse o f wat er
W hen soundi n g s m e m a
nd
de with sy stem and uniformity a
i s necessary that they be m a
,
I
I
M A K N G S OU N D N GS
a
t sui table
1
4
distances a p a rt i n o r d er that no ti me w i ll be lost i n
mak i n g u nn ecessary s o undin gs and that s o u nd i n gs w ill not be re
i
s
F
o
ver
a
n
area
that
has
previ
o
usly
b
e
en
s
o
u
nd
d
o
r
t
h
e
t
e
e
d
p
reaso n it is cust om ary to make the s o u nd i n gs al on g li nes who se
po sitio n s are design ated by fixed obj ects o n sh o re which re v isible
fro m th e s o u n ding b o at d uring the s o undi ng o peration s
S uch
li n es are called ra nges n d the obj ects designating them re c ll ed
range S ign als S ince ranges are o ften used as factors o f location i n
fix i ng the p o siti o n o f in d ividual s o undings it is impor tant that the
subj ect of r n ges a nd range S ign als be fully u n derstood befo re
taking up the matter o f l o cating soundings
Range lines should be desi gn ated by at least two obj ects u h o se
distance apart should be great enough t o a fford a go o d b se for
proj ecting the ra n ge o ver the water t o the required distan ce
i
r l l el R n es
s n ot l rge t e
Where
the
area
t
o
be
sounded
Pa
g
t
uiring
ra
n
ges
o
f
on
ly
m
od
erate
len
h
the
arrangement
show
n
i
n
g
q
I n this cas e A B C D
Fi g ure 1 5 will o fte n be found suitable
represent the front r a
nge points
etc
’
re
o r signals and A B C D etc a
the back r nge signal s The dotted
line s I 2 3 4 etc are the resp ective
ra nges ; these as sho w n re parallel
h
T
a
e
and at a unifo rm dista
nce a
rt
p
n d bac k
lines upon w h i ch th e front a
range signal s are p l a
ce d are called
i
respectively the front base line fo r
ranges and the b a
ck base line for
ranges Th e b a
se lines sh o uld be
laid off with atransit the d ista n ces
being
measured
with
a
chai
n
or
a
ll l S
R
d
a
Fn P
g
g
Th e se li n es are usually
steel tape
i
s
a
arallel
the
locations
for
the
se
eral
r
n
e
gnals
r
m
rked
wi
h
v
e
t
;
g
p
s takes o r hubs
nd the
Ra
ng es
d i l Ra
W here the area t o be so u n de d is large a
ran ges are t o be pr o j ected for a considerable distance the fron t a n d
back ra n ge signals m ust be a considerable distance apart in o rder
I n such a case
to a ffo rd a goo d base for proj ecting the ranges
s ome prominent obj ect of the landscape is usually selected for a
back range si gnal This S h o uld be far enough dista n t from th e
front range sign als to a fford a ba se of su fli ci en t length fo r th e
mo st d ist n t s o u nd ing and als o to permit its use as a c ommon
back ra nge sign al fo r all the front range si gnals with o ut causing t oo
,
a
,
.
‘
a
,
aa
a
.
,
.
a
,
.
a
a a
a
.
.
,
,
.
,
,
,
.
,
’
a
,
,
,
,
'
'
,
,
.
,
,
.
.
,
,
,
,
a
.
,
.
,
i
or e
'
e
ou n
es
n
in
.
a
a
.
a
.
.
,
,
.
.
a
,
,
,
,
HYDROGRAPH I C S U RVEY I N G
2
4
great a divergen c e
in the ra n ges at their
outer e n ds S uch an
arr n gem e n t is sho wn
in Figure 1 6 In this
case the p o sitions o f
the fro nt range sig
are sh o wn by
n ls
the d ots ; they are
spaced at know n i n
terv l s alo n g the base
Fi g \ 6
Ra
d i fl
R
S
d i
a
e
g
g
line A B Th e back
ra n ge sign al is a pr omine n t obj ect as a church spire at 0 no t shown
in the cut This is used as a central range point the ranges repre
se n ted by the d o tted lines being radial lines passing through the back
range po int and the several fro nt range poi n ts as shown C D is a
base li n e at wh o se extremities C and D are instrument stati ons
fo r locating the soundin gs
S uch a base is usually placed in
front o f the row of range signals as shown in order that an
unobstructed View can be had at all times from either station
to the so u nding boat
m s
In the ca s e of a river o r stream
R nges A cr oss S tr ea
eve n when of considerable size where either shore is easily
visible from the other side s o u n di n g ranges are ge n erally lai d
in directions n o rmal to
off extending e n tirely acro ss the stream
its axis I n such a ca s e two set s of range poi n ts are l aid off ; one
a
.
.
a
a
n
n
o u n
c
.
.
s
-
.
,
,
.
,
,
,
-
.
,
,
.
,
,
,
a
.
.
,
,
,
,
.
Fi
J T S ou n d
'
g
.
in g R
ag
n
es
Ac r os s
0
S tre
a
m
.
set is on either bank a
In this figure A
s s h o wn in Figure 1 7
B C D E are angle point s or s tations in the line of a t raverse
.
,
,
,
,
,
OU N DI N GS
M AKI NG S
43
al on g the river ba n k and A A B B C C D D E E are the
s o u n di n g ranges Th e d ots i n dicate the po sitions o f the range
sign als ; these are placed on either bank as may be m o st co n
ven i en t f o r u se in the s ounding work
'
'
-
-
-
,
-
-
,
,
’
'
'
,
,
.
.
S I GN A LS
RA N GE
.
Various forms of sign als are used for designati n g sounding
ra n ges ; the kind a n d size of signal re q uired will d ep end up on
the place where used a n d the distance to which the ran ge is to
be pro j ected Fo r ranges o f moderate length straight po les o f
suitable size may be used fo r both front a n d back range sign als
I n ma n y cases ordinary transit poles which are painted i n
alternate red and white bands make excellent range sign als
They ca n be quickly placed in positi o n at the re q uired places by
having their poi nts pressed firmly into the gr o u n d ; a n d they can
be readily sh i fted fr om one ra n ge t o an o ther as the s o un di ng
work progresses Th e auth o r has made use of transit ro ds fo r
ra n ge signals with satisfacto ry results in sou n ding operati on s
under his supervisi o n on river w o rk Ran ges so design ated we re
pro j ected t o a distance of
feet and were readily discernible
fro m th e s o u n ding bo a
t
Fo r r n ges o f considerable le ngth signals of larger size than
an ordinary sized transit rod must be used
A good form o f
range si gnal ca n be made of a st raight piec e o f sc n tling 4
inches by 4 inches in dimension s a
n d from 1 0 to 1 4 feet l on g
S uch a signal when whitewashed can be seen a l on g distance
I t should be firm ly set in the ground in a ho le dug fo r the pur
pose or i f set in rocky ground it sh o uld be secure d by stones
lso by bracing or by guy ropes i f required
p iled arou n d its base ; a
rg ets
Ta
W hen a numbe r of adj acen t
ranges are design ated by range signals it is
necessary to distingu ish the di ff erent ran ges
by distinctive marks ; such marks are called
ta
rgets In Figure 1 8 is sh o wn a ra n ge si gn a
l
to which i s a
tta
ched aS imple but e ff ective
form of target This is made by nailing laths
or strips of w o od from I t o 2 inches wide
nd a
bout 3 feet long across the face of th e
a
range po le in such a manner a
s to f o rm a
loz enge shaped frame ; a horizo ntal strip is
U
used to giv e additional strength Th e face of
" 9 3 ° “( m ge
th e fr a
me thus formed is covered with cloth
.
,
,
.
,
,
.
,
.
,
.
a
.
a
.
,
,
.
,
,
.
,
,
,
,
,
.
.
.
,
,
,
.
.
H YDROGRAPH I C
44
S
URVE Y I N G
of such a
color or combination o f colors as may be decid ed upon
Thus for example the target for range I may be all whi te ; that
for ra n ge 2 all red ; and that fo r ra n ge 3 red an d whi te etc
In a case where the ranges are o f such
length that the co l o rs on the targets are n ot
re dily distinguishable o ther forms of targets
should be used A good fo rm of target for
u se in such cases is made of a framework
covered with cloth and forming an oval
shaped ball s ometimes called a balloon which
fits loosely o ver the ran ge pole
This form
of target which is illustrated in Figure 1 9
ca n readily be raised or lowered as required
a
n d serves to S how at once by its po siti o n on
th e po le i f the range is to be sounded
A
modi ficati o n o f this form of tar get is shown “ S J Q
e s jg na
L
n
in Figure 2 0 where a ran g e p ole is shown
with a balloon at the top and a hexago n al S haped targ e t belo w Th i s
latter form of tar g et con sists of an o p en frame with strips of cl oth
of suitable color crossi n g its face in lattice fashion I t can be raised
s
s sistant a
or lowered by a shore a
requir
d
ther
forms
of
targets
e
O
r ?”
according to available
u sed
a
re
materials that may be had therefor
fl p
I n some instances targets have b een
made of branches or limbs o f
trees o r of small bushes cut and
trimmed to proper size and shape
ttac h ed to the tops of range
nd a
a
Fi gf o R n e S i gn l
g
poles
Range poles used to mark perman ent r a
n ges
or ranges over which soundin gs are to be r e
m et i m es de
a
n
mber
of
times
are
so
a
t
e
e
d
u
p
si gn a
ted by laths barrel staves or strips of
wo od which are attached to the face of the
pole in the form of Roman n u merals as illus
tr ted in Figure 2 1
S uch targets when read from the top down
ward denote the nu m ber of th e range ; fo r
example tha
t shown in Figure 2 1 designates
U
range nu m ber 4 Range po les can be made
i
F
l
con spic uo us by c oatin g them with whitewash ;
g
.
,
,
,
,
a
.
,
,
.
,
,
,
.
,
,
.
,
,
.
O
,
-
.
,
,
.
on
o
.
m
”
.
,
,
aa
.
a
.
.
.
,
,
,
,
a
,
.
,
,
,
.
a
-
M A K I N G S O U N D I N GS
45
a
this is especially e ff ecti v e in the case o f a wood ed b ckgro u n d
S peci l Form s of R ng e S i g n l s
In shall o w water where the
depth do es not exc eed a few feet fo r l o ng d istan ces fro m sh ore a
s pecial fo rm o f ra nge sign al suitable fo r placi n g in a stati on ary
m
osition
i
n
the
water
ust
be
used
A
g
o
od
form
o
f
range
p
signal that has bee n successfully used
is sho wn i n Fi gure 2 2 This c on sists
esse ntially o f a tripod made of three
pieces of gas pipe ab o ut 1 i n ch in
d ia m eter a nd o f suitable len gth The
lo wer e n ds o f the pipes are pressed
firmly i n t o t h e s o il o r mud o f th e bot
tom ; their t o ps are the n bro ugh t to
gether a nd fasten e d fo rming a tripo d
as show n A suitable target is mad e
by wrapping on e o r tw o pieces o f suit
ably co l o re d cl oth aro u n d th e tripo d
abo ut midway bet w een the wat er sur
s
o
face
and
the
t
o
p
o
f
the
trip
d
Flag
n e S i gna
l
Ra
Fi g 2 2 Tr i p o
g
are also placed i f re quire d i n the
upper ends o f the pipes to further designate the range
a
a
a
.
.
,
,
,
.
.
,
.
,
,
.
,
.
.
a
.
.
,
,
.
,
B U OY S
.
frequently n eces sary in hydrogr a
phic surveying to use range
s ign ls i n the water where the depth is c o nsiderable a nd w here
fixed sign al s can n ot be u sed
I n the case o f a heavily w ood ed or
precipito us s ho re where there is not roo m t o set the back ra nge
sign a l s very far back bu oys are generally used to designate the fro nt
ra n ge signals The use o f bu oys fo r fron t ra nge signals is no t
always satisfactory especially i n tidal waters o wi n g to the te n de n cy
o f a buoy t o change its surface p o sition at d i ff erent stages o f the
tide
In all cases where statio n ary sign als can be used it is pref
c rable t o do s o
but in ma n y cases as ab ov e stated this ca nnot be
done W he n bu o ys are used for range signals due care must be
exercised in setting them and s u itable allowance made i n taking
observati on s t o them for cha n ge o f position d ue to sta g e o f tide
A bu o y co nsists of a float to which is attached arope o r li ne ;
this is fastene d to a stone o r o ther heavy weight which rests upon
the bo tto m and serves as a n anch o r In hydrographic survey w o rk
buoys are generally used fo r range signals as described above ; t h e y
a
re also used to mark the cha n nel submerged ro cks sho als o r o th er
places u n d er wat er th a
t require to be show n o n the surf ce
It
is
a
.
,
,
.
,
,
.
,
,
,
.
.
,
.
,
,
.
,
,
,
,
a
.
H YDROG RAPH I C
6
4
S
URV EY I N G
A simple form of bu o y is sh o w n in
This c on sists esse n tially o f tw o
Figu re 2 3
pieces : a fl o at a n d a pole Th e float ca n be
ma d e o f a sin gle cylindrical shape d piece
of w ood usually a secti o n of the trunk of
a small tree abo ut one foot i n d iameter
an d about three feet in length The upper
thir d of the fl oat is usually left full size
the remainder being tapered to fro m 4 ins
in diameter t the lower end
to 6 ins
Thro ugh the cen ter of the fl o at o n i ts
lo n gitudinal axis a h o le is bore d of j ust
sufli c i en t size to admi t the p o le to be i h
The p o le sh ould be long eno ugh to
sert ed
proj ect from 6 ins to a foo t below the
lower en d of the fl oat an d from 2 to 3
Th e pole is u su
feet above its upper end
all y from I V; to 2 ins in diameter ; after
9 °
”
3
”
fl
being inserted in the fl o at it should be I
wedged fi rmly to place Near the l o w er
end oi the pole a hole is b o red h o rizontally through i t fro m side to
side through which is passed the anchor rope as sh o w n A flag c a
n
be attached to the upper end of the pole to serve as a target This
for m o f bu o y is suitable fo r use in non tidal water a n d in water
where th e r nge o f the tide is small
A n o ther fo rm of buoy is sh o wn in Figure
24
I n this form the float is of con siderable
len gth and is tapered at both e n ds as shown
In the uppe r end a hole is bored fo r the fla
g
p o le which is driven to place and is held
firmly by a wedge in its lower e n d
A
simil a
r pole i s i n serted in the lower end as
shown with a hole through it fo r inserting
the anchor ro pe I f pre ferred instea d of
using a pole a stout iro n ring or h o ok can
be screwed into the lower end o f the float
fo r securing the anchor rope This form of
bu o y is suitable for use in tidal waters where
a
M
d
t
e
f
F g 24 B
y
f Ti d e
the
rang
When
e of the t i de 1 5 n o t too g reat
Ra
g
the range of tide i s considerable it is gen
l ly preferable to use spar buoys for ra n ge signals
era
A spar bu oy
is simply a straight piece of wood of ap p roximately cylindrical shape
.
.
-
,
,
,
.
,
a
.
.
.
‘
,
,
,
.
.
,
.
.
.
,
.
.
a
-
.
.
.
,
.
,
,
.
,
,
;
.
i
.
.
u o
n
or
e
o
o
er
.
.
.
,
HYDROG RAPH I C
8
4
S
URV EY I N G
are made and l ocal requireme n ts Th e following list compri ses
metho ds i n c ommo n u se that are adapted to di fferent obj ects and
conditio n s
1
Lo cati on by time in tervals upo n a ra n ge of k no wn length and
di recti on
2
By one angle measured by a n observer on shore
n
By
two
angles
measured
by
two
observers
simultane
o
usly
o
3
s hore
e
By
an
les
m
asured
with
sextants
in
the
soundi
n
g
boat
t
w
o
4
g
By
co
pass
bearings
observed
in
the
s
o
undi
n
g
b
o
at
m
5
6
By transit and stadia
fi
By
the
intersection
of
xed
permanent
ran
es
g
7
By direct measurement on the ice
8
By
a
xed
line
marked
by
a
graduated
rope
or
wire
fi
9
These several metho ds will be discussed and described i n de t il
When this meth o d is used for
Loc ti on by Ti m e I nter v ls
locati ng soundings the extremities or two design ated po i n ts on a
given co urse or range are fixed by two buoys or other suitable oh
whose
relative
p
o
sitions
are
kn
o
w
n
with
respect
to
previ
o
usl
s
t
e
c
y
j
located obj ects on sho re S uch an arrangement is sho wn in Fi gure
s e s th e fi rst an d last soun d ings on the range are
In som e c a
26
.
.
.
,
.
.
.
,
‘
,
.
,
.
.
,
.
,
.
.
,
.
.
.
.
,
.
.
.
a
.
,
a
a
.
.
,
,
,
.
.
3
2
r
Fi g E 6
.
.
S
ou n
d i n gs
a
d
Sp
In t e
b y Ti m e
ce
r v
“
i
g
et
al
s
“
s
.
l o cated by measurement or observation and the positions o f the
i n te rmediate soundings are interpo lated Th e soundi n g b oat
traverses the range at uni form speed while the leadsman makes the
s ou nd i n gs at kn o wn intervals of time calling o ut to the reco r d er
the depths o f the several s o undings The recorder enters in his
n ote b oo k the observed depth n d the number of e a
ch sounding als o
the exact time each sounding is made I f it is required to kn ow the
character o f the bottom this is observed by the leadsman a n d no ted
by the recorder as often as m a
be
required
U
sually
it
is
n
o
t
y
necessa ry to do this at e a
ch s o undi ng but on l v at such places where
ach a
t eri a
n ge in the m a
l of the bo ttom occ u r s
,
.
,
,
a
.
,
.
,
.
,
.
M
A KI NG
SO
U N D I N GS
49
When th e sou n dings are thus ma d e fro m a
b o at movi n g al o ng a
fixed ra n ge at a u n ifo rm a nd kno wn rate o f spee d the time interv als
betwee n successi v e s o u n di n gs bein g k no wn the po siti o n o f a n y gi ven
s o undi n g on th e ra nge ca n be d etermi n ed by pro porti o n This c n
be ex presse d by f ormula as fo ll o ws
t
wo
r
o
be
the
dista
n
ce
between
the
e
x
tremities
betwee
n
Let L
design ated p o ints on a given range ;
T = the time re quired by the soun d i n g bo a
t to traverse the d is
ta n ce L ;
speed i n units of ti m e o f sou n di n g boat
S
t = the time interval betwee n any tw o given soundings ;
the required distance between s o u n dings ;
X
The value o f X is determined by mea n s of the propo rtion
,
,
a
,
.
ex ample if a sounding boat tra verses at unifo rm speed a
range
feet long in ten minutes a n d s oundings are made from
the b o at at the rate o f four per minute a t otal of 40 s ou nd ings will
be mad e after passi n g the initial point on the ran ge In this case
the time i n terval between successive s o undings is one quart er o f a
m inute and the dista n ce between any two given so undings o n the
ran g e can be found by propo rtion as j ust expl a
ined Thus referring
t o Fi gure 2 6 let L = 2 640 T
10
t=
S ubstitutin g these values and reducing we have
For
,
,
,
,
,
.
-
.
,
,
,
:
,
,
,
66
fee t
.
This method is employed for locating soundings in cases where
great accuracy is no t esse n tial a n d where there is little o r no current
i n the Water It is also use d t o interpo late the p o siti on s o f inter
med iate s o u nd ings betwee n th o se that re located at state d i n terval s
.
,
a
a
a
.
Whe n this meth o d
is
rem a
ining thereon
a
until all the soundings req u ired on that ran e have b een made
The
g
bo at th en pro cee d s t o the next range where soundin g s are to be
ma d e the require d so undi ng s are made thereon ; then to the ne x t
range th is operati on bei n g repeated u ntil the s o unding o perati on s
r e co mpleted
I n this meth o d e ch s o unding ran ge is a facto r o f
l ocati on an d it is therefo re necess ry that all the ranges be accu
ra
tel y l ocated
Loc ti on by One A ngl e M e s ur ed on S h or e
used the sou n ding boat travers es fi xed range
,
.
,
.
.
a
,
.
,
.
a
a
H YDROGRAPH I C
0
5
S
URV EY I N G
This
method is illus
Figure 2 7 i n
tr ted i n
which A and B represent
two instru m ent statio n s on
shore wh o sep o sitions have
bee n determined by tri
M’
angulation or by direct
measurement Th e respec
tive ranges are parallel ;
they are design ated by
ra
n
ge
p
o
les
which
are
fl?
2
marked with suitable tar
gets D E F G H are
po ints of intersectio n of
the base line with the re
ranges ; the dis
sp ec ti ve
tances between the ex
An
On e
e
l
t on
f t g i l Lo c a
by
g
t rem i ti es O f the base line
o
S h or e
Me a
s u ed
and the respect i ve range s
a
s well as the intersecting angles
are known Th e posi ti ons of the
s ou n ding b o at at di ff erent periods and on di ff erent ranges are sh o wn
a
t M M , and M ,
A regu l a
r s o unding party for this method of locati o n is composed
o f a n o bserver on shore
wh o is e q uipped with a transit or a plan e
table the necessary shore assistants and the boat party
This latter
party c o mprises a recorder a leadsman a si gnalman and the b oat
crew W here the sa m e range poles are used for successive ranges
o n e or more shore assistants will be required to set up and take
dow n the poles and to move them from one range to an o ther I n
tidal waters a tide gage reader will be required to observe and reco rd
Th e order of sounding
th e stage o f water at required intervals
work is as fo ll o ws
The bo at traverses the ra nge being kept o n li n e by the steersman
wh o sights to the tw o signals design ating the range and is careful
to keep the boat as nearly as po ssible on the strai ght line passing
thr o ugh b oth signals
In so me cases the front ran g e pole is shorter
than the o ne in the rear in order that the back si gn al may be seen
Th e leadsman
w hen necessary oVer the top of the one in front
h
a
s tands u on his platfo rm
e
n
d
near
t
b
o
w
of
the
boat
makes
h
t
e
p
s oundi ngs at suitable intervals
usi n g a pole or a
lead line as may
W hen sound
be required a
n d in the manner previ o usly described
in gs are obs erv ed at o n e m i n ut e i n t erv a
l s the record er n ote s the
a
,
,
.
“
,
.
,
,
,
,
‘
i
.
n
r
.
,
.
,
,
,
.
,
,
.
,
,
.
,
.
.
,
,
.
,
,
.
,
,
,
,
.
,
.
M
AK I NG
SO
U N DI N GS
1
5
time of each sounding and j u st before the full mi n ute he calls
out ready at which the sign alman raises his flag to n otify the
observer on shore that a sounding requiring observati on is about to
be made A t the full minute the recorder calls o ut flag o r
so u nd as he may prefer when the signalman drops his flag at
the same instant that the lea d sm n makes the sounding When
s o undings are m de rapidly it is not usually practicable to observe
each sounding and in such cases it is customary to observe th ose
made a
t the end of each minute and to interpo late the interme diate
soundings by time intervals A S each s o unding is made the lea d s
man calls the observed depth to the recorder who enters it i n his
n d the exact
note book together with the number of the sounding a
ti m e
The observer sets up his instrume n t preferably a transit over
selected point o n the base line sets the vernier at zero sights alon g
the base line and fa stens the lo w er clamp H e the n loo sens the
upper clamp and turns the i n strument in azimuth until the li n e of
sight is directed toward the S ounding b o at ; as soo n as the S i gn al
flag is raised he sights to it and by gently turning the telescope in
azimu th keeps the line of sight fl xed on the flag u ntil it is lowered
A t the instant the flag dro ps the o bse rver ceases to turn the tele
sco pe observes the time by his watch which sh o uld be lying o pen
with face up o n the instrument before him ; the n reads the angle
as aFigure 2 7 and enter s in his note b o ok the angle a n d the time
Angu lar measurements are m a
de at suitable po ints on the base li n e
or at either extremity of the base care bei n g taken to secure goo d
intersecti on s with the respective sounding ra nges
Wh en this meth o d of locating soundings is used there are tw o
facto rs o f l o cati on the so unding range con stituting one fact o r a n d
the observed a ngle the other Thus referring t o Figure 2 7 i n o r d er
to l o cate the sou n di ng made when the b o at is at M th e fo ll o wi n g
meth o d is applicable : The directio n of range I is k no w n by the
angle of intersection between it and the base li n e at D ; the distan ce
A D and the angle a
are known Th e triangle A D M ca n th en be
so lved and the distance D M determined ; this locates the sounding
on th e range n umbered I
s ur ed s i m u l t n eous l y on S h or e
Loc ti on by tw o A ngl es m ea
In
using this meth o d two observers re required wh o are statio n e d t
suitable po i n ts on a base line an d wh o measure si m ultaneo usly th e
ngles between the base line and the two respective lines o f sight
t o the s o unding b oat at each soundi n g I f s o u n ding ranges are not
use d the factors o f lo cation are the base line up o n which the oh
,
,
”
,
“
”
.
”
,
a
,
a
.
,
,
.
.
,
,
a
.
,
,
,
,
.
,
.
,
,
,
,
,
,
,
.
,
,
.
,
.
,
,
,
-
.
-
a
a
a
.
a
,
,
,
.
.
,
.
a
H YDROGRAPH I C
2
5
S
URVE Y I N G
v ers are stati oned and the two angles that are read from
ser
i ts
,
i ties
extre
base ;
This
is illustrated in Figure 2 8 in which A B is the
A and B are the two obse rv ation stations and A C a n d B C
are the two lines of sight A n i n
strument preferably a transit is set
up at each observation stati on with
the ve rn ier of each i n strumen t set at
zero upo n the other transit ; each 0 b
nd
s erver has his watch lyi n g open a
face up on the upper plate of h i s
tra
nsit Th e lower plate of each
transit i s clamped and the upper
plate is free ; the m ovement o f the
boat i s followed by the telescope
F i g 28
moving
in
azimuth
in
the
manner
pre
L
i
a
A gl
t
b y Tw
Th e sounding boat
v i ou s l y explained
being at th e p o sition C at the time a given so u ndin g i s made the
angles and b are measured Then in the trian gle A B C the S ide
A B a n d the two adj acen t a ngles a
re known ; the trian g l e
and b a
ca
n be solved
n d the point C located w ith resp ect to A and B
I n practice it i s custom a
ry to make the soundings up on est a
b
l i sh ed ran ges both for convenience in p l atti n g a
n d for facil i ty in
determinin g where to mak e th e successive soundings Th e range s
s S h o w n in
m
or radial a
y be parallel
a
s sh ow n i n Fi g ure 1 5
s e th e r nges s erve as f a
ct or s of l o cat i on
Figure 1 6 I l l eith er c a
a
s well as to check the acc u r a
c y o f the an gu lar measur em ents
I n Figure 1 6 the sounding boat is shown tra
ver sing range I I and
go ing from shore A perspective view of thi s i s sh own i n Figur e
29
in which the so un d ing bo a
t a s team launch is in the for e
m
.
-
,
-
-
.
,
,
,
,
.
,
.
oc
.
on
o
n
es
,
,
.
a
,
,
.
-
a
,
.
"
,
a
.
a
,
.
,
,
.
.
.
,
,
Fi g 29
.
.
S ou n d i ng P
,
aty i
r
n
S te
a La
m
u nch
.
gro u nd the back range s i gn al a churc h spire is in th e backgro und
n d the fr o nt ra
n ge si gnals are in the middle distance The s o und
ng party consists o f
m
a
boat
n
who
acts
as
steersman
a
recor
d
er
i
a leadsman and a sign alma n The soundi ngs are l o cated by the
ob servers on S h o re at one mi n ut e i n terva l s
A few seco n ds b efo re
a
,
,
a
,
,
.
,
,
.
.
,
M A K I N G S OU N D I N GS
53
a
the end of ea
ch minute the signalma n raises his flag n d at the
full minute th e flag is lowered simultaneo usly with a s o u n di n g
made by the leadsman The observers on shore foll o w with their
li nes of sight the sign al flag and as it is l o wered observe the re
sp ec t i ve angles and the time
an d recor d both in their note boo ks
In this case the distances from the i n struments to the sounding bo at
are co n sid era
ble and sights are taken to the flag instead o f to th e
s ounding pole in the hands o f the leadsman
as would be the cas e
for s h o rt distances
On this accou n t the signalma n is stati o ne d
d sm a
n i n orde that the distance between the observed
near the lea
a
n d the tr u e position of each sounding may be as small as po ssible
A s the boat moves over each range at unifo rm speed the sou nd
i ngs are made regularly three or four to the mi n ute acc o rding to
the depth o f th e water Those made o n the full minute are located
by observati o n a n d the intermediate so undings are interp o lated by
t i m e intervals as previ o u s l y described
A fter each range is run o ut the bo at starts back o n the n ext
ra
nge thus alternately begi n ning and endi n g at the S h ore for suc
c essi v e range s
,
,
,
.
,
,
.
,
,
.
r
.
,
,
.
,
.
,
,
.
COOP ER S M ET H OD
For very rapid w o rk
re lo
wh e re soun d in g s a
by two a
ngles
te d
ca
ob served on S hore 3
method devised by M r
A S Cooper United
S tates A ssistant Engi
n eer
and used by him
in hydrographic surveys
i n the S avannah Geor
i
district
is
well
a
g
ada pted The following
n d illustra
descri p tion a
tion of thi s method are
taken from an article
written by M r Cooper
and published in E ngi
’
.
,
,
,
.
.
.
,
,
,
,
,
.
.
n eeri ng
1
N ew s
,
a9
M y
1
,
0
9 4
.
sounding boat
Fi g 30
S ou n d i n g
used was a 40 foot
s team l a
unch a view of which is give n in Figure 30
Th e
.
-
,
.
.
a
Bo t
.
The s o und
HYDROGRAPH I C
54
S
URVEY I NG
ing pa
rty on the boat consisted of tw o leadsmen a
reco rder a
The o rder of s o u n d
sign alman a n e n gi n eman a n d a steersman
ing operation s as described by M r Cooper is as fo llows :
Th e tw o le dsmen occupy s ounding platforms one o n ei ther side
of th e boat as sh o wn ; they m ake s o undi n gs alternately t i n ter
vals o f 1 0 seconds i n depths o f from 2 0 to 35 feet I n shall o wer
water the soundings are made more rapid l y a nd fo r depths greater
tha n 35 feet the ra
te o f speed is less The bo at as sh o w n has a
sign al mast which is provi d e d with a sign al ball oo n capable of
bei n g raised and l o wered Th e reco rder calls lea d at the e nd o f
every 1 0 seconds thus noti fyi ng a
leadsman to sou n d ; at 1 0 seco n d s
before the full minute in additi o n to calling lea d he calls fo r
the sign alman to hoist the balloon ; at the full minute as a soundi ng
is made the signalman d rops the balloon thus notifying the tw o
observers on sho re to n ote the an gles to the signal mast at the
i n sta n t the S i gn al begins to fall
t
This
Loc ti on by tw o A ngl es m e s u r ed i n th e S ou nd i ng Boa
m eth o d
which i s exten sively used in harbor surveys requires the
previous l ocation of three prominent objects on shore which are
isible
from
every
portion
of
the
area
to
be
sounded
a
nd
which
v
re suitably located f o r good intersections from the sounding bo at
s each so unding is made two angle s are meas u r ed in the boat to
the th re e fix ed sh o re p o i nts
The angles are measured simultan
eousl y b y tw o observers each usi n g a sextant or by one obse rver
with a d oubl e sextant
W hen rapid work is n ot
re q uire d b oth angles m a
y
be measured successively
by o ne observer with a
plai n sexta n t ; in s uch a
case the b oat is brought t o
a stop fo r each soundi n g
This process h o wever is
slo w a n d the metho d com
m on l y empl o ye d is that in
which tw o obse rvers make
f
il L
t i on b fiext a
Fa
f
o
a
n t A n l es
s
c
imultaneous
ob
ervati
o
ns
s
e
t
O
e
o
m
s
t
o
a
B
g
y
g M
A complete soundi n g
n
c
s
i
rty
for
this
meth
o
d
o
sts
of
two
extant
bse
v
rs
a
le
d
man
s
s
e
o
a
p
a rec o rder n d the necessary boat crew In tid l waters a tide gage
observer is required on sh o re otherw ise the entire party is carried
i n t he s o u n di ng bo at
In o rder to clearly describe this method of
,
,
,
,
.
,
a
.
,
,
,
,
,
a
.
,
.
,
,
,
”
.
,
“
”
,
,
,
,
,
a
.
a
,
.
,
,
,
,
'
i
,
.
,
,
.
.
,
,
,
l ur
.
a
a
.
.
r
-
.
,
.
a
,
,
H YDROGRAPH I C S U RVEY I NG
6
5
value of tan y may be determine d in the s a
me way ; o r
havi n g d etermi n ed x its value is substituted in e q uati o n ( 4) a n d
the value o f y is found direct
H avi ng found x and y the values o f A B a n d D B are determi n ed
by trigo nometry as follows : In the triangle A B C the side a and
=
=
x
T
h
e
re k n o w n
n g les E a
th e two a
nd
a
e n g l A GE 1 80
E+ x ) 1 0 )
Th e
,
,
.
-
-
,
a
.
sin
sin
E
—
a A B ; wh e nc e
A CB
simil a
rl y in
,
tri
th e
ngl
a
e
D
B
°
=
A B
-
C DCB
1 80
,
b
Ex
mp l
a
e
en
a
=8S O f ee t
Referri n g
=
b 76 0 f e e t
.
.
'
°
(11 )
E
$ 1 11
—
wh en c e D B
—G iv
M
(F
Sin
DC B
sm
F
=
E 41
(12)
y)
( 1 3)
°
=
F 35
°
t o Fi gure 2 7 what are the values of the a n gles x an d y
?
a
nd o f the sides A B and D B
S olution S ubstituting these values i n equation ( 3 )
,
,
-
-
.
x +
°
=
360
y
8
si nc e S i s i n th e se cond q uadr a
n t co s
s ubstituti n g in equati on ( 9 )
co s ( 1 80
S
,
°
S
)
c os
760 XO 731 5 XO 66 26 2
.
.
0
6 7 49
x
sub stituti n g in
eq
.
y
1 33
°
uation s ( 1 0 ) a
nd
A CB
DC B
th e n s ub stituti n g in
eq
1 80
°
1 80
0
0
'
0
'
1 09 1 9
1 00 41
0
70 41
uation s ( 1 1 ) and
A
SS OXO 94370
.
B
D
7GO><O 9826 7
.
B
0 5 80 70
.
This
work ;
method of locating soundings is extensively used
it i s p rob a
bly the b est known g eneral method
in
harbo r
.
B A CON S M ET H OD
A very rapid method of plattin g soundings when the locati ons
r e made by me a
n s of sextant ob s ervation s from a bo at h s been
a
J am es H Bacon United S tates A ssistant Engineer
u s ed by M r
A de
for hydrog raphic s u r v eys made off the c o ast of Fl o rida
written by M r B ac o n was published in
s cription of this method
the report of the Chief of En gineers U nited S tates A rmy and also
1 90 3
m o f M arch 2 6
i n Eng i neer i ng N
’
.
a
,
.
.
,
,
.
,
a
.
,
,
,
,
.
I
M A K N G S ou N DI N Gs
57
I n describing this method it is first
necessary to explain the principle upon
which it is based In Figure 33 let
A and B represent two known points
on sh o re
and C be the position of
the sounding b o at at any given
s o unding I f a circl e is drawn
through A B and C an observati o n
ma
de at any point on the re A C B
will subtend an a
ngle equal to the
angle at C This is evident fro m the
well known principle o f geometry
l n s c r i b e d An g le s
that all the angles inscribed in the
63
sam e segme n t o f a circle are e q ual Thus i f th e angle B A C
an o bs erv ati on made to A and B at any other po int on th e same re
a
s at C w i ll also me a
sure
If a
number of arcs of different r d I I re
d rawn through the same tw o p o i n ts t h e i n
s cribed
angle ou each re will d epe nd
upo n the length o f its radius I n Fi gu r e
n
is
sh
o
w
a
series
o
f
arcs
wh
o
se
ce
n
ter
s
34
all lie on a line wh ich is d raw n perpen
di cu l r t o the line A B at a p o int h alf way
f “
F
34 S
5
between A and B For c o nvenience these
s
arcs are draw n s o that successive i n scribed angles will differ by
constant interval In this case any gi ve n n gle subscribed by th e
tw o p o ints will be on one o f the arcs o r c n be interpolated between
t w o adj acent arcs
I f a second series of arcs is drawn
thr o ugh two other p oints suitabl y
lo cated the intersecti o ns of the tw o
seri es will locate readily the po siti on
n y point within the area c o vere d
of a
by them Let A B and C D FIgu re
represent
two
base
lines
through
35
whos e extremities are drawn tw o
as sh o wn ; the po ints
s eries o f arcs
m a
h ns A
.
A B and C are prominent obj ects on
w h ose po sitions are kn o wn Th e centers of each series are
sh o re
locate d on a li ne perpe n dicular t o th e base li n e a nd passi ng th r o ugh
its ce n ter ; and the a
rcs are drawn with an interval o f 1 betw een
rcs A point whose observed angular values are w hole
d j acent a
.
,
.
,
,
a
.
.
°
a
aa
.
,
:
,
,
a
,
.
a
'
°
e r ‘e s
-
1 3
-
,
:
a
.
a
a
.
.
,
,
-
-
,
.
,
,
,
n
e c
“
,
.
,
,
a
°
.
HYDROGR A PH I C S U RVEY I N G
8
5
a
a
a
d egrees will be fo un d t the i n tersection o f the two rcs co rrespon d
i n g with the observed n gles Intermediate p o ints are f o u nd t
d i stan ces interpolated between adj acent arcs
In some cases whe n th is
meth o d is used the s o u nd i n g
boat is kept o n a fix ed ra n ge
while t h e s o u n dings re l ocated
by sexta nt ngles to tw o k no wn
po ints on sh o re W h e n this is
d o ne the s o u n di ng ranges may
be either radial o r parallel th e
for m er arrangeme n t bei n g usual
In the case o f
l y preferable
ra d ial ranges a promi n e nt oh
j cet whose position is kn o w n
as 0 Figure 36 is selected fo r
a b ack range point and a num
b er o f ranges ra d iati n g there
Fi g 3 6 Rc1 d l ot l In t e r s e c t i ons
from t regular intervals are
laid off The back range point 0 should be at a distance fr o m any
fr on t range p o int not less tha n the distance from the front ra
nge
po int to a n y sounding to be l o cated o n that range ; it should be a con
S p i cu ou s w ell d e fined obj ect such as a lighth o use a church spire
a wi nd mill a water t o wer or other prom inent available o bj ect In
o rd er to a ffo r d goo d locations the b ck range po int 0 sh oul d p
pear fo r all o bservatio ns between the tw o extremities of the bas e
in
T h e front range poi nts a
A B
re marked by suitable sign als
the ma nn er previ ously expl ined
Whe n parallel ranges are used the arrangement will usually be
similar t o that shown in Figure 37 In such a case the ra n ge
p o ints are located a nd the ranges are
1
laid o ut according to the manner pre
f
f
7
I
f
?
i
i
us
l
described
The
back
ra
n
ge
v o
I
y
l
l
points sh o uld be located far en o ugh back
fro m th o se in front t o a ff o rd good bases
for pro l on gi n g the s o un d i n g ranges
M eth ods of Loc ti on In using these
methods the s o undings are l ocated by
sextant observati ons in the same ma n ner
as that previ o usly describe d for such
w o rk
When tw o base li n es are use d as i llus
ra
flS
“
3
P
T
O
l
l
a
c
t
l
7
s
e
I
fl
er
l
e
9
t r ted in Figure 35 simulta n e o us obser
,
a
.
.
,
,
a
a
.
,
.
,
,
,
,
,
,
a
’
‘
.
.
.
.
,
,
,
,
,
,
,
a
,
,
,
,
a
.
,
,
,
,
-
a
.
,
.
.
d
e
‘
i
,
.
a
.
.
.
a
,
'
°
,
MAK
i
a
I NG S OU N D I N GS
59
are made by two observers for each s o u n ding ; on e observer
n gu lar distance b etwee n A and B while the other
m easure s the
obse rv er m easures that between C and D
In l ocati n g sou n dings
by range a n d base line as illustrate d in Figures 36 a n d 37 the
sou n ding boat is kept on the ra n ge by the steersman while the
s o undi n gs are made S ince only one an gular measurement is re
quired fo r each s o un ding the observati ons can be t a
ken by o ne
sextant observer
T h e meth o ds j ust desc ribed are best adapted for hydrographic
w o rk when a n u m b er o f surveys are to be made over the same area
successively and each survey i n volves many s oundings
Whe n sou nd ings are located by sex tant observations from a b oat
practically the entire party is carried in the sounding boat thus
a ff o rdi ng unity of action and av o iding loss of time w hen a
change
of plans is re q uired
Locations made with transits are perhaps m ore
exact but sex tant observ ations are usually sufficiently accurate to
conform t o the scale of t h e m p or chart
v
t on s
a
,
,
'
.
,
,
.
,
.
,
.
,
,
,
.
a
,
.
a
a
a
L oc ti on by Com p s s
This m eth d
B e r i ngs
o
.
o f locati ng s o un d ings is
rather cru d e an d should
not be used where accu
rate results are re
quired In order to use
this m eth od it is m eces
sary that two conspi c u
ous obj ects on shore
that can be readily seen
from the soundi n g bo at
as A and B Fi gure 38
shall fi rst be l o cated and
Fi g 38
Loc a
ti on b y C om p a
their positi ons kn o wn
ss B ea
ri n gs
I n locating the soundings two observers each with a compass are
req uired in the sou n ding boat in addition to the boat crew Each
observer selects a di fferent obj ect for observati o n and as so on as a
s o u n ding is made the two observers read th e magn etic beari ngs
to their respective obj ects Thus referring t o Figure 38 fo r th e
s o undin g made at C o ne observer n o tes the b earing C A w h ile
th e o ther n o tes the beari n g C B
I f rapid w o rk is n o t re q uire d both
observations may be made successively by one o bserv er in w h ich
ca
se the boat m ust be br o ught t o a st 0 p for each s o unding
.
,
,
,
.
.
,
.
.
,
,
.
,
,
,
.
,
,
-
,
,
-
.
,
,
.
H YDROGRAPH I C S U RVEY I NG
60
a
Loc ti on
ad
ai
Tr
w i th
ns t
I n locati n g
so u nd i n gs by this meth od
th e co mplete party is usual
l y d i v ided as f o ll o ws : I
Th e ob server on sh o re with
a tran sit equipped with
2
The boat
sta d ia wires
party consisti ng o f a t e
a leadsman a
eo r d e r
Fi g 3 9 Loc a
ti on b y S t u d i o on R n ge
n
a signalman
st d i m
and t h e necessary bo at crew S everal v ariati o ns of this meth od may
be use d acco rd i ng to l o cal conditions a n d the degree of accuracy re
quired i n the w o rk W hen soundings re made on an established
range the transit is set up over some k n own point on the range as t
A Figu re 39 and ob servations a
r e taken f o r s o undings on that range
I n this case the azimuth of the range is k no wn a
n d the dista n ce
of each sounding from the transit station is determined from the
observed interval on the stadia rod A s the boat tr a
verses the range
m a
n st a
n ds i n the bow or the ster n of the bo at according
th e st di a
to whether th e boat is approaching or going from the obser v er ; he
h o lds his ro d v ertical and always facing the observer The leadsman
makes the s oundings at the required intervals calling out to the
reco r d er th e depths and when required the char a
cter of the bo ttom
The reco rder e n ters this i n formation in his n otebook als o noting
th e time and the number of each sounding The signalman raises
a nd d r o ps his flag to notify the observer when soundings are ma de
in the man ner th a
t has been
previously described The ob
server notes the number of
the sounding the time and the
sta
dia interva
l fo r each observed
sou n di ng The method j ust de
scribed is suitable for locatin g
sou n di n gs made on ranges
across rivers or sheets o f wate r
where the distance from sh o re
to shore i s not too great for
stadia re a
dings
W hen the soundings are not
F19 4 “ Lo c t i o n b Y
made on ranges or when they
U
h
I
t
m
z
n
d
A
‘
d
S fi
are made on aran g e and it is
n
S tud i o
.
.
,
.
.
,
a
‘
aaa
,
,
.
.
.
,
.
a
.
’
,
,
,
a
.
,
a
.
,
.
,
.
,
,
,
.
,
.
,
.
'
“
.
a
a aa
.
,
'
.
,
‘
.
MAK
I NG S OU N DI N GS
61
a
not convenient to set the transit up o ver a po int o n the r nge the
a
zimuth for ea ch o bserved s ounding is noted in additi on t o the
stadia interval therefor
The azimuths can be determined with
reference to a true or a
n assumed meridian
or b y measuri n g the
angular distances fr om a previously e stablishe d base li n e w ho se
a z imuth is known
This is illustrated in Fi g 40 in which
A B is the kn o wn li ne A the position of the transit an d C the
position of the soundi n g boat at the time of a given s o u nd ing
Th e factors of location are the angular distance a determined by
azi m uth reading and the distance A C determined by the stadia
interval W hen soundings are made on a range it becomes a third
factor of location
W here accuracy is not es s en t i al and rapid
w o rk is req uired the directions to the sev
eral soundings ca n be determined by com
pass bearings and the distances by stadia
In such cases it is not necessary to use a
ba
s e line ; it will be su ffi cient to know the
location of the shore point fro m which the
observations are t a
ken Thu s refer ring to
i
Figure 4 1 the tra
nsit is S et up over the i i g
gggd i i go m i és s
shore p om t A t c h has been p rev10 usl y
n d re a
located a
din g s are taken to the soundin g boat as the sound
’
in gs are m a
de as for insta
nce a
In this instance the
t B and B
m agnetic bearing from A to B is N
6
B
and
that
from
A
to
is
E
4
N 28 E
W hen the area visible from A has been sounded the
transit is moved to another shore station as at C and the same
process continued Th e new shore station can be located by observ
ing the be a
ring and the stadi a
interval thereto from the previous
station
Loca
I n a case where
ng es
ti on by th e I n ters ec ti on of Fi x ed R a
asounding range is to be sounded many times and where it is re
quired that soundings shall be made at the same p oints each succes
s ive time
it is genera
lly a
dvisable to provide some a
rrangem ent by
ny i n
fi
e
be
identi
d
any
time
I
n
ma
a
t
w hich selected point s m a
y
stances i t is necessary to determine the cros s section of a river or
at a discharge station at successive periods ; often a
series
stream
of observations must be made across a channel to ascert in i f the
b o ttom is scouring or is filling u p with sediment In such cases the
l oc tion of successiv e sounding s may be e ff ected by intersecting
n ge s
ra
,
,
.
,
,
.
.
,
-
,
,
.
,
,
-
,
,
.
.
.
,
.
,
.
,
n
,
.
,
,
,
,
,
,
.
'
°
,
°
.
,
,
,
.
.
.
,
,
.
-
a
,
a
.
.
H YDROGRAPH I C S U RVEY I N G
62
S uch
ranges can be
l id out in several d if
ferent ways ; a good ar
rangement is that sh o w n
i n Figu re 42 in which
A D is a s o un d ing range
acro ss a river a nd 1 2
t
etc
are
the
poi
n
ts
3
which successive soun d
ings are t o be m de
a
,
-
a
a
,
,
.
,
,
.
a
Loc fl on
by
ag
R
In t er s e c fl n g
n
es
.
a
C and D ; those n e r
est the water are sh o rter than the back range poles in order that
the latter may be readily seen o ver the to ps o f the fro nt range poles
The ranges numbe red 1 2 3 4 5 and 6 are also design ated by range
po les as sh ow n I f desired the back r nge po le in each range is
marked with Rom a
n numerals sh owing the num ber o f th e range
The intersecti ons o f th e numbere d ranges with the range A D l o
cate the respective sounding points
An other arrange
ment fo r intersecting
ranges is that sh o wn
in Fi gure 43 I n this A
l
A
instance all the num
bere d ranges o n a side
are referred to a sin
gle back range pol e ;
the front range po les
may be marked with
e
s
a
n
R
r
e
c
m
r
s
e
I
n
t
t
i on
b
ca
o
7
L
g
g
y
R o man numerals de
noting numbers of respective r n ges
W he n making soundings in a current usi n g this meth od of l oca
ti o n the boat is started at a short dista n ce upstream a n d is all ow e d
The lea d sma n casts th e lead in
to d ri ft downstream to the range
ti m e fo r t h e line to beco me vertical as th e proper place is reached
Care should be take n no t to cast the lea d too soo n since i n a str ong
current the lead line will have a deci d ed sag i f expo sed t o the
fo rce o f the current fo r an appreciable time after the lead t o uches
botto m
W hen climate and seas on re
Loc ti on by M e s u r em en t on I ce
favo rable a hydro graphic survey may be made upo n th e fro zen s ur
B
,
,
.
,
,
.
,
a
,
,
.
,
-
,
.
.
.
.
a
,
.
,
,
.
.
,
,
a
.
a
.
a
HYDROG RAPH I C S URVEY I NG
64
stretched and afterward graduated by i n serting between the strands
foot
arks
were
m
d
e
m
h
T
e
I
bits o f clo th at intervals of
foo t
5
con spicu o us by using red cl o th for tags ; the
5
other graduati o ns were marke d with white cloth
When used fo r design ating a ra nge the ro pe
was held fi rmly a g inst a stati on stake at s ome
con venie n t foot mark and was pulled taut acro ss
the can al and held aga i nst the stake on the op
F
or such work two assistants were
s i te b an k
o
p
re q uired on e on either bank ; they held the rope
in place while s o u n dings were bei n g made pull
ing it suffi cien tly hard to prevent undue sag
The s o undi n g party i n a bo at consisted of a
reco r d er a leads m an pr o vided wit h a s o unding
po le an d a b oatma n
In sounding a range the
bo atma n hol d ing the ro pe with his ha nd s pull ed
hn
o
s
A
B
t
n
o
s
s
A
ng
the boat acr o ss the canal on the range from on e Ra
side t o the other as the s o undings we re made Th e leadsma n i n mak
ing a s o undi ng held his po le vertical and against the rope noti n g the
depth and als o the gra d uation on the rope that was next to the pole
Depths were noted i n tenths and horizon tal distances were observed
t o whole feet ; these were bo th called out by the leadsman to the
recorder wh o e n tered th em in his n otebook A fter a range had been
soun d e d the two assistants on shore proceeded to the next ra n ge
carrying the rope between them and holdi n g it clear of the water
A t the next range the rop e was stretched from stake to stake as
before ; the b o at in the mea n time having been paddled o r towe d by
th e boatma n t o the proper place the new range w a
s soun d ed in the
same ma n ner as before These operations were continued for suc
l l the soundin g work that w a
s required pri o r
c ess i v e ran g es until a
to dredging operations was fi nished
A fter the channel had been dredged the r a
nges were again
the sounding work was done in the same man n er as t
sounde d ;
Th e o riginal sounding places on a range were identi fie d by
first
h ol d in g the rope a
gainst the same stakes at the same graduations
as fo r the o rigi n al s o u n dings
a
,
-
.
m ,”
.
a
,
,
,
.
,
,
.
,
,
,
,
,
.
,
,
,
cr o
es
,
,
u nc
-
.
,
’
me
.
,
,
,
.
.
,
,
,
.
,
,
.
,
.
,
a
,
.
,
,
.
Th e P l
TH
a
E
R EDU C TI ON
or
S OU N DI NGS
.
fer ence A ft er soundin gs have been made in
Re
a
f
i
s nece ss a
ive
n
locality
or
over
a
given
area
it
ry
to
reduce
them
g
tum or plane in order to determine correct elevati on s
to a com m on d a
of the bottom at all points where individu a
l s o un d ings were made
ne o
,
.
,
.
M A K I NG S OU N D I N GS
65
a
a
S i nce
i n all bo dies o f water the water surface is subj ect t o fl uctu
tion s in height it is customary in sounding work to take f o r a d atum
s ome k now n st ge o f the water t o which all observed depths re
referre d S uch a d atum which is usually a very l ow stage o f the
water is c o mm o nly called a plane of reference
In tidal waters the elevation of mean low tid e is generally taken
s the pla n e o f reference a n d upon maps or charts showing depths
a
of s o u n dings ma d e in tidal waters unless otherwise indicated the
depths S h own are below the level o f m ean low ti d e When s o u n d
i n gs re ma d e in a lake or a reservoir or other similar b o dy of
water is is customary to use as the plane of reference the lowest
known stage o f the water In rivers or streams or vari ble stage th e
l ow water stage of the river is used in some instances as the plane o f
refere n ce ; in other i n stances the bottom elevations as determined by
S ou n dings
are referred to the general datum of the survey In
m any cases the plane o f reference is taken as the l o w w ter contour
of th e porti o n o f the river so unded and n o t the horizo n tal p l n e
passing thro ugh the l o w w ter mark at s o me selected po i n t
W ter G g es In o rder t o determine the height of the water t
any req uired time during a hydrographic surv ey it is necessary to
empl oy s o me suitable method to indicate the water level at all times
This is generally done by mean s of water gages which sh ould be
l ocate d at such places as are most suitable a
n d convenient for obser
re of two general kinds viz
vati o n Water gages for this pur p ose a
nd a
sta ff gages a
utomatic ga
ges
”
The type of water gage co mm only
S t fi G g es
used in regular sounding work i s the staff gage
which resembles in general appearance a self read
ing level rod A commo n form of staff gage is
fro m three t o
m a d e of a b o ard o r strip of w oo d
6 i n ches wide and from one half inch to one inch
thick a n d o f suitable len gth It is pai n ted wh ite
an d is graduated on the face to feet and tenths
The n umerals indicating tenths are black and those
ff
designating feet a
A good form of st a
re red
gage is illustrated in Fig 46 ; in this form the 5
te n th marks and the foot mark s are made con
spi cu ou s in order to facilitate reading
A staff g ge for use i n sounding work S hould
usually be securely attache d in a vertical po sition
to a stak e or a pile driven in the water or to the
face of a wharf or a sea wall or other suitable place w here it w ill
,
a
.
,
,
.
,
,
a
,
.
,
,
a
,
.
,
,
a
,
a a
-
a
.
a
,
a
.
.
,
.
,
.
,
a a
.
.
,
-
.
,
-
,
.
,
.
,
.
,
.
a
,
.
,
66
HYDROGRA PH 1 c
R
S U VEYI NG
a
be at all times accessible and where it can be e sily read I n s ome
insta nces in ti d al waters a small piece of b o ard is attached to th e
gage for a marker or indicator When this is don e the m rk et
should be s o arranged that it will fl oat up o n the water
d irectly i n
fr o nt o f the gage at all stages the arrangement bein g such that the
graduati on d esignating the water level will show at the upper su r
face oi the marker Th e marker should be pai nted white ; when it is
use d the gage reading ca n be q uickly see n
On rivers of widely varying stage it is usually not practicable t o
set in a vertical position a
sin gle gage that can be conve n iently read
at l l stages of the water In a case o f this sort two or more gage s
set separately may be used ; each gage is attached to a po st or a tree
or other suitable obj ect that is conveniently loc ated They shoul d
be so arranged that when the top of the lower g a
ge is submerged
the lower part o f the next higher ga ge will show the proper reading
I n a case where the stream has
e
slopi n g banks the gage m a
be
y
set at a suitable inclination t o
conform to the S l o pe of the bank
5
I t sho uld be attached to per
manen t obj ects or to s takes or
o
sts
d
riven
fi
rmly
into
the
p
ground It may be arranged in
several
sections connected to
G ae
te
Wa
d
in l
Fi gA l
g
gether but of varying inclina
tions t o c onform t o local changes of sl o pe ; such an arrange m ent is
show n in Figure 4
graduations
should
marked
on
the
r
od
N
o
b
e
7
until it h s been properly secured in pl a
ce Th e graduations sh o uld
’
then be determined by the aid of an engineer s level ; they can be
marked by painted lines or by copper tacks or by metal strips as
m
be
m
ost
conveni
nt
for
use
e
y
e
A u tom ti c Ga
hen
a
continuous
record
of
the
fluctuations
o
f
W
g
the water surface is req u ired an automatic or self registering gage
s hould be used
A simple form of automatic water gage for use
i n ti d al waters consists of a float which is enclosed within a per
for ted vertical box or case a n d which rises and falls with the
tide The enclosing box which is long enough to cover the entire
ra
nge o f the tide has a
n ope n ing near the bottom
through which
th e water enters ; by this means the water s u rface inside the b ox
nd
is always the same as that outside a
not being a
ffected by the
m o ti on of the outside water is always s m ooth The moti on o f th e
fl oat a
fter being reduced by mechanism is rec o rded by a scribe or
,
,
.
a
,
.
,
,
,
.
.
a
,
.
,
,
.
.
.
.
i
.
,
"
-
c
r
ine
.
,
a
a
.
.
a
,
,
,
.
.
-
,
.
a
,
,
,
,
.
,
,
,
,
.
,
,
,
M A K I N G S O U N D I N GS
a
a
a pencil on a ro ll o f p per which passes at u n iform speed o ve r
cyli nd er rev o lve d by cl o ckwo rk The path o f the pe n cil o n t h e
paper i n dicates the stage o f water during a n y give n peri o d o f time
of the observati on s
A form of automatic ti de gage w hich
S el f R e d i ng Ti d e G ge
is called a self reading gage was devised by M r J ames H B ac o n
U S A ssistant Engineer for use i n hydro graphic w o rk i n Cum
Th e arrangement comprised a rectangular shaped
berla n d S ound
structure built at the edge of the water and enclosi ng mechanism
fo r operating the gage The structure consisted of a ro o m o f
cubical form about 8 feet each way inside a n d mounted on suitable
suppo rts with its bottom 1 2 feet above the level o f mea n l o w
water On the east west and south sides of the cube were painted
c ircul r di ls o f a pattern similar to that sh o wn in Figure 48
,
.
a
-
a
.
,
.
-
.
,
.
.
,
.
,
-
.
,
,
.
,
,
,
a a
.
,
.
Fi
4
8
g
.
.
a
l f
Di
or
S
e
lf r e a
d ing
-
Ti d e
a
Each
dial was provided with a large pointer or hand that w s
actuated by a float being connected thereto by gearing so that for
a u se o r f ll o f 1 foot th e han d m o ved thr o ugh exactly one twel fth
of the circle E ch dial was graduated into twelve I fo ot mark s
th e feet b eing subdivided into tenths as shown
Th e p o siti on o f
the hand on the dial indicated at any time the exact height o f ti d e ;
°
a
.
,
,
a
-
-
,
,
.
HYDROGRA PH I C S U RVEY I NG
68
p o sitio n sh o wn i n Figure 48 reads
feet abov e the zero p o int
o f the gage which p oint is referred to mean low tide
I n Figu re 49 is sh o wn
i n plan and secti o n the
mechanism o f this gage
adapted fo r a ra nge of
tide of fr o m 5 to 8 feet
The geari n g was so ar
ranged that each shaft
carrying
dial ha n d re
vo lved once during a
vertical movement o f the
gage fl oat thro ugh 1 2
feet
The float w s
heavy en o ugh to furnish
the power necessary to
move the m echa n ism as
shown and also t o oper
ate a recording tide
Ball
gage
beari n gs
were used to reduce fric
ti on
Th is gage could be
read under fav orable
conditions a c o nsider
able distance ; the height
ni s
of S e l fi r e a
Me h a
O f tide Cou l d be d eter
T
d
e Ga
l
e
q
g
mined from the dial to
within
of a foo t at the dista n ce of 1 mile
G g e R e d i n gs
In order that pr o per reductions may be deter
mined for obse rved soundin g s it is usually necessary to observe and
note the gage readings at suitable intervals durin g sounding w o rk
W hen sounding in tidal waters it is customary to employ a ti d e gage
r eader whose duties consist in readi n g and recordi n g gage height s
at i n tervals o f from 30 minutes to 1 hour or more according to th e
stage of water and the range of the tide
In the case of a lake or other similar body of water where but
little variation in height of water is li a
ble to occur gage readings
may be necessary only at infrequent interva
l s I t is often the case
that tw o readings a day one in the morning and one in the evening
In some instances however a small lake is quickly
re sufli c i en t
a
ff ected by heavy rains or by the condition of tributary streams an d
th e
,
.
,
.
a
a
.
,
.
.
,
,
m
c
a
a
“
.
.
.
.
,
,
,
.
,
,
.
,
,
a
.
,
,
,
MAK
I NG
SO
U N DI N GS
69
rises and falls with co nsiderable rapidity Under such cond iti ons
freq uent gage readi ngs are re q uired
I n river that is subj ect to variati on s in stage the gage sh o ul d
be read with m o re or less fre q uency as m y be require d I f the
water is rising or falling during the s o un d ing w o rk gage rea d i ngs
may be necessa ry at h o urly intervals or even oftener ; o rdinarily
h o wever two readings a day will be suffi cie nt
.
a
.
a
.
,
,
,
.
H YDROGRAPH I C S U RVEY I N G
0
7
C H A PT ER I I I
NOTES
.
—
WOR K S O U N DI N G
—
BOO K A N GLE
BOO K
OFFI CE
—
—
S OU NDI NG NOT ES S EX T A N T NOT ES CO M P LET E NO T ES
—
—
T I DE BOO K PLATTI N G NOT ES THR EE A R M PROT RA CTOR
A ND
-
H YDROGRAPH I C M AP S
CHART S
A ND
.
The field no tes taken during s o unding operati o ns are kept i n vari
o us forms acco rding t o the method s empl oyed in l ocating the s o un d
i n gs Wh en locati ons are made with o n e or two instruments o n
sh o re or i n the s o unding bo at tw o ge n eral forms of notebooks are
used ; these are called respectively A ngle B ook and S ounding Book
F o r o ther metho ds o f locati on the f o r m of notes will depen d upo n
the m eth o d used For work in tidal waters where a ti d e gage
reader is req uired an additional fo r m o f notebook is used called the
Tide Boo k
When sou n dings are located by m eans of time intervals between
kno w n p o i n ts the field no tes contain the depth and the exact tim e
fo r each s o un ding In this case the s o unding n otes are kept by the
rec o rder i n th e s o u n ding bo ok in the m anner S h o wn in Form 1
The no tes take n in the boat are recorded in the first three columns
on the left A fter determining the lead line correction s and a
scer
taining fro m the n otes of the tide gage rea d er the corrections n eces
sary for the stage of tide the reductio n s are applied to the observed
depths and the notes are completed as sh o wn
This f o rm of notes is practic a
lly the same for all methods except
th e tw o meth o ds of location that were last describe d
I n all cases
w h ere used these notes are kept by the recor d er in the s o unding
book ; when completed as j ust described they m a
be
kept
in
that
y
fo rm for permanent record
The fiel d notes taken by each of the obse rvers who locate the
s o un d i n gs are entered in the a n gle boo k in the manner shown in
Fo rm 2 wh ich represents a page from an angle bo ok
When s o u nd i ngs are loc ted by one angle measured on shore
two and s o metimes three field books are required t o contain the
co mplete notes
These comprise : I the soundi n g b ook sh o w n in Fo rm 1 used
by th e reco r d er ; 2 the angle bo ok use d by the o bser v er and sh o wn
For work in tidal waters a third fi eld book is required ;
i n Fo rm 2
.
,
,
.
,
,
-
.
,
,
,
.
,
,
.
.
,
.
-
,
.
.
,
,
.
a
,
,
.
,
,
,
.
,
,
,
.
,
,
,
HYDROGRAPH I C S URVEY I N G
2
7
this is called the tide book and it is used by the tide gage reader
’
I II Form 3 is represented a leaf from the tide gage reader s note book
in which is shown the fo rm of notes required to be k ept It i s
see n that there are columns in which to reco rd the direction a n d
force of the wind and als o to enter the reduced readings of the tide
gage In many l ocalities the e ff ect of the wind upon the water level
is c o nsiderable un der certain c onditions of wind a n d tide I n such
cases it is necessary to take into account the variati on s cause d in
the height of the water surface thereby and to make the necessary
reducti ons
For convenience in platting the reduced sou n dings are frequently
entered in the angle b o ok in th e two columns show n ; in such c ses
the a n gle b oo k forms a c o mpl ete record
When s o undings are l ocated by two angles measure d o n sh o re
each observer uses an angle bo ok in which to enter his field n o tes
’
These are kept in the manner S h o w n in Form 2 while the rec o rder s
notes are kept as shown in Form 1 In non tidal waters the three
sets of n otes that have been descri bed are all that nee d be used
For w o rk in tidal waters a tide gage reader will be required wh o se
notes are kept as sh o wn in Form 3 The complete notes may be
condensed for convenience i n the manner shown in Form 4
W hen tw o sextants are used in locating soundings the notes of
the reco rder and o f the tide gage reader kept as S hown in F o rms 1
E ch sextant observer enters his n o tes i n his
a
n d 3 respectively
field b ook noti n g for each sounding the number the time a n d th e
sext n t a ngle to two o f three selected shore Obj ects In Form s 5
l ocating
n d 6 are shown the fi eld n o tes of two sextant o bservers
a
identical s o undings Th e tw o sets o f notes may be co n d ensed i nto
on e in a manner similar to that explained for tra n sit o bserv ati on s
For s o undin g s located with transit and stadia the fo rm o f field
notes taken by the obse rv er is practically the same as for similar
dia observations on land S ince such forms o f notes are ge n er
st a
lly familiar to engineers and surveyors it is not c onsidere d necess ary
a
The other f o rms o f notes which are k ept
to illustrate them here
by the recorder and the tide gage reader are practically the same
for most methods of sounding l ocati o n
Wh en soundings are located bv ma g netic bearin g s the fo rms o f
notes used by observers is ver y similar to that used f o r sextant
observations The only essential di ff erence in form is that for
work the w o rd bearings is substituted fo r the w o rd
c ompass
f ngles in Forms 5 or 6 and the several bearings are given instead
of a
n gles
-
,
.
-
,
.
.
.
.
a
.
,
.
,
-
.
.
-
,
.
.
a
.
a
-
,
,
.
,
.
.
.
.
,
-
,
.
.
,
.
‘
a
“
”
,
.
”
N
OT ES
A ND
O FFI CE
L IGH TH O
US E W H A R F
D at e of M onth 1 7
O B S E R VA T I O N S O F T ID E S A T
Ye ar , 1 90 3 M onth , A u g
.
00
55
15
70
35
1
1
2
2
00
30
00
30
8
8
9
9
3
Form
3
.
Ti d
e
k
B oo
.
N
.
N
.
W
W
w
w
w
W OR K
.
.
.
Li g ht W ind fr om
N W chan g i n g
to W
.
Y O F M OB I L E B A Y
J u n e 20 1 90 2
.
.
.
,
9
58
13
20
2
19
12
25
26
27
32
35
28
35
30
44
22
9 32 7
4
Fo rm
I
4
.
.
Co m p l e te N o te s
a
.
.
.
.
.
,
.
.
.
1
3
.
d sm a
n
WI L LI A M S Ob s erv ers TA Y LO R L ea
COR T R I G HT Ob s erv er
—
D avi s ! ero s to S taB H
B Tr n sit N o 331 2
—
B Tra n s it N O 2408
W ill iam s ! ero s to S taA B
,
.
.
,
O F O N S L OW B A
M y 23 , 1 90 2
W I L L I A M S , S ext nt N o 1
R e cord e r
A R R I S L e adsm an
MA S ON
,
Y
Y
a
.
a
.
.
H
.
.
,
.
R E M AR KS
—
23
Li g hth o u s e
S ta
—
25
S ta
Churc h S p i r e
23 2 5
5
.
S ext
at N
n
o te s
.
.
.
.
.
.
.
,
.
S UR V E
Fo r m
,
,
DA V IS
.
.
.
.
S UR V E
No 1
No 2
.
,
10
10
10
10
10
.
.
.
.
.
.
HYDROGRA PH I C S U RVEY I N G
74
S URV EY OF ON S LOW
M
a
y 23
J A CK S O N
M A S O N R e c o r d er
,
,
1 90 2
S ex t
nt N
a
B AY
.
2
d sm a
H A R R I S L ea
n
,
.
o
.
.
.
,
RE M
25 2 7
6
aN
S ext
.
nt
AR KS
—
25
Ch urch S p ir e
S ta
—
27
Fact o ry Ch im n ey
S ta
-
Form
,
o tes
.
.
.
.
.
.
S OUN DI N G S I N M O R R I S C A N A L
M o nd a y
J u n e 6 1 904
Pr e vi ou s to D r ed g in g W or k
J ON E S
,
In
a
,
,
.
S M ITH ,
ch r g e
W I LLI A M S
.
.
.
A s s i stants
R E M AR KS
48
13
7
00
40
3
00
—
—
7
Form
21
_
14
.
27
6 2
31
26
—
6 4
19 5
27
S ou n d i n g N o te s
7
22
64
15
7
35
18
32
fl
37
1
47
50
00
36
34
40
a
t
a
da
i
D th a
t
d i
a
t
a p
d i ta
d
ad
i a
t
a i f t ad
th
a
a
d f
“
ta
ti
k f
ta
i h
W
s u rf ce
er
um
ep
.
49
_
46
ey
00
—
49 5
n
re
re m e
l e ft to
r
g
re s s
n
t
or ;
n
ro m
10
r om
es
s
ex;
or ,
ee
s u re
on
s
re
en o m
s
e
s
re ex
n ce s
s
s
n n u m er
p re s s e
73
—
_
.
,
S ou n d i n g s
4
.
.
.
I
S OU N DI N G S I N M O R R S C A N A L
Thurs d a y ,
J un e 9
,
1 904
A ft er d r e d g in g
S M IT H
char g e
W I L LI A M S
.
.
.
J ON E S ’
In
at
A S S I st
.
n s
,
R E M AR KS
S ou nd i ng s
.
QQ
2
L
L3
4
12
22
.
.
00
-
F orI T S
.
8-2_
_
.
.
32
82
80
42
l
W
50
tu m
00
fro m
th e y
fil m
3
11
21
31
41
49
00
81
81
8 2
81
00
S ou n d i n g N o te s
.
a i da
a
di ta
i
a
k
ta
a f l ft t
a
t
s u rf c e
er
.
s
s
re
s
nces
t on
r om
st
e
re
es :
o
N
OT ES
OFFI CE
A ND
W OR K
75
When s o undings are l oc ated by direct measureme n t on th e ice
the field meth o ds are similar to th o se used i n land surveys I n such
c ses n o parti cular form o f notes need be speci fied for rec o r d i ng
s o und ing l o cati o ns since the ordinary form s o f n o tes used in su rv eys
are suitable for this purp o se
Fo r s o undings that are located upon a fix ed range desi gn ated
by a gr aduated wire or ro pe the n otes m y be kept i n a f o rm similar
t o that used fo r recording cro ss secti on n o tes A good form fo r
reco r d ing notes of this kind is sh o wn in Fo rm 7 The n o tes there
shown represent soundings across the canal shown in Fig 45 at
three of the stations shown The soundings were made previ o us to
d redgi ng operations the ob ject being to ascertain the depth o f
dredging required and also to determine the quantity of material
required to be removed from the channel
I n Fo rm 8 is s h own the notes of soundings made over the same
ranges after dredging o peration s were completed
These latter
soundings were made to ascertain if sufficie nt dredging ha d been
d o ne t o make the cha n nel c onform to the required dimensi on s
S peci l For m s of N otes
For locations of soundings made by
’
Cooper s method in which tw o leadsmen are empl o yed as previously
described a special form of not es is used I n order to e x plain
clearly th e m eth od s used for keep i n g notes a full set of notes will be
given ; they are fi eld notes from an a
ctual survey made under the
superv ision of M r Cooper
a
.
.
a
,
,
-
.
.
,
.
.
,
,
.
.
a
.
.
,
,
,
.
'
.
.
form of sounding notes taken is sh ow n in
Fo rm 9 Th e notes as shown are complete as regards depths ; they
sh o w the time of making l o cated soundings gage readings and
observ ed and reduced soundings On the right hand page is sh o wn
the test measurements of the two lead lines that were used
S ou n di ng B ook
Th e
.
.
,
,
-
.
ai
.
The two sets of locatio n notes taken are sho wn
in Forms 1 0 and 1 1 They contain the number of the range o r
s o unding line the time and number of each located position also
the angles read to positions of observed soundings In this i n
stance one of the observers read the tide gage and entered the read
ings in the colum n headed Gage
Th e three sets of notes wer e
k ept i n ordinary transit books 4% ins by 7 ins in size
’
B c on s M eth od
I n Form 1 2 is sho wn the form used for record
’
ing sounding notes that were taken when Bac o n s meth od w s used
A s indicated two sextants were used the observations bein g take n
t o fo ur kn o wn obj ects on sh o re as explained o n page 5 7 and s
illustrated I n Fi gure 35
Tr
ns t
B ooks
.
.
,
,
.
-
“
”
.
.
,
a
.
.
a
.
,
,
,
.
,
.
a
H YDROGRAPH I C
6
7
URVEY I N G
S UR V E Y , LON G I S L A N D C R O S S I N G
M y 1 6 , 1 904
A S H A R TR I DG E R ecord e r
P N S TR O N G i n char g e
ES T
I M A TE
S
a
.
.
,
.
.
.
.
.
LI N E
NO
.
,
.
42
R E M AR KS
Ho wa
rd on
aWi n g
aV nu
St
D m , N o 33
O strom on S t
Po i n t
Os trom r e ad i n g
1
a
.
.
.
e
.
s
.
Ga g e
.
TE S T O F L E A D
LINES
2
.
Fred J ones
a Ta
p
C
Le d
12
14
16
18
20
22
24
26
28
30
3
1 0 40
4
9
Fo rm
k
S ou nd i ng B oo
.
I
.
on
aV
St
.
.
nd ers on
Ta
p
Le d
‘
12
14
16
18
20
22
24
26
28
30
e
I
t
I
I
I
l
l
l
l
l
l
I
I
I
I
.
E S T M A TE S UR V E
I n st
e
A
a
.
Y L ON G I S L A N D
M
e
nu s
E
.
a
y 16
,
Poi n t
.
OS T R O M
,
,
1 904
.
aWin g D am
! e ro to S t
Tr n sit N o
a
CR O S S I N G
.
.
1
,
.
No 3
.
.
.
R E M AR KS
42
1 0 :37
38
39
40
41
42
43
Form
10
.
i
I
-
N
“
h-
N
U
G
“
k
A ng l e B oo
.
G a g e r ead at V en u s Poi n t
m e a n l ow w ater on G a
ge
,
T
ES T
I MA TE
S UR V E
.
St
on
aW in g D am
.
R
S
.
77
1
6
a
y
CROS S I NG
,
1 904
.
,
N o 33
.
,
H OW A R D
.
W OR K
Y L ON G I S L A N D
M
I nst
O FFI CE
A ND
N O ES
,
ro to
Tr n s it N o
.
!
St
e
a
.
2
aV
.
e
nu s
.
Poi
nt
.
.
R E M AR KS
38
39
40
41
42
43
Form
11
Ang l
.
e
3
4
5
6
7
k
B oo
45
01
50
05
23
14
57
328
326
323
32 2
320
31 9
31 7
1
2
42
!
e
ro to
St
aV
.
e
n u s Poi n t
.
.
D A TE
LI N E N o
BA CK
.
RA N GE
ON
A B
98 46
-
h
1
m
.
sd
2
m
3
15
16
17
18
19
.
4
3
2
1
9
.
95
10 4
11 3
12 2
14 0
14 9
15 7
16 6
99-45
CD
73 40
-
.
4
72 35
5
71 30
-
-
N or m
Tr
—S tat
ai t
ex
ns
a
a
S t ti on s u s ed
S ex t n t w or
n
or
e
k
R E C O R DE R :
OB S E R V E R :
Form
12
.
S
ou nd i ng
k
B oo
.
.
on e
.
A
.
B
.
ad C
n
c
.
D
a
.
F orm
c
ab
n
e u s ed
ei th er
HYDROGRA PH I C
8
7
S
URV EY I N G
Va
ri o u s o th er forms o f no tes tha n th o se that have been sh o w n
S uch variatio n s i n
re used fo r rec o rdi n g s o undi n g observations
a
fo rm d epe n d largely upon the individual preference o f the sur v eyo r
for so me particular form of notes as well as upon th e met ho d s us ed
i n perfo rming the w o rk
.
,
.
PLA TTI N G S O U N D I N GS
.
A fter s o undings h a
ve been made an d located they must be platte d
i n their co rrect po siti ons upon a map or chart in order to properly
design ate the sub aqueo us co n tours or to show the con figurati o n of
the bottom as may be req uire d In ma
ny instances especially when
a large area is sounded many m o re soundings are made tha n are
n ecessary fo r mapping purpo ses The reason fo r this is that since
th e bo tt o m is not visible th e en tire area is thoroughly s o unde d in
or d er t o avoid missing important changes of S lope I n platti ng
h o we ver it is customa
ry to sho w only Characteristic soundings ;
,
-
.
,
,
,
.
,
.
,
,
that is such soundings as will show with sufficient accuracy the
depth s of a give n area and the conformation of its bottom
I n platting s o undings upon a map or chart the po sition o f a
s o un d i n g is s hown by a dot lightly marked with a pencil The
depth o f each sounding is written in ink directly over the po int
desi gnat i ng that so undi ng aft er which the pencil mark is erased
The methods employed for platting s o undings vary according to
the methods by w hich they are located In a case where soundings
have been located on a range whose position is kn o wn a pencil line
representing the range is draw n to scale in its correct po sition on
the map or Chart Then if the positions of given soundings are
k no wn with respect t o the extremities of the range and the dis
tances between intermediate soundin g s are also known the positions
o f the known soundings are marked on the pencil line and the
po siti ons of the inte rmediate soundings are determin ed by scale
I f soundings h ave been located on a range by intersections either
by o ne sh o re angle or by t w o shore angles they C n be platted in
th e fo ll o wi n g manner : The range is fi rst laid Off on the map as
prev i o usly described ; the angles from the shore po ints t o the re
sp ect i ve l o cated positions are then measured on the map with a
pro tractor or th ey may be determined by natural tangents Lines
defin ing the several angles are drawn i n pencil t o intersect the line
represe n ting the range Each intersection will design ate the positi on
of a n observ ed sounding ; the positions o f intermediate soundin gs
can then be scale d
,
.
,
,
.
.
,
.
,
,
,
.
,
,
,
,
.
,
a
,
,
.
,
.
.
HYDROGRA PH I C S URV EY I N G
80
a
r e in the
and with a radius of 890 feet draw in pen cil a circu l r a
approximate locati o n and l ong enough to cover the positi on o f the
s o un d ing Next with B as a center and with a radius of 7 1 4 feet
draw an o ther circular arc intersecting the first ; the intersecti o n of
the tw o arcs l o cates the s o unding on the map
This meth o d of platting inv o lves a l on g an d te d i o us pro cess an d
is seldom used for locati ng soundings I t may be used as a ch eck
upo n impo rta n t l ocations that have been platted by a m o re rapid
meth od ; o r for the purpose o f locating impo rtant obj ects such as
buoys reefs etc
W hen soundings have been located by means o f se x tant angles
fro m the s o unding bo at t o three fixed po ints o n sh o re the m o st
co nvenient way to plat them o n a map upon which the three sho re
po ints h ave be e n previously platted is by the use of three arm pro
tracto r S ince this instrument is exclusively used fo r platti n g s o un d
i n gs that have been l ocated by sextant angles
description o f it will
be give n here
TH R EE A RM PROTR A CTOR
This instrument which is sometimes called a stati on po inter con
s ists o f a graduated a
rc to which is attached three arm s one fix ed
,
,
,
.
,
,
,
.
.
,
,
,
.
,
,
,
-
,
a
.
,
.
-
.
,
,
,
Fi g 5 2
.
ad
.
Th ree -A rm
Protr
at
c or
.
tw o m ovable the tw o latter revolvin g about a cen ter which is
comm o n to the three arms The two movable a rms are located on e
on either S ide of the fi xed arm ; they have their inner edges beveled
as shown in Figu re 52 Th e circ l e is divided into 360 degrees ; the
fixed or zero arm F is set so that its beveled edge is proj ected
th ro ugh the zero mark on the circle and also through the center C
o f th e i n strument The tw o movable arms M M re provided with
n
,
.
,
,
.
,
,
,
.
,
,
,
a
,
,
N
OT ES
I
81
W OR K
A N D OFF CE
vern iers readi n g to si ngle mi n utes ; als o with Clamp and ta ngent
screws T T as sh o wn A magnifying glass G is pivoted and
hinged t o the center of the circle and moves p a
ra
llel to the gradua
t io n s
,
.
,
,
,
,
,
.
ch instrument
a
is usually pro vided with three inter
cha n geable cylindrical centers On e center is provided with a
glass
botto m upo n which is etched two lines intersecting at the center of
the circle ; this is used for the purpose o f identifying locations after
they have been made An other center has a tr nsparent horn bot
tom with hole through its exact center ; when this is used the loca
tions are d o tted through the hole wi th a pencil point The thir d
fo rm of cen ter has a spring needle point which is d irectly over the
center o f the circle ; this is used for pricking the c en ter on the map
or chart when the protractor is in position
Three arm protractors are made in several d i ff er ent si z es ;
S i ze
they are u sually provided with extensions E E E for len gthening
the arms whe n required Th e graduated circle varies in size from
6
ins
ins
in
dia
eter
and
the
arms
are
made
fr
ins
t
o
o
1
m
m
5
%
5
to 1 8 in s lo n g W hen ex t ensions are used the arms extend from
2 5 ins t o 2 7V ins beyond the edge of the circle
Tes ti ng
Before making extensive use o f a three a
protr a
c tor
rm
it should be tested for centering and for accuracy of gr a
duation
To test for centering : First bring the two movable arms Close up
r m ; then Clamp bo th movable arms
against the stationary or z ero a
on e tightly and the other j ust tight enough to require a slight e ff ort
to move it M ove this arm entirely around the gr a
dua ted circle and
then back again to its former position Clamp it tightly then loosen
the oth er movable arm and proceed in the same mann er as with
the fi rst one I f the m ovable arms meet with slight and uniform
resistance while bein g revolved the instrument is well centered I f
however the resistanc e is uneven causing the arms t o stick or bi nd
at some places the instru ment requires adj ustment or proper cen
tering
d u t i on : First set one of the m ovable arms a
In testing for gra
t
1 80
and clamp it ; the n l a
the
instrument
flat
on
a
sheet
of
u
y
p
drawing paper and draw a pencil ma
rk along the edge of the clamped
arm also along the edge of the zero arm and m a
rk a point through
the center of th e instrument R emove the protractor and place a
straight edge on the paper so it will c oincide with the first pencil
line ; it should als o pass th rough the central poi n t and coincide
with the line which was drawn along the edge of the zero arm
Ma k e the same test with the other movable arm A S imilar test can
Cen ters
E
.
.
,
,
a
,
a
.
,
.
,
.
,
.
,
,
,
,
.
.
.
.
.
,
.
.
,
,
»
.
.
-
.
.
“
,
.
.
,
.
.
,
,
,
,
,
,
.
'
a
°
,
,
.
,
.
.
82
H YDROGRAPH I C
‘
S
URVEY I N G
a
als o be made by clamping the two movable arms o n e at 90
nd th e
other at
and also at o th er selected po ints arou n d the circ l e that
are 1 80 apart
Us e of Th r ee A r m Pr otr ctor I n usi n g a three arm pr otractor to
plat the p o siti o ns of s o undings that have been l ocated by se xt n t
an gles to three kn o w n sh o re p o ints the fo ll o wi n g met ho d is that
com m only employed Fi rst plat in their co rrect po siti on s the three
sh o re po ints ; then in o rder to plat the positi o n of a gi v en s o undi ng
set the m o vable arms to the two observed angles and cla m p th em in
positi o n Then place the instrument o n the Chart so that the edges
of the three arms will coincide with the platted positi on s o f the
three S h o re points ; th e center of the i n strument being i n a p o sitio n
on th e map corresponding to that of the bo at on the water at the
time the s o unding was l o cated Th e center of the i n strument will
then represent the positi on o f th e S o u n di n g and a po i n t is d otted o r
pricked thr o u gh the center o f the instrume n t on the map The pro
t ract o r is set i n the sa m e way f o r each o bserved s ou n ding and the
rocess
j
ust
describ
e
d
is
repea
ed
in
platting
individual
l
o
cations
for
t
p
s u ccessive soundings
°
,
°
a
.
-
-
a
.
,
.
,
,
.
.
,
.
.
ai g
,
It is o ften the case that the position s
of s o undings tha t have been l ocated by sextant angles require to
be platte d w ithout th e use Of a three rm protractor A go od way
to plat s o undin g s so located is as foll o ws : Fo r any gi ven s o u n ding
draw on tracing paper or tracing cloth three lines passi ng through
acommon po int an d including between them the two observed
a
ngles fo r that soundi ng Place the traci n g on th e map in such a
o
sition
that
the
co
m
on
point
will
be
i
n
a
p
o
sition
c
o
rresponding
m
p
to t h at of the soundi n g boat on the water a nd s o th at the three
lines wil l pass through the three platted po in ts The p o i n t o f inter
s ecti o n o f the three lines will then indicate the p o sitio n o f the sound
ing on the m p ; it sh o uld be pricked through th e traci n g o r other
w ise marked ou the map
S ince when this meth o d is used it is
n ecessary to practically m ke a protracto r for each l o cati o n the
method is seld om empl o yed especially when many soun dings are to
be platted
M eth od by C l cul ti on
Obser v e d l o cations made by sextant
ngles can be platted by calculating the respective d istances from
a
t he shore point s that have been previ o usly located t o the s o unding
A method of calculating such
bo at o r to the gi ven l o cated poi n t
d istances has been gi ven in the solution of the three point problem
previ o usly expl a
ined The distances h ving been f o und may be
r cs
u se d as radii and with the r esp ective sh o re poi n ts as centers
M eth od by Use of Tr
c n
.
-
a
.
,
,
,
.
,
.
a
a
.
,
,
,
,
aa
.
.
,
.
,
,
.
.
.
,
,
a
,
,
,
a
‘
,
T
O FFI CE
A ND
N O ES
W O RK
;
83
ca n be drawn t o a comm on intersecti o n thus l oc ating the soundi n g
I f pr eferred th e a n gles betwee n the base line and the respective li n e s
f
f
be
laid
and
li
n
es
o
un
d
ing
of sigh t f or a g ive n soundi n g m
o
b
y
these angles draw n to
comm o n p o int of intersecti o n whic h will
l o c te th e s o u n di ng This pro cess is both tedious a nd labo ri o us ;
it is no t give n as
method suitable for practical use in platting
s o u nd i n gs It is a d apted for use where pos iti ons are to be platted
w ith c on sider b le accuracy o r where it is necessary to check the l o ca
ti on o f a n importa n t o bj ect such as bu oy a wreck a sunken ro ck
or other obj ect o f similar impo rtance
Com p s s L oc ti ons
When sou n din gs have been located by com
pass bearings observed in the s o unding bo at their p o sitions ca n be
platte d i n the fo ll owing ma n ner : Th e two fixed points to which
r e fi rst platted in their c o rrect p o si
observatio ns ha v e been made a
ti on s o n the map Then in order to locate the positio n of a given
s o u n di n g pencil lin es havi n g the bearings given in the n otes fo r
that s ounding are drawn i n their proper relative positions thr o ugh
the tw o platted po i n ts The intersection of the tw o lines thus dr w n
l oc ates t he sounding o n the m p
’
B con s M eth od
S oundi n gs that have been l o cated by Bac on s
which has been described ca n be platted accurately a n d
m eth o d
rapidly when suitable preparati on s are made I n o rder t o facilitat e
platti n g the po siti ons o f soundings located by this meth o d fo r each
locality sounded a protracting sheet sh o uld first be draw n t o the
req uired scale up o n a skeleton or outline map of the area soun d e d
re subte nd
Th e protracting scale con sists o f a series of arcs each a
i ng a give n angle an d passi n g t h ro ugh the extremities of the platte d
bas e l i n e The ra nges are drawn radial o r parallel as the case may
be ; th e c o mpleted scale will resemble Figure 34 Figure 35 or Figur e
n
d
acc
o
r
d
i
n
g
t
o
the
met
hod
use
d
i
n
laying
o
ut
the
base
lines
6
3
ra n ges The base li n es ra nges a nd arcs sh o ul d be platte d to s om e
con ven ie n t scale upo n a sheet o f d rawing paper I n o rder t o pre
vent shrinking or wrinkling the paper used S hould be paste d
smooth l y on a drawing board which has previously been coated th o r
oughly on both sides with shellac The outline m p and the protract
ing scale sh o uld be d rawn i n their proper relative po sitions in indi
in k thus fo rming a basis to which all subsequent surveys over th e
same area may be referred T h e surv eys s ho uld be platte d o n trac
i n g cl o th to t h e same scale as that used for the s k eleton map I n
order t o plat the soundings ma d e in the successive surv eys the tr c
ing is lai d o v er the S k eleton map i n such a manner that correspond
The po siti on o f each ob se rv e d
i n g p o ints o n b oth maps will c o incide
.
,
a
,
a
a
,
.
,
a
.
'
.
a
a
,
,
a
a
,
,
,
.
.
,
,
.
,
”
,
.
,
a
,
a
.
a
.
’
.
,
,
.
,
,
.
,
,
,
.
,
a
,
,
,
.
.
a
.
a
,
.
,
.
.
,
.
a
HYDROGRAPH I C
84
S
UR VEY I N G
s o u nd ing ca n then be quickly l oc ated fro m the fi eld n o tes on the
skeleto n m p an d m arked on the tracing
Fo r e x ample : I f a sounding has been l o cated by observ ati on s to
tw o base lines as illustrated in Figure 35 n d the angular values
’
are as fo ll o ws : A ngl e to extremities o f base A B—6 3 oo ; angle
—
t o e x tremities o f base C D 56
then the point of intersection
o f the re thro ugh A B subtending
with the re through C D
s ubten ding
is readily found and locates the soundi n g at o nce
I f the s o u n di ngs have been made on radial ranges as illustrated in
Figure 36 or o n parallel ranges as illustrated in Figure 37 they
are platted by noting on the map the intersection of the given range
with the arc co rresp o nding to the angle measured Thus a sound
ing mad e on a radial range as for example range 1 Figure 36
whose angular measur ement is
is readily loc ted at the inter
section of these two factors at the point m rked x S oundings
made o n parallel ranges can be located and platted in a
similar man
n er Fo r intermediate angles between platted arcs soundings can
l to the an gular
be platted by interpo lating distances proportion a
interval
’
A method of platting with g reat rapidity the
Cooper s M eth ods
o
siti
o
ns
of
soundings
that
have
been
located
by
intersection
from
p
Cooper w hose method
S hore stations has been devised by M r A S
o f locating soundings has been previously described Tw o general
cases are contempla ted each requirin g di ff erent treatment I n a
case where a number of successiv e surveys are required over the
same area and the successive locations are m de from the same base
the foll o wing method is used : An outli n e map of th e area to be sur
tted on dra w ing paper w ith the base line drawn to
v ey ed is pl a
scale in its proper position Tw o protractors are then drawn with
their respective centers at the two extremities of the b a
se line or
corresponding to tw o
These
fixed s tations
protractors are drawn
suffi ciently large to
cover the sounded
area ; they are divided
degree s an d
i nto
the division lines are
drawn to intersection
This is called the
protractor S heet ; its
arrangement is illus
t r ted in Figure 53 i n
F
5
P
r ot r a
3
t
c
o
h
t
e
S
e
s
which th e e x tremities
a
.
,
a
,
°
-
°
-
a
a
-
,
‘
-
,
.
,
,
,
,
.
,
,
,
a
.
,
a
,
,
.
,
.
.
.
.
.
,
.
.
,
a
,
,
,
.
,
,
,
.
.
a
,
'
-
.
r
.
N
OT ES
a
OFFI CE
A ND
W O RK
85
A a nd B o f th e b se li n e A B are the respec tive centers o f th e tw o
pr otract o rs sh o w n The graduati ons for 5 are marke d with h ea vy
blac k lines th o se fo r degr ees wit h lighter li n es tho se f o r half
degrees with full red li n es and th ose fo r q uarter degree s with
d o t ted red lines The survey map is d raw n o n traci ng cloth t o th e
same scale as the skelet o n map ; it sh o ws the base li n e the sh o re
line and other necessary tOpogr ph i c features The skeleto n n d
the survey maps are so draw n that when the tracing is place d over
the outline map corresponding lines o n each will coincide
In
platti n g s o u nd ings located by i n tersections from the extremities o f
the base within the area c o vered the tracing is lai d o ver the o utli n e
map so that co rrespo ndin g lines will coincide ; any gi ven s o u n ding
is then platted at the i n tersecti o n of the two lines on the pr otractor
sheet c o rrespon d i ng to the observed angles of l o cation Thus re
n gles at A a nd B to a
ferring t o Figure 53 whe n th e o bserved a
’
the po siti o n
gi v e n sounding are respectively 2 1 30 and 44
of the sounding is seen to be at C This method is adapted fo r plat
ti n g l o cati o ns made in a circumscribed are ; it c n be us ed only fo r
the area f o r which it is designed
-
°
.
,
,
-
,
.
a
a
,
.
.
,
,
,
,
.
,
°
°
a a
.
.
Pl o tt i n g
Th e
foll o wing meth o d als o devised by M r Coo per is adapted
fo r platti n g rapidly and accurately the po sitions of s o u n di n gs lo
c ted b y i n tersections fr o m a kn o w n base
Th e survey map is drawn
t o sc l e on traci n g cl oth with th e base li n e platted i n its proper posi
ti on W h en so u nd i n gs are to be platted the su rv ey m p is place d
u pon
d r wi n g bo ar d o r table with one o f the instrument stati ons
s A
Figu re 54 directly o ver the cen ter of a large paper protrae
tor that has been graduated t o quarter degrees
The map and pro
a
a
aa
a
,
.
,
.
,
a
,
.
,
,
,
,
,
,
-
.
H YDROGRAPH I C S U RV EY I N G
a a
t r ctor re fasten e d to the drawi n g board after adj usting an even
t
h
e
li
n
e
on
pro tracto r to coincide with the base o r zero li n e o f the
5
survey The graduati on s o f th e pro tract o r are numbered at 5
interv l s t o co rrespon d with the azi m uth angles ; these numbers are
writte n i n p en cil on the survey map s o as no t t o di sfigu re the pro
tr ctor fo r future use From the other instrument station as at
B Fi gu re 54 radial lines are draw n at i n tervals o f
with the
z er o o f the graduations on the base A B
These li n es are in pencil ;
th ey are of suit ble len gth a n d are suffi cie n t in number to c over the
rea s o u n d ed Over stati o n B is fastened a l o ng paper arm so
rra n ged that it will revo lve around the stati o n as a center with o ne
edge passi n g through the center
This paper arm is secured I n
place by n ee d le passin g through its center ; it is o f suffi cient le n gth
to reac h t h e positi o n o f the m o st distant s o unding The outer end
is pro vi d e d with a vern ier reading to si ngle mi n utes
In l o cating the po siti o n of a given S o u n ding the line on the pro
tractor design ating th e angle read from A is noted ; the paper arm i s
the n revo lved until its vernier marks the ang le read from B Th e
p o sition o f the sounding is fo un d at the intersection o f the fiduci l
e dge o f the paper arm with the designated line on the pr otracto r
Fo r e x ample a s o undi n g whose observed a n gular values at A and
’
’
B are r espective ly 30 2
2
0
and
is
l
o
cated
at
positi
o
n
I
in
3
7 55
Figure 54
H YDROGRAPH I C M AP S A N D CHART S
M aps o f hy d r ographic su rv eys are made in a similar manner to
that us ed i n making ordinary to pographic maps A n o utli n e map
of a lake o r river survey should S h o w the lines and angles of the
survey th e triangulation s tations if any als o the shore line and such
details o f the adj acent topography as may be considered necessary
A co m plete hydrographic map of a river lake reservoir or of
other b o dies o f water shows in addition to the outline of the water
n d the surface t o pography the shape or con figurat i o n of the bo t
a
to m or o f the submerged porti on of the containi n g basin or valley
I n th e case o f a pro posed reservo ir wh os e area is to be subse
q uen tly flood ed a regular topo graphic map is ma d e sh o win g con
t our li n es at r eq uired intervals an d other necessary details
I n the case o f an existing body of water in which s o undings have
been made li n es o f eq ual depth corresponding to con to ur lines o n
a to po graphic map are draw n These lines are l ocate d o n a hy d ro
graphic map o r chart i n the f o ll o wing mann er : The s ou nd i n gs are
first platted acco r d i n g to o ne o f the meth o ds that h te bee n de
sc ribe d an d the depth of each s o unding is written directly o ver
,
°
°
a
.
a
.
,
,
,
-
a
a
a
.
.
,
,
a
.
.
,
.
,
.
a
.
,
°
°
.
.
.
,
,
,
.
,
,
,
,
,
,
.
,
,
,
.
,
,
,
,
,
,
.
a
H YDROGRAP H I C S U RVEY I NG
88
mi n us S ign is pre fixed to figures indicating elevati on s t o deno te that
such elevati on s re above and n o t bel o w the datu m
The curv es o f equal depth i n dicating the cha nn el lines a nd the
s u b aque o us c o nt ours
co rresp o nd to contour curves o n o rdi n ary
to pographic maps and are drawn i n a similar man ner I n th e case
of sub aque o us conto urs it is customary to i n dicate di ff ere n t depths
by characteristic lines a special form of li n e bein g used to design ate
each depth sh o wn The fom I s common ly used in drawing lines o f
equal depth are as fo llows
Fo r the shall o west c onto ur
For the co n to ur n ex t in depth :
Fo r the cont o ur nex t in d epth
an d so on fo r successive c o nt o urs
I n a d dition t o such details as have been described th e direct i on
of the curre n t is sh o w n by an arr o w and the direction s of true n d
magnetic n o rth are sh o w n b y suitable symbo ls
I n m n y cases it is co n sidered advisable t o S h o w th e p o siti on s of
survey stations and sounding ranges on a hydro graphic cha rt Thi s
practice h o wever is not comm on especially i n cases of cha rts i n
tended fo r navig tion purposes al one
a
.
,
,
-
,
.
,
-
,
.
.
a
,
a
.
.
“
,
a
,
,
H yd r o
g
r
a
h
p
i c.
Ch
a
r
t of
Ri v e r
.
I
O
A N D OFF CE
N TES
a
a
89
W OR K
In
Figure
is
give
n
a
hy
d
r
o
f
55
graphic chart o f part of a n avigable river showing the various
details that have been described including sounding ranges depths
and limits of cha n nel Th e lines of survey are drawn in light full
lines the ranges are shown by broken lines ; the angle stations are
numbe red consecutively d o wn stream and the ranges are design ated
by letters o f th e alphabet as S h own Depths of s o undings are ex
pressed i n feet and tenths at located positions of respective so un d
ings
The soundings w ere made on ranges acro ss the axis of th e
stream They were located by two angles measured on sh o re c
co rdi n g to the method previously described In this case the survey
line between adj acen t angle stations was used as a base an observer
w ith a transit being located at the angle point at either end o f the
base that was bei ng used A fter locating all soundings to which
goo d intersections could be had from a given base the upper transi t
was shifted d o wnstream one station beyond the other instrume n t
an d the survey line between the tw o stations was used as a new base
fo r locating s o undings This process was co ntinued until the entire
area had bee n s o unded
The o utline of the navigable channel and the successive depth
con to urs are each indicated by a characteristic line such as has been
described Th e Character of the bottom is written a
t such places
on the chart as correspond to the points where samp les were ob
t i ned during the soundi n g work
rt o
t
H y dr ogr lph i c Ch a
o
s
a
C
A
hydrographic
chart
o
f
a
harbor
f
or of an entrance to a bay is made in a m anner somewhat similar
to that described fo r a navigable river
I n making a chart of thi s
n ature such details and information should be placed thereo n as has
bee n speci fied fo r navigation or hydrographic maps and Charts in
gen eral Li n es of equal depth indicating sub aqueous contours are
draw n at the required interval apart Whe n required the p o siti on s
of r a
nges range points and of angle stati ons on the survey line are
also shown
I n Figure 56 is given a hydrographic map of the entrance to a
bay The o rigin al chart from which this map was taken is con
i n ed i n the An nual Report for 1 89 7 of the Chief of Engineers
ta
Unite d S tates Army having been m ade from actual surveys
In
this case for si m plicity many o f the s o undings sho w n o n the
origi nal chart h ave bee n omitted only characteristic soundi ngs being
sh own Th is is a goo d example o f the use of radial ra nges the
so u n di n gs h avi n g been made on range lines radiating fr o m the ligh t
H ydr ogr ph i c Ch
rt
R i ver
o
.
,
,
,
.
,
,
,
.
,
.
a
,
.
.
,
.
.
,
,
,
.
.
,
.
a
a
.
.
,
.
-
,
.
,
.
,
,
.
.
,
,
,
.
,
,
.
,
H Y DROGRA P H I C
0
9
S
U RV EY I N G
ho u se which is sh o wn on the No rth S pit an d which was used a
s a
centra
l ra n ge sign al The depths of s o undings are give n in w h o le
feet a
n d the su b a q ueo us c ontours are indicated by characte r i stic
lines i n a ma nn er similar to that used for the river chart
Th e two c h a rts that have been illustrated and described are fa
i
typ es o f this cl a
ss o f w o rk and se rve to S how in a gen eral way h ow
such maps o r charts are made There a
re various me thods o f filli n g
i n d etail s and o f expressing info rmati on on hydrographic maps a
nd
charts These meth o ds vary in mi n or details according to lo c al
practice a
W h en
n d the Obj ect f o r which a given map is intended
such maps are made for o rdinary engi neering purposes as fo r in d i
cat i n g i m pro vements to a channel or for proj ecting a new chan n el
or fo r sh o wing pro p o sed i m pr ovements etc depths are generally
nd c on t o u rs
e x presse d i n whole feet or in feet a n d t enths of a foot a
are usually draw n at intervals of from 3 t o 6 feet as in the t w o
cha rts gi ven o r at c l o ser intervals when required
Fo r n avi gati o n charts depths are c o mmonly expressed in feet to
the n ea rest qua rter of a foot up to a certain depth which is usu a
lly
2 4 feet o r f o ur fatho m s ; when this limit is passed depths are e x
pressed i n fath oms The deepest contours a
r e usually drawn at
i n terv als o f one fathom or 6 feet to the required limit
,
.
-
.
r
.
.
.
,
,
,
,
.
,
,
,
.
,
,
,
,
.
,
,
.
M EA S U RE M EN T OF DREDGED M A T ERI A L
C HA PTE R
IV
9
1
.
—
M EA S URE M E N T I N PLA CE
MEA S U RE M EN T OF D RE DGED M AT ER I
—
M EA S U RE M E N T I N S c o w s S URVEY To D ET ER M I N E CAPA CIT Y
—
—
M ET H OD B Y CON T OU R S M ET H OD B Y CROS S
OF A LA K E
S EC TI O N S
AL
.
When a
chan n el i s to be deepened or an excavation is to be made
u nd er water the w o rk is ordinarily d one by dredgi n g o r other
si m i lar meth o ds an d it is customary to dete rmine by suitable mean s
of measurement the depths to be obtained and the q uantity o f
material to be ex cav ted S uch measurements are usually ma d e by
s o undi n gs which are made and l ocated acc o rdi n g to such o f th e
meth o d s that h v e bee n described as may be suited to the cas e
In m os t cases th e area i nvolved is sounded both before a nd after
dredgin g o peration s the second measurement being made to scer
t in i f required depths have been attained als o to obtain data fo r
co m puting the quantity of material dredged I n s ome cases the
s econ d series o f soundi n gs
made after the completion of dredgi ng
operations is simply for the purpose of determining depths ; i n such
cases the q uantity of material excavated is usually m easured in
s cows or barges
W hen dredged material is measured i n place b y
means of sou n dings the operation is called M easuremen t i n
Place
W hen it is measured in sco w s or barges the operati o n is
called S cow M easurement ; both methods of m easurement will be
d is cussed and explained in order
,
,
a
.
a
,
a
.
a
,
,
.
,
,
.
“
,
”
.
-
”
.
M EA S UR E M EN T
PLA C E
IN
I n measuring ma
terial in place by means of soundings it i
important that corresponding soundings made at successive pe ri o ds
shall be in the same positi ons ; or else that the two series of s o u n d
.
,
s
,
,
,
ings S hall be made at such points as will correctly i n dicat e the
differences i n elevatio n of the bottom a
I n c l cu
t suitable points
lati n g the vo lume of material indicated by the di ffe re n ce i n heights
s h o w n by the tw o sets of measure m e n ts
meth o ds o f c o m putati on
simil r t o those used for calculating earthwork are used Thus
for examp le when material is dredged from a can a
l the excavati o n
i s rc lcu l ted as for a r a
ilroad c u ttin g ; when a large area is dredged
a
.
a
aa
,
.
,
,
,
,
,
HYDROGRAPH I C S U RV EY I N G
2
9
the e x cavati on is divided i n t o figu res m ost c o nven ien t i n shap e for
co mputati on an d the ordi n ary rules o f mensurati on re applie d
For e x ample it is required to calculate the q ua n tity o f m ateri a l
dredged in a can al fr o m s o u n din g notes that were take n befo re a nd
after dre d gi ng the n otes used will be th o se give n i n Fo rm s 7 a n d 8
I n this case three secti ons are sh ow n with an interval o f 1 0 0 feet
between adj acen t sections These correspon d to 1 0 0 f oo t station s
re computed in a si m ila r
in a railr o a d cutting and the quantities a
ma nn er to that used f o r earthwork computations in railroad w o rk
Th e two sets of s o undings at each stati o n are platted together o n
cross secti o n paper as S how n i n Figure 57 In this figure the
a
,
,
.
,
,
.
,
-
.
,
.
-
.
,
r
-
a
a
t
Di s t
nc e s
l
l
_ _
.
Fi g 5 7 C r
'
.
.
.
. .
n
l
-
i n Fe e t
-
S
os s
i
-
.
e c
ti
of
on s
C
_J
a al
n
.
d otted li n e and the lower full line for each station represe n t re
sp ec ti v el y
the canal bottom before and after dredging Th e area
included between the dotted line and the lowe r full line is the c ro ss
sectional area of the dred ged material This area is determined
for each station either by calculation from the notes or by countin g
the s m ll squares included between the two design ated lines on the
cro ss section plat or by measuring th e platted area with a pla n i
meter Th e areas o f th e sev er l sectio n s h aving been determi n ed
the quantities are calculated either by the method of average e n d
l formula
areas o r by use of the p ri sm od i a
I n this instance the
meth o d o f average en d areas is applicable and the calculatio n is
made as follo ws : The tota l cross sectional areas before dredgi ng
at stations 1 37 1 38 and 1 39 are re spectively :
and
A fter dre d ging the cross secti o nal areas at these re
square fe et
,
,
.
,
.
a
,
,
-
a
,
.
,
,
.
-
,
,
,
-
.
I I Y DROGRA PH I C S
94
URVEY I N G
I n this way the q uantity of material is readily determined by
In the case of a deck scow the material is placed in con
m easure
scer
ven i en t fo rm for measurement and its dimensions are then a
ta
i ned an d its volume calculated
.
.
.
,
W hen m easure m ent is made by displace m ent the volume of water
that is displaced by the barge is determined by first finding the re
specti ve depths to which the scow is i m mersed before and after
loadi n g The n knowing the dimensions of the scow an d the t e
sp ecti ve weights of unit volumes of the water in which the sc o w
floats an d o f the ma
terial with which the sco w is loaded th e l o ad
on the scow is determined by calculati o n
When a scow is not loaded the average depth of its botto m bel o w
th e water surface is called the depth of i m m en si on l i g h t
Whe n it
is load ed the average depth of its bottom below the water surface is
called the depth of immersion loa
ded
The process of determini ng
th e depths o f immersion on the S ides of a scow is called gagin g
W he n a sco w is light that is not loaded the line of the water sur
face al o ng its side is called the light waterline W hen the scow is
lo a d ed the w ater line along its sides is called the load water li n e
Thus i n Figure 58 in which is represented the longitudinal secti o n
,
.
,
,
.
.
.
.
,
,
.
.
,
.
aS
Long i tu d i n l
Fi
5
8
g
.
.
S
c ow
,
ec
fi on
Lo
ad
e
d
ad
n
Li
t
h
g
.
of a sco w o n the water E—
F is the po sition o f the light water line ;
W L is the p ositi on of the l oad water li n e h is the depth o f im m er
s i o n light
an d h is the depth of immersi on l oaded In o rder to
measure a load o n a scow it is necessary to kn o w its average depth
of immersi on both light and loade d ; also the respective le ngths o f
the light w ater li n e an d o f the loa
d water line
The average dept h o f immersion is generally the average o f ten
i
n
s
as
f
o
ll
o
s
on
e
at
the
ce
n
ter
tw
o
at
the
e
n
ds
and
two
:
w
g g g
mi d way b etwee n th e cen ter a nd the e n ds ; this makes five g gi ngs
on a side or te n g gi ngs i n all
The depth of each gagi n g is no te d ;
then to the sum o f the fo ur e nd depths add twice the sum of th e
fo ur intermediate depths a n d divide the total by 1 6 The resul t
w i ll be the average d epth o f i m mersi o n of th e sco w either light or
loa d ed as t h e case may be The average length o f; tw o m ea sure
,
'
-
,
.
,
,
.
a
.
,
,
a
a
.
.
!
,
.
'
,
’
,
.
.
A URE M E NT
ME S
T
DR EDGED
OF
M A ER
I AL
ments one on e i ther side of the s cow i s taken as the le n gth o f th e
water line
nner j ust explai n e d can for
Th e information obtai n ed in the m a
con venience be expressed by formula as fo llows : For an y giv en
scow :
’
length of light water line in feet ;
Let 1
le n gth of load water in feet ;
Let 1
’
Let h
depth of im m ersio n light ;
depth o f immersion l o aded ;
Let h
Let b
width o f s cow i n feet ;
weight i n pounds o f a cubic foot of water ;
Let k
weight in pounds of a cubic yard o f the m aterial to be
Let w
m easure d ;
the load of the scow
Let x
,
,
.
,
,
—h ‘ ) k
>< b
a
bod ies Of fresh w ter k
for salt wate r k
64
An empty sco w floats in a river with a d epth of
Example I
’
2 feet ; the length o f th e light water line 1
2
immersion h
4
feet A fter bei n g l oaded w ith dredged material the depth o f i m
8 feet and the length of t h e l o a d water li n e
m ersi on l o aded h
2
1
feet
The
width
of
the
sc
o
w
b
0
feet
a
n
d
the
weight
8
4
o f the material per cubic yard
po u n ds Req uired the
number of cubic yards o f material com po sing the l o ad By sub
sti tu ti n g the given values in equatio n and using the value o f k fo r
fresh water we have :
For
.
.
'
,
.
,
,
,
,
,
,
,
.
,
.
.
.
x 20
—
x ( 8 2) x
cu
F
2 750
.
yd s
.
I f instead of the n umber of cubic yards the wei ght o f
l o ad
in tons is required make w
number of pounds in a to n
S ubstituting this value i n e q uati o n and reducing we have
to ns
A sc ow floating in a bay was loaded with bro ken
Example 2
The results of g gi ngs made befo re a n d after l o ading were
s tone
a
s f o l lo ws
’
h
feet ; h
feet ; i
feet ; 1
feet The
width b
po u n ds
2 6 feet ; the weight o f th e broke n st on e
r
t
h
u
m
b
e
f
n
b
C
cu
uir
ubic
yards
of
st
on
e
l
d
R
e
d
o
e
d
e
r
d
e
e
q
y
p
,
,
th e
.
,
.
.
.
a
,
,
,
f
.
,
'
‘
.
.
a
HY DROGRAP H I C S U RVEY I N G
6
9
the sc ow By substituti n g the given values i n equati on and
u si n g th e value o f k for salt water we h ve
on
a
.
,
s
e
—zfl w m
w
cu
26 5 0
S URV EY
To
DET ERM I N E C A PA C I T Y
LA K E
OF
.
yd s
.
.
It is freque n tly n ecessary to determine with m o re o r less e x act
ness the vo lu m e of water c on tained in a lake or a sto rage reservo ir
o r any similar bo dy of water of considerable size In a case o f this
kind it is cust o mary a
n d proper to determine the require d v o lume
by m eans of a hy drographic survey S uch a survey sh o uld be made
in accordan ce with such of the meth o ds that have been descri b e d i n
this manual as are bes t suited to the case in hand In maki n g such
de te rminati o ns two general met h ods are used ; these are called re
spec ti v el y
M eth o d by Contours and M ethod by Cross secti on
as in the case previously described of calculating the capacity o f a
proposed reservoir Th e corresponding me thods of determinati on
for both cases are entirely similar in pri nciple ; the es s ential di ff er
e n ce betw een them consists in the method of conducting the fiel d
work of the necessary sur v eys I n order t o explai n Clearly the
rocess
o
f
making
a
capacity
survey
of
a
lake
o
r
of
a
sim
lar
b
od
y
i
p
of water bo th methods of determination will be discussed This
will inv olve some repetition because o f the similarity a
bove referred
to of the methods used fo r computing vo lu m es n d capacities in
the tw o cases
M ET HOD B Y CO N T OU RS
W hen a close approximation of the volume of water c o ntai n e d in a
lake or reservoir is required th e method of determinati on by c o nt o u rs
will generally a fford th e most nearly exact results W h en this meth od
is used an o utli n e s u rvey o i the lake is fi rst made ; then by means
of soundings depths at a s uffi cient number of points are found to
designate a series of contours of th e subm erged area Th e cont our
interval or the vertical distance betwee n adj acent contours is fixed
according to the slope of the ground and th e degree of exactness
req uired in the work Th e notes th us Obtained are platted and
map is made showing the o utline of the water surface and the
po sitions of the several cont our lines The surface of the water
an d the successive contours will lie in a series of parallel pla n es
Th e fig ure included betw een any tw o adj acent planes w ill t e
semble a prismoid whose end areas are th ose enclosed withi n the
co rrespo nding co ntou r lines a nd wh o se heigh t i s the contou r i nterval
.
.
.
“
“
”
”
-
,
,
,
.
.
.
,
a
,
.
.
.
,
.
,
.
,
,
-
a
.
,
.
.
,
,
.
H YDROGRAPH I C S U RVEY I N G
98
the height o f the pri smoid so taken is t wice the c on tour inte rval
In this case using the same symbo ls as abo ve the fo rmula for
volume i s
.
,
,
v + v
l
th a
t a
lake o r reserv o ir basin
contains an odd number of p rismoids and when the prismoi d al
formula i s used there will be a prism o id for which there is no
known middle area In a case of this kind the odd prism o id which
t the bottom may be calculated by average end areas
is usually a
with o ut causi n g m uch error I f the prismoidal formula is used a
m iddle area must be interpolated ; when this is done the process i s
s th a
the same a
t ex pl a
ined fo c a
lcul a
ti n g the capacity of a reservoir
I n s ome instan ces it will
be fo u n d
,
,
.
,
,
,
.
r
M ET H OD
.
BY
CROS S S EC T I O N
-
.
W hen it is required to determine with only a fair degree of a
p
o
r
o
ximation
the
volu
m
e
of
water
in
a
l
a
ke
a
n
d
it
is
not
desire
d
t
p
i n cur much expense or to devote much time to the w o rk the method
by cross section will usually be found both practical and e ffective
Wh en this method i s used the outline of the water surface is first
determined by s urvey using such method as is most suitable for
the ca se in hand The notes are then platted and an o utline map is
made of the water surface showing such topography as is required
The next step is to divide the area covered into a series of trape
z oi d s by parallel lines
extending entirely across the area from s id e
to side These lin es are proj ected on the map by se lectin g p o ints
on t h e outline for extremities of the parallel lines in such a man n er
s to form the best conditioned figures
The se lines are then located
a
in the field and con stitute aseries of sounding ranges ; at each
r ange
by m eans of soundin gs a
profile of the lake basin is made
a
n d the cros s sectional a
r ea
of the lake is determined for that ra n ge
This will divide the lake b a
sin into a series of figu res resembling
s
ris
o
ids
whose
ba
e
s
r
the
c
ross
sec
ional
areas
and
whose
m
a
t
e
p
ltitudes are th e p erpe n dicular distances between adj acent ranges
a
Th e vo lume of water c ontained in the lake i s determined by cal eu
la
ting independently th e volu m e of each prismoid and adding to
t
s thus found to ob ta
ether
the
partial
volume
in
the
total
con
ents
g
ke
lculati on may be made by the method of
o f th e l a
S uch c a
verage en d a
rea s or if more ex a
ct r esults are wanted the pri s
a
m oi d a
l formula is used
,
,
,
-
.
,
,
.
.
,
,
.
.
,
,
-
.
-
,
,
.
. .
,
,
.
ME
In orde r
A S UR E M E N T
OF
T R AL
DR EDGED
99
MA E I
illustrate this method of determini n g volumes a n ex
a m ple will be give n sh o wi n g its applicatio n in the case o f a small
lake A plat o f a lake is represented in Figure 60 in wh i ch th e
outline of the water is shown by the irregular line ; the series o f
to
,
,
.
Cro s s
S
t
ec ion s
60
f g
i
.
Pl
Pi
.
a
t
a
of
L ke
“
h
ow i n
e
g
,
ll
aa
P
r
el
c
S
n
e cr i on e .
straight full lines near the water line represent the several co urs es
o f the survey
which in this ca se is a closed traverse Th e dotted
horiz ontal li n es are parallel soundi n g ranges and the vertical dotted
lines sh o w the perpe n dicular distances between ranges
Let A A 1 A 2 A 3 and A
the a
reas of cross sections at A B
C D a
n d E respectively ;
ab c and d perpendicular distance s between the ranges A B
C D and E respectively ;
vo l u m es o f pri s moid s whose altitudes are a b
v
and v
v
v
c a
n d ( 1 respectively :
v
t otal volum e of water in lake
v
Va
V
v2
The ends A a n d E o f the figure representing the lake
re simply
n d the figure included between A a n d the cross
straight lines a
section on B is a
wedge ; similarly the figu re included between E
and the cro ss section on D is a wedge I n computing the volumes
,
,
,
.
,
,
.
'
-
,
,
,
,
,
,
,
,
,
,
,
0,
,
,
,
3
,
0
,
,
1
,
,
,
'
-
.
a
.
,
HYDROGRAPH I C S U RVEY I N G
I OO
o f the end figures each wedge is calculate d a
rism
o
id
on
e
o
f
s a
p
w ho se en d areas is z er o
I n c o mputi ng the t otal v olume of water in the lake by th e m etho d
of a
vera
ge end areas usi ng the s ymbols that have been gi ven we
ve the following equati o ns
ha
,
.
,
,
A, + A
aa
n
2
=
v A
( 3)
a
When the prism o idal formul is used fo r computing v o lumes i t
is good practice to fin d the middle areas by interpo lating
m ean
cro ss secti o n between t h e t w o end cro ss sections o f each prism o id
This is d one f o r a give n prismo id by platting t ogether o n cr o ss
s ec ti o n paper its tw o en d cro ss sectio ns and dete rmining th e m ean
This meth o d is illustrated in Figure 6 1 in
s ecti on graphically
which A B C and D E F represent respectively the cro ss secti o ns
made o n ranges B and C in Fi gu re 60 The d otted cross secti on
a
-
,
-
.
-
.
,
-
-
,
.
l
-
L
Fi
-
L _ L
l
6
g
.
-
L _
Met h od
.
L
.
of i nt e rpol
a g Mid d l
tin
e
Ar e
a
H I w h ich is interp o lated midway between the tw o secti o ns first
drawn is the middle area o f the prism o id wh o se end areas are the
two measured cr o ss sections
The mi ddle area of each prism o id is
determi n ed in a similar m anner I n the example under considera
r e shown in full lines whil e t ho se
tion the m easured cro ss sections a
that are interpo lated are sh own in d otted lines in Figure 60 Thes e
interpo lated cross sections are designated respectively by the sym
bo ls m o m
m
m a Then
using the same symbols to design ate
G
,
,
-
.
.
-
,
.
-
,
l
,
2,
.
,
II
PA R T
.
M EA S U R E M E NT O F S TR EA M FLO W
.
I N TRODU CTI ON
A n important department o f hydrographic surveyin g is that c on
n d measurements for the purp o se o f
cer n ed with observations a
dete rmi n ing the discharge of streams
.
.
The great increase i n the utilization of water power in recen t
years due t o the effi ciency of modern methods o f power transmis
si on by electricity has directed public attenti o n t o the value of rivers
s a s o urce of power
a
n d streams of considerabl e size
The value for irrigation purpo ses of water obtained from stre ms
has bee n dem o nstrated by its use in the reclamation of vast areas of
arid land This is especially true in the western part of the United
S tates where the general Government is conducting on a l rge scal e
a series of reclam a
tion proj ects inv o lving th e use of many streams
for irrigation
A third i m porta nt use to which rivers are s ubj ected is as a
source
of water supply to Citie s and towns A S the population i n crease s
and cities grow larger the qu estion of water supply increases i n
imp o rtance and streams of sufficient size for such a purpo se become
more and m o re valuable
In view of these facts the m ea
surement of stream flow o r as it
is sometimes called th e gaging of streams is a m atter of common
interest I n most case s where a strea m is to be gaged it is i m
p o rtant that the w o rk be correctly done especially where the
stream is to be utilize d for some speci fic purpose suc h s has bee n
stated
In m ost cases w h ere it is necessary to ga
ge a stream it is i m
po rtant that the discharge be correctly det ermined not only at o rdi
nary st a
ges of water but at period s of maxim u m and minimum flow
Th e latter sh o uld be especially co n sidered s ince the minimum flow
of a stream m arks its li m its as a
source of supply M any co stly
tions and estimates u po n
m ista k es have been made by basing calcul a
discharge measurements that were made in a s tream at o rdinary
l o w water stage instead o f at extreme l o w water stage in the stream
measured S uch c onsiderations h o wever are largely a matter of
n d are not strictly spe akin g within
j udgment rather than of detail a
,
a
,
a
.
,
,
a
.
,
,
.
.
,
,
.
,
,
,
,
,
.
a
,
,
.
,
,
,
.
,
,
.
,
.
,
,
,
,
HYDROGRAPH I C
104
S
U RVEY I N G
the sc o pe o f this manual The vari ous m eth o ds o f maki ng d ischarge
t h at re in common use will be discusse d ; these
m easureme n ts
meth o ds are applicable fo r any stage o f w ater i n give n stream
I n m aking measurements o f stream fl o w it is o f c o urse d esirabl e
that rapi d and ec ono mical methods be used when such meth ods re
of suffi cient accuracy There are i n co mmon u se
number o f
meth o ds o f measuring the fl o w o f streams I n general these m y
be classe d u n der tw o heads as fo ll o ws : 1 By determ ini ng th e
m ean vel ocity a nd the cr o ss secti o nal area of a strea m
f o r a gi ven
l o c tion ; 2 by means of weirs T h e latter meth o d is only ppl i
cable i n special cases and under favorable c o nditions ; it will be
discussed and described in detail later
In using the several meth o ds included under the first hea d th e
tw o facto rs t o be co nsidered are th o se that have bee n menti oned
vi z : th e cross secti on al area of the stream a n d the mea n vel o city
of the current The units comm o nly empl o yed are th o se expressi ng
the area of cross secti o n in square feet and the mean vel ocity o f
current in that cross section in feet per sec o nd
The cross s ectional are is c omputed from the soundings ma d e
at freq uent intervals acro ss th e cha nn el o f t h e stream These i n
terv l s sh o uld be s o selected that the bo ttom o f t h e stream m y be
con sidered a straight li n e between adj ace nt s o undings
The current vel ocity is usually dete rmined in secti on s o f th e
strea
m channel such sections e x te n ding between th e positi on s o f
a d j acen t sou n dings ; the summation of the areas o f the several sec
ti ons gi ves the t o tal area of cro ss section W hen the to tal flow o f
the strea m at s om e given point or stati o n is known and this fl o w o r
discharge is divided by the cro ss sectional area of the c ha n nel at the
stati o n the result is called the mean vel ocity o f the stream t the
po int in q uestion I n most me thods of stream measureme nt it is the
mean velocity that is s o ught to be determined ; it can not be deter
mined de finitely however until the total flow is known F o r de
term i ni ng the mean vel o city o f the current i n
stream there re
nu m ber o f meth o ds givin g results mo re o r less accurate A ll o f
these should be familiar to the hydrographic surveyor in ord er that
the meth od best suite d to the c o nditions at hand may be applie d
a
.
,
a
,
.
a
a
a
.
.
.
,
-
a
a
.
.
.
,
-
,
.
-
,
-
-
a
.
a
a
.
.
,
-
.
,
-
a
,
.
,
a
,
aa
.
,
.
,
,
.
D I S C HAR GE S TAT I ON
.
W h en it is req uired to dete rmine the discharge o f a gi ven stream
by a meth od i n which the area o f cross secti o n and the m ea n vel ocity
are factors a suitable place sh o uld be selected at which to m ke th e
necessary me surements and observ ati o ns ; such a place is called a
-
,
a
a
10
HYDROGRA PH I C
6
S
U RV EY I NG
a
a
t o 30 0 feet in lengt h ; t distances 1 0 0 feet apa rt o n th e b se
a nd at right an gles theret o two li n es co n stituti n g s o u nd i n g ranges
are laid off exte n di n g acro ss the stream S uch an arran ge m ent is
illustrated in Figure 6 2 which represents a discharge stati o n on a
river I n th is figure A B is a base 1 0 0 feet long and A C and B D
are the upper a nd l o wer ra nges respectively This arrangement is
suit ble fo r a base n ot mo re tha n 1 0 0 feet lon g ; for a lo n ger base
li n e additi o nal soundi n g ranges spaced at equal intervals apart
shoul d be lai d off
The base line and th e r a
nges havi n g bee n l id
Cross S ecti ons
off soundings are m ade and the cross section of the stream at each
ra n ge is d etermined I f the stream is not too wide the soundings
are spaced on a graduated wire or rope i n the manner previ o usly
descri be d I f the depth o f water does n o t exceed abo ut fo ur feet
the s o undi ngs can be m de by wading the depths being read o n a
graduate d ro d t o feet and tenths I n case w ding is impo ssible on
account o f th e depth of the channel or the temperature of the water
aboat sh o uld be used in m king the soundings
On large rivers where
a graduated rOpe can
~
wg
R
i
n
i
n o t be utili z ed the po
t
e
s
a
o f th e several
s i ti on s
so u n di n gs S ho uld be l o
c ted by a n gular me s
Dsc h a
ri on
e S ra
g
u rem ent
o r by st dia
b o th o f which meth o ds o f l o cati o n have been described W h ere a
series o f measurements are to be ma d e at successive peri o d s on the
Same sections the soundings may be l o cate d by the intersecti o n of
fixed ranges in the manner that h a
s been described
s
s
o
u
n
ding
T
h
e
—
r
w
T
T
T
r
T
T
T
r
T
T
T
T
havi ng been made
at suitable inter
vals the cross sec
ti on o f th e cha nnel
at e ch range is
d ivi d e d i n t o a
s e r i e s o f trape
zoi d s w ho se paral
lel si des re the
depths o f adj acent
n d
sou
n
di
n
gs
i on
t
t Di
C os s S e c t i on a
ha
t
a
S
g
wh o se altitudes are
10 0
,
.
,
,
.
,
,
-
-
-
.
a
.
,
,
,
a
.
.
-
,
,
.
,
a
.
,
a
,
.
a
,
,
.
,
'
c
‘
c
“
v"
:
,
a
a
a
i
r
.
,
.
,
,
‘
-
‘
.
-
-
T
-
-
-
-
-
-
-
-
-
fl
-
,
a
a
,
r
sc
r
e
,
.
a
IN
T RODU CTI ON
10
7
th e di st a n ces between th e respective s o undings I n each cross sec
ti on in additi o n t o the trapez o ids that have been men tioned the two
en d figu res ne rest the bank o n either side may be c on sidere d as
trian gles S uch arrangements are illustrate d at a
and b Figu re 63
whic h represe n t respectively the platted cr o ss sections on the ran ge s
A C and B D shown in Figure 6 2
-
.
a
,
,
,
,
,
.
-
-
-
.
,
S UR FA CE FLOA T S
.
In a case where exact results are n o t required or where facilities
fo r Observati on are li m ited vel ocities may be determined by the use
o f surface floats These may consist of small wooden chips o r
small disks of some light material that will float on the surfac e a n d
will not be a ffected inj uri o usly by water They S h o uld be s o c o n
structed as to fl oat n early flush with the surface so as to be but
little ffec te d by the win d In making observations the fl oats s ho uld
be p l ced in the water a considerable distance above the upper ran ge
in or der to acquire the full e ffect of the current befo re p ssi n g the
ra n ge On a narro w stream the ranges are marked with graduated
ro p es in the m anner previ o usly described Th e fl oats sh o ul d be
started successively at di fferent distances from sh o re in order to
determ i ne the current vel o city in di ff erent parts of the Channel The
observer notes the time of the passage of e a
ch fl o at between the
upper and l o wer ranges preferably by a stop watch an d als o no tes
the po siti on of each fl oat with respect to th e graduati o ns o n the
r opes In this way those porti o ns o f the stream that are covere d by
the paths o f di ff erent fl o ats can be n oted and th e co mputati o ns
thereby S impli fied The observations should be continue d until all
parts o f the channel have been covered
On wide rivers where the ranges are designated by range po les
o n the ba nk s the l o cati on of each float as it crosses a range c n be
determine d accurately by instrumental observation Fo r this pur
pose the instrument S h o ul d be set up over some known p o int on the
b se li ne preferably a sounding range and clamped with its vernier
at zer o w h en the telescope is S ighted along the base line or al o ng
the ra n ge up o n which the instrument is located Th e upper plate is
then uncl m ped n d the telescope is turned in azimuth with the line
o f sight fo ll owi n g the float A t the instant the float crosses the
upper ra n ge the observer is n oti fied by sign al from an assistant ; he
immediately ceases to tur n the telesc o pe no tes the time by his
watch Whic h is lyi n g open and face up on the upper plate o f his
i ns t ru m ent als o the angl e o n the vernier and records the i n for
mation i n his n ote bo ok This o peration is repe a
ted as the fl oat
,
,
,
.
,
.
,
a
a
.
a
,
.
.
,
.
,
,
.
,
.
.
,
a
"
,
,
,
.
a
,
,
,
a a
’
.
,
.
,
,
,
,
.
HYDROGRA P H I C S U RV EY I N G
108
crosses the l o wer ra n ge T h e i n strument u sed fo r reading the
angl es shoul d preferably be a tr n sit al tho ugh a pla n e tabl e may be
u se d w i th eq ually g ood results
Or d inarily the results obtai n e d by the u se o f surface fl o at s re not
of suffi cien t impo rtance to j ustify the use of instrum en ts f o r ob
se rv i ng th e po siti ons or paths o f such fl o ats on the water S i n ce the
observe d vel ocities when using surface floats are only r o ugh p
pro xim ti on s of the m ea n vel oc ities of th e filaments o r vertical sec
ti on s o ver which they fl oat it is a n unnecessary re fine m en t to
observ e th eir m o veme n ts with great accuracy
A good way to observe surface float vel ocities and o ne that is
sufli ci en tl y ac c urate for ordinary work
is as foll o ws : The fl oats
are launche d by a n assistant fr o m a bo at or wading at s o me dis
tance above t h e upper ra n ge The observ er with a stop watc h n otes
the time e x actly th at a fl o at passes the upper range ; he the n pr oceeds
quick ly t o th e l o wer range and no tes the e xact time the fl oat passes
that ran ge ; this operati o n is repeated for each fl oat that is launch ed
M uch time will be s ved if an assistant is stati on e d o n o ne range
t o sign al the p ssage o f floats t o the observ er w h o is at th e o ther
ra n ge
S urfac e fl oats s ho w approximately the surface vel oc ity o f the
stream t th e place of measurement The results obt ine d by thi s
meth od o f velo city deter m inati o n are su bj ect t o errors due to wi nd
and t o surface curre n ts and eddies The observe d vel ocity is t h at
o f the water surface while that require d for calculating the d is
charge i s the mean vel o city o f the entire cross section
The relati o n
of th e surface vel o city to the m ean velocity of the filament o r ver
tical secti on is n ot c on sta n t but for stream s of the same gen eral
c h aracter o f bed banks velocity etc the ratio is suffi ciently c on
stant t o be c o mputed with fairly good results fr om surface v elocity
obser vati o ns
Fro m the res ults o f a large nu m ber o f experiments and observ a
ti on s the c o effi cients obtained for converting observ ed surface
velo city into mean vel o city are as foll o ws : For ordinary s treams
d isc harging not mo re tha n 1 0 0 cubic feet per secon d on ston y beds
o f th e mean surface vel ocity o f the cross section will represent
In general it may be stated t h at
th e mea n vel o city f o r that secti o n
an d
depend
th e c o effi cie n t is c o mprise d wit h in th e limits o f
in g upon th e S i z e o f the cha nnel a nd th e nature of th e be d Th e
c oeffi cie nt w o u ld b e greatest f or large d eep rivers w ith sm oo th
u n i form ch ann els a nd le st for s m all shall o w stream s with ro ugh
bed s
a
.
,
a
.
a
.
a
,
,
.
,
,
,
,
.
a
,
a
.
,
.
a
a
.
.
,
-
.
,
,
,
,
.
,
.
,
,
,
,
,
-
.
.
,
.
a
,
,
,
HYDROGRAPH I C
I 10
S
URV EY I N G
illustrated a fo rm of d ouble float that has been used by the U nited
S tates Engineers in current observations in the M ississippi R iver
Th e surface float is an air tight buoy of galvanized iro n circular in
pla n and elliptical in cross section i ts m j or axis being ab o ut 1 0
inches and its minor axis about 5 inches The sub surface fl oat con
s ists of two sheets of galvanized iron each 1 2 inches by 1
i
n
ches
fas
5
tened at right angles as shown The flagsta ff c onsisting o f a small
woo den stick fits into a tubular tin socket 94; o f an inch in diameter
Th e principal obj ection to the use of double fl o ats in current oh
s erv ti on s is the uncertainty as t o whether the cord is ve rtical and
the consequent uncert a
inty as to the position of the submerged
fl oat An oth er obj ection is the m o difying e ff ect of the surface float
an d the cord upon the velocity o f the lower fl o at It is probable that
in all cases the velocity of the lower float is a ff ected to some extent
At
by that o f the upper one as well as by the fricti on of the cor d
a great depth the exposed surface o f the cord may exceed that of
the fl o at A third obj ection is the uncertainty as to the vertical
positi on o f the lower float since owing to changes i n depth of the
n d to local condition s
water a
the point of mean velocity may
c ha nge while the len gth of th e connecting cord must remai n co n
s tant in each run
This la st obj ection however should not prov e
seri o u s if t h e discharge station has been selected with proper care
so as to i n sure approx i mate u n iformit y o f depth throughout i ts
le ngth
ts
Loc ti ng P os i ti ons of Fl oa
ts a
re used for
S ince d ou bl e fl0 a
determining velocities in streams of considerable S ize it is generally
advisable to locate their ex a
ct positi o ns when crossing the upper
and l o wer ranges of a discharge station This may be done by
instrument observation in the following manner : Two observers
r e stationed
each with a transit a
on e at the upper and the other
at the lower range Each observer h a
s his instrument set at zer o
on the other instrument ; th e observer on th e upper range has the
u pper plate o f his instr u m ent unclamped w ith the telesc o pe directed
along the range The observer on the l o wer ra
n ge with the upper
plat e of h is instrume nt unclamped follows with his telescope t h e
t und er o bservation Th e floats are launched
m o vement of the flo a
t intervals at some distance above the upper ra n ge an d at t h e
a
instant a float crosses that range the observ er stati o ned th ere on
n d at the same instant starts a st o p
S ignals to the other observer a
watch with which he S hould be provided ; he then directs his tele
n d fo llows it with the line of S i ht
s cope t o ward the fl o at
e
r
O
n
g
.
-
a
-
,
,
-
.
,
,
.
,
.
,
a
.
.
.
,
.
,
,
,
.
,
,
,
a
.
"
'
.
,
.
,
,
,
.
,
.
,
,
.
,
,
,
,
a
,
,
.
I N T RODU CT I O N
I I I
the signal the o bserver o n the lower ra n ge wh o se tele sc ope
has bee n fo ll o wi n g the fl o at arrests i ts motion a n d no tes the ngle
between the line o f sigh t and the base line A s a ch eck on t h e
r eading o f the stop watc h he notes the time by his watch H e then
directs his telescope along his ran g e A t the instant the fl oat cro sses
his range he m akes a signal to the other obse r ver and al so no tes
the t ime by his watch Th e observer o n the upper range whe n h e
arrests the m oti o n of his telescope at the same
r eceives the s ignal
instant stopping his stop watch ; he then n otes the interval o f time
that was required f o r the float to pass fro m the upper t o the lower
and the a
ngle made by the line of sight with the base line
r ange
This Operation i s repeated with other fl o ats until a su ffi cient num
ber of observations have bee n made
I n Figure 6 5 let A C
n d B D represe nt the u p
a
s re
r
and
l
o
wer
range
e
p
sp ec t i v el y
of a d ischarge
s tation
and F and F the
Ri ver
respective positi o ns of a
iven
float
in
cr
o
ssing
g
t he m
The p o sition F is
4
A
located by the intersection
line O f S ight B F
O f the
Fi g 6 & Me1 h od of 0 b 5 e vm
P
ot h oi Fl oor
g
nge A C S imi
w ith t h e r a
la
rl y the position P
is loca ted by the intersection of the line of
s ight A F w ith the ran ge B D
A s each observer notes the passage
n ge u pon which he i s stati o ned he noti fi es
o f the float across the r a
the observer on the oth er range by a prearra
n g ed s ignal In s o m e
cases a wire circuit i s laid connecting th e two stations and signals
re gi ven with a telegraph S ounder
O rdi n arily however S ignals
m
be
given
by
sh
o
uting
or
preferably
by
calling
through
a
mega
y
ph one The path O f th e float between the tw o ra nges will usually
be a
curved l ine so mewhat longer than the perpendicular distance
bet w ee n the two range s Thi s will not a ff ect the computati o n h o w
ever
since the p a
th ta k e n by the fl oat is co nsidered that of the
v ertical filament in which the float moves ; the obj ect o f the meas
u r em ent is to de t erm ine the mean velocity o f discharge rather than
the actual vel o city o f s ome particular fila m ent or vertical secti o n o f
the water The vel o city of each fl o at is obtained by divi d ing the
distance in feet betwee n the upper an d lo wer ranges by t h e n umbe r
of s eco n ds required to pass from one range to the other
c ei v i n g
a
,
,
.
.
.
,
.
,
,
.
,
.
-
-
1
,
e
.
“
n
'
r
.
-
.
I
-
-
.
,
.
a
a
,
.
,
,
,
.
,
.
,
,
.
.
HYDROGRAPH I C S U RV EY I N G
T U B E OR ROD FLOAT S
T ube o r rod fl o ats co nsist o f h o ll o w tin cylin ders o r wood en rods
o f un i fo rm si z e usually from 2 to 3 inches i n diam eter They m y
be o f adj u stable len gth and weighted at the bott o m so t h at they will
flo at ve rtically with on ly 2 or
i
n
ches
o
f
their
le
n
g
h
ex
t
3
posed above the surface o f the
w t er as illustrate d in Figure
66
W h en h o ll o w tubes re
u se d they m y be w eighted by
filling th e lower part with
s and o r sh o t until th e tube
floats at the require d depth
Th e velocity of a ro d floa t
t
r e s Ro d Fl o a
is theoretically the same as
g
the mean velocity of the fil
The closeness o f the results will
m ent o r section in which it moves
depend largely upon the am o unt of clearance between the foot o f
the float and the bottom of the stream ; this clearance s ho ul d be as
small as possible without causing the low er ends of the flo ats t o
scrape upo n rocks or other obstructions a
t the bottom thus re
tarding t h eir m o vements I f the floats have much Clearance they
will n o t be ff ected by the fil m s o f least vel o city nearest the bottom
and the vel o city sh o wn will be too great
I t was state d by M r J B Francis as the results o f experimen ts
m ade by him
that ro d fl oats travel a little faster tha n the mean
velocity o f the water even for the depth of immersi on On the
other hand Coi Cunningham ano ther goo d auth o rity as a result o f
his experiments states that such fl o ats m o ve somewhat slower than
the water in which they are immersed
For o rdinary stream measurements however when rod fl o ats of
suitable length are used it is suffi ciently exact to call the observed
vel o city o f the float the m ean velocity o f the sectio n o r filament in
which it moves
The positions of r o d fl o ats in cro ssing upper and l o wer ranges
may be determined by the s a
me methods a
s those that have bee n de
scribed as being suitable fo r surf a
c e and double floats
Rod or tube floats are free fr o m many of the obj ecti on s
p
plicable to double floats since there is no uncertainty as to their po si
tion nor as to the point of mean vel ocity i n the chan nel They are
however not suitable for very deep rivers or for channels w h ere th e
depth varies co nsiderably o r wh ere weeds grow in the bed o f th e
stre a
m
.
a
.
,
,
,
a
a
,
a
.
.
a
a
.
.
.
,
a
.
,
.
.
.
.
,
,
.
,
,
.
,
,
,
.
,
,
,
.
a
.
,
,
.
,
,
,
.
,
‘
H YDROG RA P H 1 C
S U RV EY I N C
is given an illustration of a
Fteley curren t meter
A s there shown the instrument c on si sts o f
a whee l with helical va nes m o unted on a h o rizo ntal a x is or spi n dle
n d c o nnected by beveled gearing with a registe r o r c o unter
which indicates on a dial the number of revolutions o f the wheel
Th e registering mechanism can be thrown i n or out of gear by
pulling an attached cord
The dial wheels are protected fro m
floating particles of detritus by being encased in a box with a glass
Cover
Fo r observations w here i t is not convenie n t to draw the
meter out of the water or to th e surface fo r reading the register an
This is co nnected with the beveled gearing
electric register i s used
by an insulated wire as shown ; it can be kept close to the o bserver
i n a bo at o r on land as m o st co nvenient
The meter is attached to a metallic rod which is graduate d t o f eet
a n d tenths the zero of th e g radua tions being at the botto m o f th e
m eter frame
W hen in use the meter must be held in the water with the wheel
facing the current which causes it to rotate The ha n dle must
be maintained in a vertical po sition and the face o f the wheel must
be perpendicul a
r to the stream lines so as to obtain the full fo rce o f
the curr ent W hen the instrument i s i n p o s ition and i n readines s
for a measurement the observer aft er n oting the reading on the
dial o f the register warns his assistant who sho uld be pro vide d with
a sto p watch that he is ready A t the instant the observer pulls the
t rele ses the rev olving mechanism he calls o ut start
string t h a
to the a ssi st a n t who immediatel y starts his stop watch W h en the
stop to the assistant who i m
O bservati on i s ended he calls out
mediately stops th e watch and then notes the exact peri o d o f time
that has elapsed a
lso the number of revoluti o ns of the w h eel as
In the autho r s practice he has found th a
t
shown by th e dial
nd
th e best way to obtain simultaneou s action of both observer
s s istant in the matter of starting and stopping the meter and the
a
i s for the assistant t o closely watch the motion o f the
stop watch
t
observer s hand h olding the cord starting and stoppin g his watch a
the instant the cord is pulled
The Ftel ey meter as described is well adapted fo r w o rk in
on acco unt of its lightness simplicit y and
S hallow s treams
s mall
se of handling Th e author has ma de e x tensive use of this type
ea
with sati sfactor y r esult s in sm all streams that were not
o f meter
too d eep for w ading
On account of its f o rm this meter can be
stream thus obtaini n g velocitie s
h eld very close to the bottom of a
I t is how
c c ess i bl e fo r o t h e r t y p es of meters
a
t p oint s not fu l l v a
Th e Ftel ey M eter
In
.
Figure 6 7
.
a
,
,
,
.
.
.
,
.
.
,
,
.
.
.
,
,
,
,
a
,
.
“
,
.
,
“
,
,
,
'
a
.
,
'
,
.
,
,
,
,
,
.
,
,
.
,
.
,
I N T RODU CTI O N
Fi g 68
.
.
Pr i c e E
l ec tri c
C u rren t
1 15
Meter
,
w i th B uzze rs
.
a
especi lly
ev er not well adapted fo r observations in deep water
where the current is of appreciable force In such cases the
meter is n exc el lent type of instrume n t to u se
,
,
a
.
.
Price
H Y DROG RA P H I C
-
i ce
Th e P r
S
URV EY I N G
Cu rr en t M eter This is a di ffere n t type of m eter from
th t j u st described as will be seen by o bserving Figure 68 in w h ich
i s s ho w n a ph o t o graph o f two Pri ce meters with their e q uipment
n
Tw o fo rms o f this meter are m de On e fo rm is provided with a
similar to that described for th e
ele ctric re gi stering apparatus
The other form has an arrangement by w h ich t he
Fteley meter
revolutions of the meter wheel can be detected by sound ; this fo rm
is c lle d an ac o ustic m eter
The Price ac o ustic meter is extensively used i n the hy d rogra phi c
observatio ns o f the United S tates Geol ogical S urvey Th e following
descriptio n together with acc o mpanying illustrati ons have been
abstracted from W ater S upply and I rrigation Papers issued bv th e
S urvey
The m eter consists of a wheel containing five conical cups rota
ti n g ab o ut vertical axis which is con n ected by a copper wire cable
to a small battery buzzer and is so arranged as to make and bre a
k
co ntact with e a
ch revolution of the wheel ; this is indicated by a
peculiar sound called a
buzz In Figure 68 is shown two sizes of
Price acoustic meter as used by the D ivisi o n of H ydrography of
the United S t a
tes Geol ogi cal S urv ey
The manufacturers now
mak e only one size of this m eter which i s a
da
pted for both dee p
a n d shall ow water
Wh en in use in deep water the meter is suspended by a
double
co nductor cable of No 1 4 or No 1 6 flexible Copper wire heavily
i n sulated W ire of th a
t size is of suffi cien t stren gth to hold the
n d i t obvi a
meter and the weights a
tes the necessit y of addition a
l
rope for susp ending the equi p m e n t
I II Figure 69 is sho w n a
cros s section of
Cons tr u cti on o f M eter
a s m all Price Current m eter sho w ing details of c onstructi on Ref
erence will be mad e to this figure in the follow ing explan a
tion The
cable fo r holding the meter is attached thereto with a spring snap
h o oked into the circul a
r end o f the trunnion Th e heavy Copper
wires are connected with the two meter binding posts by smaller
p
n d m o re flexible wires ; one w i ze is threaded through a m etal l oo
on the yoke as sh o wn These wires should be flexible and l oo se
to allow the meter to swing free in the metal frame when it is in
use The meter is supported in the t runni o n a
s sh o w n
a nd is free
to swi n g i n a vertical plane Th e v ertical a
xis or cup shaft ter
m i n tes at the lower end in an inverted cone which be a
rs or turns
on a con e shaped point called the po int bearing This is the mo st
d elicate part o f the meter and sh ould be gi ven the greatest care sinc e
n d is li a
i t is ma
de o f highly tempered s teel a
ble t o be fractured or
"
a
.
,
,
a
.
.
,
.
a
.
.
,
,
.
a
,
,
,
,
.
.
.
.
.
,
.
,
.
-
.
.
,
.
.
a
.
.
,
a
.
,
-
.
,
H YDROGRAPH I C S U RVEY I N G
1 18
a
with a n o val shaped ecce n tric which m kes a contact with the spri n g
at each rev o luti o n o f th e meter wheel This c o ntact can be pro
l o nged o r sh o rtene d by bending the poi n t of the c o ntact spri ng in the
contact chamber in the desired direction Th e oval shaped eccentric
end of the cup shaft is d etachable and c n be removed by taking off
the cap holding the cups firmly n d pplying a
screw driver to th e
sm ll sl o tted head
Th e insulating nipple is made of hard r ubber and is likely to
b reak i f the bindi n g post receives a sharp bl o w
Before rem o vi ng
or replacing th e bindi ng post the eccentric shaped top of the cup
shaft should be taken out I f this is n eglected the contact spring
will be destro yed by the turning o f the binding post
In charging the battery cell used with the electric buzzer fur
n i sh ed with the current meter one half teaspo onful of bisulphate of
mercury is s ufli c i ent Fill the cell with water and insert the zinc
po le with the rubber sto pper attached W hen putting the battery
cell i n the leather case care must be taken to have the sm a
ll pl a
t
inum point on the lower end of the cell and the screw he a
d of the
rubber stopper make perfect Contact with the copper p l ates If the
buzzer makes but a faint clicking so und instead o f a buzz the metal
cap covering the buzzer should be removed a
n d the s m all
upright
brass point adj usted with a knife blade by bending until the arm a
tur e
pro duces the desire d sound The liquid should n o t be a
llowed to
s and pro
s it wou l d generate ga
remai n in the battery o vernight a
duce pressure su ffi cient to cause the cell to leak a
t the rubber stopper
and the solution escaping would de stro y th e l ea
th er o f the case and
the bra ss p a
rt s of the buzz er
-
,
.
-
a
aa
.
a
,
,
.
,
.
-
,
.
.
,
-
,
.
.
,
.
,
,
,
,
.
,
,
,
.
a
d Wigh
e
Fi g 70
.
In
.
Wei gh ts
ad W
n
e i gh t
V
a
ne o f
Sm
a
ll P i
r ce
E
l ec tri c
e
ts
C u rre n t Mete r
a
.
there are shown the form of weights n d weight
vane that are use d with this type of meter in deep streams for h o ld
i n g it in positi o n The lead weights are attached to the lower en d of
the trunni on by mea n s o f a detachable weight stem to hold the
meter steady in moving water ; the high er the velocity o f the cur
rent the greater the weight requir ed to h e u sed
Figure 70
.
,
.
I N T ROD UCTI ON
1 19
l l times
weight vane sh o uld be attached to the weights at a
when the m eter is suspen ded from a ca ble W hen gaging small or
s hall o w streams it m y be necessary to make the observati o ns by
wadi n g Un der such Circumstances it will be m ore convenient to
dispe n se with the lead weights and attach the meter to a
light rod
or po le
W he n prepari n g t o make d ischarge measurements the battery c ell
of the buzzer is charged a n d the m eter is taken from its case and
attach ed t o a po le or to a cable with weight ste m an d weight vane
acco rdi n g t o whether the observ tions are to be made in shallow or
deep water
’
A fter making a discharge measure m ent or at the close of a day s
w o rk with the meter the i n strument should be carefully examined
to d etect po ssi ble inj ury a n d freed from water the n carefully dried
a nd pac k ed i n its case The battery cell S hould be emptied washed
with water an d packed up The beari ngs of the cup sh aft S hould
be kept well oiled so that the cups will revolve freely and without
friction
re
This style o f meter in which the revolutions of the wheel a
i nd icated by sound is especially adapted for use in ordinary sized
s treams an d i n currents of moderate vel o city
It is quite exten
s i vel y used i n the hydrogr aphic work o f the U nited S tates Geo logic a
l
S urvey for stream measurements and in irrigation investigations
Each revolution of the wheel is indicated by a buzz the observer
being re q uired to count the number of buzzes in a
given period of
time usually 50 seconds
I n cases where the current is quite swift as at peri o ds of high
water it is often quite di ffi cult to count the revo lutio n s of the meter
o w i n g to the velocity o f the current and the consequent rapidity
of revolutio n I n such cases an electric register should be used to
register the revoluti ons of the meter wheel A
goo d fo rm of register is illustrated in Figure 7 1
this is actuated by a battery of three cells Th e
e lectric current is transmitted between the t w o
a
o
les
of
the
b
ttery through copper wires which
p
are attached to the meter in the sa m e manner s
sh o wn in Figure 68 Th e electric register i s en
m R gi t
close d i n a brass case showing three di a
l s und er Fig 7l m a
ti g th
l u
f
a glass face I t has an electro magnet t Ch
th l ot Wh l
when the circuit is m ade m oves a lever at t h e end of which is a
pawl carrying forward a ratchet wheel one tooth at every c on t ct
of the c u rren t Th e l a
rg e di a
l counts ea
ch revolution up to o ne
Th e
a
.
.
.
,
a
,
,
.
,
,
,
,
.
,
.
.
,
,
.
,
.
,
“
,
.
,
,
,
.
.
.
,
a
.
,
.
e
.
coun n
-
.
,
,
.
,
o
s er
e revo u
er
oo
ons o
.
a
H YDROGRA P H I C
I 20
S U RVEY I NG
hu n dred ; the small dial on the right counts on e th o usa n d rev o lut i on s
by each hun d red a n d the small dial on the left co u n ts te n th o us n d
revolutions by each th o usand as indicated by the graduation s
a
,
,
US E
OF
.
CU RRE N T M ET ER
.
current meter may be used to determi n e the mean vel o city of
astrea m in fo ur ways as fo llows
I
By making one measurement in a vertical secti on
t a depth
corresponding to the approximate po siti on o f the fi l m e n t o f
mea n v eloc i tv
2
By making observations at several points in a vertical a n d de
d uc i ng the mea n vel oc ity t h erefr o m
B
the
integratio
n
method
3
y
r
m
s
u
t
point
mea
e
ents
made
re
ular
intervals
thr
o
ugh
o
ut
B
a
4
g
y
the cross sectio n
These several methods will be discussed and explained
Or dinarily when this m etho d is used the
Uni t M e s u rem en ts
cro ss section of the strea m is divided into a
c o nvenient n umber o f
at a po i n t
s ectio n s and a meter observ ati o n is made in each sectio n
that is estimated to be the po int of mea n velocity fo r the secti on In
king measurements of small rivers it has been the cust o m o f the
m
hy d r ographic division of the United S tates Geo logical S urvey to
divide the cro ss section of the stream into secti o ns o f regular wi d th
e locity in each sec
or
ten
feet
and
to
determine
the
mean
v
s
fi
v
e
y
ti o n by h oldi n g the meter at a po int six tenths of the to tal depth
of the section below the surf a
ce and mid w ay between the two side s
of the section
u li c i a
A s the result of numerou s experiments by h y d ra
n s it i s c o n
s i d ered that the point of mean velocity in a given vertical secti o n
is at a depth varying from six te n ths to tw o thirds of the t o t l depth
of the section me a
sured from the surface down Th e shape of the
cross sectio n will usuall y exercise a considerable influence upon the
location o f the po int of m e a
n velocity I n the case of a
wide shal
l ow stream observ a
t six tenth s of the depth g ive fair values
tion s a
Th e
a
a
,
,
.
.
.
.
.
.
.
.
-
.
a
.
.
,
-
,
a
.
,
-
a
,
,
-
,
.
-
a
-
,
.
-
.
,
-
,
fi q 72
Wi d e
a sh aw C
l lo
nd
ross
S e ct i on
.
for mea n vel o city I n a canal or fl um e or in a narrow a nd deep
natural channel the obse rvation s for mean velo city sh o uld be take n
at abo ut
o f the depth Thus in Figure 72 which sh ow s th e
cross section of a wide shallow stream the vertical d otted li n es rep
.
,
,
'
.
,
,
-
,
HYDROGRAPH I C
122
S
URVEY I N G
M U LTI P LE M EA S U REM E N T S
.
When observati o ns are made at several p o ints properl y space d
ave ti a
l the mea n o f these observations will give approxi a
tel y
h mea
n vel o i ty o f the section in which they are made The res l
w i ll b e
o re o r less exact acco r d i n g t o the n umber o f bser ati o
ma
d Usually it will be sufficie ntly ex act to ma k e these bser a
ti on s i n a
ch vertica
l at h to p middle a nd bottom respectivel y
Th
a
n o f the three vel o cities will be the mea n vel o ity o f h
s ti on T his practice h o wever is n o t recommended when cl o
re l ts a w a
n ted
,
in
r
c
t e
m
,
c
,
o
ns
v
e
O
.
e
t e
:
.
t
c
.
re
e
se
,
,
su
v
,
e m e
ec
t
u
.
m
,
.
M ET H OD
B Y I N TEGRATI O N
A ra
pid an d e ff ective method of dete rmining the mean curren t
velocity i n a secti on is to mo ve the meter u n i formly i n a ve rtical from
top to bo tt o m the n back to the surface ; re peati n g the o perati o n
as o fte n as d esired In this way th e vel oc ities are i n tegrate d m e
lly a n d the mea n vel oc ity ca n be c omputed by n oting th e
n i ca
ch a
ti m e a
n d the number o f the up a n d d o wn m o vements made
S i n ce th e resulti n g vel o city in a given secti o n will be a ff ected by
th e ve rtical m o tio n of the meter care should be taken that the m o ti o n
be u n i fo rm a n d suffi ciently slow to prevent the intro ducti o n of err o r s
fro m this cause A s a result of experiments made by M r F P
.
,
.
,
.
,
.
.
.
.
s it has been found that i n moving a Ftel ey meter vert i cally
at a vel o city n ot exceedi n g 5 per ce n t of the vel o city of the current
no material err o rs are intro duced
The constructi on of th e meter used should always be t k en into
ac co u n t i n co nsidering o r all owi n g for errors o f this kind Thus
i n the use o f a Ftel ey m eter a too rapid ve rtical m o ti o n cau ses a
decrease i n the velocity indicated while with the Price meter the
results will be too large I n case it is re q uired to make all o wan ce
for erro rs due to up and d o wn moti o n in order to secure exact
results the meter should be tested by m o ving it vertically through
‘
still water and noting the efi ec t
A method Involving the I n
tegr ti on o f the e n tire cr o ss
sectio n o f a stream w h ich
has been use d with s ti s f c
t on
t b i nt eg a
Fq M M t h od of Mea
tory results by the auth o r is
y
a
s
follows : The meter i s
sta rted at o ne bank and is moved across th e stream obliquely d o wn
n d up alter n ately at an angle of about 45 d egrees t o the h o ri zon tal
a
Th is method is illustrated in Figure 74 which represents a cro ss
s ection of a
n d in which the dotted line sh o ws the path O f
stream a
S tea m
,
,
.
a
.
,
.
,
.
,
,
.
0
a
,
'
e
s u re m e n
r
i
aa
.
,
,
.
,
,
.
I N T ROD U CTI O N
123
a
meter cro ss the stream ; the arro w heads sho w the directi on s i n
w h ich the meter is moved
In makin g a run or observati on with a meter the st o p watch is
started as t h e gagi n g begi n s a nd the n umber o f ti m es the meter
crosses the stream as well as the time req uire d t o mo ve fro m ba n k
to ba n k is recorded W here the depth of the water in the secti on
varies greatly it may be advisable t o rec ord also the n u m ber of times
the meter is lo wered a nd raise d It is gen erally sufli c i ent to cro ss
th e stream twice
This meth od can be use d to a d van tage where pro visio n h s b ee n
made fo r c r o ssi n g the channel of the stream easily a n d where the
meter ca n easily be raised and lo w ered in the section Th i s may be
imp o ssible if the curren t is to o swi ft or if the stage o r platfor m on
which the ob server stands is too high abo ve the water or if th e
water is too deep It possesses co n siderable adva n tage o ver oth er
methods o f curren t meter observation s in the spee d with whic h the
gagi n g ca n b e ma d e permitti n g n o change in the discharge w h ile
’
the w o rk is go in g o n In the autho r s practice this method has been
fou nd particularly applicable fo r streams not too deep fo r wadi ng ;
also on flum es where the depth is u n ifo rm and a plank ca n be thro wn
acro ss upon which to stand It is als o suitable for use in a c n al
where the observer stands i n a bo at working the meter w hile an
a
ssistant pulls the boat fr o m bank t o bank by a
rope stretched acr o ss
the ca n al
th e
.
,
,
.
,
,
.
a
.
,
.
,
,
.
,
.
a
.
,
.
,
,
H
YDROGRA PH I C S U RVEY I NG
C H A PT ER
II
.
—
—
M ETHODS OF F I ELD WOR K RA TI N G CURRE N T M ET ERS REDU CTI O N
—
—
OF
OB S ERVA TI ON S RA TI N G TA B LE FORM U LA FOR DI S
—
WE I R
C H A R G E M E T H O D S A N D C O M P U T A T I ON O F D I S C H A R G E
—
—
M EA S U REM E N T S M EA S URE M E N T OF H EAD CO N D ITI O N S FOR
—
—
A CC U RA CY
D I S C HARGE TA B LE A N D CON D ITI O N S TH E
—
—
E
W ETTED PER I M ETE R COEF FI C I E N T OF RoU GH N ss I RRI GA
—
TI O N CA N A Ls FLow O F W AT ER I N OP EN CHA N N ELS
—
—
VELOCIT Y CU RV ES COEF FI C I E N T OF REDU CTI O N S EDI M E N T
O B S ERVA T I ON S
,
“
,
.
M ET H ODS
OF
W OR K
FI E LD
.
operati ons necessary in the measurement of stream fl o w
by current meter co mprise two successive steps as follows :
1
Laying out a sounding range and measurin g the cro ss secti o n
of the stream thereo n 2 Observations of velocity
W hen a current meter is used to determine
S ou ndi ng R nge
vel o city in a given stream a
suitable location is selecte d fo r a dis
charge stati o n as i n the case of the float observations For m eter Oh
serv ti on s
however no base line is necessary and on ly one c ros s
section is required This shou l d be as nearly as p o ssible a typic l
secti o n o f the stream ; it should be l o cated where the flow is regular
n d free from n atural or a
a
rti ficial obstruction The water gage
s h o uld be set s o that n o minu s re adings will occur
the zer o bei n g
p laced o ne or two feet below the lowest kn o wn stage of the water
A bench m a
rk should be e st a
blished to which the zero of the gage is
referre d ; it should be loca
ted a
t s ome convenient point above high
water mark
Th e range having been established soundings are made at suitabl e
intervals along it Th e first sounding should be at the e d ge of th e
water its de p th bein g recorded as zero and its distance from th e
initial po int o n the range also recorded For streams o f ordinary
size s oundings are usually made every
I O or 2 0
feet ; fo r sma l l
s treams the interval between so undin s i s about
feet
g
5
Vel oci ty Obs er v ti ons
I n a case where the depth of the water i s
not too great the Observatio n s are m de by wading I n some cases
where the ch a
nnel i s narro w a
pl a
nk or footway is laid from bank to
Th e fi eld
,
-
.
a
a
.
.
.
.
.
,
,
a
,
.
.
,
.
.
,
.
,
.
a
.
a
.
,
,
.
HYDROGRAPH 1 C
71 2 6
S
URVEY I N G
bank u po n which the Observer stands w h ile m aki ng the observatio n s
W he n there is a bridge con ve n ien tly and suitably l o cate d the d i s
c harge stati o n may be located directly beneath it a n d Observati o n s
made from the bridge W here streams re deep it will be necess r y
to use a
b oat
W here a permanent discharge station is required the arrangem e n t
sh o wn in Fi gure 75 will often be f o u nd suitable
This consists o f
aw ire cable stretched securely across the stream a n d carryi ng
movable platform upon which the hydrographer and his assist n t
a
re stati o ned while making observation s
The illustration represe n t s
one O f the river gaging stations o f the United S tates Geologi c a
l
The hydrographer holds in one hand his watch while wit h
S urvey
the o ther hand he holds to his ear a
buzzer to indic a
te the num ber
unit of time Th e ass i s
o f rev o luti o ns of the meter wheel during a
tant h o lds th e meter in the wat er in the required position duri n g
nn e r
t he observation s
W here the revolutions are counted in this ma
each Observation is usually for a
period of 50 sec o n d s W here poi n t
m easurements a
de it is customary to ma k e two observation s
re m a
t a
of 50 seconds each a
poi nt and i f these do n o t all agree t o mak e
athird a
n d a fo u rth i f necessary c o n tinuing until they are s ti s f c
a
tory
I f these observation s a
pe
r
to
have
nearly
e
q
ual
value
h
t
e
p
r e of doubtful value th e
verage o f a
ll i s t a
ken ; if on e or more a
a
doubtful one s are rej ected
In cases wher e a recordi ng register is used with a meter th e
readi n g of the dial is noted be fore and after eac h observation ; th e
di ff erence between the two readings indicate s the n umber o f th e
’
meter wheel s revoluti o ns for that observation The number o f
seconds required for each observation is also noted ; the n umber o f
revolut i on s divi d ed b v the number of seconds gives the revolution s
r second of ti m e
e
p
.
,
a
a
.
.
,
a
a
.
,
,
.
.
.
.
'
.
,
,
,
,
aa
.
.
.
.
R A T I N G CURR E N T M ET ERS
.
When a current meter is used to determine the current velocity
in a given stream the observed results sh o w t h e number of revol u
tions o f the meter w heel during a given number of seconds In
order to determine the velocity of the current in feet per secon d
from a meter Observation it is necessary to know the rati o between
the revolutions per second of the meter wheel and the vel o city of the
current turning the wheel in feet per second The individual action
of each instru ment used must be noted since it has been fo u n d th t
there is a noticeable di ff erence i n the Operation of di ff erent cu rren t
meters even when made from the same patterns and at th e same
,
.
.
,
,
a
T H ODS
ME
t ime
I
D
O F F EL
W OR K
127
Th e
operation o f d etermining the ratio between the Observed
results fo r a curre n t meter is called rati n g the meter
The usual method of rating a meter is by running it thro ugh still
water the assumption being that the same relation will h o ld be
tween th e turns O f the wheel when running through still wate r s
when held in one position in flowing water
The U nited S tates Geol ogical S urvey maintains two rating sta
tion s for current meters one at Chevy Chase M aryland and on e at
Los A ngeles California Th e apparatus used at Chevy Chase c o n
s ists of a pl a
tform abo ut 2 0 0 feet in length built along the edge o f
asmall deep pond the waters of which a
re c omparatively stagn ant
On the outer edge of this platform is a track laid with light iron
ra
ils on which is placed an ordinary mine car or truck with an out
ri
er
so
that
the
meter
can
be
held
vertically
over
the
water
an
d
gg
i m m ersed to the required depth
On the platform a measured
c ourse of 1 0 0 feet i s l a
i d off and the car is pushed by hand care
being taken to pass over every 1 0 or 2 0 feet in a
given n umber o f
s econds so that the same velocity can be maintained from start to
finish
Th e device used a
t Lo s A n g ele s c onsists o f a cement lined trough
c on taining water : A bove this a
n d parallel to its length is stretched
n iron cabl e
a
s u itably supported on which is a trolley frame wit h
t w o wheels by means of which the meter i s supported beneath the
s urf a
ce of the wate r Th e meter is propelled through the water over
am ea su red course usually one hundred feet long for tw enty or
more times in succes sion at di fferent rates of speed the speed
varying from less th a
n
of a foot per second to about 6 or 8 feet
per sec o nd o r even more ; the number O f revolutions per hu n dre d
n d the numbe r O f s econd s re quire d to make the run a
feet a
re noted
for each run
I n ordinary practice such elaborate equipment is not available
a
n d mete r ratin g i s usually conducted fro m a small row boat o r
s ki ff
M eth od of R a
ti ng
B efor e rating a
m eter it is a
good plan to
c a u se the meter wheel to revolve by h a
nd counting the number of
revo luti ons or the number of seconds during which it will rev o lve
before stopping i n this manner ascertaining in a general way the
condition of the bearings as regards friction Th e bearings sh o uld
a
t all times be kept well oiled i n o rder to make the friction as n early
u niform as possible
re
The field notes a
eported in a n o teboo k having s ufli ci ent space
to enter the results of the computations th us making a complete
.
.
a
,
.
,
,
,
'
.
,
,
,
,
.
,
,
,
,
,
,
.
,
,
.
-
,
,
,
,
,
.
,
,
,
,
,
.
.
.
,
,
.
.
r
,
I I YDROGRA PH I C
S
URV EY I N G
ab
6
b
5 8
t
o u 3 3
m
2
?
“
.
0
S
2 8
2 8n
.
o
z
5
0
o
o
n
o
8
3
0
0
0
: 9
0
3
m
3
0
0
9
o
n
3 3 0 N
a
“
2 m n 00
5
0
£ o
t
3
3 0
5 8
5 2
N
w
S
9
0
0
3
3
2
w
E2 0
o
N
0
N
0
m
N
“
.
m
+
I
l
0
a
s
fl
0
0
0
0
|
|
N
+
u
m
m
0
N
m
0
m
0
m
0
0
0
m
fl
N
m
H
w
0
N
w
10
N
O
u
CO 0
0
o H
¢
0
N
N
H
N
0
N
m
5
m
o
9
m
w
o
w
0
fi
0
m
o
0
4 0
v
m
w
m
w
N
N
o m
n u
m
N
o
+
7
0
“
0
N
.
N
m
n 5
o 0
w 0
N
m
u
0
m
m
0
5
a30
2
m
w
m
m
0
0
fi
0
N
A
o
+
!
S
a
+ + +
.
N
m
o o c o
n+ + +
N
o
n
3
O
N
5
fl
N
0
“
0
0
m
0
m
N
0
0
“
«
V
O H
H
H
I
0
0
0
fi
$
N
m
fi
3
e
N
0
N
m
x
m
$ 93 1
0
m
0
R
M Q ‘ W Ct
0
CD CO Q
0 N 0
H
N
5
N
O O N
N
0
N 0
O N
m
N
8
E5
fi
0
.
0
m
o
—
Q
Q
w
”
0
0
N
N
O H
r-i
n
6 n m
8
0
0
c 0
o 0
N
0
0
o
.
H
0
0
.
N
0
m
N
5
n
v :
0
0
4
a
m
3
8
0
m
m
0
fi
m
o
9
.
0 0 0 0 0 0
| + !
! + + !
a
a g
u
0
m 6
3
0
o
a
1 ! +
+
a
w
w
«
a
5 i
0
9
a
0
5
n
£
8 9
9
fl
0
5
8
8
0
0
”
3
c
c c
o
.
.
0
n
3
.
0
g
8
5
E
8
o
2
“
2
O
h
0
“
0
3
.
a
m
v
o
O
o
a
a
a
3
6
B
m
a
9
5
a
3
E
2
a
3
3
a 8
o
N
x
0
0
9
0
2
n
o
o
0
m 5 5 3
s
o fi ?
3
5
n
2
2
fi m
5
e
a
3
a2
m
m u
op
o
0
m
3
O “
H
0
N
N
N
N
—
N
CQ Q ‘ IO
r-l v i r-i r -i
w
HYDROGRAPH I C
S U RVEY I N L
described Th e speed was varied for each run the results being
n o ted a n d tabulated as sho wn i n Table No I
The field no tes c om
p risi n g the n umber of each observatio n the number of revoluti on s
of the meter wheel and the time in seconds req uired to pass over th e
co urse are entered in the order given in the three left hand co lum n s
shown in Table No I
.
,
.
.
,
,
,
-
,
,
.
.
R ED U CT I O N
a
Gr ph i c M etho d
.
,
OF
O B S ERVA TI ON S
.
I n order to determine graphically the relation
between the number of revolutions O f the meter wheel and the
vel ocity of its motion thr o ugh the water for the series o f observa
tio n s a diagr am should be drawn to scale as follows : The observed
values are platted on cross sec
,
,
-
per second as abscissas rep re
and the
s ented by the symbol x
v elocities in feet per second as
c
e
represented by the s
o r dinates
symbol y
S uch a diagram is
r
e
shown in
Figure 77 in which p
the observed values in Table
f
No 2 are platted their p o sitions
c
o
being design ated by small cir
9
V
cles
It will be observed that
they all fall nearly in a straight t
e
line ; such a line i s called a rat
e
F
It is assumed that
i n g curve
this line w ill pas s through a
3
point representin g the mean of
e
the observed values of x and y ; S
thi s point i s located and aline /
a
ssing
through
it
and
swung
a
p
h
as to average the other re
so
V
oints
drawn
for
the
rating
i
s
p
c u rve
b- /
fd
I f all the observations for de
t er m i n i n g velocities were entire
l y with out error and if there
ti n Cur ve for Cur ren t Met er
Fi gfn Ra
g
were no friction in the bearings
of the wh eel all of the platted values of the several obser v ati on s
would lie i n astra
i ght line pa ssing through the origin o f co
,
,
,
.
,
i
.
,
.
.
.
a
c
’
.
a
.
,
.
,
.
.
ME
o rdinates
T HODS
I
D
OF F EL
W O RK
I
I
3
a
a
It is evident however that on account o f the resist n ce
due to friction some vel ocity o f curre n t will be re q uire d t o st rt
the meter wheel to revolve from a state o f rest This vel ocity ho wever
small
is appreciable a n d must be taken into acco unt i n rati n g a
meter It is expressed in the rating eq uati o n by the c o nst n t b a n d
i s shown on the diagram by the distance from the origi n o f co
ordinates to the po int of intersecti o n o f the rati ng curve with th e
axis of ordinates A t this point the number o f rev o luti on s per
s econd is zero
and the velocity o f the curren t is so me appreciable
value which is characteristic for each meter and is usually consi d
ered a constant
The rating curve having been draw n in acco rdance with the oh
se rved values
any intermediate value within the limi ts o f Observa
t ion can be interpol a
ted on the curve by observation or by m e su r
ing with a scale
A n ly ti c l M eth od
The rating curve f o r a current meter ca n be
ex p re s sed by the equation
I
y
ax
b
( )
in which b is th e distance from the o rigi n of co ordinates to the
poi n t of intersection Of the curv e with t h e axis of o rdinates rep
resenting fricti onal resistance ; and a is the tangent o f the angle
made by the rating c urve with the axis o f abscissas The values of
aand b could be derived fro m any two observations at di ff erent
s peeds
but in order to fin d the best and most probable values for
them a great many Observation s are usually made in practice
a
nd
In making computations to determine probable values for a
b fro m a series of observations the observed values of x and y are
tabulated n d a
and b are determined analytically
A goo d method t o u se for such determination is that given in
Theory and Practice o f S urveying by the late Prof J B J o hns o n
This method will be explained in detail by applying it to a rating
operation made in actual practice In the case under considera
tion the results of a series of fiftee n o bservations are show n in T ble
No 1 in th e three left hand c olumns which sh o w the numbers of
the observations and the observed values of x and y Fro m this
table the mean values of x a
nd y
which are respectively x and y
re deri v ed as sh o wn
a
—
=
Eq uati on ( 1 ) can be written : ax
E
very
o
bserva
b
o
y
tion equation may be written in this form using correspon ding
O bser v ed values for r and
D
n
esi
ati
n
g
the
successive
o
bser
v
ed
g
y
va
lue s Of x a nd y by corresp o nding subscripts the successive oh
s ervation e q uations are written
—
—
_
=
=
=
x +b
x
X
b
a
v
V
b
Vls
z+
2 ;
ls+
;
y1
Y2
YI5
.
,
,
,
,
.
,
a
,
.
,
.
,
,
.
a
,
,
'
,
,
a a
.
.
,
-
,
.
,
,
.
a
,
.
”
.
,
.
.
a
.
-
.
,
.
0
,
.
.
,
.
.
.
a
,
1
a
1
H YD ROGRA PH I C S U RVEY I NG
2
3
S i n ce b
enters alike into all o f them it is evident that these e qua
S i n ce the m o st probable
ti on s are o f e q ual value fo r determining b
value of a n umero usly observed q uantity is the pro perly weighted
ri th metical mea n n d si n ce in this case the eq uati on s or o bserv a
ti on s hav e e q ual weight fo r dete rm ining b we can fo rm fr o m the
give n series o f eq uation s a si n gle standard or no rmal eq uati o n which
M ake thi s
w ill be the arithmetical m ean o f the observed equati on s
eq uati o n eq ual to zero and use for finding the value o f b Calling
x 0 and y 0 the mean o f all the observed values of x a n d y we obtain
by addi ng all the equati o ns t ogether and d i viding by their n umber
.
a
,
a
,
.
.
,
,
—
=
a
x
b
o
Y
=O
-
S ubstituti n g
O
this value of b in equation ( 2 )
a
(
—
a
(
_
x1
X2
)
—
—
Xo)
( Yz Yo)
( 3)
‘
we
ha
ve :
x0
—X ) ( Y —Y )
V2
v ;
a ( xi s o
is
o
( 4)
There is only one unknown quantity involved in this series of
eq uations but they are evidently not of equal weight in determining
this unkn own quantity or s ince its coefficients are di fferent The
relative value of these equat i ons for determining a
is in direct pro
tio n s
p ortio n t o th e S i z e s of th e s e c o effi c i en t s i n th e r e s p ec ti v e e q u a
They should all be weighted in propo rtion to the values of these co
effi ci en ts ; a convenient way to do this is to multiply each equation
through entire by the corresponding coeffi cient Th e resulting mul
ti pl i ed equations then have equal weight and may be added t o gether
to produce another normal equation for fi ndin g a In this c a
se th e
resultin g equation is
i
,
,
.
.
.
.
—
X
X ) ! a
[(
—Xc )
2
(y
(S)
In this eq u ation the sign of summation is indicated by brackets
thus :
I f this equation h d been divided by the nu m ber of obser
v ti on s I 5 it would n ot have bee n changed so far
s the value o f
is concerned Th e me an or most probable v lue of can be fou n d
fro m equation
S ubstituting the values found in Table No 1
=
n d reducing we have :
The m ea n value of b is found
—
=
x
ubstituting
the
v
alues
o
f
from equatio n 3 ) to be : b
S
0
y0
x 0 and y 0 gi ven in Table No 2
and the value of a j ust found w e
= o 1 74
have :
b = 4 739
Then for the m eter under consideration equation ( 1 ) becomes
=
u
y
37
o
a
a
,
.
a
a
,
a
a
a a
,
.
a
.
.
.
.
which
i s th e
e qu a
tion for
,
,
.
r
tin g
a
.
.
I S4
HYDROGRAPH I C
SU
RV EY I N G
0
c
c
“
s
o
m
e
;
.
3
3
0
8
w
h
e
n
E
m
w
m
o
0
0
N
a3; a
e
3
m
m
3n
g
n
6 d
o
d
X
XNX
i
m
n
0
0
N
“
NN
H
m
0
0
o m
:
m
N
N
m
.
m
m
“
v
.
.
0
m
0
v
0
0
3 :3 2
a
0
0
0
0
0
m
m
m
0
0
0
0
G
0
0
n
A
2
0
w
0
0
0
0
0
0
N
m
m
0
m
m
s
:
am
: ~2 g :
N
N
.
m
a
0
m
o O 0
0
fi
H
fi
H
m
n o m
H
N
.
0
oo e ‘ c v
( D r-i N M M r -I CQ
F i r-i H
r-i H
CQ Q ‘
a
0
m
::
.
“
H
m
”
5
W
CO N
M E TH
ODS
OF
I
D
F EL
W OR K
1 35
TA B LE
Th e algeb raic e x pressi o n given abo ve is not convenient fo r rapid
use in the field a n d should therefore be transform ed int o numerical
terms suitable for determining the relati on between observed values
within the limits o f probable current velociti es This is best don e
by c o nstru cti ng a rating table for the meter gi v i n g directly the
vel ocity per sec o nd o f the current in terms o f rev o luti o ns of the
wheel S uch a table if carried out su fli ci entl y far d oes away w ith
all multiplicati on in the field notes the values being taken directly
from the table
I n Table No 2 i s shown a rating table for the meter that was
used in the series of o bserv ati ons rec o rded in Table No I Cor
respo nding vel ocities i n feet per secon d are sho wn f o r every two
hu n dredth part of a rev o lutio n per sec on d fro m a state of rest t o
the highest observed value For smaller fracti ons of a sec on d t h an
those given in the table the correspon ding velocities are fou n d by
interpolati on
By the use o f a rating table much tedious calculation is avo ided
s ince fo r any observed rate of velocity of revolution the c o rresp on d
ing velocity o f current in feet per second can be found i n the table
A rating table for a given meter is generally found to be f i rl v
con sta n t until the meter becomes inj ured or the friction noticeably
ring a
increase s by the we a
wa
v of the more delicate part s O f the
bearings
l l y t es t th e friction of the bearing s
si on a
I t is a good plan to occ a
of a meter by giving the wheel a s mart tu rn with the hand n d
n o ting the length of time it will run before sto pping The time
will of course become shorter as the friction of the be a
rings i h
creases
RED U CTI ON OF D I S C HAR GE M EA S U RE M EN T S
In c o mputing the discharge of a stream in which the current
vel oc ities have been determined by m ean s of fl oats or by current
meter observations the cross section o f the stream is divided into
s ections and th e m ean velocity of each section ascertained by obser
va
ti on s as previously described
Th e are a
of each section is ob
t i n ed by multiplying the w idth by the mean depth
The discharge
is the pr o duct of the area by the mean velocity of the given section
The discharge of the stream or of the entire cross section is the sum
of the partial discharges
R A TI N G
.
.
,
.
,
,
,
.
.
.
,
.
,
.
.
,
,
,
a
,
.
,
.
a
.
.
.
,
-
,
a
.
,
.
.
-
.
D I S C HARGE
Th e discharge of a stream or o f a secti o n o f a stream may be
av ( I ) in which Q is the
expressed by f o rmula as follows : Q
FOR M U LA
FOR
.
.
' 30
H YDROG RA F H I C
S
URVEY I N G
r ea
qua n tity o f water discharged in a given unit of time ; a is the a
of the se cti on in s q uare feet ; a n d v is the vel o city o f th e cu r r e n t
expres sed i n feet per u n it This is the fu n dame n ta
l fo rmula for t h e
bl e
discharge o f a n y given sectio n of a stream It is e q ually applic a
for e x pressing th e en tire discharge o f a stream whe n suitable va
l u es
are giv en to the fact o rs of the e q uati on Ge n erally i n c om p u t i n g
discharge o f streams the symb ol Q designati n g q uan tity is e x
se
pressed i n cubic feet o f water per secon d o f time I n su ch a c a
nd
the symbo l a design ating a rea is e x pressed i n s q uare feet ; a
the sym bol v desi gn ating vel o city is e x pressed i n li n eal feet p e r
,
.
.
,
.
,
,
,
.
,
,
,
seco n d
,
.
D I S C HARGE B Y FLOA TS
A n e x ample sh owi n g the m eth o d o f c omputi ng stream d isch a
rg e
when fl o ats are used to determine curre n t vel ocities is give n h ere
Referri n g t o Figure 6 3 let a
and b represe n t th e platte d cros s
secti on s on two so u n ding ranges at the upper a n d l o wer extremit i es
s
respectively Of a measured base li n e fo r a given discharge stati on a
A B Figure 6 2
The dimension s o f the respectiv e secti on s are d e
te m i ned by measureme n t as previ o usly explained
In the pres en t
case the mea n velocities i n the respective section s were asce rtai ned
by ro d fl o ats S ince there is some variatio n in the dimen si on s o f
the tw o end cross secti ons a
m ean cr o ss section is i n terpolate d f o r
c on venie n ce in computatio n
This i n fo rmation is tab ulated as sho w n in the acco mpa n yi n g Ta b le
No 3 The discharge o f each sectio n sh o wn in the last c o lum n is
easily d etermined by substituting the known values aan d v i n
fo rmula ( I ) and solving the equati on to determi n e Q The sum o f
th e partial d ischarges is the total discharge of the stream
.
,
.
,
,
,
-
.
.
r
.
,
.
-
-
,
.
.
.
,
,
,
,
.
,
.
D I S CHARGE B Y CU RRE N T M ETER
W hen the current velo cities in the several secti on s o f a str eam at
adischarge station are determined with a curren t meter the wor k
is do n e in one cross sectio n as previously explai n ed In th e e x
ample of computation o f discharge measurements that will no w be
con si d ered the cross secti on is divided into secti on s having a u n i
i
re no t
fo rm w dth of 1 0 feet except the tw o end secti ons which a
s o wide Depths are determined by s o undings at the division po i n ts
a
l s o mi d way betwee n them where the meter observati on s are made
A plat o f the cro ss secti o n is given in Figure 78 in which the d i
vision li nes of the secti on s are sh o w n as full lines ; t ho se mi d w ay o f
where meter observati on s are made are sh o wn as
each secti on
d otted li n es
.
,
,
-
,
.
-
,
,
,
,
.
.
,
-
,
,
.
,
1 38
H YDROGRAPH I C S U RV EY I N G
a
c
c
2
2
o
Q
3
i
n
s
0
2 8
2
a a
n
n
N
v
6
d
d
d
N
N
S
”
A
fi
A
88
88
88
88
0
0
N
M
.
98 33
s
:
d
”
s
a
o
w
3
$
w
e
H
o
w
.
d
a
0
5
”
Q
.
R
gm
3
88
88
e
n q
n h
fi
u
m
fl
o m
x
oo x
N
N
“
a2
0
8
88
88
e
8
S
m N
r n
N
N
-t
N
m
e
N
Cfi
0
s
'
d‘
~
N
v
~
8
5
a:
0
«
2
N
88
88
0
m
A
A
n
q
co wfi m
a
a
n
.
33
a
m
m
0
lD
CD
M ET H ODS OF F I ELD W OR K
dead or still water I n s om e cas es in order to get a true expression
of discharge o f a stream it may be a
d visable t o leave o ut o f the
c omputations a po rti on o f the cro ss secti on near the s ho re i n wh ich
there is n o perceptible current I n computi n g the average d epth s o f
the triangular secti ons at each end Of the cro ss secti on the depth at
the sh o re is taken as zero this being added to the o ther depths an d
the total divided by four as in the case o f a trapezoidal section In
determi n in g the mean velocity of a triangular section the m eter is
not held on the vertical hal f way betwee n the sh o re a n d the side o f
the adj acen t section as i n the ca se of a trapezo idal sectio n The
author s practice is to use a verti cal about two thirds o f the d istance
from the shore to the side o f the adj acent section
In making discharge c o m putatio ns it is not necessary in practice
to carry them out to a degree of re fin ement n o t warra n ted by th
exactness of the field measurements U sually two places of decimals
will express with suflI Ci ent exactness b oth the observations a nd th e
results of stream measure m en ts V el o cities sho uld be given in feet
and hundredths of a foot per second ; for unifo rmity the gage read
ings may be expressed in hu n dredths of a foot altho ugh it is cus
tom a
r
to
ex
ress
them
to
the
n
earest
hundredth
of
a
foot
It
is
e
fi
v
y
p
s ufli ci en tl y e x act to give the computed results o f a d ischarge m eas
u rem ent t o decimals of a foot per second ; a n y cl o ser statement
would be useless re finement not warranted by the degree o f exact
ness with which the fi eld w o rk can be don e Th e field work should
be conducted with great care but o n the other hand the computa
tions in the offi ce while they sh o uld be accurately made sh ould n ot
be carried out to a degree or re finemen t inconsistent with the o riginal
.
,
,
-
,
.
-
,
,
,
.
,
,
-
.
,
’
-
.
e
.
’
,
.
,
.
-
.
,
.
,
,
,
wo rk
,
.
CO M PU T ATI O N
D I S C H A R GE
OF
.
I n Figure 78 is sho wn the cross section of a stream platted from
the notes gi ve n i n Ta ble NO 4 Th e vertical broken lines i n dicate
-
,
the boundaries of adj a
cent sections w h ile the dotted lines show the
verticals on which meter rea d i n g s were taken ; the latter are midw a
y
b etween the sides in each trap ezo i d a
l s e c tio n a
n d two thirds of t h e
d ja
c e n t s e ctio n i n e a c h
d i s t n c e from th e s hor e to th e si d e of th e a
s
de a
t the s e several points a
t riangular secti o n
S ou n dings were m a
In this case there w ere no eddies or still water
sh o w n in the notes
n ext to the sh o re ; the triangular sections were made shorter than
the i n te rmediate trapez o idal secti ons but otherwise were treated i n
n d in computing the
the same manner in maki ng the observ a
tion s a
resu lts
.
.
,
-
a
.
,
.
.
,
,
.
HYDROGRAPH I C
1 40
S
URV EY I N G
it is seen that observati o ns were ta k en
a
t six tenths o f the depth below the s u rface in each vertical thu s
obtaini n g the mean velocity of the secti on in one Operation
The d ischarge i n each secti o n is Obtained by multiplying togethe r
the rea and the mean vel o city ; the total discharge is o btai n ed by
d ding together the partial discharges Th e mean velocity o f the
a
s tream is found by dividing the t o tal discharge by the area o f the
cross section or by the sum o f the areas o f the several sectio ns
I n measurements of stream discharge by the use o f curre n t
meter accuracy of results is merely relative as compared with o th e r
meth o ds that by the use o f floats for ins tance The measurem ent
of fl o wing water i n an open channel can not usually be determined
with absolute accuracy since the quan tities to be measured are not
fix e d but fluctuate considerably in a short period of time o ften
duri ng th e process of measurement Th e elevation of the water
extendi n g over i n
s urface is subj ect to the influence of pulsations
terv l s of from 30 to 50 seconds and causing vertical oscillations o f
ppreciable extent Th e velocity of the current is liable to vary at
a
di ff erent points in the same section and even at the same po int
during successive m o ments Taking these facts into consi deration
it is evident that i n the measurement of a stream there is ro om fo r
variati on from absolute accuracy in results ; this variation may be
a
nywhere from 2 to 5 per cent in the total
Referring
to
Table No 4
.
-
,
.
a
.
a
-
.
,
.
,
,
,
,
.
a
,
,
.
,
,
.
,
.
.
W EI R M EA S UR E M E N T S
.
I n some instances in streams of m o derate size it is practicable to
build weirs for gaging the flow A weir is an obstruction ge n erally
of timber built acr o ss the channel of a stream through or o ver
which the water is caused to flow thus a ffo rding Opportu n ity f o r
c o nvenient measurement
This is probably the most accurate meth o d
,
,
.
,
,
,
,
,
.
of measurement applicable to small streams
Weirs are of various forms the shape varying acco rding to l o cal
c o n diti o ns a n d requirements
In some instances even in stream s o f
co nsiderable size where dams have been built for po wer purp oses
such dam s i f o f proper fo rm may be used as weirs with good re
su l ts
A suitably con structed dam may consequently be considered
as one general type of weir while a specially constructed weir is the
other general type
By o bservi n g the head o n the weir that is the height of water
abov e the crest of the weir c omputatio n s o f the discharge can be
mad e S uch computations are made by the use of empirical f or
mulas which vary a
ccording to the type a
n d form of weir used
.
,
.
,
,
,
,
,
.
,
.
,
,
.
,
.
HYDROG RAP H I C
1 42
S
UR VEY I N G
n d level o n to p than the latt e r
water tight and to be sm ooth a
which are liable to settle o ut of line and to bec o me uneven on th e
crest In ma n y cases h o wever well constructed timber dams r e
fou n d that are adapted for accurate work
A good f o rm of dam suitable for use as a weir i s sh o wn in Figure
M
s
which
is
a
ph
o
tograph
of
a
masonry
dam
at
Ho
ly
o
ke
as
79
W hen a dam has been selected f o r use as a weir a careful su rv ey
sh o uld be made to determine the crest line and the cross secti o n o f
dam This information i s impo rtant since the c o effi c ien t o f flow
va
ries acc o rding to the form of cross section of the darn
be
-
,
.
a
,
,
.
,
,
.
,
,
,
-
.
-
.
FOR M U LA S
FOR
D I S C HARGE
.
M any experiments have been made to determine discharge for
mulas applicable to dams o f various f o rm s of cross secti on No
single fo rmula can be g iven that will be suitable for general use in
rn
c o mputing the discharge o ver a
da
In making computatio n s for
discharge i n such a
case it i s customary to select s o me form of dam
for which a formula or a coeffi cient has been derived by experiment
and which confo rms most nearly to the form o f dam upo n which
the measurement has been m ade
The f o rmula which expresse s i n general ter m s the fl o w of water
over a da
or weir is in its simplest form
m
=
1
C
L
H
3
(
)
Q
in which Q is the volume of di sch a
rge in cubic feet per secon d ; L is
the e ff ective length of the crest in feet ; H is the depth i n feet o f
water fl o wing o ver crest of dam ; C is a numerical c o effi cient called
‘
the coefli c i en t of disc h arge
m
in
K Vfi
The value of C may be written : C
which g is the accelerati o n o f gravity say
feet per sec o nd ; K
and m are const a
nts determined by experiment S ubstituting these
:
val u es for C eq uation ( I ) m a
be
written
y
( 2)
Then in order to determine the discharge over a d am its crest is
measured and its e ffectiv e l ength determined ; als o the d imensi ons
s previously stated
Th e head o r d epth o f
of its cr o ss section a
water H above the crest of the dam is no t measured directly o ve r
use o f the vertical co ntraction o f the water there ; it
th e crest b ec a
m ust be measured in quiet water
a few feet abo ve the dam This
havi n g been d one all the factors i n the second term o f the e q uati o n
a
r e known except the coe ffi cient of discharge
A s has been stated
thi s co effi cient varies with the for m of cro ss section o f the d am
-
.
.
.
,
.
,
.
.
,
.
,
.
,
,
,
-
.
,
,
,
,
.
,
,
,
.
-
,
T HODS
D
ME
OF FI E L
W OR K
1 43
a
ad
must be derived from s o me d m of similar fo rm whose
c oefli c i en t has been determined by experiment
In co mputing the discharge over the crest of a dam the width O f
crest sl o pe fo rm of apro n etc must be taken int o acco unt in
s electi n g the value of the coe ffi cient C as has been s tated
I n a case
where the profi le of the dam is irregular varying in height and
sh a
pe at di ff erent places a
long the le ngth of the dam the crest
s hould be divided int o sectio n s in such a man n er that all c o rrespo nd
i n g p o ints in a given section will be as nearly as possible at th e
s ame elevation
Th e discharge of each secti o n is then computed
s eparately
the aggregate being the total discharge over the dam
In some cases where a dam has a
for rough
n irregular pr o file
ca
lculations or computati o ns of flood discharges the average crest
n d the discharge calculated for the entire dam at
elevati o n is taken a
one operation This meth o d gives results that are too small sin ce
the discharge o ver the lo w er part of the crest is greater in pro p o r
tion to the head th a
n that over the higher po rti ons of the crest
I f a gaging is made on a dam when th e mill gates are open the
water fl o wing through the gates must be measured and a d ded to
th e quantity fl o wing over the dam in o rder to determ ine the total
discharge of the stream U sually the water flowing through the
u
ates
ca
n
be
measured
with
the
aid
of
a
current
meter
as
pre
v
io
sly
g
described
I n case aturbine mill wheel is used the discharge
throu gh the wheel can be determined directly from the rate o f
revolution of the wheel itself or from the known rating o f th e
turbine
s been d escribed
gagi ng as h a
when carefully mad e will
S uch a
dam is of good constructi on
a
ff ord fairly accurate result s
W hen a
witho ut leakage and with con dition s favorable as to sm oothness o f
crest a n d uniform ity o f fl o w the results o f a gagi ng thereo n wi ll
often pr ove m o re satisfactory than a meter measurement ma d e
u n der un favorable con d itio n s
On the other h and dams that are
s
le a
ky and that have ragged uneven crests are unsuite d for use a
n d m ea
s urements m ade on them will h a
w ei rs a
ve little pra
ctic a
l
value
M EA S UR I N G W EI R S
W eirs constructed for the ex press pur po se of gagi n g the flow o f
s treams are in ext ensive use in the western part of the United
S tates a n d i n other co untries where irrigati o n is practiced o n a large
s cale
The measurement of strea m discharge by the use of weirs is
especially applicable in irrigation where water is usually c on vey ed
in streams and can als Of m od er te size an d where accurate measure
m ent s a
re required
n
,
.
,
,
.
,
,
,
.
,
,
,
,
,
.
.
,
,
,
,
.
,
.
,
.
-
.
.
.
,
,
,
.
,
,
°
.
.
,
,
.
.
.
a
.
HYDROGRA PH I C S U RVEY I N G
1 44
a
a
W h e n a weir is built acro s s a stre m f o r the purpose of g gi n g
the fl o w it is generally intended either fo r permanent use o r f o r a
series o f accurate measurements ; it sh o uld there fore be l o cated
and built with a V iew to obtaining th e best results in the way o f
accuracy A weir sh o uld be loc te d as n early as p o ssible with its
face at right a ngles to the axis of the stream The upper face
sh o uld be ve rti cal and the crest o f the o pening or notch over
which the water flo ws sh o uld be truly horizontal Th e weir s ho uld
be str on gly built with s o lid f o undation a n d substantial bracing The
planki n g sh o uld be rigid s o as to prevent vibrati o n o f the frame
w o rk or crest an d the sides and bo tt o m sh o uld be properly j oine d
to the surro u n di n g material in order t o avo id leakage under or
ar o und the weir A n apron o r floor of planks should be placed on
the lower side of the weir to receive the f a
lling water and prevent
underminin g
There are i n common use tw o gen
eral forms of weirs as fo llows :
aThe rectangular weir with an
open ing whose sides are vertical ;
with an
b Th e trapez o idal weir
opening whose sides are inclined at a
slope o f one vertical to four hori
These w ill be discussed in
zon t l
order
Fi g 8 0 0 os s S e c t i on or We i
For any form of measuring weir
the hori zontal edge of the Openi n g o r
notch is called the crest of the weir W hen a weir has no end c on
tracti o ns the c rest only is made sharp as shown in section in
Figure 80
For a weir with end contractions the inner edges o f
the Opening both horizontal and v ertical s h ould be made sharp so
lon g a
line
that the water in passing through it touches only a
For o rdinary work th e edges of
the planks in which the Opening is
cut are chamfered off at an angle of
bo ut
as sh o wn in section in
a
For accurate w o rk and
Fig u re 8 1
i n localities where the edges are sub
e
t
t
o
abrasion
by
drift
pa
s
sing
over
c
j
the weir the edges both horizontal
n d vertical
should be made with a
F g 8l
Fi g 8 2
thi n plate o f iron firmly attached as
ils
of
Cr e s t
De t a
shown in section in Fig ure 82
,
,
,
a
.
,
,
.
,
,
,
.
.
,
,
,
.
.
,
,
,
a
.
.
.
r
.
r
.
.
,
.
,
,
,
.
,
,
.
a
,
,
,
i
,
,
.
.
.
"
.
.
.
H YDROGRAPH I C S URVEY I N G
1 46
a
alle d the Fra n cis fo rmula This f o rmula with suitable m odi fic
ti o ns adapted to the fo rm o f weir under considerati on is ge n erall y
u se d in c o mputing the fl o w o f water over weirs
Bo th forms o f
recta ngular weirs will be discussed sep arately an d the applicati on
of the discharge formula to each fo rm o f weir will be sh o w n
c
.
,
,
,
.
,
.
W EI RS W IT HOU T
END
CO N T RA CTI O N
.
Whe n a weir has its crest ex tending entirely acro ss a stream
,
here is n o c o ntraction i n the sheet o f water flowing over it except
a
t the t o p and bo tt o m o f the sheet ; this is called the crest c o ntra e
The form of crest c ontracti on is illustrate d in Figure 80 in
tion
which the to p an d bo tt o m c ontracti on s are show n at M C a nd at A
respectively I n com puti n g the discharge o ver a weir o f this ki n d
the crest contracti o n must be taken int o acco unt
I t has been seen that the formula f o r computi n g the flow of wat er
over a dam o r weir in which end c ontractions are n ot co nsidere d is :
=
L
H 3
C
)
Q
t
,
.
,
.
.
a
a
,
,
in which C i s th e c o effi cient of discharge the other facto rs h vm g
the signi ficance previ o usly explaine d
A s has been previously stated the c o effi cie n t of discharg e varies
cco r d ing to the fo rm o f cro ss section of the dam o r weir Fo r a
a
w eir with a sharp crest as in the case o f a m easuring weir the
formula de ri v ed f ro m the Francis fo rmula is
=
( 3)
Q 3 33 L H i
This formula is c o rrect in cases where there is no vel o city of
pproach that is where the water has no appreciable velocity j ust
a
bo ve the weir I n practice such a con dition fo r the f o rm o f weir
a
un d er consideration is never found since water i n fl o wing over a
or weir wh ose crest extends across the full width of the chan
da
m
must necessarily have an appreciable current in o rder t o pro
n el
The fo rmula j ust gi ven must therefore be c o rrected
d uce discharge
for the vel o city of approach befo re it can be applie d t o the c om
utati
on
o
f
discharge
over
a
weir
without
e
nd
c
on
cent
ati
on
s
r
p
,
.
,
-
.
,
,
.
,
,
,
.
,
,
,
,
.
.
V ELOC IT Y
OF
A PPROA C H
.
The velocity of approach is the m ean vel ocity with which the
w ater fl o ws through the channel leading to the weir at the poi n t
w here the head is measured
I n a case where there is an appreciable
the surface o f the
vel o city o f appr o ach in a stream above a weir
water will have an appreciable slope for s o me d istance abov e the
,
.
,
ME
T HODS
I
D
W OR K
OF F E L
region o f q ui et water
a few feet ab ove th e
weir This is sh o w n
o n an exaggerated
scale i n Figure 87 i n
which H is the head
abo ve th e weir meas
u red in q uiet water
S e c ti on
of
on
Axi s
S tr e a
m
several feet abo ve th e
crest a nd h is the vel ocity h ea d or the head due t o the sl o pe It i s
evident that the true hea d pr o duci ng the fl o w over the weir is
H
h This value must be substituted in formula 3) to obt i n
the co rrect d ischarge I n order to fin d h the velo city o f approach
must be d etermi n e d The determination o f the vel o city o f approach
in the curre n t m y be e ff ected by the use o f fl o ats o r by current
m eter as previously d escri be d
It is custom ary h o wever to d eter
mine i t by fo rmula i n which case the foll o wing m eth od may be used
Let v = th e mea n vel o city o f appro ach ;
H = th e head of water fl o wi n g o ver the weir measure d i n
q uiet water ;
h
the vel ocity hea d ;
the
approximate
q
ua
n
tity
o
f
water
fl
o
wing
over
the
weir
Q
,
.
,
,
,
.
,
.
a
,
.
.
a
.
.
,
,
,
,
,
,
i;
LH
A = th e cro ss secti onal area o f the channel j ust abo ve the
-
Then
weir
fro m e q uation
.
v
the vel o city h ea d
=2
£
2 s
:
ad
n
,
to
find
h
3 31 L H
.
2
3
,
v
2
v
2
2g
The value o f h is fo und by substituting observed values i n e q uations
E quati o n ( 3 ) th en b ec o m e s
( 4) n d
h
L
H
(
)§
Q
(6 )
This is the simplest fo r m of discharge fo rmula f o r a w eir with no
end con tracti on s a n d one that will give fairly accurate results wh en
applie d to a weir con structe d un der pr oper cond iti on s
a
,
.
W EI R S
W IT H E N D
CO N T RA CTI O N S
.
The m o st co m m on fo rm fo r r ecta n gular weirs is that i n which th e
crest d o es not exte n d the full width o f the chan n el that is wh er e one
or b oth ends o f th e Opening re co ntracted The e ffect o f such con
a
,
.
,
HYDROGRAPH 1 C
1 48
a
S
URV EY I N G
tr ction is to preven t or dimi n ish the vel o city of approach i n th e
stream to such an exten t that it will be i n appreciable Wh en suit
ble contraction is made it will therefo re obviate the necessity of
taki ng int o ac count the velocity head h thus elimi n ating a tr ouble
some factor fro m the discharge equation The equation expressi n g
discharge over a weir with end c ontracti o ns will be the fo ll o win g
m o di ficati o n of the simple for m of the Franci s fo rmula :
a
-
.
,
,
,
.
Q
in which L
is
:
LI H
g
the e ff ective length of the cre st
EF FE C TI V E
L E N GT H
.
CRE S T
OF
.
I t is seen that in the fo rmula j ust giv en in place of
L
denoti n g
actual lengt h of crest the factor La denoting eff ective len gth of
crest is used Th e e ff ective len gth is not the same as the actu a
l
length o f cres t as will be se en fro m the fo ll owing explanation
Th e e ffect of end contraction s in a weir i s to diminish the are a
of cross section of the st ream passi n g through the weir making i ts
width less than the a
ctual length O f the crest of the weir This i s
illustrated in Fi gure 86 in which L i s the measured length of the
crest and L is the width of the stream i s suin g from the weir It is
seen that L is shorter than the actual length L of the crest In such
a case L is called the e ff ective length of the weir ; it is f ound by
applying a correction to the measured length For a
weir with end
co ntractions the value of L in the dischar g e form u l a
is therefore
not the m easured len gth of th e crest but i ts e ff ective length
,
,
,
,
.
,
,
.
-
,
.
,
1
.
i
.
1
.
,
,
,
.
CO M P LE T E CON TRA CTI O N
moun of contraction or
a
tre
m
from
a
weir
with
a
g
.
of diminution in width of the
issui n s
end contractions d ep ends upon
the r elation between the distanc e from the s ides of the opening to
the parallel s ides of the weir also th e de p th O f water above its
crest W hen this distance as D Figu re 86 is abo u t twice as great
as the head H there is practic a
lly no further change in the con
traction of the water with ny increase in the distanc e D I n s u ch a
case the c o ntracti o n i s said to be compl ete
A weir is said t o h a
ve one or two complet e contraction s a
ccord
ing to whether o ne or both ends of the opening are contracted in
re contracted midway
I n some c ases weir s a
th e ma nner described
of their lengt h ; there may be all degrees o f contraction in weirs
fro m complete c o ntracti o n to n o contraction
The a m oun t of diminution in the w idth of the sheet of wat er
Th e
t
,
,
,
.
,
,
a
,
.
.
.
.
.
I
HYDROGRAPH I C S U RVEY I N G
0
5
The fu n dame ntal idea o f the trapezoidal weir is that the c ross
s ect i on al area o f the stream of water flo wing thr o ugh it i nc reases
s uffic ien tly with i n crease in d epth to exac tly balance the l o ss d ue to
thus all o wi n g the u se of the simple fo rm o f d is
end c on t racti o n
c h rge f o rmula with o ut req uiring correc ti on fo r end contracti o n
A trapezo i dal weir
has a n open ing wh ose
si d es instead o f bei ng
vertical as in the cas e
of a rectangular weir
S
lope
outward
at
a
n
i
n
Fi
F
or m
6
0
of Tra
e oi d a
l
i
r
W
e
g
p
c l i n ti on
of on e h o ri
z ont l to fo ur ve rtical
Th is form which is illustrated i n Figure 88
i s e q ui v l ent t o that o f a rectangular w eir with a triangle a dd e d t
e ch e nd
The theo ry upon which this form of weir is base d which
w s d eri v ed fro m e x periment and calculation is that the fl o w
thr o ugh the ad d ed triangles is suflfc i en t t o balance the l o ss due to
end co ntractio ns I f this theo ry is true the discharge will be th e
~
same s that o ver a rectangular weir with the same lengt h of crest
with o ut end c ontraction s and with n o appreciable vel ocity o f p
pro ach I n such a case the discharge formula would be th e simple
f o rm o f the Francis fo rmula : Q
L H g
Ci p pol etti f o und h o wever fro m experime nt that the coeffi cient
u sed i n th e Fra n ci s f o r mul a
s houl d b e i n cr e a s ed ab o ut o n e p er c e nt
i n o rder to give co rrect results This being done the discharge
1
formula fo r the trapezoidal weir is Q
L H
0
( )
This is c o rrect when there is no vel ocity of approach In case
there is a n appreciable ve locity of appro ach the velocity h ead h
must be fo u n d and the correction applied as in the case of a rec
t ngu l r weir
M EA S UR E M E N T OF H EAD
In all weir measurements it is n ec essary to know accurately the
depth of water o ver the crest of the weir ; this depth being expressed
in the discharge fo rmula by th e s vm bol H A s previously stated
this depth or head must be measure d in still water usually at a
distance o f several feet upstream from the weir
In measuring the head care must be t a
ken to avo id waves ripples
and other disturbances of the w ater surface ; also t o provide gai n st
capillary attracti o n when using a rule or measuring ro d to obtain a
readi ng
F o r ve ry accu rate w o rk in whic h it i s required to determine very
b
e
cl o sely the true level of the water surf a
ce a hoo k ga
e
should
g
a
,
.
,
,
,
,
.
z
.
a
a
a
a
a
.
.
a
,
,
.
,
,
a
.
a
,
,
.
,
,
,
.
.
,
.
,
,
a a
,
.
.
,
.
,
.
,
.
,
,
a
ME
T HODS
D
OF FI EL
W OR K
1
1
5
used Th i s c on sists o f a long graduated rod provided at i ts foot
with an uptur n e d book or point I t is arranged to slide vertically
i n a fix e d supp o rt to which is att c he d a vernier i n dicati ng o n a
scale th e height of the p o int W h e n the zero o f the scale a nd o f the
ver n ier are to gether the p oint o f the h o ok gage sh o uld b e u nd er
water a n d at the ex act level of the weir crest I n o rder to find the
depth of water over the crest the book which sho uld previ o usly be
lowered be l ow the water surface is raised sl o wly u n til th e po i n t
j u st reach es the surface The rea d ing o f the vernier will the n gi ve
the depth of water corresponding t o the hea d H Wh e n
h ook
gage is use d the water level i s usually take n i n a vesse l o r si d e
cham b er which commu n icates by a pipe or c on duit with the m in
chann el The vessel bei n g protected from wind an d o ther disturb
ing i n flue nc es the water c ontained therein has a calm sm ooth
surface suitable fo r accurate observati ons The use o f the h ook
gage is not c o mm o n i n o rdina ry survey w o rk i n which the fiel d
meth o ds employe d do n o t re q uire such great re fin ement of obser
vati on It i s especially adapted fo r use in hydraulic experimen ts
a nd observati on s and in the measurements where great accuracy is
req uired as i n rating water wheels turbines etc
Fo r o rdi n ry w o rk the fo l l o wi n g is a goo d meth o d to use in de
term i n i n g the head : A post or stake is set in the water where it is
quiet at s o me c onvenient point a few feet above the weir s o as to
The top sh o uld be cut off s quare
be easily accessible from shore
and sh o uld be horizontal an d at the exact level of the weir crest
The depth of water is me a
sured with a graduated r o d o r rule
plac ed vertically o n top o f the post the reading of the water surface
on the side o f the rule being carefully observed
A con venient metho d for obtai n ing an accurate readi ng o f the
water surface is described and illustrated in a booklet written in
1 8 8 by M r R obert C Gemmell S tate Engineer of Ut ah
I
n
usi
g
n
9
this method a stake is set in the water with its top at the level of
the weir crest as j ust described On the top of the stake a car
’
n
r
s
squ
re
is
held
in
a
vertical
p
o
sition
in
the
manner
illustrated
e
t
e
p
in Fi gure 8 5 and sh own in detail in Figure 89 A slide made of
tin with a sharp p o i n t o n its
upper edge is used to deter
mine the exact water surface
as sho wn This fo rm o f slide
is illustrated in Figure 90 I n
fi
use
it
is
placed
o
n
the
squar
e
n
w
m
fl
fi
ym
o
g
g
n
m
f
g
ggstm ggfiggg
in such a manner that w h en
.
,
,
a
.
,
,
.
,
.
,
,
a
.
.
a
,
.
,
,
,
.
,
,
.
,
,
a
,
.
,
,
,
,
.
,
.
,
,
.
“
.
.
.
,
,
a
.
,
.
,
,
,
.
.
f
o
,
I
H YDROG RAPH I C
2
5
S
URVEY I N G
square is held in a vertical posrti on the upper edge o f the sli d e
a
The slide is l o wered
n d the p o int are in the same horizontal line
until it is well bel ow the surface of the water ; it is the n gradually
raised until the upper ed ge j ust reaches the surfac e which is i n
nce of a
pimple on the s urface of the water
d i c ted by the appeara
immediately over the point
A nother method of me a
suring the head is by means of a glas s
water tube set vertically at some co nvenient point bel o w the weir
a
n d graduated to feet and decimals with its zero leve l with the crest
of the weir I t is connected with still water above the weir by
means of a pipe of suitabl e size and len gt h This device however
shou l d not be u s ed when ther e is dan g er from freezing
th e
,
.
a
,
,
.
,
,
,
.
,
,
.
.
CON D I TI O N S
FOR
A C C URA C Y
IN
W EI R M EA S UR EM E N T
.
formulas given for weir discharge as has been previ o u s ly
s tated
are empirical that is they have been derived fro m ex
E
a
h
formula
will
give
results
in
practice
that
will
be
i
e
er
m
n
t
c
p
correc t within about one per cent when applied to the form o f weir
re Observed
for which it is given provided proper conditi ons a
Th e results obtained by the use o f the formulas are exact or
nearly so only so far s experimental knowledge goes ; it is there
fore safe to apply a gi ven fo rmula onl y within the limits of the
experiments upon which it is based
Fro m experimental i n vestigations the followin g condition s have
been found necessary in order to obtain accur a
te results :
1
The channel leading to the weir on the upstream side sho uld
be straight and of c onstant cross section with its axis perpendicular
to an d passing through the middle of the weir ; it should be O f
su ffi cient size and len gth for the wate r to flow with uniform v el oc i t v
without internal a
gitation or eddies
2
For a
weir with compl ete end contr a
ctions the foll o wing con
Th e ope n in g must be in a plane surface
ry : a
d i t i on s are necess a
a
erpendic
lar
to
the
course
of
the
stre
m
pening
should
u
b
T
h
e
O
p
have sharp edges on its crest and sides on the upstream face ; for
depths less than 5 inches the thickness of its walls at the p o i n t o f
d ischarge should be not over on e fo u rth the depth and for depth s
th e thickness of the walls should be not
o f from 5 to 2 4 inches
o ver one tenth of the depth
e Th e distanc e of the crest of the weir
from the bott om o f the stre a
m should be at least three times the
depth of water o n the weir crest d The distance of the vertical
sides of the opening from the side s O f the chan n el should be at least
twice the depth of water over the c re st or of the head H e The
Th e
,
,
,
,
.
,
.
,
,
a
,
,
,
,
.
.
,
.
-
,
,
.
.
,
.
,
-
,
,
-
.
.
,
.
1
HYDROGRAPH I C
54
S
URV EY I N G
TA B L E NO
DI S CH A R G E
5
.
6
TA B L E FOR S A N
AT
.
T A BL E FOR C A N A L
TA B L E N 0
DI S CH A R GE
.
H E R N DO N
,
.
.
J O A QU I N
CA L I F O R N I A
R
I VE R
,
.
lower stages Th e fo rm of
cro ss section o f the c n l
is sh o wn in Figure 9 1 Fo r
co nvenience the fo rm i s
sh o wn regular with regu
l
n
n
C
a
a
t
i
o
o
f
e
S
s
s
o
i
C
Fi 9 9
sl
o
pes
In
racti
e
l
l
c
r
t
e
W
a
P
e
o
f
t
s
r
s
n
a
e
e
f
f
w
m
D
h
o
s
g
q
however such regularity
in cro ss section is seld om found since ordinary streams or eve n
after con siderable use have rather irregular cross secti on s
c anals
In such cases values interp o late d between observed d ischarges wil l
necessarily be only approximate though suffi ciently close for prae
tical use
aa
.
-
.
.
c
r
.
i
,
r
a
,
’
.
.
,
-
,
,
-
,
.
,
,
.
ME
T HODS
I
D
W OR K
O F F EL
1
55
a practical example a discharge table giving the res ul ts o f
s
r
i
s
R
eld
bser
v
ati
on
s
on
J
o
q
ui
n
iver
in
C
lif
o
n
ia
ho w n
h
n
t
e
S
O
fi
in Table No 6 This is take n from a repo rt o f t h e Un ite d S t tes
fi
u
m
e
e
logical
ur
ey
and
is
s
ho
wn
as
an
x
a
ple
o
f
act
al
eld w o rk
v
S
Go
For
a a
.
a
,
a
,
.
.
DI S C H A RGE CURVE
a a
.
The rates o f fl o w o f a given stream at a disch rge st ti o n may
be sh o w n grap h ically i n the fo rm o f a d ischarge curve withi n th e
limits o f ob serv e d va l u es I n o rder t o fo rm suc h a disch arge curv e
the results o f the vari o us g gi ngs as entere d in the d isch arge table
are platte d on cro ss secti on paper with the gage heights as o r d i n ates
an d the discharges as abscissas, all values bei n g referre d to the o rigin
of c o o rdinates
Whe n this is don e the result of each gagi ng will be sh o w n as a
poi nt at s om e design ate d place on the paper I f there are a num
f
f
of
these
p
o
ints
well
d
istribute
d
acc
o
rding
t
o
di
eren t stages o f
ber
x
i
r
o
w
the stream it wi l l usually be fo un d that they ill all lie p p
e
S
mately in the path o f a parabo lic curve
uch a curve is sketch d
through or near the p o i n ts ; the survey o r fro m o bservati o n an d
knowle dge o f l o cal con diti on s s ho u ld give greater weigh t to s o me
poi n ts tha n t o o thers
I n Figure 92 is sh o w n a d ischarge cu rve d raw n fro m the d t
,
,
,
a
.
,
,
,
-
-
.
.
,
a
,
,
.
,
,
a
a
.
g fi g g fi g ai g é g é i i i
Fi g 92
.
.
Di sc h
a
rge
Di
s ch
a
Cu b i c Feet p er S ec ond
for H ern d on S t ti on , on S
rg e i n
C u rve
C
f
i i i i éi i
F r om
U S
.
li f
a
.
a
a
orn i
Geol og i c l S u r vey )
a
.
.
.
i
aJ a
q
n
o
u n
R i ver ,
I
H YDROG RAPH I C
6
5
a
a
S
URV EY I N G
a
a
given i n T ble No 6 The g ge heights re platted as ordinate s
in feet nd the d ischarge values are platted as abscissas in cubi c
feet per sec ond in the ma n ner that has been described ; their po si
ti on s are sh o wn by the small Circles Th e curve drawn throu gh th e
several po ints is the discharge or rating curv e it is seen to resemble
in for m a parabo l a For any value s lying W i thin the limits of the
points are interpo l ated on the curve wh o se corre
p latted values
es en t respectively the ga ge
s on di n
o
rdinates
abscissas
repr
n
d
p
g
rge value s required
h ei ghts and disch a
,
.
.
,
,
,
.
°
.
a
,
,
.
RA TI N G TA B LE
.
W h en adisc harge c u r v e has been drawn in the manne r j ust
described a rati n g table may readily be prepared showing the dis
charge fo r every tenth of a
foot of ga ge height within the limits of
the o bservations S uch a ratin g ta
ble is simply a numerical expre s
s i o n of th e discharge curve previously described
In preparing a rating t a
ble the first figures representing the
l owest values are taken from the discharge curve drawi n g be
gin ning at the lower left hand corner The lowest abscissa i nter
t
h
secti n
the
axis
of
ordinates
at
e
nearest
tenth
of
a
f
oo
t
to
the
g
o rigin of c O ordinates is fo llowed from left to right until it intersect s
the curve and the value represented by the distance is entere d in
the table oppo site the tenth of a f oo t taken Th e abscissa c orrespon d
s
i n g to th e ne xt tenth of a
foot in height is then followed o ut a
j ust described and its l en gth from the a
xi s of ordinates to the curv e
a
t the right is also fou n d a
n d recorded
This process is co n tinued
fo r each succeeding tenth of a foot of gage height ; the corre spond
ing distances to the curve are tabulated as discharge s
W hen a table has been prepared in this manner it will be fo und
that there is an increasin g value for the discharge and that the
di fference between the successi v e va l ues is constantly increasing
Ow ing however to th e sm a
ll scale to which such a sketch is m eces
s r i l y drawn
the figure s taken from the drawing do not alway s
have this c o nstantly increasing value ; some being pro p o rtionately
too large a n d others t oo small
I n order therefore to s m ooth out
the curv e it is a goo d plan to set off bet w een the lines o f the rating
ta
ble the di fferences in the quantity of discharge making a third
c olu m n
U pon exami n ing thi s column s ever a
l poin ts are quickly
detected where the di fferences are n ot r egul a
r A fter c onsidering
t hese it will be se en that a slight adj u stment Of the di ff erences and
t h e additi o n o r subtraction of a small amount t o or fr om the fi ure s
g
of discharge will smooth out thes e irregu l arities This adj ustment
,
,
,
,
.
.
,
,
,
,
.
,
-
,
,
.
,
,
,
.
.
,
.
.
a
,
,
,
.
.
,
,
,
.
.
,
,
.
1
8
5
HYDROGRAPH 1 C S URV EY I N G
'
a
a
for ll o rdina ry pu rpo ses since stre m measuremen ts are n o t usually
ma d e t o a d egree o f refinement that will require ny c lo ser figures
I n Table No 7 is given a rati n g table fo r the S n J o a q uin R iver
at H erndo n Cal which was prepared in the man n er j ust describe d
fro m the discharge curve sh o wn in Figure 92
The d ischarge
c urv e d ischarge table and rating table sh o w n are all taken from the
repo rt o f the Un ited S t tes Geo l ogical S urvey previ o usly referre d
to ; they are given as representing goo d examples of actual practice
fo r such w o rk
Th e le ngth o f time d urin g which a rati n g table ca n safely be p
plie d t o o bservati on s at a given discharge stati on sh oul d be d eter
mi n ed by the surv ey o r nd note d upon the table in o r d er th at it may
n ot be used bey on d pro per limitati ons Where the cha nn el is c on
st ntl
cha
n
gi
n
g
as
is
the
case
in
m
o
st
streams
a
tab
l
e
c
n
ot
be
n
y
used fo r man y weeks o r m o nths unless it be referre d t o the r ea d i ngs
o f h eights as in terpreted by a dd itio nal s o undings
,
a
a
.
.
,
.
,
.
a
,
,
a
.
a
a
a
.
,
,
.
DI S C HARGE
FOR M U LA
BY
.
I t is s ometimes required to compute the d ischarge o f a stream
through o ut a given stretch o r po rti o n of its length u nd er c on
di ti on s where it is not convenient t o under take close measuremen ts
or where approximate values are su ffi ciently close fo r the purpo se
req uired
I n s o m e cases after d etermi n i ng the discharge o f a stream by on e
of the m eh ods that have been described it is a d visable t o c ompute
th e flow by s o me di ff eren t meth od f o r purpo ses of c o mparis on
I n ei ther o f the abo ve cases it is c ustomary whe n an alter n ati v e
nd fo r
method is re quire d to co mpute the d ischarge by fo rmula ; a
this purp o se the well known formulas o f Chezy and o f Kutter are
co mm only use d
Th e Chezy f o rmula which i s the fundame n tal f o rmula fo r stream
,
,
.
,
,
.
,
,
.
,
discharge is :
,
A
V
Q
t h e discharge o f the stream usually in c u bic feet
i n whi ch Q
per seco nd ;
A
the area o f channel cr o ss secti on usually in square
feet ;
the vel o city of fl o w usually in feet per s econ d
The vari o us method s o f ascertai n i n g curren t velocities by fl oats
an d by meter which have been discussed in this manual req uire
In applyi n g the
th e measureme n t of velocity by direct observati o n
Ch ez y fo rmu l a however to the determi n ati on o f str eam discharge
,
-
,
.
,
,
,
.
,
,
,
M ET HOD S OF F I ELD WORK
av l o it of at ai c on i d
ad o f the wetted perim ter o f a stream
fo r ul a
as fo l lo ws
the
m e n
e
c
s re m
y
n
s
s
e
m
.
1 59
a
a
r
fu ncti on o f th e sl op e
This m y be e x presse d b y
e ed
:
-
In
V c VR?
( 2)
the hydraul ic radius or the hydraulic mea n depth o f
w hich R
the chann el ;
th e sine o f the surface m pe f o r which owi n g t o
S
its small value the surface sl ope is substitute d ;
C is a variable coefli ci ent depend i ng upon th e n ature o f
the cha nn el
,
,
,
,
.
S LOPE
.
The sl o pe o f a stream or rath er o f a section of a stream i s the
d i ff er en ce in e l evation betwee n t h e upper and lower e nd s of th e
c o mmonl y calle d the fa l l divi d e d by the d is t n ce o r th e
s ecti on
l en gt h o f the s ecti on
The value of the S l ope may b e e x pressed by
a
n equation thus
,
,
a
,
,
.
a
( )
L
fall i n f eet from the upper t o the l o wer e nd o f
the secti on ;
L
the le n gt h o f the S l ope s ecti o n in feet
The m p e secti on should be o f suitable len gt h ; such le n gth will
d epend largely up on the nature o f the stream the accuracy require d
in the results a n d the size a nd l ength o f the stream u n der con
s id erati on
Th us in the case of a ca n al o r an irrigation ditch where the
v alues d eterm ine d by formula are c o mpared with th o se o btai n e d by
d irect measuremen t se ction s o f 1 0 0 or 2 0 0 feet in length are c om
m onl y c on sidered
I n th e case o f a river o r o ther large stream where the obj ect may
be t o d etermine discharge s at ma x imum stages of t h e water sl o pe
secti on s varying i n length fro m several hu n dred feet to several
m iles are used
In suc h cas es the extremities of the sl o pe section s
are l o cate d as cl o sely as possible at the pri n cipal poi n ts o f change
of sl o p e i n the stream I n th e gaging o f the M ohawk Ri v er by the
New Yo r k Barge Ca n l su rv ey t h e river fr o m H erkimer t o Coh o es
miles was d ivided i n t o thirteen slo pe secti o ns
ad istan ce of
each secti o n being fro m
to
miles lo ng
It is d i ffi cult to ascertai n accurately the sl o pe of the water surface
in a str eam si n ce in n early all streams th ere re pu l sati on s i n the
water causi n g the surface to ris e an d fa ll l o ca ll y In m o st streams
in
F
which
th e
.
,
.
,
,
,
.
,
,
.
,
,
,
a
.
,
,
,
,
.
,
,
,
a
.
1 60
H
YDROG RA PH I C
S
U RVEY I N G
the sl ope of the bo tto m is far fro m u n ifo rm a n d the fl o w o f water
i n a n y given se cti on is mo re o r less i n fluenced by the fl o w in th e
a d j ace n t secti o n abov e o r bel o w Fo r exa m ple if
secti on 50 0
feet l on g has a sl o pe o f 5 feet t o th e mile and th e s ec ti o n o f th e
same length next bel o w has a fall o f 4 feet t o the mile the i n
flu ence o f the steeper S l o pe of the upper secti o n will be felt in the
l o wer s ecti on For this reas o n it is a good pla n t o c on sider a num
ber o f a d j acent secti on s c o mpri si n g a c on siderable po rti on o f the
len gth of a given stream in o ne com putati o n bei n g careful to take
i n to acc o unt the diversity of cross sectio n at v a
rious places in the
len gth
In d etermining the slope of the surface of a stre m levels are
take n o f the water surface at each en d o f the sl o pe section and re
ferred t o s ome datum o r bench m ark A go od plan is t o set fi rmly
a stout w oo den stake bel ow the water surface at each e n d o f th e
slo pe secti o n and the n to drive a n ail into the top o f eac h stake so
that the nail head will exactly c o i n cide with the water surface
Levels can then be ru n fro m o ne sta k e to the o ther ; the di ffere n ce
i n elevation between the two nail heads divide d by the dista
nce
betwe en the stakes will give the sl o pe
I n case it is not possible to have the nail heads exactly at the
water surface the results wi l l be th e same i f they bo th have the
same relative p o sition with respect to the water surface Un d er
o rdi n ary conditi on s this meth od o f determining the m pe will gi ve
a
n d satisfactory results
ccurate a
,
,
.
,
.
a
,
,
,
,
.
,
,
,
-
a
.
,
,
.
,
,
.
,
.
,
.
.
TH
E
W ETT ED
PER I M ET E R
.
The wetted peri m eter is
that po rtion o f a stream chan
nel that is i n c on tact with the
water Thus in Figure 93
in which is sho wn th e cro ss
F g 9 3 C o s S e t i o n of S t re a
m
s ecti o n of a
stream
that
p
o
r
Pe i m e r e r
W
sh ow i n
efl e d
g
tion o f the perimeter o f the
cha nn el that 1 5 shown below the water surface is th e wette d pe rim
eter The fo rm of o utli n e Of the wetted perimeter o f a stre m has
an importan t i n fluence upon the vel ocity of the curre n t
.
i
.
r
.
s
c
,
.
r
,
,
a
.
-
.
TH
E
H YDRAU LI C
RA D I U S
.
The hydraulic radius which is s ometimes called the mean radius
o f stream is th e mean depth o f the ch an n el bel o w th e w ter Sur
a
,
,
a
‘
1 62
H YDROGRA PH I C S
U RVEYI NG
a
fo r ca n als in earth abo ve the avera ge i n o rder n d
regimen ;
fo r ca n als a n d rivers in ea rth o f t olerably u n ifo rm
cr oss secti on slope and direction in mo derately goo d
order and regimen a n d free fr om ston es and weeds ;
f o r ca n als and rivers in earth bel o w t h e average i n
order a n d regi m en ;
fo r canals a n d rivers i n earth i n rather ba d or d er n d
regimen an d havi n g stones and wee d s occasio n ally
and Obstructed by detritus
fo r rivers a n d c nals with earthen bed s in ba d o rder
a n d regime n a n d having ston es a n d w eeds i n great
quan tities
fo r t o rren ts en cumbere d with detritus
,
-
,
,
,
,
a
,
,
,
a
.
,
,
.
.
I RRI GATI ON CA N ALS
A series o f experiments o n the fl o w o f w ter i n irrigati on d itc hes
and canals w s co nducte d in U tah i n 1 89 7 by Pro f S amuel Fo rti er
un d er th e auspices o f the Unite d S tates Geo l ogical S urvey and o f the
gricultural e x periment stati o n of Utah The results o f these ex
a
P
s
were
emb
o
died
in
a
paper
written
by
r
o
f
F
o
rti
e
r
a
n
d
n
i
m
e
t
r
e
p
p ublishe d as on e o f the Water S upply and I rrigati on papers o f the
United S tates Ge ological S u rv ey This paper con tai n s a n umber o f
values fo r n applicable to ir rigati on ditches and ca n als these values
having been derived from the results o f the ex perime n ts j ust t e
ferred to The f o ll o wing values fo r n are taken fr om this p per
11
fo r canals in earth in exce llen t con d itio n well c o ted
with sediment regular in cross sec ti o n a nd free
fro m vegetati on l oo se pebb les a nd c obbles
fo r canals in earth i n goo d c ond iti o n li n ed with
well pack ed gr avel partly cov ered with sedime nt
an d free fro m vegetati o n
fo r can als in earth in average c ond ition havin g few
sharp ben d s and bei n g u n ifo rm i n cro ss secti on ; the
water sl o pes and bo tto m bei n g lined wi th se d iment
nd minute alg e
o r co mpo se d o f l oos e c oarse
gravel an d fragme n ts o f ro ck less tha n 2 i n ches in
diameter and free fro m v egetati on
fo r ca nals i n ea rth i n rather po or c o nditi on havi n g
the bed partially covered with debris ; o r havi n g
c omparati vely sm oot h sides a nd bo tt o m with bunches
of grass a nd weeds pro j ecting i n t o th e w ter nd
with aq uatic plants growing i n the c h a nn el
a
.
a
.
,
.
.
.
,
,
a
a
.
,
,
-
,
,
.
,
,
,
,
,
.
,
,
-
,
a
a
,
,
.
,
,
,
a a
,
,
.
ME
T HODS
I
D
W ORK
OF F EL
1 63
a
for s m all ditches having a r o ugh uneve n bed ; nd
fo r ca n als i n earth i n fairly good cond i tion but
pa rtially fil le d with a quatic pla nts
11
fo r ca n als i n ea rth th e chan n els o f which re bout
half full o f a q uatic v egetati on
n
for canals i n ea rth the chan nels o f which re bout
tw o thirds full o f a q uatic v egetati on
Fro m his experi m e n ts Pro f Fo rtier derived a n umber of con
el usi on s am on g them bei n g the f o ll owi n g
The co effi cien t o f fricti o n i n ca n als well li ned with sed i m en t
in goo d c ondition and lon g in use is less than has usually been
s uppo sed
b The e ffect o f water plants i n checki n g the flow nd lesse n i ng
the capacity o f irrigati o n c n als may be much gr eater tha n a r o ugh
un even chan nel
c R o ughness o f perimeter i n a small ditch exerts a gr eater i n
fluen ce in retar d ing flow tha n the same de gr ee of r ough n ess exerts
in a large canal o r a river
An ex mple will be gi ve n sh o wing the applic ti on o f
Ex m pl e
the Chez y fo rmula t o the c ompu tation o f discharg e The measure
men ts and o bservati on s were made i n th e Lo gan H yde Park nd
Thatcher canal near Logan Utah bei n g con ducted as on e o f th e
ex p eriments j ust mentione d The sides o f the chann el were sm ooth
and c o ated with sediment The bo tt om con siste d o f earth gravel
Th e val u e assigned to n is
a
A discharge
n d pebbles
1 0 0 feet in le n gth
and a n aver ge o f three
s tati on was laid Off
cro ss secti on s at the two ex tremities and midway O f the disch arge
stati on was take n fo r the mean cr o ss secti on ; this is sh own i n
Figure 94
n
,
,
,
,
aa
aa
.
,
.
,
-
.
.
a
,
,
,
a
.
a
,
.
a
a
.
a
.
,
a
.
,
,
,
,
.
.
,
a
.
,
,
-
,
-
,
.
Cr os s S
e c t i on
of
C
aa
l h
n
,
s
owi n
S
g
ub di vi s i ons
.
fo llo wi n g values were obtained from m eas ure m en t
A
s q uare feet
area of water secti on ;
P
lineal feet
wetted perimeter ;
hu
nd
red
feet
sl
o
pe
S
e
r
p
The h ydraulic radius is ob tai n ed b y substituti n g k no w n v l ues
the eq uati on
Th e
.
w h i c h th e
n b ec o m
es :
R
a
HYDROGRA PH I C S U RV EY I N G
1 64
aa
a
substituting i n Kutter s f ormula the v lues giv en h ere
v alu e
is found f or c
The values o f the sev er l kno w n f ct o rs
are t h en su bs tituted i n the Ch ezy fo rmula : V
c
R S fr o m
w h ich V
The fu n dam ent l d ischarge fo rm ula is the n p
plied a nd th e v alue o f Q is fou n d t o b e
cub ic feet per second
Th is value fo r d ischarge a gr eed cl o sely with th e me surem en t s
m ade wit h a current m et er
’
By
,
a
a
,
a
a
.
.
F LO W OF W AT E R I N OP E N CHA N N ELS
The phe nome n a c onn ected wit h th e flow o f water in ope n chan
n el s h ve been the sub j ects o f m uch stu d y and obse rvation b y
vari o us h yd r u li ci ns A great d ea l has been learned abo ut this
subj ect a l th o ugh the th eo ry o f the fl o w o f water is still i n co mp l ete
nd the laws go vern ing it are n o t suffi ciently u n d erst oo d to all o w o f
go ing bey ond t h e data ac q uired fr om experie n ce Ther e are h o w
ever certai n c o nditi o ns an d pri n ciples attendi n g the fl o w o f water
which are suffi ciently well kno w n to be co nsi d ere d as practically
fix e d and which may be stated i n the fo rm O f rules o r laws
Th e
well k n o w n fo rmulas o f Chezy and of Kutter are ge n erally acc epted
s c o rrec t alth o ugh th ey are e m pirical being base d upon the resu l ts
o f ob servation and e xperiment The same is true in a general w y
o f all o ther fo rmulas o r laws that are applied to the flow o f water
i n open cha n nels
TH E
a
.
aa
.
a
,
.
,
,
,
,
.
a
,
a
,
.
.
VERTI CA L T RA N S VERS E VELOCITY CU RVES
I f we i m agine a fl o wing stream to b e intersecte d at right an gles
t o its axis by a vertical pl a
n e di ff eren t points i n that pla n e w ill have
d i fferent velo cities or rates o f flow The bottom a nd si d es o f the
ter cl o se to th em i n pro po rti on to
c hannel retar d the fl o w o f the w a
their ro ugh ness the retar d ati on bei ng d ue to the i n fluen ce o f e dd ies
i n the water and als o to the f riction o f the fl owi ng water against
the perimeter o f the chan n el The velocity at the surface o f the
water has been found to be s o me what less tha n th at a litt l e l ower
i n the secti on
The retar d ati on of the surface vel ocity has b een attribute d to
several di fferent causes ; one cause is said to be the risi ng b y v erti cal
moti o n of the lower water t o the surface after b ei n g ch ecke d i n i t
fl ow b y c o mi n g i n co n tac t wi th th e rou g h p lac e s i n th e p eri m eter of
s attrib ut ed th e r ed ucti o n
rns h a
Mr Fred eri c k P S t ea
th e c h a nn el
o f surface v elocity t othe general retar d ing by frictio n of the layer
o f water a d j acent to the banks of th e stream ; this water risin g to
the surface a n d th erebv m aking t h e water surface at th e e d ges of
.
,
.
,
.
.
.
s
,
,
__
.
.
.
s
,
1 66
YDROGRAPH I C S URV EY I N G
H
depth give fair values fo r mean vel o city in shall o w streams this
ratio sh o ul d be inc reased to abo ut tw o thirds depth in the c se o f
canals and flu m es and n arrow n atural chan nels
In Figure 9 5 is illustrated a vertical transverse s ection o f a
stream showing lines of equal velocity in di fferent parts of th e
cross secti on It will be seen that the line of minimum velocity is
the on e n earest the perimeter ; that th e vel o city increase s toward the
surface until the maximum velocity is reached a sh o rt distance be
low the surface
On account of the resista n ces on the perimeter o f
the channel and at the surfac e o f the water the maxi m um velo city
of a stream i n a straight reach is generally found Over the deeper
pa rt o f the channel and always below th e surface except whe n wi n d
is bl o wing d o w n stream at a velocity equal to or greater tha n that of
the current The line of mean velocity in each section is sh own by
th e heavy br o ke n line in the figure ; it is seen t o be ab o ut six te n ths
of the depth bel o w the surface in each secti on in accorda nce wi th
the principle prev i o usly explained
a
,
-
.
,
-
.
,
.
,
,
,
,
.
-
,
.
H OR I ! O N TAL VELOC IT Y CU RVE
I f we imagine a horizon tal plane to be passed through th e water
at the place where the c ro ss sect i on shown in Fi gure 9 5 was taken
a foot below the water surface th e curren t vel ocities at that depth if
a F
D a
f
i
a Pi
.
-
.
,
i st
IO
80
n ce s
30
$0
Fi q 9 5 Cross S e c t i o n
Di ot
‘
Pi
_
of
.
.
e er
n
40
a
nce s
,
70
60
S t re
tn
a
m
n it
ro m
,
60
s h O W I nq
Fee t f ro m
i
o nr
IOO
90
Cu rves
i n it i
l
of
al P
a
Eq u
l V
a
e l o c rr
'
'
y
.
-
oi n r
.
l
i
o
z
r
n
t
V
l
6
c i t y C o r v e , 0 n e F0 0 1 b e low
o
H
o
e
9
:
'
l40
IS O
I2 0
”0
S
u rf
a
-
ce
.
repres en ted gr aphic ally w o uld app ear as sh o w n i n Figu re 96 In
thi s figu re the distances from the i n itial po int t o the poi n ts where
th e respective vel ocity observations were ma de are abscissas and
th e vel o cities are o rdinates
A line passing thr o ugh th e po ints thus
,
.
,
.
ME
T HODS
a
I
D
OF F EL
1 67
W OR K
is called h o riz ontal vel ocity curv e it re se mbles i n fo rm a
parabo la A curve o f simil r fo rm will be obtai n ed by platti ng in
this ma nn er the curre nt vel o cities i n a h o riz on tal plane at any given
depth between the water surface and the b o ttom o f the c hann el
Th e greatest vel o cities are seen t o be over the d eepes t part o f the
cha nnel in accordance with the pri n ciples previously stated
I n practice the horiz ontal v elocity curves o f streams will n ot usually
be f o und as regu lar and symmetrical as that sho wn in the figu re
Lo cal conditi on s of r o ughness of peri m eter o r of obstructi o ns to fl o w
causi n g slack water and eddies will a ffect the shape o f the h o ri
In gen eral however
z on t l velocity cur ve for any given stream
such a c urve will resemble a parabola i n fo rm
l ocated
a
.
.
.
,
.
,
a
,
,
,
.
.
VERTI C AL LON GIT UDI N A L VELOCIT Y CURVE
If the stream wh o se cross secti o n is
m
ho wn in Figure 9 5 be intersected by a
m -m
vertical plane al on g its axis the relative
rate o f fl o w at di ff erent depths m a
be
y
represented graphically in the m ann er
F
sh o w n i n Figure 97 I f the di fferent
vel ocities are represented by ho rizo n tal
fi
lines whose le n gths are proportional t o
.
-
“
s
c
”
m
fl
.
P”
m
m
,
,
.
a
t
r
o
n
i
.
e
r
the respective velocities a curve passing
throu g h th e o uter extremities of the
OW “
lines thus drawn will res emble a para
bola whose axis is a sh o rt distance bel o w
the surface
In the m easurement o f streams it is n o t essential to kn o w th e
exact m athematical form o f a ve rtical v el o city curve fo r a given
strea m
It is however impo rtant to kn o w the relati o n between the
surface v elocity the m i d depth v el o city the maximum vel o city n d
th e minimum vel ocity o f a stream o r o f a secti o n o f a stream in
order to be able to co mpute the flow with reaso n a
ble accurac y when
any o ne of these is kn own ; and so that i f the current velocity o f the
measured at some known p oint in a section the mean vel ocity of the
e ntire section can be calculated
,
,
,
.
.
,
a
,
-
,
,
,
,
.
COEFFI CI E N T OF REDU CTI O N
It has been sh o wn that in a given stream the surface vel ocity is
somewhat greater th a n the mean vel o city ; that the m aximum
velocity is bel o w the water su r f ce bu t abo ve mid depth ; and that
the po int o r fila m ent o f mean v el ocity is fro m six tenths to tw o
t h ird s O f the to tal depth below the surf ce o f the water Th e rela
TH
E
.
a
-
,
a
-
.
H YDROGRAPH 1 C
1 68
S
URVEY I N G
ti o n betwee n the surface vel ocity and the mean vel o city is i m p o rtant
in the use o f surface fl oats n d in usm g current m eters when the
current vel ocity is measured on ly at or near the surface since in such
eases a c oe ffi cie n t must alw ys be a p plied in o rder t o ascertain the
mean vel ocity in the vertical secti on in which the m easurement is
made
I n determining the proper co effi cient to apply fo r current observa
tions at the surface o r at any given depth recourse must be had to
the results o f experiments an d observati o ns t h t have been made by
h y d r uli c i ns and by hydr ographic engineers
The fo ll o wing ge n
eral rules are given as being in acc o rdanc e with goo d practice a n d
a
s representing the results o f car eful and th o rough i n vestigati o ns
Fo r ordinary streams o f m o derate size it is ge n erally true that
the mea n velocity i n the section o r p ortion o f the cross secti on
w here the Observati o n is made is nine tenths o f the surface vel oc i tv
o f the se cti on
I f the surface vel ocity is determ ined only at the cen
ter of the channel o r at the place o f maximum surface vel o city the
mean vel o city fo r the entire c ro ss secti on is ab o ut eight tenths o f th e
s urface vel o city found
In such ca ses
and
will be the respec
tive values o f the coeffi cien t o f reducti on to be applied in or der to
obtain the mean vel ocity required
For rivers o f consi d erable size t h e values o f the c o effi c ie n t that
have been given will vary somewhat the true value d epen ding
largely upon the shape and size of the channel and the nature o f the
wetted perimeter
The co effi cie n t w o uld be greater for large deep
rivers with smooth unifo rm channels ; it would be least for small
with ro ugh beds In m o st cases the value o f the
shall o w strea m s
and
The
c oeffi cien t will be f o und b etween the limits of
variatio n o f the coeffi cient t o be appl i ed to the surface vel ocities i s
s uch t h erefo re as to rend er this m ethod of obtaining mean vel o cities
unsuitable for use w h en accurate results are required I n the case
of rapids or in time of high fl oods it is often impo ssible t o ascertain
a n y but surface velo cities an d in such cases the use o f a coeffi cie n t
fo r determinin g mean vel o cities from observed surface vel oc ities is
n ecessary
A great many observati on s and experiments have been m de by
di ff erent investigators t o determine the relati on between th e vel o city
t mid depth and the mean velocity in a vertical secti o n of a stream
a
I n the acc ompanyin g Table No 8 is given the results o f observ ti on s
derived from som e of the best kn o w n experimen ts that hav e been
made in order to determine c u rrent v elocitie s
,
a
a
,
.
a
,
,
a a
.
,
.
-
-
.
,
,
-
-
.
.
,
,
.
,
.
,
,
.
,
,
,
.
,
a
.
-
a
.
.
.
I
HYDROGRAPH I C
0
7
S
URVEY I N G
the same area as that of the required cross section D raw the sid e
sl o pes o f the chan n el as ta ngents to the arc and con n ect them at the
re drawn h o riz o ntally ; the resulting
bo tto m by
ta n ge n t t o the
figure will be similar to th t sh o wn in Figure 98 t h is will gi ve a
some wh at larger cross secti o nal area than required but the cc u m u
lati on of silt in the channel will generally reduce it
In a c se where the slope of a prop o sed ditch o r canal is steep n d
it is desire d to produce minimum or a reduced fl ow the c ro ss sec
n d shall o w with flat side
tion o f the cha nn el should be made wide a
slopes
M EA S UR E M E N T O F S T REA M FLO W U N D ER I CE
It is frequently required to m easure the flow of stre ms t hat hav e
been frozen over and bec o me coated with a solid ice c ov er
I n such
cases the o n ly practic ble meth od of measuring curre n t velocities i s
W ith a current meter since the water surface is not accessible f o r
the use o f floats Th e author has m de number of current meas
u rem ents in ice covered streams among the Po con o M o untains in
Pennsyl vania in which the use of a current m eter a fforded satis
facto ry results I n many cases the measurements w ere made under
a so lid ice co ver o f from three to six inches in thic kness In ma k ing
such m easureme nts a path or channel from one t o three feet wi d e
was cut i n the ice from bank to bank and n orma
l to the a x is o f the
stream Care was taken to make the edges o f the cut as regular as
possible an d t o remo ve all the loose ice from the water all o wing no
tilted o r i n clined pieces in the ch a
nnel a n d no loose pieces to escape
under the ice downstream
The velocity measurement s were made eithe r by velocity observa
ti o ns at several points in each vertic al or by the integrati o n metho d
ccording to the size of the strea m and the convenience o f Observa
a
tion These methods were used in preference to single point obser
va
ti on s f o r mean velocity on account of the uncertainty of the p o s i
tion o f the point of mean velocity
It is evident that the form of vertic a
l velocity curve for a stream
fl owing under an ice co ver will n ot be the same as for the same stream
in a
n Open channel
In the former case the surface vel oc ity is re
ta
rd ed considerably by frictio n of the water against th e ice cover ;
in many instances especially in sma
ll streams the flow is under
head
From the results of measurements made by the author and fro m
observati o ns of other en gineers it appears th a
t there are in such a
vertical vel o city curve two points of mean velocity one po int being
n ear t h e surface
a
l m ost thr ee fourths o f th e to tal
n d the other a
-
.
a
a
a
,
-
a
a
,
,
a
.
a
-
,
.
a
.
a
.
aa
,
.
-
,
.
.
,
,
,
.
,
,
.
,
,
.
,
.
.
,
,
.
,
,
-
,
M ET HODS OF
I
D
F EL
W ORK
1 71
depth below the surface A ccording to M r Pressey s paper to
whic h reference has bee n made these po i n ts o f mea n vel o city are
situated respectively at thirteen hun dredths a nd sev en ty three hun
d redth s o f the depth fo r the strea m s wh o se m easurements are gi ven
i n the paper me n tion ed
I n ma n y case s it may be preferable to make the ve locity measure
ments in a n ice covere d stream at mid depth in each vertic l an d to
apply thereto a coeffi cient t o Obtain the mea n v el ocities The value
of this c o effi cient fo r o rdi n ary sized streams is gen erally
that
is the mean velo city o f the current for each v ertic l will e qual the
mi d depth velocity multiplied by
’
.
.
,
,
-
-
-
,
.
a
-
-
.
a
-
S ED I M E N T OB S E RVATI O N S
.
I n making a survey of a silt bearing stream it is often necessary
to determine the n ature a nd extent of the se d ime n t that is c arrie d
in suspension in the water While sediment o bservati ons may prop
erly be considered as being rather beyo nd the scope o f H ydrographic
S urv eying it is th o ught advisable to include a brief e x pla n atio n of
the subj ect in this M anual Co nsiderations of turbidity color etc
which are of interest ch iefly to the sanitary en gi n eer will n ot be
treated ; on ly the meth o d o f d etermi ning the q uantity and the na
ture of the sedi m en t and its e ff ect upon th e physical ch aracteristics
of streams will be co n sidered
The sediment or silt carried in suspensio n by the water of a river
or stream often has an impo rtant bearing upo n the regimen of the
stream Th e finer a nd lighter particles of silt po ssessing a speci fic
gravity of unity are subject to the slightest acti on of the curren t
a n d unless caugh t in s o me sta gnan t place will be carri ed to the
mo uth of the stream The heavier particles as the current is checked
at some bend or by s o me o bstacle fin d l odgmen t in various places
an d fo rm shoals sa nd bars is l ands etc
The character and volume o f this water b o rn e material will vary
ac co rding to the stage o f th e water and als o at di ffere n t depths in
the cha nn el S ediment observations req uire that samples of the
water be obtained the percentage of sedimen t determined in each
sample and the se d i m e n t fo und therein weighed t o fin d its speci fic
gravity The samples o f water should be collected fr om di fi erent
parts o f the cross secti on and at di ff erent depths especially near the
surface a n d at o r n ear th e bo tt o m S ampl es fro m intermediate
d epth s sh o uld als o be taken if required The peri od o f co llection a n d
o f observation sh o u ld exte nd over as l o ng a time as may be c onsidered
n ecessary
-
.
,
.
,
,
.
.
,
,
,
,
.
,
,
,
,
.
,
-
.
,
,
.
-
,
,
.
.
.
,
HYDROGRAPH I C S URV EY I N G
1 72
W ater samples sh o uld be collected daily duri n g
this peri o d S everal forms of apparatus h ve b een
d evised fo r c ollecting sam ples of water at the exact
depths required Perhaps the m o st c onvenient p
paratus of this kind is that designed by the late
Pr o f J B J ohnson and used by him in se diment
n
observations on the M ississippi River
S uch a
a
pparatus which is called a hydroph o re is illus
’
tra
ted in Figure 99 which is taken fr o m J o h n s o n s
By its use samples o f water can be
S urveying
obtained at any desired depth and bro ught to the
surface e xactly as secured
The various samples sho uld be placed in closed
glass j ars ; on each j ar sh o uld be a label c o ntaini n g
the date the speci m en was Obtaine d the d epth fro m
which it was taken and such o ther info rmati o n as
may be necessary The speci fic gravity o f the sedi
ment in a sa m ple may be determi n ed by straini ng
thro ugh filter paper which sh o uld be weighed be
fo re use and dried and re weighed t o determine t h e
weight of sediment c o ntained o n it The v o lume o f
the sample should be noted befo re straining Fr o m
the
data
thus
o
btained
the
percentage
a
n
d
weight
H y d op h on
of the silt carried in suspensi on t any req uire d depth can be scer
a
.
a
.
.
.
.
.
,
,
,
.
.
,
.
,
-
,
.
.
r
i d
a
t
ne
.
.
a
a