BLACK HILLS (South Dakota)
FLOOD OF JUNE 1972:
IMPACTS AND IMPLICATIONS
THE
by
Howard
K. Orr
USDA Forest Service
General Technical Report
RM-2
March 1973
Rocky Mountain Forest and
Range Experiment Station
Forest Service
U.S.
Department of Agriculture
This file was created by scanning the printed publication.
Errors identified by the software have been corrected;
however, some errors may remain.
Abstract
of 12 inches or more in 6 hours fell on the east slopes of
Resulting flash floods
Hills the night of June 9, 1972.
disastrous toll in human life and property. Rainfall and disgreatly exceeded previous records that recurrence intervals
been presented in terms of multiples of the estimated 50- or 100-
Rains
the Black
exacted a
charge so
have
year event. Quick runoff was produced in the heaviest rainfall areas
regardless of hydrologic condition. Flood sources included all major
geologic and soil types and practically all land uses in the Black Hills.
The highest measured peak runoff per unit area came from a 7-squaremile drainage, all on sedimentary formations, the upper portion of
which burned over in 1936, but which is now well vegetated, apparently stable, and in good hydrologic condition. Greatest damage
occurred where man-origin debris piled up against bridges, highways,
homes, and other improvements.
Keywords:
Floods,
watershed management, hydrologic data, flash
floods, storm runoff, record rainfall.
.
March
USDA
Forest Service
General Technical Report RM-2
The Black
Hills
1973
(South Dakota) Flood of June 1972:
Impacts and Implications
by
Howard K.
Orr, Hydrologist
Rocky Mountain Forest and Range Experiment Station
'Research reported here was conducted at Station' s Research Work Unit at
Rapid City, in cooperation with South Dakota School of Mines and Technology;
central headquarters is maintained at Fort Collins in cooperation with Colorado
State University
Contents
Page
The Storm
1
Hydrologic Condition
2
Antecedent Rainfall and Moisture Conditions
Flood Peaks
Experimental Watershed Response
3
3
8
Summary and Conclusions
12
Literature Cited
12
The Black
Hills (South
Dakota) Flood of June 1972:
Impacts and Implications
Howard
K.
Orr
Hills storm and flash floods of
1972 will long be remembered
not only
for the tragic loss of life and property but also
as a hydrologic event of such magnitude and
rarity that the recurrence interval is more than
ordinarily problematical. It also has provided a
unique opportunity for land managers and researchers to study and observe environmental
and land management responses and implications under the stress of a rare storm event.
The purpose of this report is to examine
and describe physical factors and relationships
involved in the production of excessive flood
flows from a number of Black Hills drainages
The Black
June
—
9,
on June 9, including the Sturgis Experimental
Watersheds, and to postulate supporting theory.
The Storm
The storm was concentrated in an area about
long by 20 miles wide. The area includes downstream portions of nearly all the
40 miles
watersheds draining east out of the Black Hills
from Bear Butte Creek on the north to Iron
Creek (tributary to Battle Creek) on the south
(fig. 1).
According to recording gages on the Sturgis
Experimental Watersheds (in the northern part
of storm area, fig. 1), precipitation began at
about 1450 (m.s.t.), and gradually built up to a
maximum intensity of nearly 6 inches per hour
about 1630. Rain continued steadily but at
gradually declining intensity until between 0200
.and 0230
on June
10.
At the
Black Hills Experimental Forest,
about 15 miles south and slightly west, the
storm began between 1600 and 1615. Less rain
fell (total was 5.82 inches in one gage) than
either to the northeast or southeast, but rainfall
ended at about the same time (by 0230 on June
10). At Rochford, about 5 miles further southwest, total storm precipitation was only 1.77
F-iguAd
June. 9
At Pactola Dam, about 12 airline miles east
Experimental Forest and slightly further
south (about halfway along the north to south
axis of the storm but still slightly west of the
rain
fell
mon.viing
o{
Commence
after 7.03 inches of rain
The
Jam
10,
79 72
(U.
S.
79 72).
fell.
best available information from locations further east, and nearer the apparent
center of heavy precipitation cells in the Rapid
Creek drainage, indicates rainfall started about
1900 and accumulated to 13 inches by 0700 on
approximate north-south line of heaviest precipitation cells), light rainfall started between 1400
Maximum
into
duxlng cvzyiing
fiouLYi^aJUL
2100 (1.83 inches) and by midnight 6.86 inches
had accumulated. The maximum 6-hour precipitation, 6.30 inches, fell between 1700 and 2300.
The storm ended there between 0200 and 0300,
of the
1500.
--Total
V^pcuvtrntvit
inches.
and
7.
between 2000 and
1
,
June
10. Nearly 12 inches of rain fell in 6 hours
(about 1930 June 9 to 0130 June 10).
Putting these facts together, the heavy rainfall obviously started earliest in the northern
Hills. As separate cells fed in on strong east
and southeast winds, the storm built to larger
and larger proportions as it spread southward.
H. J. Thompson, Office of Hydrology, National Weather Service, described the general
meteorological circumstances in which the storm
developed (Thompson 1972, p. 163). Strong lowlevel winds from the east forced moist air
upslope on the east side of the Hills. Sustained
orographic effect helped force the air to rise
and cool as it fed in from the east. At the
same time, midlevel moisture was impinging
from the south. Another especially significant
contributing factor was the unusually light wind
at higher atmospheric levels which did not
disperse the moisture or move the thunderstorms
eastward as rapidly as usual. The result was
repeating thunderstorms in an apparently unusual combination of meteorological conditions.
Under "reverse shear" conditions (St. Amand
line
et al. 1972), an almost continuous
of
thunderstorms formed and remained quasistationary over the eastern Hills for as long as
6 to 8 hours, whereas the more
ordinary
thunderstorm moves out in 1 to 2 hours.
Thompson (1972) asserts that the recurrence
interval of such an extraordinary event cannot
be computed with any degree of accuracy, but
adds in effect that the measured rainfall was in
an amount unlikely to occur more than once
in several thousand years. In a report from the
National Oceanic and Atmospheric Administra-
four times the amount to be expected once
every 100 years.
Hydrologic Condition
In all of the most heavily flooded watersheds
examined, there was consistent evidence of
surface runoff from slope areas even where
there were no clearly visible drainage patterns,
and further upslope than in the case of more
ordinary storms. The consistency of this kind
of evidence, irrespective of site, is a key factor
in analyzing the production of the flood flow.
Surface runoff occurred from all types of areas,
including dense forest and well-grassed slopes.
In other words, classification in "good" hydrologic condition did not in this case preclude the
production of excessive surface runoff. Surface
runoff is here differentiated from overland flow
in the sense that surface runoff was evident in
shallow depressions of microtopography not
ordinarily observed, but there was little evidence
of sheet movement of water that resulted in
sheet movement of soil or its protective cover
of litter and humus. This is a generalization
that applied across forest types and densities,
other vegetation types, slopes, topography,
parent materials, geology, and soils. Thick forest
floor, where present, apparently acted as an
efficient water conveyance system, but without
displacement except where water was diverted
or concentrated by stones, roots, or other obstacles (fig. 2). The storm and runoff produced
were obviously of a magnitude that plays a
major role in shaping topography as we see it
today.
-
(U.S. Department of Commerce 1972) it
stated that the 6-hour rainfall averaged about
tion,
is
FiguK.2 2.--Wate^ appa/izntLy
{Lotozd tkh.ou.Qk thiA tki.ck
^oh.2J>t
{Look, uxltkout
cLUtuAbance. antiL it
pondzd by
cLLveAtdd
ok.
i>tonz£>.
Wkm thu
ha.pp2.nzd,
u)<u
tkz LittzK
{Loatzd and movzd
downALopz.
[
Knight to Lz{t)
Leaving a maJLL
ba/i2.
6
minzhal 6otL.
ack i>po&> coutd
on 6om2. 6Lop2A
2
6 pot
.
o{
Many
be. 6 2,2.n
1
1
ing the usual patterns up to June of 1972. Some
stations received practically no precipitation in
the week preceding June 9, while others (Pactola
Dam in table 1) received relatively large amounts
Antecedent Rainfall and Moisture Conditions
had not been excessive, JanMay,
at any of the continuous
uary through
measuring stations in the Hills. Distributions
by months were near average, and totals for
representative stations varied from slightly
below to slightly above average (table 1). Temperatures had not been extreme. In short, there
were no apparent clues leading up to the
extreme storm and flood event of June 9-10.
Apparently it was a random event, neither preceded nor followed by distinctive extremes.
On the other hand, the topography and
Precipitation
as late as
June
4.
Flooding occurred from watersheds in all
of the major geologic types in the Hills.
Though the nature of flooding was clearly influenced by soils and geology, precipitation
amounts and intensities were the primary factor.
Type of vegetation and biomass per unit area
(relative evapotranspiration) no doubt also had
less effect than they would have had later in
the growing season. Effects of differential evapotranspiration would not yet have accumulated
location of the Black Hills in relation to the
nature and movement of major weather systems
would appear to make the area a more likely
prospect for development of the kind of storm
that occurred on June 9 than most parts of the
to as great a degree.
continental United States. In other words,
atypical behavior of meteorological elements,
such as the low-velocity winds aloft which
Peak unit area discharges (as computed from
USGS measurements) do not coincide with
ranking of mean area rainfall (table 2). The
occurred over the Hills on June 9, might, in
combination with other factors, be expected to
evoke a more violent reaction than in other
highest
Flood Peaks
2
areas.
By June 9 evapotranspiration usually exceeds precipitation input, and soil moisture
storage deficit is increasing. Before the end of
May, soon after the start of the growing
season, streamflow is usually declining while
precipitation increases to maximum in June.
Precipitation and flow were, in general, follow-
Table
.
1
mean
0
,
Data obtained from Rapid City Subdistrict
Office, Water Resources Division ,
U. S. Geological Survey.
--Preci p tat on at selected stations (from January 1, 1972), Drior to the June 9,
Black Hills storm and flood, in comparison with average
i
i
Experiment Forest
Sturgis
I
Janua ry
1
.
31
k]
1
07
67
52
2
62
2
2k
2
k5
48
k 2k
2
89
3
19
13
93
3
91
65
6
32
6
91
12
8
]k
6
k8
10 23
7
25
Ma rch
1
32
May
5
June 1-8
Sum through May
1972
1
13- 29
Long-term average through May
Ik 56
Sum through June
13
8,
1972
nches
76
01
k
Rapid
0 3k
0 96
1
1
Pactola
1972
21
37
Feb ruary
Apri
area rainfall (of the watersheds
computed) occurred on Este Creek, a 6-squaremile tributary of Boxelder Creek. Parent material is primarily metamorphic. Though the unit
area discharge is no doubt among record highs
for watersheds of comparable size in the entire
United States, it was not the highest measured.
9
1
k2
10
3
58
0
3k
1
Peak unit area discharge was practically the
same from Victoria Creek (tributary to Rapid
Creek) as from Este Creek, but the recurrence
is much greater, although parent mate-
metamorphic and computed mean
was considerably less. Reasons are not
September 1936 (the 760-acre Johnston fire).
Much of this old burn has not come back to
pine (figs. 3, 4, 5). Aspen and birch are now
abundant on the more moist slopes and in
stream bottoms. Most of the remaining area is
well vegetated with herbaceous species and
shrubs. There is considerable private land and
residential development in the lower reaches
(Cleghorn Canyon). There was evidence of
runoff from all types of areas, but slope
damage was minimal, even on the kind of steep
also
is
rainfall
apparent, although they may be related to the
method used by U.S. Geological Survey (USGS)
to calculate estimated 50-year discharge (Patterson 1966). The recurrence intervals in table 2
are expressed in terms of multiples of the 50year peak discharge as computed by USGS.
The highest
per-unit-area discharge, and by
greatest recurrence interval, occurred
from Cleghorn Canyon (Wild Irishman Creek),
tributary to Rapid Creek at the west edge of
Rapid City (table 2). Area average rainfall was
not the highest, though as much as 13 inches
far the
south-facing slope shown in figure 3. This is
one of the slopes bared in the 1936 fire. Figure
6 is a closeup of the left portion of this same
slope. Pine reproduction is sparse, but the site
is well stabilized by herbaceous vegetation. One
landslide, visible in figure 3 and shown closeup
in figure 7, occurred on this slope. The slide
reportedly fell in the middle to lower reaches
of the watershed. One distinctively different
physical characteristic of the watershed (compared with others listed) is that it is almost
entirely on sedimentary formations, Deadwood
sandstone and Pahasapa limestone in upper
Table
2.
was not
large, about 32-35 feet long and about
half as wide, and apparently resulted from a
combination of water concentration from up-
--Peak discharge and area average precipitation of selected Black Hills watersheds, flood
of June 9, 1972 (in order of area average rainfall as computed by Rocky. Mountain Forest
and Range Experiment Station)
Drainage
Peak
C.f.s.
Este Creek
(near Nemo)
6,620
Deer Creek at campground 8 miles west of Rapid City
Gordon Gulch
di
1
i
scha rge
1
,078
825
Sturgis)
4, 740
797
Battle Creek (at Keystone)
10,800
794
Little Elk Creek
Cleghorn Canyon
(at
(Wild
1
Irishman Creek)
12,600
1
2
3
tor a
ron
i
C
C
6.7
8.8
1
,813
61
3
(
Grizzly Bear Creek (near Keystone)
c
23
)
(
Prairie Creek (at Rapid Creek)
i
6.0
3
Elk Creek)
6,860
676
1
,022
3
reek
(
)
From USGS measurement by slope-area method.
Multiple of 50-year peak discharge as computed by USGS.
Not measured by USGS but flooding severe.
Measurement from Rocky Mountain Forest and Range Experiment Station.
4
1
i
6.4
35
1
Area
nches
Sq.Mi
10. 69
6.14
9.
96
4.28
9.
42
"3.15
9.
09
10.
8.
78
8.
34
13.6
8.
o4
'19.7
7.
87
7. .21
)
6,230
reek
Area
ave rage
ra nf a
1
)
181
(at
i
3
(
,830
Deadman Creek
Recurrence
nterva 2
C.s.m.
3,530
(near Sheridan Lake)
Horse Creek (at Sheridan Lake)
V
1
reaches to sandstones with interbedded limestones and red shales of the Minnelusa formation
at the junction with Rapid Creek. Also, the
upper portion of the watershed burned in
interval
rial
1
7.
.
1
5.95
6.95
14.0
9.22
7. 10
12.8
68
16.3
,
6.
.
Figure 3.--A a ouuth- fading slope In the upper
[CJL2.Qh.ot1n
K2.CLch.Qj> o{ Wild Irishman Creek
Canyon).
The. 0x2.0. burned over 36 years ago,
and much o^ It has not come back to pine
The lock outcrop Is Vahasapa timeforest.
stone, with darker Veadwood sandstone outcAop [V) about 1/4 o{ the way downslope.
Vegetation Is W2.ll established and the
soils are stable. S> Indicates slide area
closeup In figure 7.
Figure 5 .--Valley bottoms In the old 1936
Johnston Vine [760 acK.es) were Invaded by
aspen and birch. These species also Invaded
on the more moist north- facing slopes, as
shown In figure 4. This view Is {rom the
top o{± the ridge In figure 3, looking almost
dlxectly east toward Rapid City In the ^ar
background.
Figure 4 .--looking back southwest ^rom high on
the slope In figure 3.
One o& the main
tributary channels ofc ttlld Irishman shows
In the lower portion ofa the photo, and
ilood- deposited material Is visible [arrow)
together with an old road.
Figure 6 .--Looking mostly west [le&t) across
the le^t portion o{ the slope In figure 3.
Vegetation Is a well-es tabllshed mixture ofa
grasses and fiorbs
Soils are stable &or the
most part.
.
,
5
ViguKZ
--To thz night 0& thz
7.
ojiza
in fiiguAZ
filow
Alidz about
6 ii>
30
long and about hal{
tka> bmaLl
to 35 {zzt
at>
Midz.
It was thz only visible, ouzo,
on thz zntOiz &lopz
appftzztablz amount
u)hzn.z
any
i>oil
oft
woa cLUplaczd.
Much
slope and liquefaction of shallow, stony soil on
bedrock (possibly upper Deadwood sandstone)
which was near but did not intersect the slope
debris (including tree branches, limbs,
and roots) lodged on the upstream side of trees
(fig. 8). Several such deposits were examined
closely. None of the debris originated as logging
slash, as was at first thought. No axe or saw
cuts were visible. The debris obviously came
from trees close enough to the channel that
record high flow literally tore them out and
stripped them of limbs and foliage. Ring counts
of some of the trees deposited in debris piles
indicate they were 80-85 years old. In other
plane. The flow slide material moved all the
way downslope to the main channel, and was
no doubt the source of some of the water-
deposited material in the lower portion of figure
Vegetation was not stripped from the slope
in the slide path, however.
Some additional channel cutting and deposition, associated mainly with old roads, was
evident in upper reaches. Practically all of that
debris was intercepted and filtered out by shrub
and herbaceous vegetation in open meadow
areas such as that shown in figure 4. Severe
channel cutting and erosion became increasingly
evident further downstream in the narrower,
more constricted lower canyon.
4.
words not since
at least 1890 had any combination of storms, fire, timber stand conditions,
grazing, or other land use produced such large
floods. In Boxelder, and undoubtedly in other
drainages, trees were downed that had been in
place more than 100 years— long before settle-
ment by white man.
FiguAz 8.--UoocU dzbnib
fizzt
8
to
10
high against thz up6tAzam
i>idz 0^ tAzzb in
Wild iKi&hman
[Clzgholn Canyon), douinittizam
{h-om
3
to
thz axzah
1
.
t>howvi
Hznz thz channzl haA
buoadznzd and thzh.z
ghjxdiznt,
in ^iguxzh
it>
lz66
but it i>tzzpznt> and
noAAom again bz&oKz joining
Rapid C^zzk at thz a)z6t zdgz
o& Rapid City.
6
This conclusive evidence negates serious
speculation that this rare flood event may indicate general environmental degradation. Severity of consequences of the flooding, though none
the less tragic, were in direct proportion to
cally erode and alter some channel sections.
Litter piles and associated upslope bare spots
again attested to the production of significant
surface runoff from a microtopography that
man's encroachment on stream channels and
floodways. Also, man-origin debris no doubt
caused more environmental deterioration or
damage than any a priori upstream land use or
management. Similar consequences, though less
spectacular and without the great loss of life,
occurred in 1962 and earlier.
Another watershed of particular interest is
Grizzly Bear Creek, which drains from a research
natural Area on the Precambrian granite of the
Harney Range (fig. 9). This area has had little
disturbance of any kind in many years. Yet the
stream flooded inside as well as outside the
boundary of theNaturalArea, enough to drasti-
dence, however, that watersheds in this general
area have low storage capacity due to coarsetextured parent material, and an obvious history
of flooding, even during much lesser storms.
A large proportion of the most heavily
flooded watersheds was in areas of metamorphic
parent material of the general type shown in
figure 10. Material of this type characteristically
breaks down to loamy soils, often quite stony.
The kind of erosion shown in figure 11 is
typical of what happened to cut slopes in residual soil. Fines were washed out, leaving stones
protruding. Slumping of steep road cuts was
not uncommon in this kind of situation.
F-iguio, 9
zvm
.--Channels iKodid 6Q.vzA.nly,
that
In
Little, tun
hth.0,
In many yzanA
.
Shown
tht Pino. C^eefe
out
UatuAal kn.ua In
VaAunt
6
k.q,cza.v<lo'
ii Gntzzly BzaA Cti2.dk,
ciuu.nA.ng
hunji
have,
n.ock
aj>
the.
HaAn&y Range.
gtianitz, which
wnathzXA to a coaAAe.-te.xtuA2,d
hallow
6 oil
ca.pa.cJXy.
with low
6 tonago.
would not ordinarily be noticed. There
is
evi-
7
.
ViguJiz 10 .-- Chan.actnnAj>ttc
moXamoKpktc patent mat&nial
Jin pcuvt
oh i>tonm aA.ua that
tec&ivzd i>omn oh
huavteAt
the.
Flooding ^nom a
Kainhall.
dJiainago. no
mote than
long cauAdd
tkii,
damage, which
mile,
1
chann&l
on tk<L
u)a6
out^tdz. oh a tuJtn.
Table 3-"~Rainfall by individual gages at the
Sturgis Experimental Watersheds,
June 9, 1972
Experimental Watershed Response
The best quality overall precipitation and
flow records that we know of are from the
three Sturgis Experimental Watersheds — 217,
in the northeastern Black Hills.
89, 190 acres
These records are used to illustrate flow timing
and distribution in relation to precipitation.
The total volumes of flood flow cannot be
determined, however, because of debris accumulations which practically covered the stations
during recession (figs. 12, 13, 14). Accumulation
apparently started at about the same time as
the peaks occurred or soon after. The stations
were not structurally damaged, however, despite
the force of debris and peak flow about twice
the design discharges computed for 1.87 inches
of rain in 1 hour (table 3). Hence, the flume
hydrographs are available from start of rise to
the approximate peaks at all three stations.
Maximum 6-hour
Total
prec p tat on
Gage
i
—
1
i
p
i
nches
A-l
8.68
A-2
11. 64
A-3
10.49
A-4
9-57
A-5
8.86
A-6
10.01
A-
10.96
1
rec p tat on
i
i
i
Hours
nches
10.47
1
500-2100
1450-2050
7.76
n
'9-72
1
By proportion, from gages A-2 and A~5;
distribution record lost, only total depth
ava
i
1
abl e.
VlguAd
11.
--An old tead cut
thAough teAidual
i>oiZ,
matamoApkic patent matanial,
ahtin. the
June
9
^lood.
TtnoA LOdte woAkad oat.
Platy teck
l<iht
wat>
ptetAuding
tkm
on.
qJMiclh.
It
h<tll
out and into an accumulation
at tha ba6& oh the 6lopz.
Tkti,
hOhX oh thing did not
kappm
teach
8
on nm&ti back-blop&d
Figure
I
2 .--to'aten>hed
1
gaging station nearly
over with
cove.ie.dl
and other debris,
4 tone,
and completely inoperable
a^tzn. the June 9
^lood.
Figure
1
3.
station
--Watershed
afiieA.
San VimaA
it>
June
faZume.
^ull o{
-4
2
9
gaging
filood.
and channeZ
tone and other
debris at le{t {upstream
farom
it>
headwall)
loo6
inoperable.
14.
--Watershed
station a^ter June.
The.
9
gaging
-
{lood.
station continued in
operation despite,
pileup.
ofi
3
the.
debris
Nearly 400 man-houAA
labor were required to
return all three, gaging
6tation£> to temporary
standby operation.
9
Weir pond
completely obscured.
Station
Figure
.
intact but
amount of rain, produced the second
highest unit area peak runoff, and the second
largest total area depth of runoff to the hydrograph peak. WS1, the most easterly of the
watersheds, received the least rain, produced
the lowest unit area peak flow, and the least
depth to peak.
Maximum peaks (fig. 16) were less clearly
recorded in WS1 and WS2 than in WS3. Nevertheless the peaks, as well as amounts already
presented, are reasonable. WS1 hydrograph did
not start maximum acceleration until about 1
hour after WS3, which is not surprising considering the fact that by the time of peak in
WS3, 2 inches more rain had fallen there than
3 (WS3) flume functioned through
the entire storm, but flow figures are not reliable after debris started to pile up following
the peak, and because some water crossed over
Watershed
largest
from WS2 to WS3 just upstream from the
gaging stations. At least up to the peak the
WS3 record is judged the best.
Rainfall started at almost precisely 1450
in all three recording gages at the
watershed. The main streams started to rise
almost immediately in all three watersheds, but
the rise was relatively slow until between 1600
(m.s.t.)
and 1700, when the heaviest sustained rainfall
began. Flow then accelerated very rapidly.
Time at which flow started to accelerate
most rapidly in WS3 coincided almost precisely
with the start of a second period of highintensity rain (at 1630) at rain gage A-2 in the
upper reaches of the watershed. Over 3 inches
of rain had already fallen
apparently enough
to fill available soil storage capacity and cause
the flow to respond almost immediately to ad-
in
—
The watersheds behaved about as would be
WS2 apparently received most rainfall
15),
at
WS1
WS2, and WS3, respectively.
The slides themselves are
expected.
(fig.
two recorded peaks
surge of water to cause another peak at the
gaging station. Several such slides may also
have been one reason why the hydrograph in
WS2 lagged behind both WS1 and WS3, particularly if the slides occurred at about the same
time. Response times were opposite what might
have been expected considering the fact that, in
calculating design discharges, the concentration
times were 12.6, 9.0, and 16.2 minutes for WS1,
From
1630 to 1820
the discharge increased steadily from 6 to 80
c.f.s. Maximum 1-hour rainfall occurred in this
time interval
3.25 inches at rain gage A-2
(1630 to 1730) in the head of WS2, and 2.12
inches at rain gage A-5 (1645 to 1745) on the
east boundary of WS1.
peak
for the
are not clearly apparent. It may be that landslides (several occurred in WS1 and WS2, fig.
17) temporarily blocked flow. The debris dams
then washed out, probably releasing enough
—
ditional high-intensity rain.
WS1.
Reasons
of interest. Most
of the ones adjacent to stream channels appear
and produced the highest unit area
4). WS3 received
second
runoff (table
F-iguAd
tha
7
5
.--IsokyeXat map o&
lam
9,
pK.odacA.nQ
79 72
filood-
htohm on thz
StuAQ-Us EvpuHyimnvvtaZ
Wa£eA6 kddi,
••
CdwtzK., Matufvbkdd I;
Zight [<KUt] watdhAkud
10
7.
:
Table
4.
:
)
1
)
.
.
--Area rainfall and storm discharge,
Sturgis Experimental Watersheds,
June 9-10, 1972
I
Watersheds
tern
2
Average precipitation
nches )
(
Th essen
sohyeta
3
i
9.28
9-59
10.83
10.86
10.47
rise (m s t
1450
Time of peak (m. s. t.
1840
Time to peak (hrs.& min.) 3:50
151^
1930
4:16
1450
832
3:42
49
349
80
269
.47
.44
i
I
10. 16
Recorded hydrograph:
Approximate start of
.
D
i
.
.
scha rge
Peak (c.f.s.)
76
Peak (c. s .m.
225
Depth to peak(area inches) .28
Computed 25~year
design discharge (c.f.s.)
45
20
37
1972 multiple of 25-year
1.7
2.4
2.2
TlguJid
7
6.
--June
hydn.ogh.aphA to
VohhJj*
1800
1600
9,
79 72 6
torn &low
about timi oh p&akb
deposits cauhid lot 6 oh
nmalndzh. o{
1400
1
.
the.
the. hydh.ogh.aphi>.
2000
Time
Ttguh.z
17.
--Flow btido. hiom
channel, bank In Stuh.gl6 WS
7
A numbch. oh 6uch AlideA
blocked channel* until enough
watch, accumulated to o\)2.htop
and cut through the
de.bhjj>
VebhlA In hono.gh.ound
aj>
.
on
man. bide oh channel, which
extend* h^om flight to leht
whe.h.e.
1
1
man
ti>
standing
hydrologic condition. For example, surface
runoff occurred under forest with thick protective litter, and concentrated in drainageways of
microtopography that would not ordinarily be
seen. The event was apparently so rare that the
flash flooding cannot be taken as indication of
general environmental degradation.
The land, regardless of condition or use,
obviously could not receive and transmit the
amount of rain that fell without changes in the
face of the land itself. Part of these changes
were the inevitable result of natural processes.
In this framework, classification as "damage"
is problematical.
On the other hand, damage was unprecedented where there was loss of life and the
works of man were involved. A lesson to be
relearned from this disaster is that encroachment on natural flow channels will inevitably
result in damaging floods
some time. Flood
have occurred as the result of liquefaction of
the toe of a slope by water flowing more than
channel deep. Most of the slides were of the
flow type (versus the rotary type). None we
have seen within the watersheds were large, but
there were enough of them to no doubt contribute a substantial portion of the bedload that
choked the gaging stations and deposited in
water supply reservoirs downstream. Several
larger flow slides occurred on talus slopes along
the main access road, which appear to have
started as moisture accumulated to low tension
along a road cut. Debris flow appears to have
started at the cut face and progressed upslope
to near the ridge crest in several cases.
Several such slides blocked the main access road.
to
—
Timber was harvested from WS3
in 1970 and
1971 (132 acres, 73 percent of total area). Some
temporary haul road was constructed, but most
was well up on a slope and away from main
channels. Harvesting activity does not appear
to have accelerated either the runoff or channel
erosion. Haul roads and skid trails suffered
minor damage, and little, if any debris reached
major channels.
—
damage in 1962 and earlier was also greatly
compounded by man-origin debris and, although
,
cause and effect were both well documented,
they were soon forgotten. All the major drainages in this 1972 flood have some known
history of flooding, and they will flood again —
some time. Extent of future damages will
depend on sophistication of engineering works
designed to control and meter flood flows, thus
permitting continued occupancy of flood plain,
or it will be necessary to withdraw from the
Summary and Conclusions
An
unusual combination of atmospheric
conditions triggered thunderstorms of unprecedented depth and duration from midafternoon
on June
9,
1972 to early
morning June
10,
most flood-susceptible
along
the east slope of the Black Hills. Flash floods
resulted in great loss of life, particularly in
heavily populated areas along Rapid Creek, and
property damages estimated at more than $100
million in Rapid City alone.
The storm was
The
final action,
Literature Cited
magnitude that recurrence interval is more than ordinarily
problematical. Six-hour amounts ranged as high
of such
Patterson,
St.
River Basin above Sioux City, Iowa.
U.S. Geol. Surv.Water Supply Pap. 1679,
471 p.
Amand, Pierre, Ray J. Davis, and Robert D.
Elliott.
Report of Rapid City flood 9 June
Report to South Dakota Weather
Control Commission 27 June 1972 by
1972.
Survey.
Portions of all of the major geologic types
of the Black Hills were present in the torrent
area. All major land uses ranging from commercial forest and agriculture, to intensive urban
development were also present. All types of
1972:
Board of Inquiry. Dec.
Thompson, Herbert J.
1972.
The Black Hills
25:
areas produced runoff of unprecedented
proportions. Some areas yielded channel flow
where long-time residents never before saw
surface flow. The obvious conclusion is that
runoff was produced regardless of how good the
Ft. Collins
James L.
Magnitude and frequency
of floods
in the United States. Part 6-A, Missouri
1966.
as 12 inches. Recurrence is variously estimated
as four times the amount expected once in 100
years on the average (U.S. Department of Commerce 1972) to once in several thousand years
(Thompson 1972). Flood flow peaks ranged as
high as 62 times the once in -50 -year discharge
as estimated by the United States Geological
Agriculture-CSU,
areas.
man
does not again forget too soon, will no
doubt be a combination of the two.
if
1972.
flood.
Weatherwise
162-167, 173.
U. S. Department of Commerce.
1972.
Black Hills flood of June 9, 1972. A
USDCReport to the Administrator.
NOAA, Natural Disaster Surv. Rep.
72-1,
1
2
20 p.
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