.4
WATERSHED RESTORATION MANAGEMEWT
PHYSICAL,CHEMICAL,
AND BIOLOGICAL
CONSIDERATIONS
AMERICANWATER
RESOURCESASSOCIATION
COME'UTEB-AIDED
RISK ANALYSIS IN ROAD DECOMMISSIONING
W. J. Elliot, R. B. Foltz,
@,
H.
Luce,
and
T. E. ~olerl
In many National Forests, much watershed restoration work
involves road removal. Most National Forests ftave more roads than can be
maintained with decreased budgets limiting the mount of roads that can be
removed in any given year. Setting priorities for road closure based on the
impacts and risks involved in closing, removing, or discontinuing
maintenance has become a major challenge for forest . m a m p r s . Stability and
erosion risks are associated with unmaintained roads, and the same rieks are
associated with various removal--st~ategies,
such as culvert emo oval, surface
ripping, outsloping, and recontrruring. Preliminary studies show that
effectiveness of ripping depends on soil textuke. Culvert failure can lead
to road fill instability and failure of eatastr~phicproportions. The WEPP
model may be a useful tool for evaluating r~d-closureaptions to minimize
off-site sedimentation.
Recontnuring the surface without considering
long-term subsurface flow impacts zday ' greatly decrease slope stability, but
well-engineered recontouring will minimize stability risk as well as
erosion.
AESTRACT:
.
KEY TERMS:
Forest, roa4, closure, hydrologic modeling, surface ripping
In a forest, infiltration rates are'high, anld runoff and erosion are
low compared to agricultural or rangeland ecosystems.
In such a
hydrologically stable envi~onment,a small percentage of roads in a
watershed can significantly alter the hydrologic response and sediment
yield. In a recent study in the Western Cascades in Oregon, Wanple (29941
found that roads can have a significant effect of the surface hydrologic
response of small watersheds. Swift 31988) attributed the entire sediment
yield fron a forest watershed to new road cmstruction.
Road closure is an increas;ingly common practice to achieve a variety of
management goals, including improvement of aquatic and terrestrial
ecosystems and reduction of casual human impacts on forest envirments.
Road closure options include stop~ingmaintenance and regular use, closing a
gate, excavating a trench across the road to stop access, removing culverts,
partially recontouring the road by excavating to form a significant
outsloge, and at the most extreme, attempting to return the hillside to its
original contour by completely recontouring the road prism. As with road
construction, however, there are major engineering considerations that must
Project Leader, Research Engineer, Research Hydrologist, and ~esearch
Geologist, respectively, Intemomtain Research Station, 1221 South Hain,
MOSC:OW, ID 83843.
-be considered for any practice requiring major earthworks under steep and
marginally stable conditions.
~ l ~ a dcw
g hawe naj,or a d m e impsets on both sarfawe atkd subsurfs@.e
m-3 use af a read 13sMem.ly distwbs both the
hy&olosy. The mn@tructi,@ii
smf&,e a& SU.bsu~daqesa,dQil,, iQcre.@aingrunoff rdteS., fe&clng subsurfaOe
fj.qwi,
& ,al.terh~;
ebllotu @ o . m water eqailipiiiui&. tJllf.~k~Wmk@lY~
informatioil
to
W&
p~iran e.E.fwt& aurfae.8 an8
s&sgr$aue h & f g l l m is limit&..
'2
\-
an obserr&tiopal study c 7 d u c u c t 8idn the western Cascades of Orcrgon
gugoested that r o e fMctYw hy&eLog&cally to @w¶ify::s&reamflowg m ~ r q t % o a
in forested waterrshe& by a l t e r i n g the s p t i a l @i$tribution of surface a@
&=face
f l m paths. Nearly @3 percent of the road netwark i n the ee&y
drains t o F;trems a n d p l l B e s sxidis, themSam,, hydr+ogically integxated
with the stman nezmrk., Field ,o$eewations suggest that roadgide ditches
and g u l l i e s func.tSoll as effective surface flow pa.ths Ghat substantially
ucreetse drainage W i t y dugifig 80m events. ~ h a a ,r d s may alter bas.in
hydrographs .by ayrextendhng the amf8ce flow network. Since. the selume of
m o f f from toads and its speed of delivery t o the bagin clutlet (which were
not messurecl i n the study1 wary acoorBing t o road design., road h i l l s l o g e
pesitioa, r ~ a@,
d
sea,sond s o i l epturatien., geologic szlbstrate, and
climate, these factors may emlain tKe eonf l i c t f ng r e s u l t s fmm pairedwatershed skudies of r o d e f d e e g s . Results crf t h i s study etlggeat tbztt
removing roads from the &drainage network may be an efLectim f i r s t step
taward natsrshed restoration ZWaple, 1 9 ) '
.
.
stristing mads have several major impacts on surface hy3sBlogy (Wemgle,,
1394) I n f i l t r a t i m m k a s of roab are much lower than Eorests ( 4 versus 80
o r mare nuam) ILuce, 199&), hewe, the surEace area emfa watereRed i n SO&
mey h9 the major, and h some eases may be b
a
b direet contributor t o s,urf&ce
r-f
from s t o m or snowmelt. WZten a road is glimned, structures like
culqeRs, ditches, and waterbare are dewigned t o handle t h i s w r f a c e flow
with minim1 .imply;ract t@ th9 mad, md i n recent yeera, t o t h e f o r e s t
erA~ronmE(nt
.,
I
One ooacasn with e l a w r e s is that a f t e r a road i s cl,aBed., the road
drainage system ean no Longer be maintained and may f a i l , leading t o
significant gully eroa'ion problems as water L~ cancentrated bgl road riaus
ar ba:dked tip by gIugged culverts. 14 ether cases, accumulated r u d f a:m
saturate seginents of a road, lesding tg road-fiL1 f a i l w e grnd &&xisflow,
that can add thawan& of tmms af sediinmt t a streams. Caz'e.fizl planning
a d d e ~ i , g no f dimmed or ael&a-ssed
rcrad aystema are necessary t o prevent
such catastroph5c prablems,
~ a a yhydrclegists hahave recagnized khe ~ruhlsnsof excess surface nuzaff
caused by newly imgarvicrus road surfaces, leading to the practices of road
rigping and s&voail~ing
t@ !+re& up imprsrmsbble l~aye-hs. Infararati~n E r w ,
vs$k d e e ~cmsrgricu2 t m l . lmw3@,, @heze',sailssre Ereqmmklv tllled., .sq+gssr,s
that riming atrd : s ~ ~ ~ i l :may
f a gneq &c:,,rea?e Qyd~awlic~:anO..~ti~i.t~ies
as
much a ~ sqm
,
ww.1~Bh w e . N y - & s u l i ~ cil~t3uctivitics oa fteskly @low;&
agai@wl~&xal
a m pf;l'@r&01~$;y
br c h raga of 4:
I:
m
@
$ h r l -tiwe
s:arf&@ed
xa;&ddsme in tke r q o af D.1 %'a 4 m&rp a& haze fsrewt sails
!i(Pr$,t.kuk
.dw&fF &B@ i.n t b i w @E D .ka 2Qi3 m d k , Zt
m$;ik.T.~
Cbt.
bvgn avb&aili~wQZi *@a&! ~DulhfeYt We: 4EdLas11is: .ifo,hdttCCt.iv2
ti&&,&ht W
bf yri&igc%!&egt
f @re@.c
1;g.m .pro@&$l.y& e @ ~ g @ r ~ gingpe.r$:aPs
,
,&?$
,cqi@ac&@, Is& ,cirgapLe *peer a@ b"bsZ~%:@&le@ti&.tfv!,have @o a @ k a c
:duff
Layer, &
mi:nly :m&aer,
mi18 C.k& a ~ :s&j&it
e
tO. ~ ~ s f . sea1j.w.
61~.
.&@&tt&l!
&&erx$@e$~&a
pf
.r$,p~riag
p m e ; s t e&a& ik r , w %
"erosien' W t tb season m y be nwce due to in@r~Eycc@
r.wg$tl~s
than o
.inr:~&md&&a~li@
mnd'ue.ti*ai;m,. M JW$tap,, ~wF w &
rl@pix%$
ha&
i i . g t h &f&& b e n d . irecaessi.ng
r e w h s on
&Bf;&3?ents@%l,s:,. a
high silt m i l tar@&W fmm a smEase -1
,&,siag klw fflist safnEa.11 mat
S'@.lJ.miggr.$g&k~,, redwain@ E b i a : f i l t . p & t t : ~ @
%a
.
the ,I;=@.hf@pe
simiiig. A &~;tLr'$faB gganitir s@&l c ~ l l s p ~ g,t l& ~ f fha
q £$?at est"lf%ll
'eym a f t w tLi,&lege,
1;eWgng to hyiWau.l$q mduUc$iv$ti@y
~smwhag.ir@rqmCi
~ s t . w . i%rmEL8t+
~ d
@nee6, l$$?j, ,.
I3u.g @till
!&ll b@lwat.those
&,
,
fmwent j:uskifi.cations .Ear mad eloswe i s to dmrcrase
Q m of .the
s-edimentation $.ram the wate.rshed. :S&imentat.ion may $e due to erosion 8o.f
the road :sur%aceox dtilrch. Lasge qwnti.ti@sof sediment may a l s o readh
s.trsauns f r w mass failutes.
~ d o n m w Risks
t
n disused zoads, eulverts m y Fail d w to blockage or &tenisration.
' If a L
failed wlvex-t ~ a v
Mt-ended: to ear.= water throngh a lapse embanlawat,
dlrain f a i l u r e can lead a? t o w a t e h ~ k i w
up an6 satnratirig the &&eat:.
Once a Z q : e embnlan~nti e p : a W t s a , i.k ia f , lw
~5 s;t;&le t B w i t was i n
the dreimod c a d i t i a n , resulti~gj.in ,&a% 5ziiLuse ('Elllot eS. a1 , 1994D)
Genclr&Lly, emba*e~ts
are &6i&~.Wa.Pi,& s,Jsg& t h k are a t a b l e wba
drahaBi but satumated road .prisiw : m y @l *.gt;3b.
If e m~ad is to.tsllqr ~reeamkmurd~%he ;svb~1.011comgaction dne :to
C s n s t r w a t i ~.an& ~amav&lw:kiqi<ift.S::m&g ,&ill
presenfl. In co&itions
.
.
Me have been inveld in the devel-t
of two phy&~elly lased made1s
to help assess the site-specific ingsc' of road closure the. Water; lirosim
Prefi&iaa
Woject (WEeP) mo&l (Flana~anand Livingstan, 19951 and the
slope stability model KSTRBL (Shamna, r99.4). Figure 1 gho* a steep
hillslape that has a road segment that e fares% wager maywish to close.
&e swpness is assumed te be 60 percsnt, and the length @f the hillslope
100 m. e
&
' r m d is a self-M,ane& dw.Fgnwith. a eat-and-fill cmpacted ta
a desired d e ~ g i t y . It is construc.t& with a 6-@er%ent @rat&, a 5 nt widt31.
a flat surface. .A typical wrtical spacitig f o r waterlaw.%?of 2 . 5 fi Hias
assaed, Leacling tto a K2 rn length of road hetween waterkus. X t .
a+amczl
that there ws 50 rn hetween the mad and a sen^^. T%e dentti Of the forest
soil was 1.5 m.
-
Surface Erosion
Sediment production from existing roads can be predicted with the WEPP
model. we developed input files describing typical road geometries. Users
can readily adopt these files for site-specific application, including local
topography, climate and soil properties. The WEPP model allows users to
determine the amount of erosion on the road surface and to estimate the
Figure 1, Section of Hillslope With 60 Percent Slope a) With
undisturbed Forest; b) VJith a Road; and c) Following
Recontouring of the mad,
lengths of sediment plumes generated by point sources such as waterbars or
culverts. For this example, we gane?=ated a climate for St. Xaries, ID, with
the climate generator provided with the hePP model. The average annual
rainfall was 757 nun. An initial run was made without the road in the
hillslope, assuming the slope was completely covered with forest (Figure
la). The model predicted an average annual runoff of 4.7 mm of runoff and
an average annual sediment yield of 70 kg from the hillslope. When a road
was added (Figure lb), the flow paths changed, and a 5 m wide flow path was
modeled, following first the road for 42 m, then the fillslope for 4 m, and
finally the forest far 30 m (Elliat et al., 19948). The runoff from this
flow path was 5.2 mm, and the sediment yield from the hillslope was 187 kg,
a substantial increase dampared to the undisturbed forest in spite of a 30 m
buffer strip between the road and the bottom of the hill.
Sedimentation From Abwk%ned
Roads
Abandoned roads slowly revert to the vegetation native to the region.
The time required for such revegetation depends on many site and vegetative
factors. The WEPP model enables users to describe the anticipated rate of
vegetation regerreration and surface residue accumulation, and then predicts
m o f f and er~sionrates that include the vegetation effects. Changes in
soil properties due to wetting and drying, freezing and thawing, and
arnoring may, reqvire additional analysis with the model, altering the soil
conditions manually for each year following closure to reflect the observed
conditions. For oux a m p l e , the soil properties were assumed to remain
unckged, but the road was allowed to revegetate rather than have an annual
maintenance operation. The resulting predicted. runoff was 5.6 mm, and the
sediment yield dropped about 20 percent to 150 kg. Incre~singthe road
conductivity and surface roughness to moclel ripping effects decreasjed the
runoff to 5.0 m and the erosion tp 95 kg. With amorhg effects, an actual
sediment yield wauld likely be even lower after several runoff ewncs. I£
an outsloping abandoned road is modeled, total runoff is less; but predicted
sediment yields remain high due to sediment from the eeoding fillslow being
transported to the foot of the hill. We madeled the fillslope as sparsely
vegetated. Fill~lopeerosion, however, can be mitigated ?ay numerous methods
aeescribed by ~urroughsand King (1989). an$, depending on the age, the
cons~lictation,and the revegetation, eroahn rates may be mdch lower than
predicted. Ripping the outslopd road appeared to have little effect on
runoff or sedimen't yield in this case.
w
Water W8bl8
Figwe 2.. Csoss Sections of a Road Pri.sm a ) Before Recentwring, b)
&fterRecontwring a t h v u t Removing the Compacted R&
S u r f m e Layer:; an@ cJ Z4t.m Bec~nkb)u:dng
:With. the SurEace
Layer remved, and F i l l mgerial compacted to .wear-watufal
Denssiti-es
.
intuitiue Since a seepage Face dloqri a to& of loo'se materials can r e s u l t i n
a &bri.s flow. In the %ST&%
anslys:i$, the f a i l u r e i a rota.tiona1 s l u m p
earthf l o w , and the shear plane coincides w i t h the contact between t& i n
d.titu soil anB be&asfe.
If tk m~eeriala.are compacted in l i f t s , t h e factor
af safety increase%, but i s still low with a r q e ,of 1.1 t a 1.2.
In
Figure 2c ths f i l l ~ l o p ematerial, road surfacing, and baste course a r e
r@hov;ed, blended, at@ placed i n t h e road prism as Pecantsu+d ,materials.
Faetare 05 safety foY t h i s &&sign P a g e from 1.0 t o 1.5, depending ood
cmpaction
the gradation of the ljlended material$. In t h i s c&se, there
is a small perturbation i n the grdgt-ia w a t e mometry caqsed by the bedrock
geometry of the r o d :pisit,but no swpIFtge faces acrcm.,
The wampIe shows that reconto,wing m y nequire. sgeoial "cansideratLen
i n unstable conditizjns. 5f a se-nt
of mad with a marginally s t a b l e
cutslope is a b . ~ Q i a @with no, mitigation, i t m a y f a i l (Figure a&) . IE t h e
same segment i s recoatou~eb,it may also f a i l ( F t W c 2 2i3) , d e m d i i i g on the
.site geology, ground water conditicms, and miti,gatioq measurte-s. Undezr these
conditions, sit&-specific emalysis can be a.powerful t s o l in avoiding mass
failWes. on abandoned roacls.,
~ o & s i n formts d i s t w h the hydrphgy, m y he :amajar s w c e .of ere&&
sediments. and may increase the pr&&ili'ty
o:f l&lides.
he construction
af the current Pore+t Se.mice r o d =two& required ,significant c3esign
e f f o r t , . Sjinilar considep~tionm a t be dven t o road closure. Several maj,'or
presmc& along &th a k i & E &-&&.on
oP ~ D W eursent
conpans
t ~ o l savailable :Loa,ss,ise r&-cllosuse p l m r s .
ailby* P. E:.,. I(. StslllP&n ,?nxj, S. El, Dunam, m,$P.. The iper?.axa$i~a
a;&
far:
o.f rwd-erurfa@e. qealF$tbmt h Emrmterl. wa.:t9cws'h.9&sin Sauthwepstaer
@ a & i i l g g t ~ ~;tibuz=,l
.
FQcf&t :@=c:@
2;5 (2.1:4553;-@$..
Builurmqhs, B. R,,, a's... md J. L9. %$ngr1.%@.
W&ctL~sl:af s@il &FO&$O& Q
P e n ~ ~ z t tw
a. 9, &part-ae.sfr af &grislu'i~u~a
F6aee.t $arvic.e
~ & : ~ a , m k sR-@$C~
in
8tatriw.,
p ~ ~amseal
.
FgQ&i:eal Reper
mT-g:@*,
m..
E1LF&k I.
R.. 0. @~,:>~t.8,
&a$ 1, D. %
&
:2.9;94a. PredSetim
.~ . .,." ~...
sed~mn$at.$q~
$gem. mads 3% i@geifia, sraw&ng&
.&e me^ ~ O & L
.pw@63n.f:&:
&k
%$:,$%d& W I X % & . w ~ & ~ @ % t $'t%b:&e
l
:%&f-&g,
Paper Q@
w'?5.$1,
. .~
@&I$
J.,
@
. wbJ;
E1liae4 W. J., P. E.. :tajXeq :qi e. c l l ~ ,wid
D :a. &ii$b%syI.%$&b+~mpgctsQ
l&#Sl&@
.on,m, e@cqptw..gp&si%td
,c& 1994 &WXsz$&raW.$~m
w~,,
,=
.
,
ia..
*~.&.EQP
*b
T m*,
J. & ~ ~ & (&@.
W nt , ZSg%.. @EP, it:aer S-Y
.m.*,$&:@ql ,&@@$,
,&&&*,.
&'*
FhtXk~rn, DL 0 . 4 $:
rZ819A
wags eer-tetn pPz%@&@gien
gkaj.e&. IJ. $.mprCP*t ~ : f Jksark,mL.&a~*e
&&i$j~a,L
&=a(&,
Zge*m. I;&~l.ert;~q,,
W., &aa&g&g@.e(
In, &&&:
m.. il. 231 pB.
P13.1tae 8 . 1.;, 5g93. M , ~ e n f
pxat@s&S
:
P 1 .wheel xut@ a t t n m ~ r . E e 4Esma.~
r-;..
t t n f - g i ~ ~f r h , ~ikw,
~gjscw..,
.
ph.~.. ~fb&~..
B&Bwn@,,C.,
HdlL,. S. r9511:~arid P. ,S%&clk,1.9%2. I&-1 Z $k.&lik:
:3urakylis fimt:S%,) &cf~%Ueil,k&tion
E@,r ~er&ibn 3.9: D. 9. R p w g - t
Q:
ag??f@~-ltuze,
Po,&& &b&oa,, MtBmtwntatn Fgw'&@@b,
@tation,,ma,
.
m,.
'~m&g&l'84*-a%&,;
K$mwd, A. X, 1.9W
'&isaal ,aLaEi:8ifific&.i
o a sf m,ile, U d f Led sail.<
~ ~ j , t . i 6 a k ' i ob~ystmi
n
.U% tghmm af R@:l;m&kiBn. &@ae%ring
*a& &sear@l
.
Qen@rj @@g@&&cal
..
me,.
m,@& mag m a ! l~ 0 , :3;
. ID& pp..
WW,. C., EL, 'f9@9,. G:B&@~Ew:
t ~;iSrMitgand wet:~a&$.,
Xn n
h
;P
E
r
&
l A. D,, a& .W.
J. E l l i ~ &t:6 .) Ew%romtZ11B%SmZ'w.. betqia .Bub,lishess, SQ&
sa?3#& FL. pp. $*$:$-2.@4,
L u w , e,, B.,, P@M.. Znfiltr;@ti&na.@gar:i,ty@h@@@es
in&~eaby ri33pi- Od
f ~r$$t rtia&,
Uader z ~i~
f * a%ilf&la f.fo@9uh?ang, IQt;&&ountair
mmamh WaXim. &Em-,
'iD. $2 m.,.
. .
@eg&hEltl.,,W. F.,, 1:9.74. Erasion @Bfigi&e
r
csn. sam@eejy
&1fio&.kred 'gra~jtj,s:
Satlo: .er faw@h. g., S. Wparg@&gg f i4gpjcvltur,,
~emi.c@,
InEentl~us1'ZainRe=&?& g@tlat:&g.&,
Qy&&,, a%,.,;&~m
-g
a;TclM. 1.8
~
.
'
'mi.
:&
T. ' D W @ u 'Y3P4. S8eb!i~wZ
@x&aotim from f p ~ m~ . ~~ d t
mrfrn~s. W&g&r Xesgwe@m-k
l?,Q.r!Xl) rI75.3-1"FIZ..
S h a m , I . , 19&.
AZt w m ~ &
s l , o&.&ility
~
,m~lys&s,
f ~ c
P@4w$W@1 C O ~ p U t e g @ . ,7$$SJS.8i.W5 .A, 1'fit,WXWCk~e&ct;V,j#@ r)e@$pl$, IfrS., ,
=w,
ED. 214 w,.
?@f8, t. W. i JZ,, 19@.
F@r@@g
$@&&:$
&@si:ga,.
@aist,@~@-, m d ~
wLI: 2 m 5 . m !
T 8 .
*
. j E@@l.~&@&l
$&1l.&$,o.&', '%@I. :&q&p&-&&.
. .,.
&&&$@
w,
@ ,,?&&&@g$
&g :p&m&sr.
$J*gin@&g#ew %&#*. 4. P,,@~*&a*; '.'
~ X # . ? i a.
, C*~#, ~ @ M V 'PT*I,I.&*b~*ggg@ @f' P@f*&
np:ag
@t.rea
. ~ ~ t ~ aLnr )M
t ~ ,,
i@%,ee&akma&e~,arm~a,,
W.id,. 8.. M,
, -
- .
@@
mi@&$$.*:,
'
.
b
:
pn:
ig;.' Q h d . ,
PROCEEDINGS
AWRA ANNUAL
SYWOSIUM
WATERSHED RESTORATION MANAGEMENT
Physical, Chemical, and Biological Considerations
NEW YURK CITY WATER SUPPLY STUDIES
Edited By
JAMES B. S ~ L I W
TetraT& lnc.
IW lkd 8ua Bivd., Suite llO
cMngsm, MD21117
O
Sponsored By The
s
ta
n
a
NEWYORKSUTESEC~ION,
AWRA
Blasland Bouck and Lee, Inc
Cityof Syacase
Cortland Line Co.
Donald W. Lab,Jr, Du Lac H n @ n e d q
Mclntire-Sfemb Foundation
M& and Assodates, Consdlting Eogfneers
Nataal Rewaxes Consema6onService W
NYC Department of Envltomnexifal Protection
A ~ ~ N CBOOK
Y
l e 8uNTAlN S T A ~ ~
N Y S WaterResourcesInstitute
The N i i Mohawk Foundation
Onondaga County Water Authority
P. H. Tucker Conwlting Engineer
Steama and Wheler
SUNY College of Environmental S d e & Fmestty
Tetra Tech, Inc
Upstate Freshwater Institnte
co-sponsors
Assodation of € o m t i o n Districts (NYS)
Consmvafion Technolow Infonnathn Center
corn& ~ o o ~ ~~xt-ion
k v e
Federation of Lake Associations (NYS)
Great Lakes Research Consortium
NattuaLRemurces C d m t i o n Wee
New York Rvers United
NYC Department of Environmental Prote&on
NYS Department of Environmental tonservation
N Y S Soil and Water Consewation Cammlttee
NYS Water Bnvi~mmentFederation
NYS Wettaads Fonrm
Soil and Water CansetcraLion Society (NYS)
Soil and Water Consemation Sodety
~~ls~f~eh
River
a m Basin
a
Commission
Wafer Environment Federation