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W~g I 2011 11 - 11

1111118 1111118

11111125 1111114 11111middot6 11111middot25 1111114 1111116

MICROCOPY RESOLUTION TEST CHAIH MICROCOPY RlSOLUTION TES r CHAIn

eXITED STATES DEPART~1ET OF CRICl-L1TRJ YASHIGTOX D C

CONDITIONS INFLUENCING EROSION ON THE BOISE RIVER WATERSHED 1

FormerJy uN~(ci(]lr rlLltlJ( examiner Intermountain Fort (llid fILlfI RrjlcrimclIStation FO)It S(rric(

CONTENTS

PUgl EVldenr- f( ~rosin on the w3Iel$heL 1 luiluen(c o(various (lct OfS (Itt rrl 1 ~ ~ ( n

lt Char1Ntrht 1(- of t hI watl~hcd ~nil _~ _ ~~~_~ __ _~_ It

rU[tltaJJ1)1 ~J()logYt nud -oil i ClimI bullbull __ _ ~ PlllUt type J middottvtlliLon nwlg-rtl7Ulfr l1St~ Ii Ilensit- of HZNtmn 2

1thod()C~tllrl- _ ___ 7 HOfllntinfcSLltiun l1 llhtllrg ohOrntl ~ ~ cccssibility to linstutk 21 ~lp h~ or InllYI~ _ _

fuflllpoundlU(l If arilllls fllto[S nn rrn-ifn l III J)i-(usinn of rC~u1t~ i

CiratiiNI ~ _ 2 ppli(aflIlIl of rt~uIr i I I( bullbull - _bull - - II -iwllullry a

EVIDE~CES OF EROSroN ON TI-m WATERSHED

to Conditions OIl the Boie Hinl wnterhed in west-cell (nil J dullO are ~ 0) lepleen tnti YC of many western dlllinn~ps wllpro accljern t((l (losio11shy constitutes n l1l(Itl(C to ngrieulturul communities Cndll Stich conshy

ditions cxcessin~ fun-off from rain and melted SIlO Dot only robs the lIplnuc1s of tho fprtilo topsoil but londs the stl(lnms whidl tlrniu them with silt tlml hPHvic1mntNini that cl()~ the strCUJ1l chnl1lwIs aud irrigation ditdl(s fill storage rcse1oir i1)(Te110 flood hpigh t nnd freluently cO(l produCtin~ land wilh glnnl Ol otilPl ltlelgt1i (IlshyCil((kecl tbis PlO(ps willlllld to hen Y ]088P8 of innstlllellt in land inigtttioll works and othe1 implOHl11tllts Iud ((ntllnll~ to s(tiou- 111lt1 abnlldoIlluen t Therefore tbe d((10 jllllPll t of pJilttic( iu wn tNsilpd lluUlugemen t to meet this probleDl is n mnt (PI of lil( impolbllwl

Tile Hois( 1iVP1 wnterlllPd an 11(1 of njJplOxilllllll1y 1700O)() nclPl SUPll(lIt~ a dllllturient illig-aINI 111(1 of ~Jlti()()() lllelt of hig-bJy ploduetinl n~li(lIltLlrnJ llllld which j tlhtli in excesl of Si1(OOOOO

I fhe wntpr ~rtltrfllll) aeklluletl~es IllS il1ltl~bj[gtdlleo 1lt1 (wralmelllloe o( th~ Intennollntllu Foret lOr Ian~o Exprmeut Slation statr who hllle 111 e~rwrlHlly helpful in the pr~rlrltltlCgtn of this report pnrli~lIlllrlY to Jormer IhrNlOr ( L Iol$hn~ who lwlrl(ltl tl) forullolle 1I1n surly whwh (flUerted thr dnta that urn herrin Dllalyzed gllle dirtrtlon to tho or~anilOtion Dnd InI~gtis of the dllI and ritienl revielled Ihe mllllll~cripl tn Reed II HUiler prpcnl direcwr of the Illlrrmvutltain stulioll for gl1oloi (ODlrthutions nud to n(oro ~tewnrt for 8ml (()JlIrihutinlls nnlaquot (ritili~mo nl~o to tho lltlnllni~tfltiYl oJlJcers of 11Hllnnuoulllmn n311tlllill fOrtSI re(ioll for lIltmiddot (ollflll( of I h( urrey I(I[k

Preparation pC tIas bultin WlI ~oIllJlleteltl ut (he Culiforllla Fl)nt IInll H1n~( ExperillWIl( Stalion

US8lJ -lll--

2 ~lECHNICAL BlTLLETIN 528 U S DEPr OF AGlUCULrURE

The developments on this stream include the AlTow1ock (fig 1) find Deer Flat Reseryoirs having a combined storage capacity of 453000 acre-feet

Already enough silt has accumulated in Arro1ock Reservoir to cause concern Heavy deposits of glflvel mel sund choke severnl of th~ tributaries that empty directly into the reservoir (fig 2) It is estImated bused upon watel-stornge datu thnt npploxul1utlly 7500 aClP-fept of silt b((tlmc lodg((l~ill the lcRIoil hptpcn H1U) the yeur of the completion of the dam and 1027 lIHl thus storage spuce thu( originnJJy (ost mOle thun $lOOO()O fo providp wus ithin 12 ypnrs pellllUll(nfly hsL This ~iJt hns bp11 dlj)nsitpd in the r(SltIoil lot wiUlslnnding IHU Y Sllli(ill~~ in (h llO f 1IIlti H[ IU III

F2S3~S5

FJ(tnl~ 1 ~middotrrorl)ck DHlIl on the Boise Hhcr ill WCSI-clmiddotntrnl Idaho (onlpINrd in 1IJ15nt 1 (o~t of over jIIiOO(XX) SLorn~e capocity of the IS-mile rc~erOir olgtoc the dUIJl is being threatened by UlIcllfUlC1 erosion

clrnnnp~ in the bottom of th s[oruge bUHin ltyery jw (111 il(11 the rcs(lOU ~ns eompl(ply dlHlJlCll

The mill pond of the sawmill at Barh(I Jdt1lO PYlt[t1 mh IwIo the )1lOw1ock Dam is almmt ltompllplmiddot fillCc with iiil III ~pifp uJ s(lllimuunl sluicing sil thus n10 IH(Ullllrln (p(llliJOO th( will pond until the pf(ctie hend or wutel 101 [L hnllo(lpctiil plant f-ihlntd th(l( has becn l(dll((d one-third 01 from ao J(lt jo nppll)xilllntlk 20 feet (fi~ 3) The excessiyc sil t load is l1ltnn whill ctlwing 11lll1P((SshyStUy oatlays for its cvntrol at the intake 01 diversion diteh(s and its renloYal flom the canals

A more serious aspect of the problem is til( apparent excessive quantity of materinl which has been procied i11to the ehullllcls 0[ many of the smaller tdbutnrl(s of the 1iy(1 nnd which in turn is being gruduuJly tnlllspolted into the J1udu (hallnd b JlIn-ofl during the spring floods uncI summel Inshds CaICful obsllvntioll llUlkes

3 EROSION ON rHB BOISE RIYER WATERSHED

it clear that this material has in part been brought into the tributaries from the adjacent slopes and in part has been dislodgcd from the formerlv stobIe strcam channels Unless udcq ua te stcps afe tnken to contiol it the erosion burdcn ellll be eq)ccted to inclease Some of the silt load of tbe stream obviously is the product of the normal accumulation that results when any current is checked by a reservoir or a dhrelsioll dum The total present aC(lIJ11ulntion however is fur in (xeess of the normnlload of the Boife Riycl

Evidrnee of an increase in the rate of cOsion is to be found on the wfltershed The first obsclTatiolls of record for the grJlclfl1 region fire those of RusselP In 1902 he described rccent changes on til( watershcd lands acljnclnt to the Snakf RiyfJ plains whilh

FlltIl~ 2-llcll~Y ~posiLS flf nlsioll Iebri ~ltlent lit low wHtcr love iI lhl) Arrowroek Heenoir fit I he mouth of ()roll~e Creek Ihis streum less thnu 7 miles in length hus within recent years braughL down on enurmous nmuunl of mutedII

inrludp l1lUS [illlila to Ihos( of t1w low(L portion of Ule- Boise Ricl wn tPlshcd II ( nUntiOlwcI Uw n PPtIltmee or l1r-h (u tgtl with l1tltJly Ytlti(nl Willis of JO(l~e fludh ~llllits on hillsir1Cs Jtlll1wrly (omplliCly (oV(ICd willt wil guldHs HCIOS roads ne(ltssitating wide lktoUls aud the dlnina~n of 11lxurillnL llltIHlos nnd till ]Pphl(C11lCllt of wild glnss(s by 8Il)rblllsh 11( ttl I libulfd this l(((nt dtlHgn to tlH inlloshydudioll of lurge nllmbtls ()r sl1c(ljl into (Ill (OlllltlY about lRRO ltis IPllsonahln to lwliln jlldgin~ flolll ttl( ptltsCnt applIUllllCCS thut tt((clelH tcd (l(lsioJl hud COHUlllJl(eci Oil ( rOllse (r(Ck VUlow Cl(ck llnd other dll1inagCs which (mpt~r into the south lork of the Boisll River about the sume time liS thlLt obsclvCC[ bY Russell nnd thnt it hilS been continuing ey(t since The topsoil on this section is badly depIcted Old erosi(111 scurs nre in c-idence nnd shcCt erosion is still yety nctiye on nUl1lY of the slopCs The canyon bottoms nre (kcply chnlllHl(d unci ehok(d with gmvC As lHurly tiS (11ll hI dctermined

-3 ItS~poundlt 1 ( (ImiddotOlOlty A 1 Wmiddotn1~ Il~~()tmiddotJlT or rllr~ ~-lo ~~ lClmiddotlolt lmiddott~Al~~ (I 111IHO~ t~ l ~(ol Survey Bull HHlJ W21P iHult IOO

4 TECHNICAL BULLErIN 528 U S DEPT OF AGRICULTURE

this widespread accelerated erosion did not extend to the higher parts of tho watersheds until about 20 years later

Officials of tho Forest Service in 1926 obseryed that excessive washshying of the soil was sprencling to the higher elevations drained by the Boise RiYer Gullies of yarious sizes on the slopes and abnormal enlargement of the nnturnJ drainage channels were found in many places Heav--y deposits of fresh debris were noted at forks and on stretches of low gradient of some of the smaller tributaries of the river The exposed roots of living plants along the sides of washes pointed to the newness of the gullies Many steep-sided gullies were to be found whi(h at best may remain steep-sided only temporarily in the loose comse soil of the region In a region where downy chess (BJomu8 tectol1l1n) ordinarily tnkes possession of fresh soil surfaces

FZt413

FttilUJo a - JJeavy rilpo-Hs or SiUId below rlla diversion dum locuwri n few miles downstrmHI1 (rom the ArrnwrrJ(k Hlrnor Thes) depoit which h~e Ilccumulated since IUt5 have lowered the fiuilable Ittad of water by lU fect

within a few yenrs Illuny gulli(s and alluvial deposits were found wJl(re this pJotertiyp (O(Ibg hncl not yet appeured Sheet erosion was obs(Jv(d to be yet) a(tie on many of the slopes In other pln(Cs hCIC thCl( haye hCC1l dCposits of soil lXCl1YfttiOllS nlOulld thl stem of hrubs iJ(1icut(1 thnt in SOJllC1 placls a loot or more of soil has beln d(posittcl within 10 y(als olmiddotlls~

flw loss of the topsoIl lichlst in orgnnic mutter oyer n ratiHI In1g( part of the middotwatCImiddotsh(d is further (~iden(e of accellUtcd CIOSiOll 1Ul11lWUS lelllJlan ts of ull(rocied soil found almost whollyin prot((tld places indicate that this original topsoil was prcsent onr most of the area to depths ranging from one-half inch to see1a1 inches Beneath this on the slopes vas n second luyer ranging from 3 to 10 inches in dfpth usunlly yellowish in color and containing considerable fine soil A third lit)Cr of 20 to 40 inches in thickulss dcpClu1ing OIl the depth of rock dccay (ontnilled liWe or no olganie mntte llnd little DIll soil

5

J

EROSION OX rHE BOISE lUVER WAJERSHEJ)

~urvey observations supported by analyses of some 200 soil samples mdlcate that on more than 50 percent of the area the top layer hus completely disappeared and over a consideruble ar(a the second laytl also is gone leaving the third layer exposed

Recognition of the potential seriousness of accelerated erosion on the wiLtershed ld to the making of an intensivc survey of erosion and related fILctors on the most seriously affected parts of the drainage within the Boise National Forest The purpose was to detelminl tlt( influcnce on erosion of the seveml lilCtors both nnturu) and introshyduced for use us a guide in planning protection und mlmagcment or this and other wllt(lshed alens wh(1( similar conditions plcvail The portion of the drninnge lying bttween the Middle and South liOIln or thC rlYCl was sCleetCcL 101 study and in 1929 und ] 980 n totnl of 371313 aCTes ClC (oYclccl try un intCllSiy( stlrvey This bulldin pr(stnts nn ann lysis of the dntn (oJlceted

CHARACTERISTICS 01lt 1HJltJ WAflmSmm

TOPOGRAPHY (a0I0(Y ANn SOIf

ThC topography of thr Boise HiveI watershed is ehurneterizCcl hy Cxceeclmgl)T siCCp slopCs nurrow ridgCs nnd lHlmerous dCep V-shapCc] (anyons Over the mea (oveled by the sUITey the slopes ave1flge in excess of 45 per(ent The elt~Tutiol1 of the watCrshed rnnges from 2700 feet (at Boise Idaho) to nll111PIOllS mOllntnin peaks hCtWftll 0000 ancllOOOO feet in height Stventy pCrclnt of the IIlea is moll than 5000 feet in e1evntion nnd 20 percent is more thun 7000 feCt )1001es Creek and the North Middlt nnd South Forks of the Hoisr Hivtl are the principnl trilmtllries of thc main strCmn

This is cssentinlly II granite (ountry Lavn J]ows alC (ommon uL the ]OWC1 ehvatiolls within the watershed bllt O(CU]JY ) rplntivel small portion of tIllt whole dmilluge Sedimentnry ro(ks IIle prncti shy(ully absent Illlt grnnite in this stCtion is n part of the intrusion callpd the Idnho hatholith It is alight-lololCcI CoHrst-gmined grny ro(k whi(h onthers rendil into a (oalso flUnd The IImount or weathering is Rtriking few iresh llllclecomposCd pi(ces of roCk being tyicltllt 011 the slIrfa(C Tho minernls making IIp themiddot grnnite nlO grny quart white l1nd pink Illdspnr mninly orthoe1us( hut with SOllW

plngio(lase nnci hio tite mi(n occlIrrmg in smn 11 flnkes 1ht gnmitc is intruded hy dikeR the commolltst Iwing qunrt-ciioritp nnd ppgmHshytitES Few distin(middott outcloppings of thCRC nrc eomnwnl sten hCcuuse of the wtnthCling of the gmnitc hut th(ir o(curlelHe is (idpnt in the flon t found Oil ridgCs mcl in stream channels IhC pqmntites mnde lip of larger (rystals or Clunr Jeldspnr and mUE((wite um comlllon aud sCel11 to be quite gCJ1eml in OCCUITen(e A few dnrk-gleen filHshyfruinfd dikes probably diabnse are found The mntClinl thnt hns ~enthered from these intrusions has influenced the soil but ]ittle

rhe granitic rock of the rcgion clisintegmtes readily forming n coarse sandy gray olYClhwish-grny soil Atower e1cvntions nnd in valley bottoms this SOlI mantle mILy be of eonslcIemble depth but over most of the ILlCn the soil is shallow and the underlying ro(k is found but a few feet below the surface The coarseness of these Boise soils is well il1ustratecl by the mechanical nnnJysis of lepresentatiye Ramples which shows thn t 31 percent (by weight) of the soil is made up of particles more than 2 mm in diameter In addition to this

G lJDCHNICAL BtTLIElIN 528 U S DEPT Oli AGlUCUUlUHB

thc sand contcut of sLightly )11111101 plllmiddotticks flYClflgccl 50 peJ(ent The perccntage of colloidallHntclinl is vcry smnll in most (asCs not cx(ceding 5 to 6 pel(cnt nnd in some instnnrcs CVC11 lpss Soil of this ()htu[tctel crodcs vcry readily in the tlbsencc or n good plunt (ovcr

CUMAT~~

Althollgh wonthcr records for the 111nin wntcrshed are comparashytiYely few those tibnt hnYe becn kept for vnrying periods nt llllJllelOUS static)J1s show n fair correlation with the re(olds Ilt Boise vlli(1t clute hnek to February 1 ISM Only one-third of the Jlormnl annual precipitation of 13 inches nt Boise comes during the 6 months of the growing scnson--April to Scptember Scant precipitation during the Inte su 11l1llel COli pled with high tempcrn turcs drying winds fOm the ntlioicing Snn ke lUyel plnins nnd thc rcsulting excessive evaporashytion mnke difIicult the llInintennnce 01 n YPgota tion coycr Oil the (xl))~(l slopcs YhilQ tho precipitation dlldn~ the 3 summer months is ordinarily Jight sudden J almost toncntinl showers cllusing scycre erosion over 10cn1 nrens nrcmiddot not inhcquent

The suuwjnll nt tho lowcr elevu tions is seldom grcatcr than 25 inches lIlHluSllUlly (()mc~ in smnU fulls 1[11c1y stnying on tho grolnd 101 more thun n week 01 so At llighel clcyutions the 11l1nllnl jnll increascs and rctunins for the most pnl in pIneo Aboye 8000 fcet by Ule time mclting stnrts in the spring the snow coyer uSllully 1CUehe8 7 to 12 feet in deptlt deMO nnd welL packed It is tbis snow muntlo tha t supplies tho water to Jill the storuge leSCIToirs ClillJntic (onditions during tho pnst deendc or so Juwo bcen unfnvorshy able JOl nhuncLnnL WHtel Fur the] 2ycnr period heginning with un9 the nverngo departure below the mcnn annual preeipitution ut Boise was 21 percent for tho (riticHI spring lllonths of April 1hy nnd JU11e und 14 pcrrcllt for the eombinecl spring and summer seasons The nnllunl defieieu(y amounted to 11 percent Only in 3 of the 12 -euls wns l)lc(ipitntioll in excess of the 67-en1 ftYclnge This d(ieiency in Ildclition to influeneing run-off htts been It materiul jaCtur in lcssening the gro-th of yegetntion on the wntershed

VeGETATION AND GRAZING USf

Vide differenccs in the Ycetntion are to he expcctcd ovcr a watershyshed with n lflngc in eleVittlOll of more than 7000 feet Fifty-one pel(rnt oJ the Ulmiddoten (Oe1e([ hy the slllTey is more or Jess open-timshybcred J1 nd j 13 peleen thus brush 01 timbel too dense fol gmzing h~T liYcsL()Ckj 11 perccnt is untimbeled grass Inncl 12 per(ent is oC(llPied by n YHriety of shrubs on 7 perccnt sngehrush is the dominant yegeshytation and tIlo remainder is composed chiefly of sllluil 1l1enS of weed meadow or nslJen

There is evicieIlre however thnt much oj the foothill COllntry onc( supported n Jnidy hellYY stnnet of bUIlch grnsses-muinly whrfltgrnss (AYloPUlon hWlme)-ill mixture with big sagebrush (t)middottemi8ia trishydentata) bu t these glasses JIlTe been tltillncd out 01 nlmosb comshypletely eliminated hy excesshc grllzing Sngebrush hus sllhsequentlY il(Jensed llntjl the C)Tcr except whero recently hUl1lt o(r 110shy(onsists of n stnncl of big sagebrush with a scanty mixture of downy ehess und other linllunl glases nnd weeds At the llighll elCutions depletion hus not progressed to the same extent for there tho unnual

1

3 EROSION ON rHB BOISE RIYER WATERSHED

it clear that this material has in part been brought into the tributaries from the adjacent slopes and in part has been dislodgcd from the formerlv stobIe strcam channels Unless udcq ua te stcps afe tnken to contiol it the erosion burdcn ellll be eq)ccted to inclease Some of the silt load of tbe stream obviously is the product of the normal accumulation that results when any current is checked by a reservoir or a dhrelsioll dum The total present aC(lIJ11ulntion however is fur in (xeess of the normnlload of the Boife Riycl

Evidrnee of an increase in the rate of cOsion is to be found on the wfltershed The first obsclTatiolls of record for the grJlclfl1 region fire those of RusselP In 1902 he described rccent changes on til( watershcd lands acljnclnt to the Snakf RiyfJ plains whilh

FlltIl~ 2-llcll~Y ~posiLS flf nlsioll Iebri ~ltlent lit low wHtcr love iI lhl) Arrowroek Heenoir fit I he mouth of ()roll~e Creek Ihis streum less thnu 7 miles in length hus within recent years braughL down on enurmous nmuunl of mutedII

inrludp l1lUS [illlila to Ihos( of t1w low(L portion of Ule- Boise Ricl wn tPlshcd II ( nUntiOlwcI Uw n PPtIltmee or l1r-h (u tgtl with l1tltJly Ytlti(nl Willis of JO(l~e fludh ~llllits on hillsir1Cs Jtlll1wrly (omplliCly (oV(ICd willt wil guldHs HCIOS roads ne(ltssitating wide lktoUls aud the dlnina~n of 11lxurillnL llltIHlos nnd till ]Pphl(C11lCllt of wild glnss(s by 8Il)rblllsh 11( ttl I libulfd this l(((nt dtlHgn to tlH inlloshydudioll of lurge nllmbtls ()r sl1c(ljl into (Ill (OlllltlY about lRRO ltis IPllsonahln to lwliln jlldgin~ flolll ttl( ptltsCnt applIUllllCCS thut tt((clelH tcd (l(lsioJl hud COHUlllJl(eci Oil ( rOllse (r(Ck VUlow Cl(ck llnd other dll1inagCs which (mpt~r into the south lork of the Boisll River about the sume time liS thlLt obsclvCC[ bY Russell nnd thnt it hilS been continuing ey(t since The topsoil on this section is badly depIcted Old erosi(111 scurs nre in c-idence nnd shcCt erosion is still yety nctiye on nUl1lY of the slopCs The canyon bottoms nre (kcply chnlllHl(d unci ehok(d with gmvC As lHurly tiS (11ll hI dctermined

-3 ItS~poundlt 1 ( (ImiddotOlOlty A 1 Wmiddotn1~ Il~~()tmiddotJlT or rllr~ ~-lo ~~ lClmiddotlolt lmiddott~Al~~ (I 111IHO~ t~ l ~(ol Survey Bull HHlJ W21P iHult IOO

4 TECHNICAL BULLErIN 528 U S DEPT OF AGRICULTURE

this widespread accelerated erosion did not extend to the higher parts of tho watersheds until about 20 years later

Officials of tho Forest Service in 1926 obseryed that excessive washshying of the soil was sprencling to the higher elevations drained by the Boise RiYer Gullies of yarious sizes on the slopes and abnormal enlargement of the nnturnJ drainage channels were found in many places Heav--y deposits of fresh debris were noted at forks and on stretches of low gradient of some of the smaller tributaries of the river The exposed roots of living plants along the sides of washes pointed to the newness of the gullies Many steep-sided gullies were to be found whi(h at best may remain steep-sided only temporarily in the loose comse soil of the region In a region where downy chess (BJomu8 tectol1l1n) ordinarily tnkes possession of fresh soil surfaces

FZt413

FttilUJo a - JJeavy rilpo-Hs or SiUId below rlla diversion dum locuwri n few miles downstrmHI1 (rom the ArrnwrrJ(k Hlrnor Thes) depoit which h~e Ilccumulated since IUt5 have lowered the fiuilable Ittad of water by lU fect

within a few yenrs Illuny gulli(s and alluvial deposits were found wJl(re this pJotertiyp (O(Ibg hncl not yet appeured Sheet erosion was obs(Jv(d to be yet) a(tie on many of the slopes In other pln(Cs hCIC thCl( haye hCC1l dCposits of soil lXCl1YfttiOllS nlOulld thl stem of hrubs iJ(1icut(1 thnt in SOJllC1 placls a loot or more of soil has beln d(posittcl within 10 y(als olmiddotlls~

flw loss of the topsoIl lichlst in orgnnic mutter oyer n ratiHI In1g( part of the middotwatCImiddotsh(d is further (~iden(e of accellUtcd CIOSiOll 1Ul11lWUS lelllJlan ts of ull(rocied soil found almost whollyin prot((tld places indicate that this original topsoil was prcsent onr most of the area to depths ranging from one-half inch to see1a1 inches Beneath this on the slopes vas n second luyer ranging from 3 to 10 inches in dfpth usunlly yellowish in color and containing considerable fine soil A third lit)Cr of 20 to 40 inches in thickulss dcpClu1ing OIl the depth of rock dccay (ontnilled liWe or no olganie mntte llnd little DIll soil

5

J

EROSION OX rHE BOISE lUVER WAJERSHEJ)

~urvey observations supported by analyses of some 200 soil samples mdlcate that on more than 50 percent of the area the top layer hus completely disappeared and over a consideruble ar(a the second laytl also is gone leaving the third layer exposed

Recognition of the potential seriousness of accelerated erosion on the wiLtershed ld to the making of an intensivc survey of erosion and related fILctors on the most seriously affected parts of the drainage within the Boise National Forest The purpose was to detelminl tlt( influcnce on erosion of the seveml lilCtors both nnturu) and introshyduced for use us a guide in planning protection und mlmagcment or this and other wllt(lshed alens wh(1( similar conditions plcvail The portion of the drninnge lying bttween the Middle and South liOIln or thC rlYCl was sCleetCcL 101 study and in 1929 und ] 980 n totnl of 371313 aCTes ClC (oYclccl try un intCllSiy( stlrvey This bulldin pr(stnts nn ann lysis of the dntn (oJlceted

CHARACTERISTICS 01lt 1HJltJ WAflmSmm

TOPOGRAPHY (a0I0(Y ANn SOIf

ThC topography of thr Boise HiveI watershed is ehurneterizCcl hy Cxceeclmgl)T siCCp slopCs nurrow ridgCs nnd lHlmerous dCep V-shapCc] (anyons Over the mea (oveled by the sUITey the slopes ave1flge in excess of 45 per(ent The elt~Tutiol1 of the watCrshed rnnges from 2700 feet (at Boise Idaho) to nll111PIOllS mOllntnin peaks hCtWftll 0000 ancllOOOO feet in height Stventy pCrclnt of the IIlea is moll than 5000 feet in e1evntion nnd 20 percent is more thun 7000 feCt )1001es Creek and the North Middlt nnd South Forks of the Hoisr Hivtl are the principnl trilmtllries of thc main strCmn

This is cssentinlly II granite (ountry Lavn J]ows alC (ommon uL the ]OWC1 ehvatiolls within the watershed bllt O(CU]JY ) rplntivel small portion of tIllt whole dmilluge Sedimentnry ro(ks IIle prncti shy(ully absent Illlt grnnite in this stCtion is n part of the intrusion callpd the Idnho hatholith It is alight-lololCcI CoHrst-gmined grny ro(k whi(h onthers rendil into a (oalso flUnd The IImount or weathering is Rtriking few iresh llllclecomposCd pi(ces of roCk being tyicltllt 011 the slIrfa(C Tho minernls making IIp themiddot grnnite nlO grny quart white l1nd pink Illdspnr mninly orthoe1us( hut with SOllW

plngio(lase nnci hio tite mi(n occlIrrmg in smn 11 flnkes 1ht gnmitc is intruded hy dikeR the commolltst Iwing qunrt-ciioritp nnd ppgmHshytitES Few distin(middott outcloppings of thCRC nrc eomnwnl sten hCcuuse of the wtnthCling of the gmnitc hut th(ir o(curlelHe is (idpnt in the flon t found Oil ridgCs mcl in stream channels IhC pqmntites mnde lip of larger (rystals or Clunr Jeldspnr and mUE((wite um comlllon aud sCel11 to be quite gCJ1eml in OCCUITen(e A few dnrk-gleen filHshyfruinfd dikes probably diabnse are found The mntClinl thnt hns ~enthered from these intrusions has influenced the soil but ]ittle

rhe granitic rock of the rcgion clisintegmtes readily forming n coarse sandy gray olYClhwish-grny soil Atower e1cvntions nnd in valley bottoms this SOlI mantle mILy be of eonslcIemble depth but over most of the ILlCn the soil is shallow and the underlying ro(k is found but a few feet below the surface The coarseness of these Boise soils is well il1ustratecl by the mechanical nnnJysis of lepresentatiye Ramples which shows thn t 31 percent (by weight) of the soil is made up of particles more than 2 mm in diameter In addition to this

G lJDCHNICAL BtTLIElIN 528 U S DEPT Oli AGlUCUUlUHB

thc sand contcut of sLightly )11111101 plllmiddotticks flYClflgccl 50 peJ(ent The perccntage of colloidallHntclinl is vcry smnll in most (asCs not cx(ceding 5 to 6 pel(cnt nnd in some instnnrcs CVC11 lpss Soil of this ()htu[tctel crodcs vcry readily in the tlbsencc or n good plunt (ovcr

CUMAT~~

Althollgh wonthcr records for the 111nin wntcrshed are comparashytiYely few those tibnt hnYe becn kept for vnrying periods nt llllJllelOUS static)J1s show n fair correlation with the re(olds Ilt Boise vlli(1t clute hnek to February 1 ISM Only one-third of the Jlormnl annual precipitation of 13 inches nt Boise comes during the 6 months of the growing scnson--April to Scptember Scant precipitation during the Inte su 11l1llel COli pled with high tempcrn turcs drying winds fOm the ntlioicing Snn ke lUyel plnins nnd thc rcsulting excessive evaporashytion mnke difIicult the llInintennnce 01 n YPgota tion coycr Oil the (xl))~(l slopcs YhilQ tho precipitation dlldn~ the 3 summer months is ordinarily Jight sudden J almost toncntinl showers cllusing scycre erosion over 10cn1 nrens nrcmiddot not inhcquent

The suuwjnll nt tho lowcr elevu tions is seldom grcatcr than 25 inches lIlHluSllUlly (()mc~ in smnU fulls 1[11c1y stnying on tho grolnd 101 more thun n week 01 so At llighel clcyutions the 11l1nllnl jnll increascs and rctunins for the most pnl in pIneo Aboye 8000 fcet by Ule time mclting stnrts in the spring the snow coyer uSllully 1CUehe8 7 to 12 feet in deptlt deMO nnd welL packed It is tbis snow muntlo tha t supplies tho water to Jill the storuge leSCIToirs ClillJntic (onditions during tho pnst deendc or so Juwo bcen unfnvorshy able JOl nhuncLnnL WHtel Fur the] 2ycnr period heginning with un9 the nverngo departure below the mcnn annual preeipitution ut Boise was 21 percent for tho (riticHI spring lllonths of April 1hy nnd JU11e und 14 pcrrcllt for the eombinecl spring and summer seasons The nnllunl defieieu(y amounted to 11 percent Only in 3 of the 12 -euls wns l)lc(ipitntioll in excess of the 67-en1 ftYclnge This d(ieiency in Ildclition to influeneing run-off htts been It materiul jaCtur in lcssening the gro-th of yegetntion on the wntershed

VeGETATION AND GRAZING USf

Vide differenccs in the Ycetntion are to he expcctcd ovcr a watershyshed with n lflngc in eleVittlOll of more than 7000 feet Fifty-one pel(rnt oJ the Ulmiddoten (Oe1e([ hy the slllTey is more or Jess open-timshybcred J1 nd j 13 peleen thus brush 01 timbel too dense fol gmzing h~T liYcsL()Ckj 11 perccnt is untimbeled grass Inncl 12 per(ent is oC(llPied by n YHriety of shrubs on 7 perccnt sngehrush is the dominant yegeshytation and tIlo remainder is composed chiefly of sllluil 1l1enS of weed meadow or nslJen

There is evicieIlre however thnt much oj the foothill COllntry onc( supported n Jnidy hellYY stnnet of bUIlch grnsses-muinly whrfltgrnss (AYloPUlon hWlme)-ill mixture with big sagebrush (t)middottemi8ia trishydentata) bu t these glasses JIlTe been tltillncd out 01 nlmosb comshypletely eliminated hy excesshc grllzing Sngebrush hus sllhsequentlY il(Jensed llntjl the C)Tcr except whero recently hUl1lt o(r 110shy(onsists of n stnncl of big sagebrush with a scanty mixture of downy ehess und other linllunl glases nnd weeds At the llighll elCutions depletion hus not progressed to the same extent for there tho unnual

1

4 TECHNICAL BULLErIN 528 U S DEPT OF AGRICULTURE

this widespread accelerated erosion did not extend to the higher parts of tho watersheds until about 20 years later

Officials of tho Forest Service in 1926 obseryed that excessive washshying of the soil was sprencling to the higher elevations drained by the Boise RiYer Gullies of yarious sizes on the slopes and abnormal enlargement of the nnturnJ drainage channels were found in many places Heav--y deposits of fresh debris were noted at forks and on stretches of low gradient of some of the smaller tributaries of the river The exposed roots of living plants along the sides of washes pointed to the newness of the gullies Many steep-sided gullies were to be found whi(h at best may remain steep-sided only temporarily in the loose comse soil of the region In a region where downy chess (BJomu8 tectol1l1n) ordinarily tnkes possession of fresh soil surfaces

FZt413

FttilUJo a - JJeavy rilpo-Hs or SiUId below rlla diversion dum locuwri n few miles downstrmHI1 (rom the ArrnwrrJ(k Hlrnor Thes) depoit which h~e Ilccumulated since IUt5 have lowered the fiuilable Ittad of water by lU fect

within a few yenrs Illuny gulli(s and alluvial deposits were found wJl(re this pJotertiyp (O(Ibg hncl not yet appeured Sheet erosion was obs(Jv(d to be yet) a(tie on many of the slopes In other pln(Cs hCIC thCl( haye hCC1l dCposits of soil lXCl1YfttiOllS nlOulld thl stem of hrubs iJ(1icut(1 thnt in SOJllC1 placls a loot or more of soil has beln d(posittcl within 10 y(als olmiddotlls~

flw loss of the topsoIl lichlst in orgnnic mutter oyer n ratiHI In1g( part of the middotwatCImiddotsh(d is further (~iden(e of accellUtcd CIOSiOll 1Ul11lWUS lelllJlan ts of ull(rocied soil found almost whollyin prot((tld places indicate that this original topsoil was prcsent onr most of the area to depths ranging from one-half inch to see1a1 inches Beneath this on the slopes vas n second luyer ranging from 3 to 10 inches in dfpth usunlly yellowish in color and containing considerable fine soil A third lit)Cr of 20 to 40 inches in thickulss dcpClu1ing OIl the depth of rock dccay (ontnilled liWe or no olganie mntte llnd little DIll soil

5

J

EROSION OX rHE BOISE lUVER WAJERSHEJ)

~urvey observations supported by analyses of some 200 soil samples mdlcate that on more than 50 percent of the area the top layer hus completely disappeared and over a consideruble ar(a the second laytl also is gone leaving the third layer exposed

Recognition of the potential seriousness of accelerated erosion on the wiLtershed ld to the making of an intensivc survey of erosion and related fILctors on the most seriously affected parts of the drainage within the Boise National Forest The purpose was to detelminl tlt( influcnce on erosion of the seveml lilCtors both nnturu) and introshyduced for use us a guide in planning protection und mlmagcment or this and other wllt(lshed alens wh(1( similar conditions plcvail The portion of the drninnge lying bttween the Middle and South liOIln or thC rlYCl was sCleetCcL 101 study and in 1929 und ] 980 n totnl of 371313 aCTes ClC (oYclccl try un intCllSiy( stlrvey This bulldin pr(stnts nn ann lysis of the dntn (oJlceted

CHARACTERISTICS 01lt 1HJltJ WAflmSmm

TOPOGRAPHY (a0I0(Y ANn SOIf

ThC topography of thr Boise HiveI watershed is ehurneterizCcl hy Cxceeclmgl)T siCCp slopCs nurrow ridgCs nnd lHlmerous dCep V-shapCc] (anyons Over the mea (oveled by the sUITey the slopes ave1flge in excess of 45 per(ent The elt~Tutiol1 of the watCrshed rnnges from 2700 feet (at Boise Idaho) to nll111PIOllS mOllntnin peaks hCtWftll 0000 ancllOOOO feet in height Stventy pCrclnt of the IIlea is moll than 5000 feet in e1evntion nnd 20 percent is more thun 7000 feCt )1001es Creek and the North Middlt nnd South Forks of the Hoisr Hivtl are the principnl trilmtllries of thc main strCmn

This is cssentinlly II granite (ountry Lavn J]ows alC (ommon uL the ]OWC1 ehvatiolls within the watershed bllt O(CU]JY ) rplntivel small portion of tIllt whole dmilluge Sedimentnry ro(ks IIle prncti shy(ully absent Illlt grnnite in this stCtion is n part of the intrusion callpd the Idnho hatholith It is alight-lololCcI CoHrst-gmined grny ro(k whi(h onthers rendil into a (oalso flUnd The IImount or weathering is Rtriking few iresh llllclecomposCd pi(ces of roCk being tyicltllt 011 the slIrfa(C Tho minernls making IIp themiddot grnnite nlO grny quart white l1nd pink Illdspnr mninly orthoe1us( hut with SOllW

plngio(lase nnci hio tite mi(n occlIrrmg in smn 11 flnkes 1ht gnmitc is intruded hy dikeR the commolltst Iwing qunrt-ciioritp nnd ppgmHshytitES Few distin(middott outcloppings of thCRC nrc eomnwnl sten hCcuuse of the wtnthCling of the gmnitc hut th(ir o(curlelHe is (idpnt in the flon t found Oil ridgCs mcl in stream channels IhC pqmntites mnde lip of larger (rystals or Clunr Jeldspnr and mUE((wite um comlllon aud sCel11 to be quite gCJ1eml in OCCUITen(e A few dnrk-gleen filHshyfruinfd dikes probably diabnse are found The mntClinl thnt hns ~enthered from these intrusions has influenced the soil but ]ittle

rhe granitic rock of the rcgion clisintegmtes readily forming n coarse sandy gray olYClhwish-grny soil Atower e1cvntions nnd in valley bottoms this SOlI mantle mILy be of eonslcIemble depth but over most of the ILlCn the soil is shallow and the underlying ro(k is found but a few feet below the surface The coarseness of these Boise soils is well il1ustratecl by the mechanical nnnJysis of lepresentatiye Ramples which shows thn t 31 percent (by weight) of the soil is made up of particles more than 2 mm in diameter In addition to this

G lJDCHNICAL BtTLIElIN 528 U S DEPT Oli AGlUCUUlUHB

thc sand contcut of sLightly )11111101 plllmiddotticks flYClflgccl 50 peJ(ent The perccntage of colloidallHntclinl is vcry smnll in most (asCs not cx(ceding 5 to 6 pel(cnt nnd in some instnnrcs CVC11 lpss Soil of this ()htu[tctel crodcs vcry readily in the tlbsencc or n good plunt (ovcr

CUMAT~~

Althollgh wonthcr records for the 111nin wntcrshed are comparashytiYely few those tibnt hnYe becn kept for vnrying periods nt llllJllelOUS static)J1s show n fair correlation with the re(olds Ilt Boise vlli(1t clute hnek to February 1 ISM Only one-third of the Jlormnl annual precipitation of 13 inches nt Boise comes during the 6 months of the growing scnson--April to Scptember Scant precipitation during the Inte su 11l1llel COli pled with high tempcrn turcs drying winds fOm the ntlioicing Snn ke lUyel plnins nnd thc rcsulting excessive evaporashytion mnke difIicult the llInintennnce 01 n YPgota tion coycr Oil the (xl))~(l slopcs YhilQ tho precipitation dlldn~ the 3 summer months is ordinarily Jight sudden J almost toncntinl showers cllusing scycre erosion over 10cn1 nrens nrcmiddot not inhcquent

The suuwjnll nt tho lowcr elevu tions is seldom grcatcr than 25 inches lIlHluSllUlly (()mc~ in smnU fulls 1[11c1y stnying on tho grolnd 101 more thun n week 01 so At llighel clcyutions the 11l1nllnl jnll increascs and rctunins for the most pnl in pIneo Aboye 8000 fcet by Ule time mclting stnrts in the spring the snow coyer uSllully 1CUehe8 7 to 12 feet in deptlt deMO nnd welL packed It is tbis snow muntlo tha t supplies tho water to Jill the storuge leSCIToirs ClillJntic (onditions during tho pnst deendc or so Juwo bcen unfnvorshy able JOl nhuncLnnL WHtel Fur the] 2ycnr period heginning with un9 the nverngo departure below the mcnn annual preeipitution ut Boise was 21 percent for tho (riticHI spring lllonths of April 1hy nnd JU11e und 14 pcrrcllt for the eombinecl spring and summer seasons The nnllunl defieieu(y amounted to 11 percent Only in 3 of the 12 -euls wns l)lc(ipitntioll in excess of the 67-en1 ftYclnge This d(ieiency in Ildclition to influeneing run-off htts been It materiul jaCtur in lcssening the gro-th of yegetntion on the wntershed

VeGETATION AND GRAZING USf

Vide differenccs in the Ycetntion are to he expcctcd ovcr a watershyshed with n lflngc in eleVittlOll of more than 7000 feet Fifty-one pel(rnt oJ the Ulmiddoten (Oe1e([ hy the slllTey is more or Jess open-timshybcred J1 nd j 13 peleen thus brush 01 timbel too dense fol gmzing h~T liYcsL()Ckj 11 perccnt is untimbeled grass Inncl 12 per(ent is oC(llPied by n YHriety of shrubs on 7 perccnt sngehrush is the dominant yegeshytation and tIlo remainder is composed chiefly of sllluil 1l1enS of weed meadow or nslJen

There is evicieIlre however thnt much oj the foothill COllntry onc( supported n Jnidy hellYY stnnet of bUIlch grnsses-muinly whrfltgrnss (AYloPUlon hWlme)-ill mixture with big sagebrush (t)middottemi8ia trishydentata) bu t these glasses JIlTe been tltillncd out 01 nlmosb comshypletely eliminated hy excesshc grllzing Sngebrush hus sllhsequentlY il(Jensed llntjl the C)Tcr except whero recently hUl1lt o(r 110shy(onsists of n stnncl of big sagebrush with a scanty mixture of downy ehess und other linllunl glases nnd weeds At the llighll elCutions depletion hus not progressed to the same extent for there tho unnual

1

5

J

EROSION OX rHE BOISE lUVER WAJERSHEJ)

~urvey observations supported by analyses of some 200 soil samples mdlcate that on more than 50 percent of the area the top layer hus completely disappeared and over a consideruble ar(a the second laytl also is gone leaving the third layer exposed

Recognition of the potential seriousness of accelerated erosion on the wiLtershed ld to the making of an intensivc survey of erosion and related fILctors on the most seriously affected parts of the drainage within the Boise National Forest The purpose was to detelminl tlt( influcnce on erosion of the seveml lilCtors both nnturu) and introshyduced for use us a guide in planning protection und mlmagcment or this and other wllt(lshed alens wh(1( similar conditions plcvail The portion of the drninnge lying bttween the Middle and South liOIln or thC rlYCl was sCleetCcL 101 study and in 1929 und ] 980 n totnl of 371313 aCTes ClC (oYclccl try un intCllSiy( stlrvey This bulldin pr(stnts nn ann lysis of the dntn (oJlceted

CHARACTERISTICS 01lt 1HJltJ WAflmSmm

TOPOGRAPHY (a0I0(Y ANn SOIf

ThC topography of thr Boise HiveI watershed is ehurneterizCcl hy Cxceeclmgl)T siCCp slopCs nurrow ridgCs nnd lHlmerous dCep V-shapCc] (anyons Over the mea (oveled by the sUITey the slopes ave1flge in excess of 45 per(ent The elt~Tutiol1 of the watCrshed rnnges from 2700 feet (at Boise Idaho) to nll111PIOllS mOllntnin peaks hCtWftll 0000 ancllOOOO feet in height Stventy pCrclnt of the IIlea is moll than 5000 feet in e1evntion nnd 20 percent is more thun 7000 feCt )1001es Creek and the North Middlt nnd South Forks of the Hoisr Hivtl are the principnl trilmtllries of thc main strCmn

This is cssentinlly II granite (ountry Lavn J]ows alC (ommon uL the ]OWC1 ehvatiolls within the watershed bllt O(CU]JY ) rplntivel small portion of tIllt whole dmilluge Sedimentnry ro(ks IIle prncti shy(ully absent Illlt grnnite in this stCtion is n part of the intrusion callpd the Idnho hatholith It is alight-lololCcI CoHrst-gmined grny ro(k whi(h onthers rendil into a (oalso flUnd The IImount or weathering is Rtriking few iresh llllclecomposCd pi(ces of roCk being tyicltllt 011 the slIrfa(C Tho minernls making IIp themiddot grnnite nlO grny quart white l1nd pink Illdspnr mninly orthoe1us( hut with SOllW

plngio(lase nnci hio tite mi(n occlIrrmg in smn 11 flnkes 1ht gnmitc is intruded hy dikeR the commolltst Iwing qunrt-ciioritp nnd ppgmHshytitES Few distin(middott outcloppings of thCRC nrc eomnwnl sten hCcuuse of the wtnthCling of the gmnitc hut th(ir o(curlelHe is (idpnt in the flon t found Oil ridgCs mcl in stream channels IhC pqmntites mnde lip of larger (rystals or Clunr Jeldspnr and mUE((wite um comlllon aud sCel11 to be quite gCJ1eml in OCCUITen(e A few dnrk-gleen filHshyfruinfd dikes probably diabnse are found The mntClinl thnt hns ~enthered from these intrusions has influenced the soil but ]ittle

rhe granitic rock of the rcgion clisintegmtes readily forming n coarse sandy gray olYClhwish-grny soil Atower e1cvntions nnd in valley bottoms this SOlI mantle mILy be of eonslcIemble depth but over most of the ILlCn the soil is shallow and the underlying ro(k is found but a few feet below the surface The coarseness of these Boise soils is well il1ustratecl by the mechanical nnnJysis of lepresentatiye Ramples which shows thn t 31 percent (by weight) of the soil is made up of particles more than 2 mm in diameter In addition to this

G lJDCHNICAL BtTLIElIN 528 U S DEPT Oli AGlUCUUlUHB

thc sand contcut of sLightly )11111101 plllmiddotticks flYClflgccl 50 peJ(ent The perccntage of colloidallHntclinl is vcry smnll in most (asCs not cx(ceding 5 to 6 pel(cnt nnd in some instnnrcs CVC11 lpss Soil of this ()htu[tctel crodcs vcry readily in the tlbsencc or n good plunt (ovcr

CUMAT~~

Althollgh wonthcr records for the 111nin wntcrshed are comparashytiYely few those tibnt hnYe becn kept for vnrying periods nt llllJllelOUS static)J1s show n fair correlation with the re(olds Ilt Boise vlli(1t clute hnek to February 1 ISM Only one-third of the Jlormnl annual precipitation of 13 inches nt Boise comes during the 6 months of the growing scnson--April to Scptember Scant precipitation during the Inte su 11l1llel COli pled with high tempcrn turcs drying winds fOm the ntlioicing Snn ke lUyel plnins nnd thc rcsulting excessive evaporashytion mnke difIicult the llInintennnce 01 n YPgota tion coycr Oil the (xl))~(l slopcs YhilQ tho precipitation dlldn~ the 3 summer months is ordinarily Jight sudden J almost toncntinl showers cllusing scycre erosion over 10cn1 nrens nrcmiddot not inhcquent

The suuwjnll nt tho lowcr elevu tions is seldom grcatcr than 25 inches lIlHluSllUlly (()mc~ in smnU fulls 1[11c1y stnying on tho grolnd 101 more thun n week 01 so At llighel clcyutions the 11l1nllnl jnll increascs and rctunins for the most pnl in pIneo Aboye 8000 fcet by Ule time mclting stnrts in the spring the snow coyer uSllully 1CUehe8 7 to 12 feet in deptlt deMO nnd welL packed It is tbis snow muntlo tha t supplies tho water to Jill the storuge leSCIToirs ClillJntic (onditions during tho pnst deendc or so Juwo bcen unfnvorshy able JOl nhuncLnnL WHtel Fur the] 2ycnr period heginning with un9 the nverngo departure below the mcnn annual preeipitution ut Boise was 21 percent for tho (riticHI spring lllonths of April 1hy nnd JU11e und 14 pcrrcllt for the eombinecl spring and summer seasons The nnllunl defieieu(y amounted to 11 percent Only in 3 of the 12 -euls wns l)lc(ipitntioll in excess of the 67-en1 ftYclnge This d(ieiency in Ildclition to influeneing run-off htts been It materiul jaCtur in lcssening the gro-th of yegetntion on the wntershed

VeGETATION AND GRAZING USf

Vide differenccs in the Ycetntion are to he expcctcd ovcr a watershyshed with n lflngc in eleVittlOll of more than 7000 feet Fifty-one pel(rnt oJ the Ulmiddoten (Oe1e([ hy the slllTey is more or Jess open-timshybcred J1 nd j 13 peleen thus brush 01 timbel too dense fol gmzing h~T liYcsL()Ckj 11 perccnt is untimbeled grass Inncl 12 per(ent is oC(llPied by n YHriety of shrubs on 7 perccnt sngehrush is the dominant yegeshytation and tIlo remainder is composed chiefly of sllluil 1l1enS of weed meadow or nslJen

There is evicieIlre however thnt much oj the foothill COllntry onc( supported n Jnidy hellYY stnnet of bUIlch grnsses-muinly whrfltgrnss (AYloPUlon hWlme)-ill mixture with big sagebrush (t)middottemi8ia trishydentata) bu t these glasses JIlTe been tltillncd out 01 nlmosb comshypletely eliminated hy excesshc grllzing Sngebrush hus sllhsequentlY il(Jensed llntjl the C)Tcr except whero recently hUl1lt o(r 110shy(onsists of n stnncl of big sagebrush with a scanty mixture of downy ehess und other linllunl glases nnd weeds At the llighll elCutions depletion hus not progressed to the same extent for there tho unnual

1

G lJDCHNICAL BtTLIElIN 528 U S DEPT Oli AGlUCUUlUHB

thc sand contcut of sLightly )11111101 plllmiddotticks flYClflgccl 50 peJ(ent The perccntage of colloidallHntclinl is vcry smnll in most (asCs not cx(ceding 5 to 6 pel(cnt nnd in some instnnrcs CVC11 lpss Soil of this ()htu[tctel crodcs vcry readily in the tlbsencc or n good plunt (ovcr

CUMAT~~

Althollgh wonthcr records for the 111nin wntcrshed are comparashytiYely few those tibnt hnYe becn kept for vnrying periods nt llllJllelOUS static)J1s show n fair correlation with the re(olds Ilt Boise vlli(1t clute hnek to February 1 ISM Only one-third of the Jlormnl annual precipitation of 13 inches nt Boise comes during the 6 months of the growing scnson--April to Scptember Scant precipitation during the Inte su 11l1llel COli pled with high tempcrn turcs drying winds fOm the ntlioicing Snn ke lUyel plnins nnd thc rcsulting excessive evaporashytion mnke difIicult the llInintennnce 01 n YPgota tion coycr Oil the (xl))~(l slopcs YhilQ tho precipitation dlldn~ the 3 summer months is ordinarily Jight sudden J almost toncntinl showers cllusing scycre erosion over 10cn1 nrens nrcmiddot not inhcquent

The suuwjnll nt tho lowcr elevu tions is seldom grcatcr than 25 inches lIlHluSllUlly (()mc~ in smnU fulls 1[11c1y stnying on tho grolnd 101 more thun n week 01 so At llighel clcyutions the 11l1nllnl jnll increascs and rctunins for the most pnl in pIneo Aboye 8000 fcet by Ule time mclting stnrts in the spring the snow coyer uSllully 1CUehe8 7 to 12 feet in deptlt deMO nnd welL packed It is tbis snow muntlo tha t supplies tho water to Jill the storuge leSCIToirs ClillJntic (onditions during tho pnst deendc or so Juwo bcen unfnvorshy able JOl nhuncLnnL WHtel Fur the] 2ycnr period heginning with un9 the nverngo departure below the mcnn annual preeipitution ut Boise was 21 percent for tho (riticHI spring lllonths of April 1hy nnd JU11e und 14 pcrrcllt for the eombinecl spring and summer seasons The nnllunl defieieu(y amounted to 11 percent Only in 3 of the 12 -euls wns l)lc(ipitntioll in excess of the 67-en1 ftYclnge This d(ieiency in Ildclition to influeneing run-off htts been It materiul jaCtur in lcssening the gro-th of yegetntion on the wntershed

VeGETATION AND GRAZING USf

Vide differenccs in the Ycetntion are to he expcctcd ovcr a watershyshed with n lflngc in eleVittlOll of more than 7000 feet Fifty-one pel(rnt oJ the Ulmiddoten (Oe1e([ hy the slllTey is more or Jess open-timshybcred J1 nd j 13 peleen thus brush 01 timbel too dense fol gmzing h~T liYcsL()Ckj 11 perccnt is untimbeled grass Inncl 12 per(ent is oC(llPied by n YHriety of shrubs on 7 perccnt sngehrush is the dominant yegeshytation and tIlo remainder is composed chiefly of sllluil 1l1enS of weed meadow or nslJen

There is evicieIlre however thnt much oj the foothill COllntry onc( supported n Jnidy hellYY stnnet of bUIlch grnsses-muinly whrfltgrnss (AYloPUlon hWlme)-ill mixture with big sagebrush (t)middottemi8ia trishydentata) bu t these glasses JIlTe been tltillncd out 01 nlmosb comshypletely eliminated hy excesshc grllzing Sngebrush hus sllhsequentlY il(Jensed llntjl the C)Tcr except whero recently hUl1lt o(r 110shy(onsists of n stnncl of big sagebrush with a scanty mixture of downy ehess und other linllunl glases nnd weeds At the llighll elCutions depletion hus not progressed to the same extent for there tho unnual

1

7 EUOSION ON IUE BOISEJ IUVEH WAIEHSlIED

rainfall iR glenter nnd the mnges hn n~ been 1I ndel nntionnl-Jo]cs( legulntioll Thc morc succulent weeds HIC less nhuuclnnt tluUl iil lIs11nl on mOlintninouH lrcns and from n Rtockmnns vim1)Qint the watershed is preponclemntly n grnss country On the upper lenches of thc Sonth Fork pnrticularly nrc extensiC arelS whelc whentgrnsR mnkes lip morc thnn hnlf of the plnnt covel At the higher eJCyntions n]moRt ))llre stnnds of Lettelmnns porcupine glHRS (Stiji(i lettemwni) nncl elk grnss (Care1 jfyai) nre common Arens of n few to seyernl hundred neres of brush nre conspicuous fentuIPS of tbe hndseupe nt modernte elevntilllls Thc cOmill011 Sl1()Whrllslt (Cealloth718 lellltin1~) is the plincipnl species nlthough hittCr chC[lY (PrUJI118 emuljillata) und cOl11mon sClvicchelry (Amelalchier alnlfolia) nTC llsuully nssoeinted with it lv[nny oi these HleUS ale so densely (overed ith hrush ns to precludc tl1eir lise for grnlillg and prnetlshyltlilly nil or them nre nt lCnst ])tlltinlly inaccessihlc to livestock 1h( ojlCllings hl tho timhoI nrc ()(eupi(cl by vegetll tinn (OIlUllOll to most of the otl1(r plnnt types rhe tiJ11bel stnuds nrc quite open excCpt for o(cflsiltmnl patches of lodgepolc pinc or Douglns fir rcplocluetion

ApplOXllnntCIT 4000 cnttle nnd 154650 shepp were grazed on tht )nngCs of the Boise Nntiollnl FOlcst during thc summer gltlzing senson 01 1nos BecaLlsc of the Juyomble 1IIin1nll conditions which obtnined for somC yenlS tlHICI1itCJ it WfiS possible for the rate of sto(king to lcmnin llllchnngcd for the ensuing] 0 ye1rs without oyergrnzing til( runge From lnD to 112G inclusive the numb( of stock ns grndunlly rcduccd but 6 oj thcsc 8 yenrs wele so deficient in precipishytation thnt the forngc produced wns continunlly infldequate nncl tlJ( rnng(s cre deptecinted By 1930 the 11tllnb(r of stock glllzing 011 the forCst hnl beenleduced to 2825 cattle find 75000 sheep but it was (stimnted thn t the sheCp mnges W(l~ still 25 percent oYerstocked purticulnrly in viCw oj the fnct thut uufnyornble elil11fliic conditions prCyuiled Primte und open publie lands within the wntershed but olliside th( llntiollul forCst hl1e hnd but little grHIing legulutioll nnt mp fur Illorc s(riollsly ()wrgluzpd tlnd d(plpoundtpoundd of HlC oliginnl plnnt (0(1

METHODS OJlt STUDY

FA (10 ItS OIlSlmvmgt

Ell( dntt1 WCrC eolle((pd hv n fi(ld party following the usuallrolCst S(Iic( ll1poundthods of lllnkillg in trllsi n lnnpe SllIT(YS~ Arens that dif1PI(d l11uUdnlly in dllune(Cl oj plnnt (OYel dCgl(o of erosion soil rodent inip-ttltion 01 HC(PHsibility (0 livestoek werc outlined on toposhygrnphic map= 1Illt~ d(tailpoundtl obselntiolls on their condition werc 1emiddot cOl(I(ld IndiYid lint lIl(ns WPIO faidy lnlg(1 it YCl1ging 310 ne1(S Some tha t (11( lllUppCd s(palntely wCre as smnll ns 10 tlCIes butmiddot th(se e1(1 nne S[)(cilie iniolllwtioll wus obtained (oY(ring nrious points as follows (1) ))CglC(l or p1Osion (2) gradient (~) tlSpcct (-1) soil (5) plnnt typC (0) dellsity of Yegotatioll (7) )odCnt ini(stntioll (8) ll((essibility to lin$toek Hnd (9) miscelluncous obsc1Ytttions

En(t nrCu was dllssif1Cd tw(olding to foul Plsily recognizuhle dCshygrees of (rosion As might bl expected ill nny nrbitrflIY grouping

bull eSITIW TTE~ I)EPUtTlIpoundST elf AmUtTITlln JmnST lllmln ISSTlttCTIOSS FOIl GIIZISG ltgmiddot COSSAISSISn OS SATlOoII~ IOItCTS middot10 Ill) HI~7 [UmcogruplIlrl]

8 1]~UHNICAL UULL1~IIN ii~ middotC H lgtI~lr Ol~ AGHJCUIJIUHI~

0111( WNr hord(l-ll1w ()(s lwlonging to mOI( thnn 011( class In spite 01 this o(CflsiollUi oyCr1apping how(YCl the dnssification proved quite fEl1siblc Jor the UrNI ns u whole These clnsses arC desclibed below

So r7osioll-rCus upon which the smfuce soil WIlS nPPllICnUy in normul COllshyclition hlIing IlO indirufion of llccelemtwl Hh(ct (lOsion or gullirs

8hre errMioll-Ghtlmctcliztd by eirence of cltrp und mOyelllcnt of the snlshyro ()il on the HIOPCH the loss or top)ltoil and occnsional gulliL~ nut moro thnn 2 flpt in d(pfh 011l of thl striking indicatiolls of sh((t (rosioll ill 1hc ulcu Hinditd was thr (ixcCsl4ilr lCClIllllilfLtioll of Roil abovc the elulllpfi of wlwHigrnss and oihcl (gpttiOll fJltqIlCIIU f1C(ollljgtnllird by undclIlIining (]II tllf loPI Ilticlr (fil 41

ror9~4

FrrilUt- I ~lj(lmiddotf (lro~jOJl o(tPl1 ObStllrt to lilt untlaitlltl (lh~elYll ~hllt ltl1l(1Il t~ l)Vl(CtH lwr( itl th~1 oil (I(lp 01( t1w ll(ul1lUltr ten) of 1IU ((lar$p oil on tlH uphill 01 It-fl sidl of I flo IwulJrt1i plantTJut pro( ifulH-ICClild will rtsult in S(irioll~nilloS~nncl will dIIPII[( till (1~cLtJt1t)1l middotO(1 h~ buryiugalld Jillill~ lOhvJdutl pllIlts

tallrI-(Il11l ()o~inl1~-middotll1CllldiJlg nnUl lIpon whir tlHlc was witiloui (C(PshyIinn widespread llhllt lrosioll SlWlSLring glllliC4 2 f(Pi or Iltss in clpptil rlistrilHltNI nlOIC OJ ](Si on tho (110( slIrface and gullics sccml fpet decp in i he cilnyon hnj(DIlIi (fig 51

j)((p-(lully cr()~iol-~In neldi ion to the C1middotiOll rhm1ci(ri4tirs ]ll(iOllsly indientld lIsnally to be found hele thcse Mcas wple seriously gullhd llot ollly in 1he lOttOlllS of t11( (allvon~ hilt on til lloj)ls ltlld in 1 hn butioms of the tribushytary drailHIglS HIgt wlll (fig HI

GHADJ1-l

T)l( glfldicni of tll( lllnin S]OP(8 flnd stl(HIll (01lIS(5 in cnell atcn WIT meusUlld with lin Al)Jwy hnnd lcycl nnd TPcordCd In CHiiCS of hloklll topoglflphy suffieicnt slope lcndings C1O inkCll to obtnin n lEliub1e ny(rnge for the hole urei

ObserYntions indicated that a malkCd v(1liution in crosion O(Cllrrcd on the difrclCnt nsppcts nnd to obtnin 11 mensurc of this vlllintion the genernl txpOSllrc whether north 110lthenst oflst dc ns lceorded in cuch instance

9 EROSION ON THE BOISE RIVER WATERSHED

f-7 lfJfHh ri -~hlllllwJtllly (ro~ill nth tlwllmJn draltllJtl dlHlIlllls lJI(ad~ (middotw IIllt -Pl 111 (I rlhl (or

Iltrl lwl rupidly (mJmting and ~hl(f tro~ion nnd IIOlstrin~ -lIl1ip1 )(lr th~ PUll)( area a ~tmiddotlIotis lHtk Iuwn ha alrrallr t((ll pl1(l (Ill thi (a~ o( 11

Ft2916 lrIIU Ii Depmiddotgullr crosion The grcllth cnlurged ~trelllll rhllllllri hlll IlIuslnllrd 1- lImru(tlrith (

the SPliOllS lullylll~ (ound Rrouplliin tho hepglllly lrosioll cia In which IIN lrltgtsinll Illd h()(SIill~gtlll)inl Ilrr nlso wJrlrsplrnd TJllllcss(Jr (OrlUS 1)( erosiQII IllI the arll iIIustlattd h Ie 1ll1oUlllf obliltI(j lor linfork mol tho cover o( UUIIOt- UIl1 somo cjfkUl(S II( hcdiug JIl IIjllIlltt

(iSS 11 --aJ--2

9 EROSION ON THE BOISE RIVER WATERSHED

f-7 lfJfHh ri -~hlllllwJtllly (ro~ill nth tlwllmJn draltllJtl dlHlIlllls lJI(ad~ (middotw IIllt -Pl 111 (I rlhl (or

Iltrl lwl rupidly (mJmting and ~hl(f tro~ion nnd IIOlstrin~ -lIl1ip1 )(lr th~ PUll)( area a ~tmiddotlIotis lHtk Iuwn ha alrrallr t((ll pl1(l (Ill thi (a~ o( 11

Ft2916 lrIIU Ii Depmiddotgullr crosion The grcllth cnlurged ~trelllll rhllllllri hlll IlIuslnllrd 1- lImru(tlrith (

the SPliOllS lullylll~ (ound Rrouplliin tho hepglllly lrosioll cia In which IIN lrltgtsinll Illd h()(SIill~gtlll)inl Ilrr nlso wJrlrsplrnd TJllllcss(Jr (OrlUS 1)( erosiQII IllI the arll iIIustlattd h Ie 1ll1oUlllf obliltI(j lor linfork mol tho cover o( UUIIOt- UIl1 somo cjfkUl(S II( hcdiug JIl IIjllIlltt

(iSS 11 --aJ--2

10 TECHNICAL BULLElIN 528 G S DEPT OF AGRIC1l1JIIrm

Soil vas examinCd in ref1pect to t11( followinp Oripin (wlwthCl gmnitic lnva porphyry or mixNl) tcxturC (whCthlI (oalflC llwdillll1 or fine) color (whether light medium or dark) littCl Ilncl humlls (whether lacking medium 01 deep) dCpth (hethel s]utllow degto 1 foot medium 1 to 2~f feet or deep 2H feet 01 more)

Each alelL was elnf1sifiecl nccordinp to the distinguishing plllnt C()Cl

as grnssland mendow weed sl1ge1gtrIl8h hlowsC timhCl nongll1zingshylnnd in denso timber 01 brllsh pruCticnlly hnlTClI und aspen

DEXSITY OJ YEGETATLOX

Density of yegdation ns rCCordcd WIlS consicCrNl to be that proshyportion of tho gronnd smface actunlly COYclCd hy herhnceous nnd shrubby YegeLlLtion within rcnch of liycstock (less thnn 5 fect in hcight) estimntcd and expressed on IL pcrcentage bllsis A dcnsity of 50 for cxample indicatcs thnt onc-hnlf of the ground surface is completely COYClwl with s~J(h YegCtation The important species were also recorded and their relntiye abundance cxpressed as it l)Crshycentnge of total Ycgetation -

Tn rccording speCiCs nnd dCpI(( of infCsflltion of lo(lcgtnts infestnshytion wns Cstimnted ns nonC 1ight ])wdillm 01 hCHVY lh( netunl IHlmher of rodents SCC11 by tho exnminel llnd the nhuntlnl(c of mounds bUllows runwnys 01 other cyitlClHe of their plrsen(C goYclllcd the estillln tC

AC(ERRIlllI]rY 10 UYERlO(K

DCg1C( of pnst glnzinp wnslC(olltl((l nt least in It 1l1rnsUlC in tCII1lS of 11((Cssi bility to 1iYCstoCk AIIJ)(H1gh (olHli tions Yllli((l flOlll OYCIshyglnzing of the more open JIlllge to non usc of tJw densC pntchCs of brush n nd timlwl dilect menSUlClll(gtn t of the n((llll1uJntiyc CfiCCt of pnst glllzing lise did not Ilppeal flflsihle Since nll of the lnnpl normally llCcCssihle to liyestock hnd however beCn ColllpletCly 11 tilizCd the ltleglcC of prnzing Yllied with the ltiCglee of ll((essihili I) in CHeh (ase iCwNl in this light thc degl(e of aCCessihility of any nlC1L offeJCl nn indilcCt melSU1( of Ow glflzing fador Thl nc(cssihility of nnv 1llCll of rllngC YlJiCs with such fHct()rs ns st((~pness of slo])C clinJlletC of 01( sulfn(~e of themiddot groulld sizc nnd density of tho brush and stll1Hling Ilnd dowll timhrr distnIHC to WlitI nnd lluturnl hnlliCIs These fndors were tnkC1l into c()l1siciCrntion in Jnting C1ICh nlen for accessihili ty

In ndditioll to the nhoyC (ol11]lIChCnsive f1Cltlllotps CI( made fol (Heh ll1l1 to indi(lltC such othCI faetol8 nfftct ing (ondi tion~ ns eyishylienee of henY trniling l((Cntiy bUlllt-oyel a1C118 nnd the Hkt

IlInllODS Ot AgtI AI )SIS

1n (lJ(1l1 to bring out thCI()lntiollshipslWIIt1l ihc (Iasses of losiol1 Hlld cHeh of thl s((n plilllipliI flldols studi((l th( dlltu (1( groll[JCd

11 EROSION ON THE BOISID lUY1lR WATERSHED

Ilccording to the fgtcYelnl rlnssifielltions of n patticulHr IncLoI These vllrious segregations nrc shown Intel in tnbl(s 1 ~ nnd 7 to IO

The ratio of the Ylllianec of thc meuns of tho groups of n fnetol to the ynrianec of nIl the groups eombiu(d measures the influOJ](c of tllllt Iador upon closion Hence it neeounts for n d(finitc p(leentllpf o the yttrinnce in erosion In statisties this lIltiO is often denoteclln ihn

Hymbol1)2I1x so that 1)2I1X=sect~fft3 d~J und tbc Sqllt1lC root ol thiH Htio 1)yr is cnllcd the eOlrelntiou ratio or 11 on 1 where J is thc dcpenc1cll t Vfllishyable nnd I lheinciepcndcnt vnJinblp In this study lIreprcsents eOsion unci l the plIJticulnl fuetor whose influencc on crosion is b(ing consiclshy(1((1 In the abovc f01l11ulnj is the number of ittms in CHc1l IIITnYJ tht originul items 1jx the mcnu of Nl(h fllTny unci fj thc gCl1clul mcnn

To test wlHtlwl nn obsclwcl vnIlle of the cOIleIl1tioll latio is signifishy(un t is to teHt whether the vILritLtioT1 hetw(ell (LlTHyS is sigllificnntly grcuter thun is to he expcet(d in the llbsPIHC of difl(lentiatioIl from the VllrilttiOll within the fl1TILVS This (1111 he done hy the nunlysis of Yllriltn(e J11(1thod6 l(n- this t(st WILS ILppli(d to the YILllOUS elftssi(i(fttioTIs of the erosion dntl1 the ohs(wd (o1lPlntioll ratio wns ill eV(J)r (nse found to hc signiflcllnt This WlIS true dpspite the fILet ns it will he no ((1 htel thILt some of the mtios WPlC quito small Thc lutios us d(s(ril)(d nhoye not only show what p(l(pntnge of tho total YltrilU1(C of PlOsion is nssoeintcd with (neh fl1(to1 but the l(lntiyc infllltlHC o one f1l(tOl IlS (ompnrCd with aJlotllCI

The dl1tn rOl tllP lHHi al(as (1( (o(](1(1 Hnd JluIHhed on eILlds for Olting Ilnd tfthulnting hy mIL(ldn( Rllntionships on the hasis of

bull For n (OIPJtot~ (((s~riJltion or (he (olllpu(nliolls US(middot(( ill I ills huliNlu N the (()liolliJl~ -rllloR F C -ITtTqTlfAf ~lfoTII()JH ~lIIII1-~1J TO lltrOO~lIrK -n Hmiddotstss pp middot11-middot150 pw York Hl2L As nn jJlu~tralionJ Ill- (Iompututiou- for dl t(1lminillj the vnriunel in lrosion uS-1(J(intNi with lHctsihility follnw

I ~ Ifl I I IIu 2 a I

lnl II I

S Jjl~I1 [IIz-- iill] r 0210 I

SOil -201 SlIIIr-lill i1t ~ bull

81111 -II ~1 II =J I d

S(U~I ~middotI17fi

(IJ Irll) bullbull JJ

k IJ --

(ornlj ion for lrotlpitlc ]tJ middot kJ l)(ln~ k i~ lIw JlIllllhlr o(llrray (ill thil (USP kfl)~ 11(111(1 1l1=(1 Irt 1-middot

Ihis UWlIIS t hut JiJ 1I((lrH of IIH- vtlrialJel in (rusiull is lIs~(l(inlld vdt h uN(dhilitmiddot t hll r1Htor e()nsjdCrt~ll FIlnIl II lTlTIHllJ III1IIOP 11111 IIJSI~Jlrll W()JlKIlIlS id middot1 p ~a tilniJur~h und

IIIndol1 lUl2

12 TECHNICAL BULLETIN 528 U S DEPT OF AGRICULTURE

number of nrens nnd of ucrenge wele found to he so nenr]) identknl throughout the study n8 to permit the use of either for the purposes of this ullnJysis ltor exumple tuhle 1 ulIots 443 111011S Ol 375 perCcnt to the no-erosion clnss I1ncl the ncreflge of this group is 126R58 out of 337913 flCles or 372 percent B(CILllse of tiw CHse in tlLbullLting the slllnIler figures flreas were llsed in the flnnlysis AIcl1s on whieh field datIL were inomplete with reglLJd to some plLrticulul fflctor were omitted in thlLt connection This IL((Olmts fol minor r1iflelellc(s in the totnllltlIllbel of nrens in some of the tnbl(s

INIltLUJ~NCE OF VARIOUS tAClORS ON EROSlOI

GHADlgNl

Th( pOL(JltilLl impolltu)(p of gmlt1i(ll1t II u fILlllll ill the Il(telemtioll of pO-iol1 on thp Bois( HiyPl wat(Jsiled is inltiilnted h~c tlH fart thnt

i 100

~ d ~ 80 +-_

V) t

~ fO

RADiENT (fRCENT)

oNO EROSIOj~ 0 SH~ET [ROSIOn bull GUll) lROSION

lmiddotmiddotnitmiddotJU~ 7-0rudlcnt HIlI degree of erosioll

tllp gmciienls Oil four-firths of till ttlPItS (xUJlliIHlt IUP in PX(CRS of Hi l)(l(pnt It J-CJl1S (JhYi()lI~ tiHtt with otiJPl fl1etors (olltnnt tho gllUtPl til( Riopp the greate( the dq~ree of PIosioll Thllc filollld ill OJlPoltunit) for tbe soil on slopes oOow gmdient to tlbsorb l11ueh of the pIe(ipitation from oldinnry rains hefore thcre is an ItCCllJllUlution of mt(1 on the surfuce sumdcnt to stnrt cxcessive llosion The force of gll1yity bccomes more (fT(dhe as the gmdient iIHrCUSCs with the nRult thnt witteI which fdls to the ground tends to run oIl more mpitllv nud (ouseq uen tlv glelltel opportunity is nflorded for 1un-of to nccumulrtte jntn smiddotift-f1owing strenmlets Furthermore the stcepcr tho slopes the more likely l11e slight disturbances by rodents gmzing I1nimals ILnd such ngen ts I1S wiud ILnd frost to cl1use n conshysidcmbly incrcnsed downwnrcl movcment of the soil

As shown in trtble 1 and in figure 71 the proportion of eroded arens increl1ses sharply bu t consistently with inclcrtse in gmdient up to rtpproximntely 35 perccnt The 21 percent of practicnlly lenl IIIpus-thmp hnying gInclients of 5 percent 01 less-that Me eroded

7 In Og 7 iludn similnrrhnrts whfrh foHolI tho datn inllw two (ullyerosion elosses have b~cn combiued to urJcg OUL cleurJy the scneruJ relationship bel ween tbu urfolls Illctors UD(J sull erosIon

13

r

middot EROSION ON THE nOISE RIVETt WImiddotl~HilH1W

nre subject only to sheet erosion The percents of l11el1 with gully erosion increase from 0 to 4 8 and 10 for the respective foul lower gradient cll1sses Although 6 of the 117 gullied areas havc grnclients of less than 26 percen t in each instancc factors other thl1n steepness appear to account for the erosion iive of them hltd blen tmilcd ovel~razcd nnd trnl11plecl much more soverely than the othors On the sixth gullies hnd eut through from 1111 adjoining arol1

TATII)1 lmiddotmiddotmiddot-J)l~llaJ1l1ion oj orcas in cach rrosion clas~ (lccoldlll(J 10 II(l(if III - ------~-------------

I No Sitelll I Hhnilow i It( 1bullbull(IIUdIQut ltln~~ (PlIlril erosion (rllsloll ~lIlil i ~1I11~ j AillllllSJ bull troslOI1 (IroSlmt ~

--------------- NU11I11If ~I Nil) ~I-~Imiddot_It1 1- O-i 11 a II r I 2 jj--i 12 11 I ~I 2 II

M~~~ ~a ~8 1~ -~ M~~Omiddot Itl~ If ~ 31)-15 06 12( Ja 2 217 20 I lttQ-lW 80 150 2S 7 2~ 21 2 m-I Iln lU3 25 a lao 2~t ur-i iU 3 li 5 tfI H ill-~ fi 1 bull M_~ ~~ i 0kfI+ 7 bullbullbullbull_ 7 11

lO(IlI--t ----m-1--oq-~2i --I) -00-0 --~------------ _-_ --- -- -

TIll ti(nd tOWllld intlnslt elosion with il1crCnsed gmdi(nt is 110t found howev() 011 ao- to 05-]gte1((11 t slopes Ill1d on grndicn Is steeper t11nn Go pelcen t the degree of crosion is n(tuuIly Jess s(Jious If0 I

IxnmpIc nllUS with 56- to 05-pllccnt glHdients hnVl) nn oven smalIcl PIOPoltion of thlit number gullild l~ncl olll~ H slightly gr(nter P1OshypOltWIl shlci-CIodNl thel11 thl 111II1S WIth gIultilCnts of 2G to36 pPIc(nl H would aPP(n tIHIltfOIC thnt sonw Jn Cto I 01 fldols 0111(1 thnn sl(CplHsS mC illvolnd Ill( I1tio of Ihp vnliall(( of i1)(1 llI(nllB of (osioll etlBSPS 101 (Heh glHriient clnBs to till vnlinncc of nil tIw grollps (olllbill(d rus found to Ill 0020 which indicnltmiddots thnt l) pprc(IIL of ill( HIlability in PIosion is duC to grucii(llt it JigTII( of smnll siz( uithollgh signifknl I

ASIgCT

Erosion conditjons 111( found 10 diO(I shnlply in tlte dinNenl direcshytions of (xposur( Ill( lttntn on til(gt r(lnlion of nspcCL to (Iosion 111(

slInJmulillPd in tuhlP 2 lilt shown glnphicnlly ill figllle 8 ArCHS JlCing thc south 11(1 in tI( most s(liolls C(lIldition with fOlll-fifths of lIll RII(h 1llPI1S (1Olti(d ElOsion Icss(J1s grl1dunlly with cIlHnge in (lXshy

POSlIJO to the sOllth(HSt (ust sOllthwlsL Wlst northwlst J1orthelst lind finn]]y to th(1 north wh(ll it is ollly hu1f ns prlvnlen t ns on SOli ill (xpOSUlefl Ill( ploportion of IIlcns gullied dolS not follow (xnctly tillS order The south nnd southeHsterll nspects Hrl tho most flPiishyously gullied but the nOithwest instenlti of tIH 1101tb(lly (xpos(d nrens HI(middot til( 1(IlRt gll]Ji((1

---------

---------- ---

14 (ECHNICAIJ nUrJIJE~LIN 528 U S DEPI 01lt AGRICULTURE

TABLE 2--Distribution oj areas in ~ach erosion class according to aspect

Shallow- Dcep-No SheetSIlCtl tlnSH gullr fulr All nrens erosion erosion erosion erosion

I NUlllfJer NItlflJer Nlmber Number trltmber PerCftlf

Soulh __ ) shy- ~5 J()O -I 0 17i 157 touthensL ali ib 2a JI HS ll EnsL 21 -19 I 2 oj 72 routhwcsL middot12 111 7 Hil H a WesL la 54 )i IIi s1l KorthwesL 7S 81j (J U 170 150 Karthensl (HI -15 Ii 0 1III U7 North_ JII 07 H I 11)5 III

-~-

Iolnl Iii 5f11 H2 21 J 12f1 IC~JO

~ _--J fH nrem er(~ (~itlllr ItI(ll 01 lxtrellwr uried ill nspeet nud were t1xlludltI from thfs tnhlc

Thesp 111nrked difl(lPJlees in (OSiOll nre trac(ahle to conditions inhppnt in tilt diflPlPI1 t nSJ)(ds Jhe lelntiy( importnne( of gmdiPT1 to

r[- ]tl lt

~ 60 r--- h _1~ 40 69 t (J

Ci 4J

D-- _ 60

j11 13 14 5 10

SOUTH SOUTHEAST EAST SOUTHWEST WEST NORTHWEST NORTHEAST NORTH

ASPECT

oNO EROSION 0 SHEET EROSION bull GULLY EROSION

IlS 11 Jllrtor in (o~iol1 hl1s lwel1 hrought out It is nppalent thnt tll( SIIJl1C tr(nd townrd lt1((](11$((1 (Iosion on steeper slopps is opcmting 11(IP 11(( north ns[wds wllich htp nn nNnge glndient of 55 pe1shy((nt ne No(hd eonsid(lnhly lpss thnn south slop(s with fill flYlrngc grlldi(11 t of 45 percen L Difi(I(I1((s in soil Y(g(tfltion cpglee of rodent ill f(stlttioll Ilnd aC(Pssibi1i ty to Ii (stoe k--Jnetols natulnlly nssoCill ted with nspeet find whose impotnl1(t ill erosion is brought out 1111e1shyynry (ollsid(lfthly with direction of slope Ilnd dou btless are more responsihle for (Ix((ssie erosion on teltnin slopts thnn the exposure itsplf The eomputations indicl1te thl1t 106 percent of the vuriance of erosion is nssociated with aspeet

SOli

Jll ftl1nlyzing the relation of soil to (rosion (olrrlations el( made of tile oligin of tll( soil its tlxtlJlO (010 nll10lnt of litt(1 Iwd hlJIlls w(sent Ilnd dltpth of soil

15

J

tshy

~

EROSION ON THE BOISE ]UVl~lt WATERSHHI)

Thnt origin or Ol( soil hns playcd S0111( pnlt in the dcgrce of cIosion is shown by the fact that 63 percent of the alens haying glllnitie soil containing a high percentage of new gritty 1l111terial deficient in bindshying properties were eroded whenas only 49 percelJt of the areas hayshying soil chiefly derived from laya 01 porphyry showed elOsion FurshytherJllore gullying was found only on areas with gmnitir soils

Coarseness is an outstanding characteristic of the soils on the area studied Mechanically analyzed lepresentntive samples ha ye all nnlIlge clay content of 9 percent nnd nIl flvemge silt content of only 10 percent Conrsel Jnaterial makes up the lellHlindel the average sand (ont(llt 1)(ing 50 p(lc(nt with nn ndditiOlln131 percent mnde up of piuticl(s in excess of 2 111m in diamctcr

S(grCgntiollor the dntn by soil-kxtulc clnss(s togethCI with the degne of clOsion round to nccompnl1y 1h(se soil conditions indicates thnt texture (xerts nll important infhWIHP upon eORion As shown in tnhle 8 (rosiou hoth sh(et nnd gully wns lpss tlllln hall as prpVIlshyllTlt 011 tIl( jine ns COJllpnl((l with the COHrSI soils

TABTl] 3-DistribulioL oj (ca~ iii each rlospoundot class accordin(J 10 ~()il llrtllrc -----------------------___----_

I So fhc~t )1~nl1o- I~P ero iOll erosioll ~1l1I) ~ul) All nrtl~

j ~ lroslon lrUSHHI f ---1--------- -------- shy

IXlwher Number Nlllllber JVlllllhcr NU1IIllfr mill Vitw~ 2middot1 10 0 2 31 3 middot1 tediullI _ i lIH Hi H I a 3jS 31Coarse 0 --i~~--j-g___IS _~ ~_fo2

__~I~ __ ~______-----i__ai_b--I_ 51l S3 2l J ()middot14 I lIX~(kl

IVhiltgt tll( colol of (he soil does Ilot influPl1(( PIosi-ity Ynlintions ill color oft(11 il1dicl1t( dilTplPllc(s in othcI plop(Itips thnt do hnp Owt (frCct On this wntNshtd soil (010[ is mninly nil indicatoJ of til( ])1PSPIIC( 01 nlgts(II)(( of olgHllie Jllltti(l in the soil lJ)lllysps or tlU rplation or soil coinl to (lOsiol1 -(10 Jound to ngl(H closely with tllp Ipsults on dpptlt of littCI nnd humus in ldntioll to (Josion nnd only tho lit tt(l is J1PI( disCllSS(d

Ac(umulatioll of a jittp[ (0(1 is normnlly a slow PIO(PSS lInd(I tlc Rpnrs( ypgPlatioll of a spmiulid (Iimntp With hPHY glllzing usC milch of the Cg(illtioll J1IHt(IinL thnt othplwise might hne gont into rnJichJl1Cnt of tIl( Roil (ithpl is Jelllond through HCtllnl grnzillg 01 is so brok(11 11 p h)r the lPPC1l t(d trniling lJl(i tablo uncipl such IISP that iL is (Ilsily (IUTipd Hlly hy wind nnd RlIrftHe run-olr Ill( ltxUnL of h(

reducUon in olganic J11llttlr ill]HI((nt of lIHIogpn nnrt in nPI-holdshying cl1pH(i (yon (Jocl((l soi Is ill th( Boise WII t(rs)Hd is RhllWIl in tn hIe 4 Trpmendom dif1(1(II((S W(IP found h(tP(ll uncrodpd soils and the elodpd phns(s of the SHIne soils Jl(il signifiCllnee 1R indicntNl hy eorrplations b(twPPIl wn tN-JlOlding cnplleity a primp fllctor ill the croshity oj soils nlld orgnllie maUrI The lnrgc siz( of this cOIlllilshytion coeHi(ipnt (O)34iOOV) indi(lllps thllt the nhilityo( th(sp soils to hold watel dCl)(I1(ls lnJgplr 011 thc (on itn t of orgllllic mnttpJ

IG lECH-ICAL BLLLElIN 528 U S DEPT OF AGIUCUlJrURE

TAnLr 1- -Chemical and 7Jzysical (naly~i8 oj compurable eroded and ullcrodec1 soil~

Jroltlel I 1llerd~(1 ~(1l oils

J-ae nt p r(~l ill Orrttrlh Ulltlpr ~ 17 111middot1 ~trot(lrl 1lIS bull al~ rUll1 rholdlur rlltlil y 11middot1 II

-----~-------

Tlwt tlie nmoullL or Jittpl and ltUlllU ha~ liad an impolllint prrLCt Oil tlie posiyity or the soil is shown in tnble 5 A((onling to tiI(S()

dntn sh((t PJoiull is molC than thlPP tim(s liS pl(Ynl(nt (il ])(II(ent) 011 soiLlnckillfjnlitt(l nnd hUlllUigt OJ lindng on1 nl110d(Inte nlllollnt ns on nlPHS with (I((p liu(I nnd humus (18 p(Iccnt) In (n11 gl(llt(I (ontlnst gully Plosion is 2 tUl1PS 11 ])f(yulent WIHIP humus nnd JittPI is lncking ns on nlens whem this P10 t(etin CO-(I is c((P In no cnse WflS d((p gully (1osio11 nssocintCC1 with lt1((1gt lithl nncl hUlllus

TAmE 5_middotlixlriiJuliol of areas in cach cllmon rla~~ (If(orriill(1 10 fllh oj litler (IJlff 110171 (Iud deplh (If soil alour

(T(lTlTlIXIl ro IHITH OF LITTEH AXil Ifl~Il

-hallowmiddot I)rfpmiddotXII hN1 (rojon troion ~lI11y I gull

pro~joJ1 lrH~ioll

Su mill f ~Yllmllr Xumtur UIl11 r If II ~U Ii I-[dlUm 11 a1ft tu )1 ~Ii HJ 1 II

IMI 1m II

~ llht Ht H 2 I J(middotJUJU In i 1(1 l~ I 11 1bull 1 lhI flY I I II W Ilt I

ii 2 n I t171 10(111

lllHII-cmiddotd dl(S( in P(OiOil lIS fOUllel with in(l(gtIs(d dppth or soil - do showll ill tnbh ) oilly ~() ])(f(pn of the l1(IIS (Iasifild liS IUillg ltI((1l Hoils (IP 110((lt1 ns (olll])al(1(1 to (j3 P(I((nt or th( a (P1S wit lr soils of lll(d i IIJll d(p t h a lld 7) ]HI((I t or lhos( wi II shlillow Hoil ~1()1( tlLHI1 OI1-hllf of tll( soil al( tllntwp( sllllilow and m(dshyium in dlplh ~how(lt1 sli(d Plosiol1 while only 2J pPJ(pnt of lll( dNPshyHoil untlS (1( shNt p(oded 1(11 ty-thl(e PlITPU t of tlu n l(tlS h ( 1(

the soils (1( shallow w(n~ gulliId us comptllld with(j PPI((lIt or soils 1l1vdiUJIl ill ((pth Illld I perr(nt of the nltllS with d(tp ~()il~Xonl of till d(pp lltoils WlS found to hI d((pl gulli(d

H (l(HI th(sr linding nr( probfl hImiddot not Imcen bIt it dtp th 01 soil nlol1(gt Tbl d((jgtPl fioils (1( found to ha ( gllH tpl Hcum uilltions of litt(I lind hllnu~ 1(gt1( dso rim in kxtulc W(I( found Oil WIlt(1 ~IOPlS nlHl 111l n dlns(l (0(1 1I(1(1s shallow soils (IP nssoeiutpd with (OtlISl t(xtUlt st((ppr grndients and thinner plant (ovel

EROSlOX ON ruB BOlSE IUmiddotE1t WATEHSHED 17

The eomputcd variance in erosion 128 percent which is associated with the combined qunlitics of dcpth of littrr and soil depth indicn tcs the marked lclntiollship betwcrn thesC soil rhnlacteJs and erosion Ylu]e othel factols have hnd their pnrt in inc ueinp erosion in thpound Boise RiveI wntpJshed thpil pCCt hns plOhnhly bcen inclensed mnnyfold b~ the pccuiiul CilllJHct(J nnd PIC~(nt (ondilioll of the soib of this nlCa

The lr]ation bctwcell plHllt type Hilt (cogne of crosion ifgt indicnted in figult 9 whicil lcplCsen ts glll phirl 11 tlH CJosion (onditions found

IOO~middot---

i8) ~--lt tr ~ I 60

~ 70 lt

~ ~Ot--~ _1__

~ zo

oNlJ EROSION 0 SHH r ERuSON bull jut L Y CROSHN

JOt Cneil typ~t~ Uull lIosi()1l is fllllticllally bad wi 1(1( thtIpound is II w((d conI flhppL Plosioll i~ id(S[)Jtlld lInd gullits H lC sClious ill gJilSS sngebnlsil hroww nne tillll)(J llJrnfgt RIHCt CIosion b ioulld onI purts of Ill( nS[H1I nnd JllCIHlow lllHfgt but tilCit aCI(nge is so small thut they nrc unimportant Whilt both sll(tt alld gully (Iosioll 1IP found ill tht JlOnplIIzing typr tht 1H1(pntHg(R nlC 1tlntivpl sllInl Tht lltUllhplS of 1I1tIS by iqH 11( gi(1 in tHhlp (i

~tl lfo tuH

~1l(Imiddott flrOlIl)

hllomiddot llIlIy

JIIlun

IlICImiddotmiddot lIly

lrowll JI nnJshy

w(c bull ____ (lruss Stt~lbrush Browse Timher A~p~n ~Icndomiddot X(JJl~rrnzin~

~Ilmt Ii

Iii 41

i 1

tjl

Sumrr

111 t

middotIh

fotul III

~Still nncHhcr (YP( hlrr(lll HS nttoJniwd ill tlw fi(ld wurk tllu hlrnttl tYJi(l iurludes areilS ith flO ~gclutinll Qr with Jlructlt~lIy II 0 Ill 1l1 macl( up o( rock ~lid~s Clilfs llc Jhlin no ~()i1111 eroIV this lyp has beCIl climinated from further (onsidcrruioCl

1 R LE(U-1ICAL DULLETIN 1)28 U S DEPT 01 AGmCULlUH1~

The woed is the most seriously eroded of nJI plant types us shown hy the fud tlutt 75 percent of the weed alcns nre ltroded and 111010

tban half of those nre gullied 9 Pnst excessive glU7ing undoubtedly caused the replueement of the o1iginnl yegetfitiou con1 by one poorly udfipted to resist erosion In con trust to thc dense fibrous root systems of the original bUllchgruss cover the present dominant piunts of this type ure largely shallow-rooted unnunls ltr perennials with a single tuproot Among the latter arc pentstemon (Pclltstemon spp) lupill~ (L7lpinlls ((lucatus Itl1d L tenflhl8) und alpine buckwheat tlconogoll1l1n pliyfoiaccaejolium) Suell sppcips are 1l1lclY 111a t-folll1 ing

Fllrl Hi HI tn1U-((t throUImiddotdl OIW of tlw lUpiries f n dominnnl plan I III tlw wlt1d IYPl sho iug hu the ~lIlgle lapruoL is forcltl dowll thu ~loJ1e nud lill plaut plrtidly hurlNI hy sheN lro~iou

and thCil slender stPl11S anti scant root sYstpnls olrc little rcsistnll(( to elosioll The chalHeter of the root RStll1IS of Ollp of the molp comlllon plants of the wlpel type is shO-n ill figure lO Sincc till w(NI anas H(C usually found nlol1g sh(tp dlin~wtls 01 otlHr exposld sitls wllNe the fioi I is shallow and su bject to cOllsiciem ble wind erosioll it is to be expedld that Nosi-c conditions woul(l Ill mom sl(ious ill thC cpel tbun in any otber type

GUASH

The gmss 11IpUS include opCn pntcli(s or whpfltgrnss olcasiOllul stands 01 gian t JYpgrnss (ElllJnlls (on((118(( tIll) LcttClI1UlllS POlCU pilH gruss fllld OIl thc OYCrglH7cd arCHS nt lowcr llentiolls lxtcnsivp

tIn tho tJMwl J1ro((~ss(s of plant SU(i~sion in l1w Hoil regiun (ht) hUl1(hgrasSl~ (UlIU till elimns her hll(IOUS type und weed nnM ilrl III thIllSI(US usulIlIy the result of sonil flttor of (i(llrIJaIlll Althou~h they cOnlprlSI hilt II slIIull proportion 01 the entire ureu lho weed IIfCOS huc bccnlnclullcd in lbe IInnhsis hc~allso of LIIS Slgnificunce bull

12 TECHNICAL BULLETIN 528 U S DEPT OF AGRICULTURE

number of nrens nnd of ucrenge wele found to he so nenr]) identknl throughout the study n8 to permit the use of either for the purposes of this ullnJysis ltor exumple tuhle 1 ulIots 443 111011S Ol 375 perCcnt to the no-erosion clnss I1ncl the ncreflge of this group is 126R58 out of 337913 flCles or 372 percent B(CILllse of tiw CHse in tlLbullLting the slllnIler figures flreas were llsed in the flnnlysis AIcl1s on whieh field datIL were inomplete with reglLJd to some plLrticulul fflctor were omitted in thlLt connection This IL((Olmts fol minor r1iflelellc(s in the totnllltlIllbel of nrens in some of the tnbl(s

INIltLUJ~NCE OF VARIOUS tAClORS ON EROSlOI

GHADlgNl

Th( pOL(JltilLl impolltu)(p of gmlt1i(ll1t II u fILlllll ill the Il(telemtioll of pO-iol1 on thp Bois( HiyPl wat(Jsiled is inltiilnted h~c tlH fart thnt

i 100

~ d ~ 80 +-_

V) t

~ fO

RADiENT (fRCENT)

oNO EROSIOj~ 0 SH~ET [ROSIOn bull GUll) lROSION

lmiddotmiddotnitmiddotJU~ 7-0rudlcnt HIlI degree of erosioll

tllp gmciienls Oil four-firths of till ttlPItS (xUJlliIHlt IUP in PX(CRS of Hi l)(l(pnt It J-CJl1S (JhYi()lI~ tiHtt with otiJPl fl1etors (olltnnt tho gllUtPl til( Riopp the greate( the dq~ree of PIosioll Thllc filollld ill OJlPoltunit) for tbe soil on slopes oOow gmdient to tlbsorb l11ueh of the pIe(ipitation from oldinnry rains hefore thcre is an ItCCllJllUlution of mt(1 on the surfuce sumdcnt to stnrt cxcessive llosion The force of gll1yity bccomes more (fT(dhe as the gmdient iIHrCUSCs with the nRult thnt witteI which fdls to the ground tends to run oIl more mpitllv nud (ouseq uen tlv glelltel opportunity is nflorded for 1un-of to nccumulrtte jntn smiddotift-f1owing strenmlets Furthermore the stcepcr tho slopes the more likely l11e slight disturbances by rodents gmzing I1nimals ILnd such ngen ts I1S wiud ILnd frost to cl1use n conshysidcmbly incrcnsed downwnrcl movcment of the soil

As shown in trtble 1 and in figure 71 the proportion of eroded arens increl1ses sharply bu t consistently with inclcrtse in gmdient up to rtpproximntely 35 perccnt The 21 percent of practicnlly lenl IIIpus-thmp hnying gInclients of 5 percent 01 less-that Me eroded

7 In Og 7 iludn similnrrhnrts whfrh foHolI tho datn inllw two (ullyerosion elosses have b~cn combiued to urJcg OUL cleurJy the scneruJ relationship bel ween tbu urfolls Illctors UD(J sull erosIon

13

r

middot EROSION ON THE nOISE RIVETt WImiddotl~HilH1W

nre subject only to sheet erosion The percents of l11el1 with gully erosion increase from 0 to 4 8 and 10 for the respective foul lower gradient cll1sses Although 6 of the 117 gullied areas havc grnclients of less than 26 percen t in each instancc factors other thl1n steepness appear to account for the erosion iive of them hltd blen tmilcd ovel~razcd nnd trnl11plecl much more soverely than the othors On the sixth gullies hnd eut through from 1111 adjoining arol1

TATII)1 lmiddotmiddotmiddot-J)l~llaJ1l1ion oj orcas in cach rrosion clas~ (lccoldlll(J 10 II(l(if III - ------~-------------

I No Sitelll I Hhnilow i It( 1bullbull(IIUdIQut ltln~~ (PlIlril erosion (rllsloll ~lIlil i ~1I11~ j AillllllSJ bull troslOI1 (IroSlmt ~

--------------- NU11I11If ~I Nil) ~I-~Imiddot_It1 1- O-i 11 a II r I 2 jj--i 12 11 I ~I 2 II

M~~~ ~a ~8 1~ -~ M~~Omiddot Itl~ If ~ 31)-15 06 12( Ja 2 217 20 I lttQ-lW 80 150 2S 7 2~ 21 2 m-I Iln lU3 25 a lao 2~t ur-i iU 3 li 5 tfI H ill-~ fi 1 bull M_~ ~~ i 0kfI+ 7 bullbullbullbull_ 7 11

lO(IlI--t ----m-1--oq-~2i --I) -00-0 --~------------ _-_ --- -- -

TIll ti(nd tOWllld intlnslt elosion with il1crCnsed gmdi(nt is 110t found howev() 011 ao- to 05-]gte1((11 t slopes Ill1d on grndicn Is steeper t11nn Go pelcen t the degree of crosion is n(tuuIly Jess s(Jious If0 I

IxnmpIc nllUS with 56- to 05-pllccnt glHdients hnVl) nn oven smalIcl PIOPoltion of thlit number gullild l~ncl olll~ H slightly gr(nter P1OshypOltWIl shlci-CIodNl thel11 thl 111II1S WIth gIultilCnts of 2G to36 pPIc(nl H would aPP(n tIHIltfOIC thnt sonw Jn Cto I 01 fldols 0111(1 thnn sl(CplHsS mC illvolnd Ill( I1tio of Ihp vnliall(( of i1)(1 llI(nllB of (osioll etlBSPS 101 (Heh glHriient clnBs to till vnlinncc of nil tIw grollps (olllbill(d rus found to Ill 0020 which indicnltmiddots thnt l) pprc(IIL of ill( HIlability in PIosion is duC to grucii(llt it JigTII( of smnll siz( uithollgh signifknl I

ASIgCT

Erosion conditjons 111( found 10 diO(I shnlply in tlte dinNenl direcshytions of (xposur( Ill( lttntn on til(gt r(lnlion of nspcCL to (Iosion 111(

slInJmulillPd in tuhlP 2 lilt shown glnphicnlly ill figllle 8 ArCHS JlCing thc south 11(1 in tI( most s(liolls C(lIldition with fOlll-fifths of lIll RII(h 1llPI1S (1Olti(d ElOsion Icss(J1s grl1dunlly with cIlHnge in (lXshy

POSlIJO to the sOllth(HSt (ust sOllthwlsL Wlst northwlst J1orthelst lind finn]]y to th(1 north wh(ll it is ollly hu1f ns prlvnlen t ns on SOli ill (xpOSUlefl Ill( ploportion of IIlcns gullied dolS not follow (xnctly tillS order The south nnd southeHsterll nspects Hrl tho most flPiishyously gullied but the nOithwest instenlti of tIH 1101tb(lly (xpos(d nrens HI(middot til( 1(IlRt gll]Ji((1

---------

---------- ---

14 (ECHNICAIJ nUrJIJE~LIN 528 U S DEPI 01lt AGRICULTURE

TABLE 2--Distribution oj areas in ~ach erosion class according to aspect

Shallow- Dcep-No SheetSIlCtl tlnSH gullr fulr All nrens erosion erosion erosion erosion

I NUlllfJer NItlflJer Nlmber Number trltmber PerCftlf

Soulh __ ) shy- ~5 J()O -I 0 17i 157 touthensL ali ib 2a JI HS ll EnsL 21 -19 I 2 oj 72 routhwcsL middot12 111 7 Hil H a WesL la 54 )i IIi s1l KorthwesL 7S 81j (J U 170 150 Karthensl (HI -15 Ii 0 1III U7 North_ JII 07 H I 11)5 III

-~-

Iolnl Iii 5f11 H2 21 J 12f1 IC~JO

~ _--J fH nrem er(~ (~itlllr ItI(ll 01 lxtrellwr uried ill nspeet nud were t1xlludltI from thfs tnhlc

Thesp 111nrked difl(lPJlees in (OSiOll nre trac(ahle to conditions inhppnt in tilt diflPlPI1 t nSJ)(ds Jhe lelntiy( importnne( of gmdiPT1 to

r[- ]tl lt

~ 60 r--- h _1~ 40 69 t (J

Ci 4J

D-- _ 60

j11 13 14 5 10

SOUTH SOUTHEAST EAST SOUTHWEST WEST NORTHWEST NORTHEAST NORTH

ASPECT

oNO EROSION 0 SHEET EROSION bull GULLY EROSION

IlS 11 Jllrtor in (o~iol1 hl1s lwel1 hrought out It is nppalent thnt tll( SIIJl1C tr(nd townrd lt1((](11$((1 (Iosion on steeper slopps is opcmting 11(IP 11(( north ns[wds wllich htp nn nNnge glndient of 55 pe1shy((nt ne No(hd eonsid(lnhly lpss thnn south slop(s with fill flYlrngc grlldi(11 t of 45 percen L Difi(I(I1((s in soil Y(g(tfltion cpglee of rodent ill f(stlttioll Ilnd aC(Pssibi1i ty to Ii (stoe k--Jnetols natulnlly nssoCill ted with nspeet find whose impotnl1(t ill erosion is brought out 1111e1shyynry (ollsid(lfthly with direction of slope Ilnd dou btless are more responsihle for (Ix((ssie erosion on teltnin slopts thnn the exposure itsplf The eomputations indicl1te thl1t 106 percent of the vuriance of erosion is nssociated with aspeet

SOli

Jll ftl1nlyzing the relation of soil to (rosion (olrrlations el( made of tile oligin of tll( soil its tlxtlJlO (010 nll10lnt of litt(1 Iwd hlJIlls w(sent Ilnd dltpth of soil

15

J

tshy

~

EROSION ON THE BOISE ]UVl~lt WATERSHHI)

Thnt origin or Ol( soil hns playcd S0111( pnlt in the dcgrce of cIosion is shown by the fact that 63 percent of the alens haying glllnitie soil containing a high percentage of new gritty 1l111terial deficient in bindshying properties were eroded whenas only 49 percelJt of the areas hayshying soil chiefly derived from laya 01 porphyry showed elOsion FurshytherJllore gullying was found only on areas with gmnitir soils

Coarseness is an outstanding characteristic of the soils on the area studied Mechanically analyzed lepresentntive samples ha ye all nnlIlge clay content of 9 percent nnd nIl flvemge silt content of only 10 percent Conrsel Jnaterial makes up the lellHlindel the average sand (ont(llt 1)(ing 50 p(lc(nt with nn ndditiOlln131 percent mnde up of piuticl(s in excess of 2 111m in diamctcr

S(grCgntiollor the dntn by soil-kxtulc clnss(s togethCI with the degne of clOsion round to nccompnl1y 1h(se soil conditions indicates thnt texture (xerts nll important infhWIHP upon eORion As shown in tnhle 8 (rosiou hoth sh(et nnd gully wns lpss tlllln hall as prpVIlshyllTlt 011 tIl( jine ns COJllpnl((l with the COHrSI soils

TABTl] 3-DistribulioL oj (ca~ iii each rlospoundot class accordin(J 10 ~()il llrtllrc -----------------------___----_

I So fhc~t )1~nl1o- I~P ero iOll erosioll ~1l1I) ~ul) All nrtl~

j ~ lroslon lrUSHHI f ---1--------- -------- shy

IXlwher Number Nlllllber JVlllllhcr NU1IIllfr mill Vitw~ 2middot1 10 0 2 31 3 middot1 tediullI _ i lIH Hi H I a 3jS 31Coarse 0 --i~~--j-g___IS _~ ~_fo2

__~I~ __ ~______-----i__ai_b--I_ 51l S3 2l J ()middot14 I lIX~(kl

IVhiltgt tll( colol of (he soil does Ilot influPl1(( PIosi-ity Ynlintions ill color oft(11 il1dicl1t( dilTplPllc(s in othcI plop(Itips thnt do hnp Owt (frCct On this wntNshtd soil (010[ is mninly nil indicatoJ of til( ])1PSPIIC( 01 nlgts(II)(( of olgHllie Jllltti(l in the soil lJ)lllysps or tlU rplation or soil coinl to (lOsiol1 -(10 Jound to ngl(H closely with tllp Ipsults on dpptlt of littCI nnd humus in ldntioll to (Josion nnd only tho lit tt(l is J1PI( disCllSS(d

Ac(umulatioll of a jittp[ (0(1 is normnlly a slow PIO(PSS lInd(I tlc Rpnrs( ypgPlatioll of a spmiulid (Iimntp With hPHY glllzing usC milch of the Cg(illtioll J1IHt(IinL thnt othplwise might hne gont into rnJichJl1Cnt of tIl( Roil (ithpl is Jelllond through HCtllnl grnzillg 01 is so brok(11 11 p h)r the lPPC1l t(d trniling lJl(i tablo uncipl such IISP that iL is (Ilsily (IUTipd Hlly hy wind nnd RlIrftHe run-olr Ill( ltxUnL of h(

reducUon in olganic J11llttlr ill]HI((nt of lIHIogpn nnrt in nPI-holdshying cl1pH(i (yon (Jocl((l soi Is ill th( Boise WII t(rs)Hd is RhllWIl in tn hIe 4 Trpmendom dif1(1(II((S W(IP found h(tP(ll uncrodpd soils and the elodpd phns(s of the SHIne soils Jl(il signifiCllnee 1R indicntNl hy eorrplations b(twPPIl wn tN-JlOlding cnplleity a primp fllctor ill the croshity oj soils nlld orgnllie maUrI The lnrgc siz( of this cOIlllilshytion coeHi(ipnt (O)34iOOV) indi(lllps thllt the nhilityo( th(sp soils to hold watel dCl)(I1(ls lnJgplr 011 thc (on itn t of orgllllic mnttpJ

IG lECH-ICAL BLLLElIN 528 U S DEPT OF AGIUCUlJrURE

TAnLr 1- -Chemical and 7Jzysical (naly~i8 oj compurable eroded and ullcrodec1 soil~

Jroltlel I 1llerd~(1 ~(1l oils

J-ae nt p r(~l ill Orrttrlh Ulltlpr ~ 17 111middot1 ~trot(lrl 1lIS bull al~ rUll1 rholdlur rlltlil y 11middot1 II

-----~-------

Tlwt tlie nmoullL or Jittpl and ltUlllU ha~ liad an impolllint prrLCt Oil tlie posiyity or the soil is shown in tnble 5 A((onling to tiI(S()

dntn sh((t PJoiull is molC than thlPP tim(s liS pl(Ynl(nt (il ])(II(ent) 011 soiLlnckillfjnlitt(l nnd hUlllUigt OJ lindng on1 nl110d(Inte nlllollnt ns on nlPHS with (I((p liu(I nnd humus (18 p(Iccnt) In (n11 gl(llt(I (ontlnst gully Plosion is 2 tUl1PS 11 ])f(yulent WIHIP humus nnd JittPI is lncking ns on nlens whem this P10 t(etin CO-(I is c((P In no cnse WflS d((p gully (1osio11 nssocintCC1 with lt1((1gt lithl nncl hUlllus

TAmE 5_middotlixlriiJuliol of areas in cach cllmon rla~~ (If(orriill(1 10 fllh oj litler (IJlff 110171 (Iud deplh (If soil alour

(T(lTlTlIXIl ro IHITH OF LITTEH AXil Ifl~Il

-hallowmiddot I)rfpmiddotXII hN1 (rojon troion ~lI11y I gull

pro~joJ1 lrH~ioll

Su mill f ~Yllmllr Xumtur UIl11 r If II ~U Ii I-[dlUm 11 a1ft tu )1 ~Ii HJ 1 II

IMI 1m II

~ llht Ht H 2 I J(middotJUJU In i 1(1 l~ I 11 1bull 1 lhI flY I I II W Ilt I

ii 2 n I t171 10(111

lllHII-cmiddotd dl(S( in P(OiOil lIS fOUllel with in(l(gtIs(d dppth or soil - do showll ill tnbh ) oilly ~() ])(f(pn of the l1(IIS (Iasifild liS IUillg ltI((1l Hoils (IP 110((lt1 ns (olll])al(1(1 to (j3 P(I((nt or th( a (P1S wit lr soils of lll(d i IIJll d(p t h a lld 7) ]HI((I t or lhos( wi II shlillow Hoil ~1()1( tlLHI1 OI1-hllf of tll( soil al( tllntwp( sllllilow and m(dshyium in dlplh ~how(lt1 sli(d Plosiol1 while only 2J pPJ(pnt of lll( dNPshyHoil untlS (1( shNt p(oded 1(11 ty-thl(e PlITPU t of tlu n l(tlS h ( 1(

the soils (1( shallow w(n~ gulliId us comptllld with(j PPI((lIt or soils 1l1vdiUJIl ill ((pth Illld I perr(nt of the nltllS with d(tp ~()il~Xonl of till d(pp lltoils WlS found to hI d((pl gulli(d

H (l(HI th(sr linding nr( probfl hImiddot not Imcen bIt it dtp th 01 soil nlol1(gt Tbl d((jgtPl fioils (1( found to ha ( gllH tpl Hcum uilltions of litt(I lind hllnu~ 1(gt1( dso rim in kxtulc W(I( found Oil WIlt(1 ~IOPlS nlHl 111l n dlns(l (0(1 1I(1(1s shallow soils (IP nssoeiutpd with (OtlISl t(xtUlt st((ppr grndients and thinner plant (ovel

EROSlOX ON ruB BOlSE IUmiddotE1t WATEHSHED 17

The eomputcd variance in erosion 128 percent which is associated with the combined qunlitics of dcpth of littrr and soil depth indicn tcs the marked lclntiollship betwcrn thesC soil rhnlacteJs and erosion Ylu]e othel factols have hnd their pnrt in inc ueinp erosion in thpound Boise RiveI wntpJshed thpil pCCt hns plOhnhly bcen inclensed mnnyfold b~ the pccuiiul CilllJHct(J nnd PIC~(nt (ondilioll of the soib of this nlCa

The lr]ation bctwcell plHllt type Hilt (cogne of crosion ifgt indicnted in figult 9 whicil lcplCsen ts glll phirl 11 tlH CJosion (onditions found

IOO~middot---

i8) ~--lt tr ~ I 60

~ 70 lt

~ ~Ot--~ _1__

~ zo

oNlJ EROSION 0 SHH r ERuSON bull jut L Y CROSHN

JOt Cneil typ~t~ Uull lIosi()1l is fllllticllally bad wi 1(1( thtIpound is II w((d conI flhppL Plosioll i~ id(S[)Jtlld lInd gullits H lC sClious ill gJilSS sngebnlsil hroww nne tillll)(J llJrnfgt RIHCt CIosion b ioulld onI purts of Ill( nS[H1I nnd JllCIHlow lllHfgt but tilCit aCI(nge is so small thut they nrc unimportant Whilt both sll(tt alld gully (Iosioll 1IP found ill tht JlOnplIIzing typr tht 1H1(pntHg(R nlC 1tlntivpl sllInl Tht lltUllhplS of 1I1tIS by iqH 11( gi(1 in tHhlp (i

~tl lfo tuH

~1l(Imiddott flrOlIl)

hllomiddot llIlIy

JIIlun

IlICImiddotmiddot lIly

lrowll JI nnJshy

w(c bull ____ (lruss Stt~lbrush Browse Timher A~p~n ~Icndomiddot X(JJl~rrnzin~

~Ilmt Ii

Iii 41

i 1

tjl

Sumrr

111 t

middotIh

fotul III

~Still nncHhcr (YP( hlrr(lll HS nttoJniwd ill tlw fi(ld wurk tllu hlrnttl tYJi(l iurludes areilS ith flO ~gclutinll Qr with Jlructlt~lIy II 0 Ill 1l1 macl( up o( rock ~lid~s Clilfs llc Jhlin no ~()i1111 eroIV this lyp has beCIl climinated from further (onsidcrruioCl

1 R LE(U-1ICAL DULLETIN 1)28 U S DEPT 01 AGmCULlUH1~

The woed is the most seriously eroded of nJI plant types us shown hy the fud tlutt 75 percent of the weed alcns nre ltroded and 111010

tban half of those nre gullied 9 Pnst excessive glU7ing undoubtedly caused the replueement of the o1iginnl yegetfitiou con1 by one poorly udfipted to resist erosion In con trust to thc dense fibrous root systems of the original bUllchgruss cover the present dominant piunts of this type ure largely shallow-rooted unnunls ltr perennials with a single tuproot Among the latter arc pentstemon (Pclltstemon spp) lupill~ (L7lpinlls ((lucatus Itl1d L tenflhl8) und alpine buckwheat tlconogoll1l1n pliyfoiaccaejolium) Suell sppcips are 1l1lclY 111a t-folll1 ing

Fllrl Hi HI tn1U-((t throUImiddotdl OIW of tlw lUpiries f n dominnnl plan I III tlw wlt1d IYPl sho iug hu the ~lIlgle lapruoL is forcltl dowll thu ~loJ1e nud lill plaut plrtidly hurlNI hy sheN lro~iou

and thCil slender stPl11S anti scant root sYstpnls olrc little rcsistnll(( to elosioll The chalHeter of the root RStll1IS of Ollp of the molp comlllon plants of the wlpel type is shO-n ill figure lO Sincc till w(NI anas H(C usually found nlol1g sh(tp dlin~wtls 01 otlHr exposld sitls wllNe the fioi I is shallow and su bject to cOllsiciem ble wind erosioll it is to be expedld that Nosi-c conditions woul(l Ill mom sl(ious ill thC cpel tbun in any otber type

GUASH

The gmss 11IpUS include opCn pntcli(s or whpfltgrnss olcasiOllul stands 01 gian t JYpgrnss (ElllJnlls (on((118(( tIll) LcttClI1UlllS POlCU pilH gruss fllld OIl thc OYCrglH7cd arCHS nt lowcr llentiolls lxtcnsivp

tIn tho tJMwl J1ro((~ss(s of plant SU(i~sion in l1w Hoil regiun (ht) hUl1(hgrasSl~ (UlIU till elimns her hll(IOUS type und weed nnM ilrl III thIllSI(US usulIlIy the result of sonil flttor of (i(llrIJaIlll Althou~h they cOnlprlSI hilt II slIIull proportion 01 the entire ureu lho weed IIfCOS huc bccnlnclullcd in lbe IInnhsis hc~allso of LIIS Slgnificunce bull

13

r

middot EROSION ON THE nOISE RIVETt WImiddotl~HilH1W

nre subject only to sheet erosion The percents of l11el1 with gully erosion increase from 0 to 4 8 and 10 for the respective foul lower gradient cll1sses Although 6 of the 117 gullied areas havc grnclients of less than 26 percen t in each instancc factors other thl1n steepness appear to account for the erosion iive of them hltd blen tmilcd ovel~razcd nnd trnl11plecl much more soverely than the othors On the sixth gullies hnd eut through from 1111 adjoining arol1

TATII)1 lmiddotmiddotmiddot-J)l~llaJ1l1ion oj orcas in cach rrosion clas~ (lccoldlll(J 10 II(l(if III - ------~-------------

I No Sitelll I Hhnilow i It( 1bullbull(IIUdIQut ltln~~ (PlIlril erosion (rllsloll ~lIlil i ~1I11~ j AillllllSJ bull troslOI1 (IroSlmt ~

--------------- NU11I11If ~I Nil) ~I-~Imiddot_It1 1- O-i 11 a II r I 2 jj--i 12 11 I ~I 2 II

M~~~ ~a ~8 1~ -~ M~~Omiddot Itl~ If ~ 31)-15 06 12( Ja 2 217 20 I lttQ-lW 80 150 2S 7 2~ 21 2 m-I Iln lU3 25 a lao 2~t ur-i iU 3 li 5 tfI H ill-~ fi 1 bull M_~ ~~ i 0kfI+ 7 bullbullbullbull_ 7 11

lO(IlI--t ----m-1--oq-~2i --I) -00-0 --~------------ _-_ --- -- -

TIll ti(nd tOWllld intlnslt elosion with il1crCnsed gmdi(nt is 110t found howev() 011 ao- to 05-]gte1((11 t slopes Ill1d on grndicn Is steeper t11nn Go pelcen t the degree of crosion is n(tuuIly Jess s(Jious If0 I

IxnmpIc nllUS with 56- to 05-pllccnt glHdients hnVl) nn oven smalIcl PIOPoltion of thlit number gullild l~ncl olll~ H slightly gr(nter P1OshypOltWIl shlci-CIodNl thel11 thl 111II1S WIth gIultilCnts of 2G to36 pPIc(nl H would aPP(n tIHIltfOIC thnt sonw Jn Cto I 01 fldols 0111(1 thnn sl(CplHsS mC illvolnd Ill( I1tio of Ihp vnliall(( of i1)(1 llI(nllB of (osioll etlBSPS 101 (Heh glHriient clnBs to till vnlinncc of nil tIw grollps (olllbill(d rus found to Ill 0020 which indicnltmiddots thnt l) pprc(IIL of ill( HIlability in PIosion is duC to grucii(llt it JigTII( of smnll siz( uithollgh signifknl I

ASIgCT

Erosion conditjons 111( found 10 diO(I shnlply in tlte dinNenl direcshytions of (xposur( Ill( lttntn on til(gt r(lnlion of nspcCL to (Iosion 111(

slInJmulillPd in tuhlP 2 lilt shown glnphicnlly ill figllle 8 ArCHS JlCing thc south 11(1 in tI( most s(liolls C(lIldition with fOlll-fifths of lIll RII(h 1llPI1S (1Olti(d ElOsion Icss(J1s grl1dunlly with cIlHnge in (lXshy

POSlIJO to the sOllth(HSt (ust sOllthwlsL Wlst northwlst J1orthelst lind finn]]y to th(1 north wh(ll it is ollly hu1f ns prlvnlen t ns on SOli ill (xpOSUlefl Ill( ploportion of IIlcns gullied dolS not follow (xnctly tillS order The south nnd southeHsterll nspects Hrl tho most flPiishyously gullied but the nOithwest instenlti of tIH 1101tb(lly (xpos(d nrens HI(middot til( 1(IlRt gll]Ji((1

---------

---------- ---

14 (ECHNICAIJ nUrJIJE~LIN 528 U S DEPI 01lt AGRICULTURE

TABLE 2--Distribution oj areas in ~ach erosion class according to aspect

Shallow- Dcep-No SheetSIlCtl tlnSH gullr fulr All nrens erosion erosion erosion erosion

I NUlllfJer NItlflJer Nlmber Number trltmber PerCftlf

Soulh __ ) shy- ~5 J()O -I 0 17i 157 touthensL ali ib 2a JI HS ll EnsL 21 -19 I 2 oj 72 routhwcsL middot12 111 7 Hil H a WesL la 54 )i IIi s1l KorthwesL 7S 81j (J U 170 150 Karthensl (HI -15 Ii 0 1III U7 North_ JII 07 H I 11)5 III

-~-

Iolnl Iii 5f11 H2 21 J 12f1 IC~JO

~ _--J fH nrem er(~ (~itlllr ItI(ll 01 lxtrellwr uried ill nspeet nud were t1xlludltI from thfs tnhlc

Thesp 111nrked difl(lPJlees in (OSiOll nre trac(ahle to conditions inhppnt in tilt diflPlPI1 t nSJ)(ds Jhe lelntiy( importnne( of gmdiPT1 to

r[- ]tl lt

~ 60 r--- h _1~ 40 69 t (J

Ci 4J

D-- _ 60

j11 13 14 5 10

SOUTH SOUTHEAST EAST SOUTHWEST WEST NORTHWEST NORTHEAST NORTH

ASPECT

oNO EROSION 0 SHEET EROSION bull GULLY EROSION

IlS 11 Jllrtor in (o~iol1 hl1s lwel1 hrought out It is nppalent thnt tll( SIIJl1C tr(nd townrd lt1((](11$((1 (Iosion on steeper slopps is opcmting 11(IP 11(( north ns[wds wllich htp nn nNnge glndient of 55 pe1shy((nt ne No(hd eonsid(lnhly lpss thnn south slop(s with fill flYlrngc grlldi(11 t of 45 percen L Difi(I(I1((s in soil Y(g(tfltion cpglee of rodent ill f(stlttioll Ilnd aC(Pssibi1i ty to Ii (stoe k--Jnetols natulnlly nssoCill ted with nspeet find whose impotnl1(t ill erosion is brought out 1111e1shyynry (ollsid(lfthly with direction of slope Ilnd dou btless are more responsihle for (Ix((ssie erosion on teltnin slopts thnn the exposure itsplf The eomputations indicl1te thl1t 106 percent of the vuriance of erosion is nssociated with aspeet

SOli

Jll ftl1nlyzing the relation of soil to (rosion (olrrlations el( made of tile oligin of tll( soil its tlxtlJlO (010 nll10lnt of litt(1 Iwd hlJIlls w(sent Ilnd dltpth of soil

15

J

tshy

~

EROSION ON THE BOISE ]UVl~lt WATERSHHI)

Thnt origin or Ol( soil hns playcd S0111( pnlt in the dcgrce of cIosion is shown by the fact that 63 percent of the alens haying glllnitie soil containing a high percentage of new gritty 1l111terial deficient in bindshying properties were eroded whenas only 49 percelJt of the areas hayshying soil chiefly derived from laya 01 porphyry showed elOsion FurshytherJllore gullying was found only on areas with gmnitir soils

Coarseness is an outstanding characteristic of the soils on the area studied Mechanically analyzed lepresentntive samples ha ye all nnlIlge clay content of 9 percent nnd nIl flvemge silt content of only 10 percent Conrsel Jnaterial makes up the lellHlindel the average sand (ont(llt 1)(ing 50 p(lc(nt with nn ndditiOlln131 percent mnde up of piuticl(s in excess of 2 111m in diamctcr

S(grCgntiollor the dntn by soil-kxtulc clnss(s togethCI with the degne of clOsion round to nccompnl1y 1h(se soil conditions indicates thnt texture (xerts nll important infhWIHP upon eORion As shown in tnhle 8 (rosiou hoth sh(et nnd gully wns lpss tlllln hall as prpVIlshyllTlt 011 tIl( jine ns COJllpnl((l with the COHrSI soils

TABTl] 3-DistribulioL oj (ca~ iii each rlospoundot class accordin(J 10 ~()il llrtllrc -----------------------___----_

I So fhc~t )1~nl1o- I~P ero iOll erosioll ~1l1I) ~ul) All nrtl~

j ~ lroslon lrUSHHI f ---1--------- -------- shy

IXlwher Number Nlllllber JVlllllhcr NU1IIllfr mill Vitw~ 2middot1 10 0 2 31 3 middot1 tediullI _ i lIH Hi H I a 3jS 31Coarse 0 --i~~--j-g___IS _~ ~_fo2

__~I~ __ ~______-----i__ai_b--I_ 51l S3 2l J ()middot14 I lIX~(kl

IVhiltgt tll( colol of (he soil does Ilot influPl1(( PIosi-ity Ynlintions ill color oft(11 il1dicl1t( dilTplPllc(s in othcI plop(Itips thnt do hnp Owt (frCct On this wntNshtd soil (010[ is mninly nil indicatoJ of til( ])1PSPIIC( 01 nlgts(II)(( of olgHllie Jllltti(l in the soil lJ)lllysps or tlU rplation or soil coinl to (lOsiol1 -(10 Jound to ngl(H closely with tllp Ipsults on dpptlt of littCI nnd humus in ldntioll to (Josion nnd only tho lit tt(l is J1PI( disCllSS(d

Ac(umulatioll of a jittp[ (0(1 is normnlly a slow PIO(PSS lInd(I tlc Rpnrs( ypgPlatioll of a spmiulid (Iimntp With hPHY glllzing usC milch of the Cg(illtioll J1IHt(IinL thnt othplwise might hne gont into rnJichJl1Cnt of tIl( Roil (ithpl is Jelllond through HCtllnl grnzillg 01 is so brok(11 11 p h)r the lPPC1l t(d trniling lJl(i tablo uncipl such IISP that iL is (Ilsily (IUTipd Hlly hy wind nnd RlIrftHe run-olr Ill( ltxUnL of h(

reducUon in olganic J11llttlr ill]HI((nt of lIHIogpn nnrt in nPI-holdshying cl1pH(i (yon (Jocl((l soi Is ill th( Boise WII t(rs)Hd is RhllWIl in tn hIe 4 Trpmendom dif1(1(II((S W(IP found h(tP(ll uncrodpd soils and the elodpd phns(s of the SHIne soils Jl(il signifiCllnee 1R indicntNl hy eorrplations b(twPPIl wn tN-JlOlding cnplleity a primp fllctor ill the croshity oj soils nlld orgnllie maUrI The lnrgc siz( of this cOIlllilshytion coeHi(ipnt (O)34iOOV) indi(lllps thllt the nhilityo( th(sp soils to hold watel dCl)(I1(ls lnJgplr 011 thc (on itn t of orgllllic mnttpJ

IG lECH-ICAL BLLLElIN 528 U S DEPT OF AGIUCUlJrURE

TAnLr 1- -Chemical and 7Jzysical (naly~i8 oj compurable eroded and ullcrodec1 soil~

Jroltlel I 1llerd~(1 ~(1l oils

J-ae nt p r(~l ill Orrttrlh Ulltlpr ~ 17 111middot1 ~trot(lrl 1lIS bull al~ rUll1 rholdlur rlltlil y 11middot1 II

-----~-------

Tlwt tlie nmoullL or Jittpl and ltUlllU ha~ liad an impolllint prrLCt Oil tlie posiyity or the soil is shown in tnble 5 A((onling to tiI(S()

dntn sh((t PJoiull is molC than thlPP tim(s liS pl(Ynl(nt (il ])(II(ent) 011 soiLlnckillfjnlitt(l nnd hUlllUigt OJ lindng on1 nl110d(Inte nlllollnt ns on nlPHS with (I((p liu(I nnd humus (18 p(Iccnt) In (n11 gl(llt(I (ontlnst gully Plosion is 2 tUl1PS 11 ])f(yulent WIHIP humus nnd JittPI is lncking ns on nlens whem this P10 t(etin CO-(I is c((P In no cnse WflS d((p gully (1osio11 nssocintCC1 with lt1((1gt lithl nncl hUlllus

TAmE 5_middotlixlriiJuliol of areas in cach cllmon rla~~ (If(orriill(1 10 fllh oj litler (IJlff 110171 (Iud deplh (If soil alour

(T(lTlTlIXIl ro IHITH OF LITTEH AXil Ifl~Il

-hallowmiddot I)rfpmiddotXII hN1 (rojon troion ~lI11y I gull

pro~joJ1 lrH~ioll

Su mill f ~Yllmllr Xumtur UIl11 r If II ~U Ii I-[dlUm 11 a1ft tu )1 ~Ii HJ 1 II

IMI 1m II

~ llht Ht H 2 I J(middotJUJU In i 1(1 l~ I 11 1bull 1 lhI flY I I II W Ilt I

ii 2 n I t171 10(111

lllHII-cmiddotd dl(S( in P(OiOil lIS fOUllel with in(l(gtIs(d dppth or soil - do showll ill tnbh ) oilly ~() ])(f(pn of the l1(IIS (Iasifild liS IUillg ltI((1l Hoils (IP 110((lt1 ns (olll])al(1(1 to (j3 P(I((nt or th( a (P1S wit lr soils of lll(d i IIJll d(p t h a lld 7) ]HI((I t or lhos( wi II shlillow Hoil ~1()1( tlLHI1 OI1-hllf of tll( soil al( tllntwp( sllllilow and m(dshyium in dlplh ~how(lt1 sli(d Plosiol1 while only 2J pPJ(pnt of lll( dNPshyHoil untlS (1( shNt p(oded 1(11 ty-thl(e PlITPU t of tlu n l(tlS h ( 1(

the soils (1( shallow w(n~ gulliId us comptllld with(j PPI((lIt or soils 1l1vdiUJIl ill ((pth Illld I perr(nt of the nltllS with d(tp ~()il~Xonl of till d(pp lltoils WlS found to hI d((pl gulli(d

H (l(HI th(sr linding nr( probfl hImiddot not Imcen bIt it dtp th 01 soil nlol1(gt Tbl d((jgtPl fioils (1( found to ha ( gllH tpl Hcum uilltions of litt(I lind hllnu~ 1(gt1( dso rim in kxtulc W(I( found Oil WIlt(1 ~IOPlS nlHl 111l n dlns(l (0(1 1I(1(1s shallow soils (IP nssoeiutpd with (OtlISl t(xtUlt st((ppr grndients and thinner plant (ovel

EROSlOX ON ruB BOlSE IUmiddotE1t WATEHSHED 17

The eomputcd variance in erosion 128 percent which is associated with the combined qunlitics of dcpth of littrr and soil depth indicn tcs the marked lclntiollship betwcrn thesC soil rhnlacteJs and erosion Ylu]e othel factols have hnd their pnrt in inc ueinp erosion in thpound Boise RiveI wntpJshed thpil pCCt hns plOhnhly bcen inclensed mnnyfold b~ the pccuiiul CilllJHct(J nnd PIC~(nt (ondilioll of the soib of this nlCa

The lr]ation bctwcell plHllt type Hilt (cogne of crosion ifgt indicnted in figult 9 whicil lcplCsen ts glll phirl 11 tlH CJosion (onditions found

IOO~middot---

i8) ~--lt tr ~ I 60

~ 70 lt

~ ~Ot--~ _1__

~ zo

oNlJ EROSION 0 SHH r ERuSON bull jut L Y CROSHN

JOt Cneil typ~t~ Uull lIosi()1l is fllllticllally bad wi 1(1( thtIpound is II w((d conI flhppL Plosioll i~ id(S[)Jtlld lInd gullits H lC sClious ill gJilSS sngebnlsil hroww nne tillll)(J llJrnfgt RIHCt CIosion b ioulld onI purts of Ill( nS[H1I nnd JllCIHlow lllHfgt but tilCit aCI(nge is so small thut they nrc unimportant Whilt both sll(tt alld gully (Iosioll 1IP found ill tht JlOnplIIzing typr tht 1H1(pntHg(R nlC 1tlntivpl sllInl Tht lltUllhplS of 1I1tIS by iqH 11( gi(1 in tHhlp (i

~tl lfo tuH

~1l(Imiddott flrOlIl)

hllomiddot llIlIy

JIIlun

IlICImiddotmiddot lIly

lrowll JI nnJshy

w(c bull ____ (lruss Stt~lbrush Browse Timher A~p~n ~Icndomiddot X(JJl~rrnzin~

~Ilmt Ii

Iii 41

i 1

tjl

Sumrr

111 t

middotIh

fotul III

~Still nncHhcr (YP( hlrr(lll HS nttoJniwd ill tlw fi(ld wurk tllu hlrnttl tYJi(l iurludes areilS ith flO ~gclutinll Qr with Jlructlt~lIy II 0 Ill 1l1 macl( up o( rock ~lid~s Clilfs llc Jhlin no ~()i1111 eroIV this lyp has beCIl climinated from further (onsidcrruioCl

1 R LE(U-1ICAL DULLETIN 1)28 U S DEPT 01 AGmCULlUH1~

The woed is the most seriously eroded of nJI plant types us shown hy the fud tlutt 75 percent of the weed alcns nre ltroded and 111010

tban half of those nre gullied 9 Pnst excessive glU7ing undoubtedly caused the replueement of the o1iginnl yegetfitiou con1 by one poorly udfipted to resist erosion In con trust to thc dense fibrous root systems of the original bUllchgruss cover the present dominant piunts of this type ure largely shallow-rooted unnunls ltr perennials with a single tuproot Among the latter arc pentstemon (Pclltstemon spp) lupill~ (L7lpinlls ((lucatus Itl1d L tenflhl8) und alpine buckwheat tlconogoll1l1n pliyfoiaccaejolium) Suell sppcips are 1l1lclY 111a t-folll1 ing

Fllrl Hi HI tn1U-((t throUImiddotdl OIW of tlw lUpiries f n dominnnl plan I III tlw wlt1d IYPl sho iug hu the ~lIlgle lapruoL is forcltl dowll thu ~loJ1e nud lill plaut plrtidly hurlNI hy sheN lro~iou

and thCil slender stPl11S anti scant root sYstpnls olrc little rcsistnll(( to elosioll The chalHeter of the root RStll1IS of Ollp of the molp comlllon plants of the wlpel type is shO-n ill figure lO Sincc till w(NI anas H(C usually found nlol1g sh(tp dlin~wtls 01 otlHr exposld sitls wllNe the fioi I is shallow and su bject to cOllsiciem ble wind erosioll it is to be expedld that Nosi-c conditions woul(l Ill mom sl(ious ill thC cpel tbun in any otber type

GUASH

The gmss 11IpUS include opCn pntcli(s or whpfltgrnss olcasiOllul stands 01 gian t JYpgrnss (ElllJnlls (on((118(( tIll) LcttClI1UlllS POlCU pilH gruss fllld OIl thc OYCrglH7cd arCHS nt lowcr llentiolls lxtcnsivp

tIn tho tJMwl J1ro((~ss(s of plant SU(i~sion in l1w Hoil regiun (ht) hUl1(hgrasSl~ (UlIU till elimns her hll(IOUS type und weed nnM ilrl III thIllSI(US usulIlIy the result of sonil flttor of (i(llrIJaIlll Althou~h they cOnlprlSI hilt II slIIull proportion 01 the entire ureu lho weed IIfCOS huc bccnlnclullcd in lbe IInnhsis hc~allso of LIIS Slgnificunce bull

---------

---------- ---

14 (ECHNICAIJ nUrJIJE~LIN 528 U S DEPI 01lt AGRICULTURE

TABLE 2--Distribution oj areas in ~ach erosion class according to aspect

Shallow- Dcep-No SheetSIlCtl tlnSH gullr fulr All nrens erosion erosion erosion erosion

I NUlllfJer NItlflJer Nlmber Number trltmber PerCftlf

Soulh __ ) shy- ~5 J()O -I 0 17i 157 touthensL ali ib 2a JI HS ll EnsL 21 -19 I 2 oj 72 routhwcsL middot12 111 7 Hil H a WesL la 54 )i IIi s1l KorthwesL 7S 81j (J U 170 150 Karthensl (HI -15 Ii 0 1III U7 North_ JII 07 H I 11)5 III

-~-

Iolnl Iii 5f11 H2 21 J 12f1 IC~JO

~ _--J fH nrem er(~ (~itlllr ItI(ll 01 lxtrellwr uried ill nspeet nud were t1xlludltI from thfs tnhlc

Thesp 111nrked difl(lPJlees in (OSiOll nre trac(ahle to conditions inhppnt in tilt diflPlPI1 t nSJ)(ds Jhe lelntiy( importnne( of gmdiPT1 to

r[- ]tl lt

~ 60 r--- h _1~ 40 69 t (J

Ci 4J

D-- _ 60

j11 13 14 5 10

SOUTH SOUTHEAST EAST SOUTHWEST WEST NORTHWEST NORTHEAST NORTH

ASPECT

oNO EROSION 0 SHEET EROSION bull GULLY EROSION

IlS 11 Jllrtor in (o~iol1 hl1s lwel1 hrought out It is nppalent thnt tll( SIIJl1C tr(nd townrd lt1((](11$((1 (Iosion on steeper slopps is opcmting 11(IP 11(( north ns[wds wllich htp nn nNnge glndient of 55 pe1shy((nt ne No(hd eonsid(lnhly lpss thnn south slop(s with fill flYlrngc grlldi(11 t of 45 percen L Difi(I(I1((s in soil Y(g(tfltion cpglee of rodent ill f(stlttioll Ilnd aC(Pssibi1i ty to Ii (stoe k--Jnetols natulnlly nssoCill ted with nspeet find whose impotnl1(t ill erosion is brought out 1111e1shyynry (ollsid(lfthly with direction of slope Ilnd dou btless are more responsihle for (Ix((ssie erosion on teltnin slopts thnn the exposure itsplf The eomputations indicl1te thl1t 106 percent of the vuriance of erosion is nssociated with aspeet

SOli

Jll ftl1nlyzing the relation of soil to (rosion (olrrlations el( made of tile oligin of tll( soil its tlxtlJlO (010 nll10lnt of litt(1 Iwd hlJIlls w(sent Ilnd dltpth of soil

15

J

tshy

~

EROSION ON THE BOISE ]UVl~lt WATERSHHI)

Thnt origin or Ol( soil hns playcd S0111( pnlt in the dcgrce of cIosion is shown by the fact that 63 percent of the alens haying glllnitie soil containing a high percentage of new gritty 1l111terial deficient in bindshying properties were eroded whenas only 49 percelJt of the areas hayshying soil chiefly derived from laya 01 porphyry showed elOsion FurshytherJllore gullying was found only on areas with gmnitir soils

Coarseness is an outstanding characteristic of the soils on the area studied Mechanically analyzed lepresentntive samples ha ye all nnlIlge clay content of 9 percent nnd nIl flvemge silt content of only 10 percent Conrsel Jnaterial makes up the lellHlindel the average sand (ont(llt 1)(ing 50 p(lc(nt with nn ndditiOlln131 percent mnde up of piuticl(s in excess of 2 111m in diamctcr

S(grCgntiollor the dntn by soil-kxtulc clnss(s togethCI with the degne of clOsion round to nccompnl1y 1h(se soil conditions indicates thnt texture (xerts nll important infhWIHP upon eORion As shown in tnhle 8 (rosiou hoth sh(et nnd gully wns lpss tlllln hall as prpVIlshyllTlt 011 tIl( jine ns COJllpnl((l with the COHrSI soils

TABTl] 3-DistribulioL oj (ca~ iii each rlospoundot class accordin(J 10 ~()il llrtllrc -----------------------___----_

I So fhc~t )1~nl1o- I~P ero iOll erosioll ~1l1I) ~ul) All nrtl~

j ~ lroslon lrUSHHI f ---1--------- -------- shy

IXlwher Number Nlllllber JVlllllhcr NU1IIllfr mill Vitw~ 2middot1 10 0 2 31 3 middot1 tediullI _ i lIH Hi H I a 3jS 31Coarse 0 --i~~--j-g___IS _~ ~_fo2

__~I~ __ ~______-----i__ai_b--I_ 51l S3 2l J ()middot14 I lIX~(kl

IVhiltgt tll( colol of (he soil does Ilot influPl1(( PIosi-ity Ynlintions ill color oft(11 il1dicl1t( dilTplPllc(s in othcI plop(Itips thnt do hnp Owt (frCct On this wntNshtd soil (010[ is mninly nil indicatoJ of til( ])1PSPIIC( 01 nlgts(II)(( of olgHllie Jllltti(l in the soil lJ)lllysps or tlU rplation or soil coinl to (lOsiol1 -(10 Jound to ngl(H closely with tllp Ipsults on dpptlt of littCI nnd humus in ldntioll to (Josion nnd only tho lit tt(l is J1PI( disCllSS(d

Ac(umulatioll of a jittp[ (0(1 is normnlly a slow PIO(PSS lInd(I tlc Rpnrs( ypgPlatioll of a spmiulid (Iimntp With hPHY glllzing usC milch of the Cg(illtioll J1IHt(IinL thnt othplwise might hne gont into rnJichJl1Cnt of tIl( Roil (ithpl is Jelllond through HCtllnl grnzillg 01 is so brok(11 11 p h)r the lPPC1l t(d trniling lJl(i tablo uncipl such IISP that iL is (Ilsily (IUTipd Hlly hy wind nnd RlIrftHe run-olr Ill( ltxUnL of h(

reducUon in olganic J11llttlr ill]HI((nt of lIHIogpn nnrt in nPI-holdshying cl1pH(i (yon (Jocl((l soi Is ill th( Boise WII t(rs)Hd is RhllWIl in tn hIe 4 Trpmendom dif1(1(II((S W(IP found h(tP(ll uncrodpd soils and the elodpd phns(s of the SHIne soils Jl(il signifiCllnee 1R indicntNl hy eorrplations b(twPPIl wn tN-JlOlding cnplleity a primp fllctor ill the croshity oj soils nlld orgnllie maUrI The lnrgc siz( of this cOIlllilshytion coeHi(ipnt (O)34iOOV) indi(lllps thllt the nhilityo( th(sp soils to hold watel dCl)(I1(ls lnJgplr 011 thc (on itn t of orgllllic mnttpJ

IG lECH-ICAL BLLLElIN 528 U S DEPT OF AGIUCUlJrURE

TAnLr 1- -Chemical and 7Jzysical (naly~i8 oj compurable eroded and ullcrodec1 soil~

Jroltlel I 1llerd~(1 ~(1l oils

J-ae nt p r(~l ill Orrttrlh Ulltlpr ~ 17 111middot1 ~trot(lrl 1lIS bull al~ rUll1 rholdlur rlltlil y 11middot1 II

-----~-------

Tlwt tlie nmoullL or Jittpl and ltUlllU ha~ liad an impolllint prrLCt Oil tlie posiyity or the soil is shown in tnble 5 A((onling to tiI(S()

dntn sh((t PJoiull is molC than thlPP tim(s liS pl(Ynl(nt (il ])(II(ent) 011 soiLlnckillfjnlitt(l nnd hUlllUigt OJ lindng on1 nl110d(Inte nlllollnt ns on nlPHS with (I((p liu(I nnd humus (18 p(Iccnt) In (n11 gl(llt(I (ontlnst gully Plosion is 2 tUl1PS 11 ])f(yulent WIHIP humus nnd JittPI is lncking ns on nlens whem this P10 t(etin CO-(I is c((P In no cnse WflS d((p gully (1osio11 nssocintCC1 with lt1((1gt lithl nncl hUlllus

TAmE 5_middotlixlriiJuliol of areas in cach cllmon rla~~ (If(orriill(1 10 fllh oj litler (IJlff 110171 (Iud deplh (If soil alour

(T(lTlTlIXIl ro IHITH OF LITTEH AXil Ifl~Il

-hallowmiddot I)rfpmiddotXII hN1 (rojon troion ~lI11y I gull

pro~joJ1 lrH~ioll

Su mill f ~Yllmllr Xumtur UIl11 r If II ~U Ii I-[dlUm 11 a1ft tu )1 ~Ii HJ 1 II

IMI 1m II

~ llht Ht H 2 I J(middotJUJU In i 1(1 l~ I 11 1bull 1 lhI flY I I II W Ilt I

ii 2 n I t171 10(111

lllHII-cmiddotd dl(S( in P(OiOil lIS fOUllel with in(l(gtIs(d dppth or soil - do showll ill tnbh ) oilly ~() ])(f(pn of the l1(IIS (Iasifild liS IUillg ltI((1l Hoils (IP 110((lt1 ns (olll])al(1(1 to (j3 P(I((nt or th( a (P1S wit lr soils of lll(d i IIJll d(p t h a lld 7) ]HI((I t or lhos( wi II shlillow Hoil ~1()1( tlLHI1 OI1-hllf of tll( soil al( tllntwp( sllllilow and m(dshyium in dlplh ~how(lt1 sli(d Plosiol1 while only 2J pPJ(pnt of lll( dNPshyHoil untlS (1( shNt p(oded 1(11 ty-thl(e PlITPU t of tlu n l(tlS h ( 1(

the soils (1( shallow w(n~ gulliId us comptllld with(j PPI((lIt or soils 1l1vdiUJIl ill ((pth Illld I perr(nt of the nltllS with d(tp ~()il~Xonl of till d(pp lltoils WlS found to hI d((pl gulli(d

H (l(HI th(sr linding nr( probfl hImiddot not Imcen bIt it dtp th 01 soil nlol1(gt Tbl d((jgtPl fioils (1( found to ha ( gllH tpl Hcum uilltions of litt(I lind hllnu~ 1(gt1( dso rim in kxtulc W(I( found Oil WIlt(1 ~IOPlS nlHl 111l n dlns(l (0(1 1I(1(1s shallow soils (IP nssoeiutpd with (OtlISl t(xtUlt st((ppr grndients and thinner plant (ovel

EROSlOX ON ruB BOlSE IUmiddotE1t WATEHSHED 17

The eomputcd variance in erosion 128 percent which is associated with the combined qunlitics of dcpth of littrr and soil depth indicn tcs the marked lclntiollship betwcrn thesC soil rhnlacteJs and erosion Ylu]e othel factols have hnd their pnrt in inc ueinp erosion in thpound Boise RiveI wntpJshed thpil pCCt hns plOhnhly bcen inclensed mnnyfold b~ the pccuiiul CilllJHct(J nnd PIC~(nt (ondilioll of the soib of this nlCa

The lr]ation bctwcell plHllt type Hilt (cogne of crosion ifgt indicnted in figult 9 whicil lcplCsen ts glll phirl 11 tlH CJosion (onditions found

IOO~middot---

i8) ~--lt tr ~ I 60

~ 70 lt

~ ~Ot--~ _1__

~ zo

oNlJ EROSION 0 SHH r ERuSON bull jut L Y CROSHN

JOt Cneil typ~t~ Uull lIosi()1l is fllllticllally bad wi 1(1( thtIpound is II w((d conI flhppL Plosioll i~ id(S[)Jtlld lInd gullits H lC sClious ill gJilSS sngebnlsil hroww nne tillll)(J llJrnfgt RIHCt CIosion b ioulld onI purts of Ill( nS[H1I nnd JllCIHlow lllHfgt but tilCit aCI(nge is so small thut they nrc unimportant Whilt both sll(tt alld gully (Iosioll 1IP found ill tht JlOnplIIzing typr tht 1H1(pntHg(R nlC 1tlntivpl sllInl Tht lltUllhplS of 1I1tIS by iqH 11( gi(1 in tHhlp (i

~tl lfo tuH

~1l(Imiddott flrOlIl)

hllomiddot llIlIy

JIIlun

IlICImiddotmiddot lIly

lrowll JI nnJshy

w(c bull ____ (lruss Stt~lbrush Browse Timher A~p~n ~Icndomiddot X(JJl~rrnzin~

~Ilmt Ii

Iii 41

i 1

tjl

Sumrr

111 t

middotIh

fotul III

~Still nncHhcr (YP( hlrr(lll HS nttoJniwd ill tlw fi(ld wurk tllu hlrnttl tYJi(l iurludes areilS ith flO ~gclutinll Qr with Jlructlt~lIy II 0 Ill 1l1 macl( up o( rock ~lid~s Clilfs llc Jhlin no ~()i1111 eroIV this lyp has beCIl climinated from further (onsidcrruioCl

1 R LE(U-1ICAL DULLETIN 1)28 U S DEPT 01 AGmCULlUH1~

The woed is the most seriously eroded of nJI plant types us shown hy the fud tlutt 75 percent of the weed alcns nre ltroded and 111010

tban half of those nre gullied 9 Pnst excessive glU7ing undoubtedly caused the replueement of the o1iginnl yegetfitiou con1 by one poorly udfipted to resist erosion In con trust to thc dense fibrous root systems of the original bUllchgruss cover the present dominant piunts of this type ure largely shallow-rooted unnunls ltr perennials with a single tuproot Among the latter arc pentstemon (Pclltstemon spp) lupill~ (L7lpinlls ((lucatus Itl1d L tenflhl8) und alpine buckwheat tlconogoll1l1n pliyfoiaccaejolium) Suell sppcips are 1l1lclY 111a t-folll1 ing

Fllrl Hi HI tn1U-((t throUImiddotdl OIW of tlw lUpiries f n dominnnl plan I III tlw wlt1d IYPl sho iug hu the ~lIlgle lapruoL is forcltl dowll thu ~loJ1e nud lill plaut plrtidly hurlNI hy sheN lro~iou

and thCil slender stPl11S anti scant root sYstpnls olrc little rcsistnll(( to elosioll The chalHeter of the root RStll1IS of Ollp of the molp comlllon plants of the wlpel type is shO-n ill figure lO Sincc till w(NI anas H(C usually found nlol1g sh(tp dlin~wtls 01 otlHr exposld sitls wllNe the fioi I is shallow and su bject to cOllsiciem ble wind erosioll it is to be expedld that Nosi-c conditions woul(l Ill mom sl(ious ill thC cpel tbun in any otber type

GUASH

The gmss 11IpUS include opCn pntcli(s or whpfltgrnss olcasiOllul stands 01 gian t JYpgrnss (ElllJnlls (on((118(( tIll) LcttClI1UlllS POlCU pilH gruss fllld OIl thc OYCrglH7cd arCHS nt lowcr llentiolls lxtcnsivp

tIn tho tJMwl J1ro((~ss(s of plant SU(i~sion in l1w Hoil regiun (ht) hUl1(hgrasSl~ (UlIU till elimns her hll(IOUS type und weed nnM ilrl III thIllSI(US usulIlIy the result of sonil flttor of (i(llrIJaIlll Althou~h they cOnlprlSI hilt II slIIull proportion 01 the entire ureu lho weed IIfCOS huc bccnlnclullcd in lbe IInnhsis hc~allso of LIIS Slgnificunce bull

15

J

tshy

~

EROSION ON THE BOISE ]UVl~lt WATERSHHI)

Thnt origin or Ol( soil hns playcd S0111( pnlt in the dcgrce of cIosion is shown by the fact that 63 percent of the alens haying glllnitie soil containing a high percentage of new gritty 1l111terial deficient in bindshying properties were eroded whenas only 49 percelJt of the areas hayshying soil chiefly derived from laya 01 porphyry showed elOsion FurshytherJllore gullying was found only on areas with gmnitir soils

Coarseness is an outstanding characteristic of the soils on the area studied Mechanically analyzed lepresentntive samples ha ye all nnlIlge clay content of 9 percent nnd nIl flvemge silt content of only 10 percent Conrsel Jnaterial makes up the lellHlindel the average sand (ont(llt 1)(ing 50 p(lc(nt with nn ndditiOlln131 percent mnde up of piuticl(s in excess of 2 111m in diamctcr

S(grCgntiollor the dntn by soil-kxtulc clnss(s togethCI with the degne of clOsion round to nccompnl1y 1h(se soil conditions indicates thnt texture (xerts nll important infhWIHP upon eORion As shown in tnhle 8 (rosiou hoth sh(et nnd gully wns lpss tlllln hall as prpVIlshyllTlt 011 tIl( jine ns COJllpnl((l with the COHrSI soils

TABTl] 3-DistribulioL oj (ca~ iii each rlospoundot class accordin(J 10 ~()il llrtllrc -----------------------___----_

I So fhc~t )1~nl1o- I~P ero iOll erosioll ~1l1I) ~ul) All nrtl~

j ~ lroslon lrUSHHI f ---1--------- -------- shy

IXlwher Number Nlllllber JVlllllhcr NU1IIllfr mill Vitw~ 2middot1 10 0 2 31 3 middot1 tediullI _ i lIH Hi H I a 3jS 31Coarse 0 --i~~--j-g___IS _~ ~_fo2

__~I~ __ ~______-----i__ai_b--I_ 51l S3 2l J ()middot14 I lIX~(kl

IVhiltgt tll( colol of (he soil does Ilot influPl1(( PIosi-ity Ynlintions ill color oft(11 il1dicl1t( dilTplPllc(s in othcI plop(Itips thnt do hnp Owt (frCct On this wntNshtd soil (010[ is mninly nil indicatoJ of til( ])1PSPIIC( 01 nlgts(II)(( of olgHllie Jllltti(l in the soil lJ)lllysps or tlU rplation or soil coinl to (lOsiol1 -(10 Jound to ngl(H closely with tllp Ipsults on dpptlt of littCI nnd humus in ldntioll to (Josion nnd only tho lit tt(l is J1PI( disCllSS(d

Ac(umulatioll of a jittp[ (0(1 is normnlly a slow PIO(PSS lInd(I tlc Rpnrs( ypgPlatioll of a spmiulid (Iimntp With hPHY glllzing usC milch of the Cg(illtioll J1IHt(IinL thnt othplwise might hne gont into rnJichJl1Cnt of tIl( Roil (ithpl is Jelllond through HCtllnl grnzillg 01 is so brok(11 11 p h)r the lPPC1l t(d trniling lJl(i tablo uncipl such IISP that iL is (Ilsily (IUTipd Hlly hy wind nnd RlIrftHe run-olr Ill( ltxUnL of h(

reducUon in olganic J11llttlr ill]HI((nt of lIHIogpn nnrt in nPI-holdshying cl1pH(i (yon (Jocl((l soi Is ill th( Boise WII t(rs)Hd is RhllWIl in tn hIe 4 Trpmendom dif1(1(II((S W(IP found h(tP(ll uncrodpd soils and the elodpd phns(s of the SHIne soils Jl(il signifiCllnee 1R indicntNl hy eorrplations b(twPPIl wn tN-JlOlding cnplleity a primp fllctor ill the croshity oj soils nlld orgnllie maUrI The lnrgc siz( of this cOIlllilshytion coeHi(ipnt (O)34iOOV) indi(lllps thllt the nhilityo( th(sp soils to hold watel dCl)(I1(ls lnJgplr 011 thc (on itn t of orgllllic mnttpJ

IG lECH-ICAL BLLLElIN 528 U S DEPT OF AGIUCUlJrURE

TAnLr 1- -Chemical and 7Jzysical (naly~i8 oj compurable eroded and ullcrodec1 soil~

Jroltlel I 1llerd~(1 ~(1l oils

J-ae nt p r(~l ill Orrttrlh Ulltlpr ~ 17 111middot1 ~trot(lrl 1lIS bull al~ rUll1 rholdlur rlltlil y 11middot1 II

-----~-------

Tlwt tlie nmoullL or Jittpl and ltUlllU ha~ liad an impolllint prrLCt Oil tlie posiyity or the soil is shown in tnble 5 A((onling to tiI(S()

dntn sh((t PJoiull is molC than thlPP tim(s liS pl(Ynl(nt (il ])(II(ent) 011 soiLlnckillfjnlitt(l nnd hUlllUigt OJ lindng on1 nl110d(Inte nlllollnt ns on nlPHS with (I((p liu(I nnd humus (18 p(Iccnt) In (n11 gl(llt(I (ontlnst gully Plosion is 2 tUl1PS 11 ])f(yulent WIHIP humus nnd JittPI is lncking ns on nlens whem this P10 t(etin CO-(I is c((P In no cnse WflS d((p gully (1osio11 nssocintCC1 with lt1((1gt lithl nncl hUlllus

TAmE 5_middotlixlriiJuliol of areas in cach cllmon rla~~ (If(orriill(1 10 fllh oj litler (IJlff 110171 (Iud deplh (If soil alour

(T(lTlTlIXIl ro IHITH OF LITTEH AXil Ifl~Il

-hallowmiddot I)rfpmiddotXII hN1 (rojon troion ~lI11y I gull

pro~joJ1 lrH~ioll

Su mill f ~Yllmllr Xumtur UIl11 r If II ~U Ii I-[dlUm 11 a1ft tu )1 ~Ii HJ 1 II

IMI 1m II

~ llht Ht H 2 I J(middotJUJU In i 1(1 l~ I 11 1bull 1 lhI flY I I II W Ilt I

ii 2 n I t171 10(111

lllHII-cmiddotd dl(S( in P(OiOil lIS fOUllel with in(l(gtIs(d dppth or soil - do showll ill tnbh ) oilly ~() ])(f(pn of the l1(IIS (Iasifild liS IUillg ltI((1l Hoils (IP 110((lt1 ns (olll])al(1(1 to (j3 P(I((nt or th( a (P1S wit lr soils of lll(d i IIJll d(p t h a lld 7) ]HI((I t or lhos( wi II shlillow Hoil ~1()1( tlLHI1 OI1-hllf of tll( soil al( tllntwp( sllllilow and m(dshyium in dlplh ~how(lt1 sli(d Plosiol1 while only 2J pPJ(pnt of lll( dNPshyHoil untlS (1( shNt p(oded 1(11 ty-thl(e PlITPU t of tlu n l(tlS h ( 1(

the soils (1( shallow w(n~ gulliId us comptllld with(j PPI((lIt or soils 1l1vdiUJIl ill ((pth Illld I perr(nt of the nltllS with d(tp ~()il~Xonl of till d(pp lltoils WlS found to hI d((pl gulli(d

H (l(HI th(sr linding nr( probfl hImiddot not Imcen bIt it dtp th 01 soil nlol1(gt Tbl d((jgtPl fioils (1( found to ha ( gllH tpl Hcum uilltions of litt(I lind hllnu~ 1(gt1( dso rim in kxtulc W(I( found Oil WIlt(1 ~IOPlS nlHl 111l n dlns(l (0(1 1I(1(1s shallow soils (IP nssoeiutpd with (OtlISl t(xtUlt st((ppr grndients and thinner plant (ovel

EROSlOX ON ruB BOlSE IUmiddotE1t WATEHSHED 17

The eomputcd variance in erosion 128 percent which is associated with the combined qunlitics of dcpth of littrr and soil depth indicn tcs the marked lclntiollship betwcrn thesC soil rhnlacteJs and erosion Ylu]e othel factols have hnd their pnrt in inc ueinp erosion in thpound Boise RiveI wntpJshed thpil pCCt hns plOhnhly bcen inclensed mnnyfold b~ the pccuiiul CilllJHct(J nnd PIC~(nt (ondilioll of the soib of this nlCa

The lr]ation bctwcell plHllt type Hilt (cogne of crosion ifgt indicnted in figult 9 whicil lcplCsen ts glll phirl 11 tlH CJosion (onditions found

IOO~middot---

i8) ~--lt tr ~ I 60

~ 70 lt

~ ~Ot--~ _1__

~ zo

oNlJ EROSION 0 SHH r ERuSON bull jut L Y CROSHN

JOt Cneil typ~t~ Uull lIosi()1l is fllllticllally bad wi 1(1( thtIpound is II w((d conI flhppL Plosioll i~ id(S[)Jtlld lInd gullits H lC sClious ill gJilSS sngebnlsil hroww nne tillll)(J llJrnfgt RIHCt CIosion b ioulld onI purts of Ill( nS[H1I nnd JllCIHlow lllHfgt but tilCit aCI(nge is so small thut they nrc unimportant Whilt both sll(tt alld gully (Iosioll 1IP found ill tht JlOnplIIzing typr tht 1H1(pntHg(R nlC 1tlntivpl sllInl Tht lltUllhplS of 1I1tIS by iqH 11( gi(1 in tHhlp (i

~tl lfo tuH

~1l(Imiddott flrOlIl)

hllomiddot llIlIy

JIIlun

IlICImiddotmiddot lIly

lrowll JI nnJshy

w(c bull ____ (lruss Stt~lbrush Browse Timher A~p~n ~Icndomiddot X(JJl~rrnzin~

~Ilmt Ii

Iii 41

i 1

tjl

Sumrr

111 t

middotIh

fotul III

~Still nncHhcr (YP( hlrr(lll HS nttoJniwd ill tlw fi(ld wurk tllu hlrnttl tYJi(l iurludes areilS ith flO ~gclutinll Qr with Jlructlt~lIy II 0 Ill 1l1 macl( up o( rock ~lid~s Clilfs llc Jhlin no ~()i1111 eroIV this lyp has beCIl climinated from further (onsidcrruioCl

1 R LE(U-1ICAL DULLETIN 1)28 U S DEPT 01 AGmCULlUH1~

The woed is the most seriously eroded of nJI plant types us shown hy the fud tlutt 75 percent of the weed alcns nre ltroded and 111010

tban half of those nre gullied 9 Pnst excessive glU7ing undoubtedly caused the replueement of the o1iginnl yegetfitiou con1 by one poorly udfipted to resist erosion In con trust to thc dense fibrous root systems of the original bUllchgruss cover the present dominant piunts of this type ure largely shallow-rooted unnunls ltr perennials with a single tuproot Among the latter arc pentstemon (Pclltstemon spp) lupill~ (L7lpinlls ((lucatus Itl1d L tenflhl8) und alpine buckwheat tlconogoll1l1n pliyfoiaccaejolium) Suell sppcips are 1l1lclY 111a t-folll1 ing

Fllrl Hi HI tn1U-((t throUImiddotdl OIW of tlw lUpiries f n dominnnl plan I III tlw wlt1d IYPl sho iug hu the ~lIlgle lapruoL is forcltl dowll thu ~loJ1e nud lill plaut plrtidly hurlNI hy sheN lro~iou

and thCil slender stPl11S anti scant root sYstpnls olrc little rcsistnll(( to elosioll The chalHeter of the root RStll1IS of Ollp of the molp comlllon plants of the wlpel type is shO-n ill figure lO Sincc till w(NI anas H(C usually found nlol1g sh(tp dlin~wtls 01 otlHr exposld sitls wllNe the fioi I is shallow and su bject to cOllsiciem ble wind erosioll it is to be expedld that Nosi-c conditions woul(l Ill mom sl(ious ill thC cpel tbun in any otber type

GUASH

The gmss 11IpUS include opCn pntcli(s or whpfltgrnss olcasiOllul stands 01 gian t JYpgrnss (ElllJnlls (on((118(( tIll) LcttClI1UlllS POlCU pilH gruss fllld OIl thc OYCrglH7cd arCHS nt lowcr llentiolls lxtcnsivp

tIn tho tJMwl J1ro((~ss(s of plant SU(i~sion in l1w Hoil regiun (ht) hUl1(hgrasSl~ (UlIU till elimns her hll(IOUS type und weed nnM ilrl III thIllSI(US usulIlIy the result of sonil flttor of (i(llrIJaIlll Althou~h they cOnlprlSI hilt II slIIull proportion 01 the entire ureu lho weed IIfCOS huc bccnlnclullcd in lbe IInnhsis hc~allso of LIIS Slgnificunce bull

IG lECH-ICAL BLLLElIN 528 U S DEPT OF AGIUCUlJrURE

TAnLr 1- -Chemical and 7Jzysical (naly~i8 oj compurable eroded and ullcrodec1 soil~

Jroltlel I 1llerd~(1 ~(1l oils

J-ae nt p r(~l ill Orrttrlh Ulltlpr ~ 17 111middot1 ~trot(lrl 1lIS bull al~ rUll1 rholdlur rlltlil y 11middot1 II

-----~-------

Tlwt tlie nmoullL or Jittpl and ltUlllU ha~ liad an impolllint prrLCt Oil tlie posiyity or the soil is shown in tnble 5 A((onling to tiI(S()

dntn sh((t PJoiull is molC than thlPP tim(s liS pl(Ynl(nt (il ])(II(ent) 011 soiLlnckillfjnlitt(l nnd hUlllUigt OJ lindng on1 nl110d(Inte nlllollnt ns on nlPHS with (I((p liu(I nnd humus (18 p(Iccnt) In (n11 gl(llt(I (ontlnst gully Plosion is 2 tUl1PS 11 ])f(yulent WIHIP humus nnd JittPI is lncking ns on nlens whem this P10 t(etin CO-(I is c((P In no cnse WflS d((p gully (1osio11 nssocintCC1 with lt1((1gt lithl nncl hUlllus

TAmE 5_middotlixlriiJuliol of areas in cach cllmon rla~~ (If(orriill(1 10 fllh oj litler (IJlff 110171 (Iud deplh (If soil alour

(T(lTlTlIXIl ro IHITH OF LITTEH AXil Ifl~Il

-hallowmiddot I)rfpmiddotXII hN1 (rojon troion ~lI11y I gull

pro~joJ1 lrH~ioll

Su mill f ~Yllmllr Xumtur UIl11 r If II ~U Ii I-[dlUm 11 a1ft tu )1 ~Ii HJ 1 II

IMI 1m II

~ llht Ht H 2 I J(middotJUJU In i 1(1 l~ I 11 1bull 1 lhI flY I I II W Ilt I

ii 2 n I t171 10(111

lllHII-cmiddotd dl(S( in P(OiOil lIS fOUllel with in(l(gtIs(d dppth or soil - do showll ill tnbh ) oilly ~() ])(f(pn of the l1(IIS (Iasifild liS IUillg ltI((1l Hoils (IP 110((lt1 ns (olll])al(1(1 to (j3 P(I((nt or th( a (P1S wit lr soils of lll(d i IIJll d(p t h a lld 7) ]HI((I t or lhos( wi II shlillow Hoil ~1()1( tlLHI1 OI1-hllf of tll( soil al( tllntwp( sllllilow and m(dshyium in dlplh ~how(lt1 sli(d Plosiol1 while only 2J pPJ(pnt of lll( dNPshyHoil untlS (1( shNt p(oded 1(11 ty-thl(e PlITPU t of tlu n l(tlS h ( 1(

the soils (1( shallow w(n~ gulliId us comptllld with(j PPI((lIt or soils 1l1vdiUJIl ill ((pth Illld I perr(nt of the nltllS with d(tp ~()il~Xonl of till d(pp lltoils WlS found to hI d((pl gulli(d

H (l(HI th(sr linding nr( probfl hImiddot not Imcen bIt it dtp th 01 soil nlol1(gt Tbl d((jgtPl fioils (1( found to ha ( gllH tpl Hcum uilltions of litt(I lind hllnu~ 1(gt1( dso rim in kxtulc W(I( found Oil WIlt(1 ~IOPlS nlHl 111l n dlns(l (0(1 1I(1(1s shallow soils (IP nssoeiutpd with (OtlISl t(xtUlt st((ppr grndients and thinner plant (ovel

EROSlOX ON ruB BOlSE IUmiddotE1t WATEHSHED 17

The eomputcd variance in erosion 128 percent which is associated with the combined qunlitics of dcpth of littrr and soil depth indicn tcs the marked lclntiollship betwcrn thesC soil rhnlacteJs and erosion Ylu]e othel factols have hnd their pnrt in inc ueinp erosion in thpound Boise RiveI wntpJshed thpil pCCt hns plOhnhly bcen inclensed mnnyfold b~ the pccuiiul CilllJHct(J nnd PIC~(nt (ondilioll of the soib of this nlCa

The lr]ation bctwcell plHllt type Hilt (cogne of crosion ifgt indicnted in figult 9 whicil lcplCsen ts glll phirl 11 tlH CJosion (onditions found

IOO~middot---

i8) ~--lt tr ~ I 60

~ 70 lt

~ ~Ot--~ _1__

~ zo

oNlJ EROSION 0 SHH r ERuSON bull jut L Y CROSHN

JOt Cneil typ~t~ Uull lIosi()1l is fllllticllally bad wi 1(1( thtIpound is II w((d conI flhppL Plosioll i~ id(S[)Jtlld lInd gullits H lC sClious ill gJilSS sngebnlsil hroww nne tillll)(J llJrnfgt RIHCt CIosion b ioulld onI purts of Ill( nS[H1I nnd JllCIHlow lllHfgt but tilCit aCI(nge is so small thut they nrc unimportant Whilt both sll(tt alld gully (Iosioll 1IP found ill tht JlOnplIIzing typr tht 1H1(pntHg(R nlC 1tlntivpl sllInl Tht lltUllhplS of 1I1tIS by iqH 11( gi(1 in tHhlp (i

~tl lfo tuH

~1l(Imiddott flrOlIl)

hllomiddot llIlIy

JIIlun

IlICImiddotmiddot lIly

lrowll JI nnJshy

w(c bull ____ (lruss Stt~lbrush Browse Timher A~p~n ~Icndomiddot X(JJl~rrnzin~

~Ilmt Ii

Iii 41

i 1

tjl

Sumrr

111 t

middotIh

fotul III

~Still nncHhcr (YP( hlrr(lll HS nttoJniwd ill tlw fi(ld wurk tllu hlrnttl tYJi(l iurludes areilS ith flO ~gclutinll Qr with Jlructlt~lIy II 0 Ill 1l1 macl( up o( rock ~lid~s Clilfs llc Jhlin no ~()i1111 eroIV this lyp has beCIl climinated from further (onsidcrruioCl

1 R LE(U-1ICAL DULLETIN 1)28 U S DEPT 01 AGmCULlUH1~

The woed is the most seriously eroded of nJI plant types us shown hy the fud tlutt 75 percent of the weed alcns nre ltroded and 111010

tban half of those nre gullied 9 Pnst excessive glU7ing undoubtedly caused the replueement of the o1iginnl yegetfitiou con1 by one poorly udfipted to resist erosion In con trust to thc dense fibrous root systems of the original bUllchgruss cover the present dominant piunts of this type ure largely shallow-rooted unnunls ltr perennials with a single tuproot Among the latter arc pentstemon (Pclltstemon spp) lupill~ (L7lpinlls ((lucatus Itl1d L tenflhl8) und alpine buckwheat tlconogoll1l1n pliyfoiaccaejolium) Suell sppcips are 1l1lclY 111a t-folll1 ing

Fllrl Hi HI tn1U-((t throUImiddotdl OIW of tlw lUpiries f n dominnnl plan I III tlw wlt1d IYPl sho iug hu the ~lIlgle lapruoL is forcltl dowll thu ~loJ1e nud lill plaut plrtidly hurlNI hy sheN lro~iou

and thCil slender stPl11S anti scant root sYstpnls olrc little rcsistnll(( to elosioll The chalHeter of the root RStll1IS of Ollp of the molp comlllon plants of the wlpel type is shO-n ill figure lO Sincc till w(NI anas H(C usually found nlol1g sh(tp dlin~wtls 01 otlHr exposld sitls wllNe the fioi I is shallow and su bject to cOllsiciem ble wind erosioll it is to be expedld that Nosi-c conditions woul(l Ill mom sl(ious ill thC cpel tbun in any otber type

GUASH

The gmss 11IpUS include opCn pntcli(s or whpfltgrnss olcasiOllul stands 01 gian t JYpgrnss (ElllJnlls (on((118(( tIll) LcttClI1UlllS POlCU pilH gruss fllld OIl thc OYCrglH7cd arCHS nt lowcr llentiolls lxtcnsivp

tIn tho tJMwl J1ro((~ss(s of plant SU(i~sion in l1w Hoil regiun (ht) hUl1(hgrasSl~ (UlIU till elimns her hll(IOUS type und weed nnM ilrl III thIllSI(US usulIlIy the result of sonil flttor of (i(llrIJaIlll Althou~h they cOnlprlSI hilt II slIIull proportion 01 the entire ureu lho weed IIfCOS huc bccnlnclullcd in lbe IInnhsis hc~allso of LIIS Slgnificunce bull

EROSlOX ON ruB BOlSE IUmiddotE1t WATEHSHED 17

The eomputcd variance in erosion 128 percent which is associated with the combined qunlitics of dcpth of littrr and soil depth indicn tcs the marked lclntiollship betwcrn thesC soil rhnlacteJs and erosion Ylu]e othel factols have hnd their pnrt in inc ueinp erosion in thpound Boise RiveI wntpJshed thpil pCCt hns plOhnhly bcen inclensed mnnyfold b~ the pccuiiul CilllJHct(J nnd PIC~(nt (ondilioll of the soib of this nlCa

The lr]ation bctwcell plHllt type Hilt (cogne of crosion ifgt indicnted in figult 9 whicil lcplCsen ts glll phirl 11 tlH CJosion (onditions found

IOO~middot---

i8) ~--lt tr ~ I 60

~ 70 lt

~ ~Ot--~ _1__

~ zo

oNlJ EROSION 0 SHH r ERuSON bull jut L Y CROSHN

JOt Cneil typ~t~ Uull lIosi()1l is fllllticllally bad wi 1(1( thtIpound is II w((d conI flhppL Plosioll i~ id(S[)Jtlld lInd gullits H lC sClious ill gJilSS sngebnlsil hroww nne tillll)(J llJrnfgt RIHCt CIosion b ioulld onI purts of Ill( nS[H1I nnd JllCIHlow lllHfgt but tilCit aCI(nge is so small thut they nrc unimportant Whilt both sll(tt alld gully (Iosioll 1IP found ill tht JlOnplIIzing typr tht 1H1(pntHg(R nlC 1tlntivpl sllInl Tht lltUllhplS of 1I1tIS by iqH 11( gi(1 in tHhlp (i

~tl lfo tuH

~1l(Imiddott flrOlIl)

hllomiddot llIlIy

JIIlun

IlICImiddotmiddot lIly

lrowll JI nnJshy

w(c bull ____ (lruss Stt~lbrush Browse Timher A~p~n ~Icndomiddot X(JJl~rrnzin~

~Ilmt Ii

Iii 41

i 1

tjl

Sumrr

111 t

middotIh

fotul III

~Still nncHhcr (YP( hlrr(lll HS nttoJniwd ill tlw fi(ld wurk tllu hlrnttl tYJi(l iurludes areilS ith flO ~gclutinll Qr with Jlructlt~lIy II 0 Ill 1l1 macl( up o( rock ~lid~s Clilfs llc Jhlin no ~()i1111 eroIV this lyp has beCIl climinated from further (onsidcrruioCl

1 R LE(U-1ICAL DULLETIN 1)28 U S DEPT 01 AGmCULlUH1~

The woed is the most seriously eroded of nJI plant types us shown hy the fud tlutt 75 percent of the weed alcns nre ltroded and 111010

tban half of those nre gullied 9 Pnst excessive glU7ing undoubtedly caused the replueement of the o1iginnl yegetfitiou con1 by one poorly udfipted to resist erosion In con trust to thc dense fibrous root systems of the original bUllchgruss cover the present dominant piunts of this type ure largely shallow-rooted unnunls ltr perennials with a single tuproot Among the latter arc pentstemon (Pclltstemon spp) lupill~ (L7lpinlls ((lucatus Itl1d L tenflhl8) und alpine buckwheat tlconogoll1l1n pliyfoiaccaejolium) Suell sppcips are 1l1lclY 111a t-folll1 ing

Fllrl Hi HI tn1U-((t throUImiddotdl OIW of tlw lUpiries f n dominnnl plan I III tlw wlt1d IYPl sho iug hu the ~lIlgle lapruoL is forcltl dowll thu ~loJ1e nud lill plaut plrtidly hurlNI hy sheN lro~iou

and thCil slender stPl11S anti scant root sYstpnls olrc little rcsistnll(( to elosioll The chalHeter of the root RStll1IS of Ollp of the molp comlllon plants of the wlpel type is shO-n ill figure lO Sincc till w(NI anas H(C usually found nlol1g sh(tp dlin~wtls 01 otlHr exposld sitls wllNe the fioi I is shallow and su bject to cOllsiciem ble wind erosioll it is to be expedld that Nosi-c conditions woul(l Ill mom sl(ious ill thC cpel tbun in any otber type

GUASH

The gmss 11IpUS include opCn pntcli(s or whpfltgrnss olcasiOllul stands 01 gian t JYpgrnss (ElllJnlls (on((118(( tIll) LcttClI1UlllS POlCU pilH gruss fllld OIl thc OYCrglH7cd arCHS nt lowcr llentiolls lxtcnsivp

tIn tho tJMwl J1ro((~ss(s of plant SU(i~sion in l1w Hoil regiun (ht) hUl1(hgrasSl~ (UlIU till elimns her hll(IOUS type und weed nnM ilrl III thIllSI(US usulIlIy the result of sonil flttor of (i(llrIJaIlll Althou~h they cOnlprlSI hilt II slIIull proportion 01 the entire ureu lho weed IIfCOS huc bccnlnclullcd in lbe IInnhsis hc~allso of LIIS Slgnificunce bull

1 R LE(U-1ICAL DULLETIN 1)28 U S DEPT 01 AGmCULlUH1~

The woed is the most seriously eroded of nJI plant types us shown hy the fud tlutt 75 percent of the weed alcns nre ltroded and 111010

tban half of those nre gullied 9 Pnst excessive glU7ing undoubtedly caused the replueement of the o1iginnl yegetfitiou con1 by one poorly udfipted to resist erosion In con trust to thc dense fibrous root systems of the original bUllchgruss cover the present dominant piunts of this type ure largely shallow-rooted unnunls ltr perennials with a single tuproot Among the latter arc pentstemon (Pclltstemon spp) lupill~ (L7lpinlls ((lucatus Itl1d L tenflhl8) und alpine buckwheat tlconogoll1l1n pliyfoiaccaejolium) Suell sppcips are 1l1lclY 111a t-folll1 ing

Fllrl Hi HI tn1U-((t throUImiddotdl OIW of tlw lUpiries f n dominnnl plan I III tlw wlt1d IYPl sho iug hu the ~lIlgle lapruoL is forcltl dowll thu ~loJ1e nud lill plaut plrtidly hurlNI hy sheN lro~iou

and thCil slender stPl11S anti scant root sYstpnls olrc little rcsistnll(( to elosioll The chalHeter of the root RStll1IS of Ollp of the molp comlllon plants of the wlpel type is shO-n ill figure lO Sincc till w(NI anas H(C usually found nlol1g sh(tp dlin~wtls 01 otlHr exposld sitls wllNe the fioi I is shallow and su bject to cOllsiciem ble wind erosioll it is to be expedld that Nosi-c conditions woul(l Ill mom sl(ious ill thC cpel tbun in any otber type

GUASH

The gmss 11IpUS include opCn pntcli(s or whpfltgrnss olcasiOllul stands 01 gian t JYpgrnss (ElllJnlls (on((118(( tIll) LcttClI1UlllS POlCU pilH gruss fllld OIl thc OYCrglH7cd arCHS nt lowcr llentiolls lxtcnsivp

tIn tho tJMwl J1ro((~ss(s of plant SU(i~sion in l1w Hoil regiun (ht) hUl1(hgrasSl~ (UlIU till elimns her hll(IOUS type und weed nnM ilrl III thIllSI(US usulIlIy the result of sonil flttor of (i(llrIJaIlll Althou~h they cOnlprlSI hilt II slIIull proportion 01 the entire ureu lho weed IIfCOS huc bccnlnclullcd in lbe IInnhsis hc~allso of LIIS Slgnificunce bull

r

EROSION ON THE BOISE RIVER WATERSHED 19

stands of downy chess Weeds or shrubs or both Ilearly alway occur in mixtures with the grasses bull

Although erosion occurs 011 a large percentage of the gruss arcus by far the greuterpurt of these (70 us against 15 percent) ure sheet eroded ruther than gullied The growth habits of the principnl grasses dUrer materiully from those of the predominating weeds nleatgruss in particulnr hus a vigorous nnd penetlUting root system which tends to hold the soil in pluce und to preyent erosion This grass however rarely forms more than a relntinly low density at the present time on the Boise River wntershed The destruction hy pust heuvy grnzing of the more succulent herbnceous plnnts in tlie gruss type and a tendency for the whentgrnss to lose much of its grazing vHllle us the dry summer season progresses result in considershyuble tn1iling with its attendant trampling and hrenking up of littel and no doubt accounts for the widespread (rosion in the grnss nr(HS Thtt heavy gruzing with its nttendnnt trumpling is tlle primnlT en usp of uccelerated erosion in the hentgrnss type is further illclicnted hy the condition of the occusional whentgrnss urpn whple gmzing vns light Eycn low densities or yegetation on StNP gllHli(llIts nlP thple effective in checking or prcyenting aceelernted PIOSiOll

8AtlEnHlfllf

The sngphrmlt type includes ull untimhered ]rrnds 11(re hig SllgPshybrush predominntes On shallow soils thpre mny be little otlHr Yegetrrtion On better sites whentgrnss bnlsrrmroot (11([8(1l1tOllIishy8agittata) nnd mountnin snowhCITv (Symphoricwp08 ollopkilus) UlC commonly found mixed with the snge

SngeiJlush nreas are the third most seyerely eTolt1pcl having Jess gully erosion than the grnss type Conditions of shp(t (rosion nn JlenTI~T identical with those of the pre(ccling grnss type hut thc PlOshyportion 0 rarcus fdlied is less Cnder the preS(ll t depleted eond itions genernlly JOllnct in this type t11ere is but a S(Ullt umount of p(renninl llCrbneeOlls pgetntion t1nd with the relntiely low pillutubilit~T of the sugebruslt itself these nr(ns nre low in Jortlge cnpneity For tllis rpuson tlt(y nrc less grnzed hy liwstock thnn grass und w(cd t~middotpes Tlte (ollsideluble erosion Joune with sngeblush covel is nttriiJlltlltl to the spars tv 0 f hNbneeous yegeta tion nnd til( sl igh L obstruction to tlte surfn(e~ movement of soil tllrorded by tlte single-stemmed though firmly rooted plants

Tlte bloqe type (onsists or n mixture of western (hoke(helT~ (Pll11l1l8 dl1Yissa) bittlr (lterry mountnin sllowherr sfli(fllllT~ snowbrush lnd 111 is((llnllN)lIS sltr hs ]lt~lOSj(J11 (onc it iOlls In SOI11(Ishy

what less criiicnl in tlte browse as compnrCCl to the stlgltbrllsh typP Although n gr(nter percentnge or browe is 1111(roded this is nwltieup for by the sligh tly grenter pfrccn t of gully prosion -i th 111 nclt of tIll ycgptn tion in the hrowse types out of rtHCh or gllzin~ nnimH Is (hpr( I naturally 11 greater flccul11ulation of litter t1 contributillg euuse to tho lack of execssive erosion

PlMBgit

rlw timher type ineludes un iU(nS ill conirlr timbpl (x((pt those classified us l1ongrnzing The qretntio 11 Othpl tltnn tIw (ollifCrs

20 TECHNICAL BULLETIN 528 U S DEPT (IF AGRIC1]LTCRE

consists mostly of pinegmss (Caiamaglostis lubescen8) other grasses lupine and small amounts of the shrubs identical to thosc found in the browse typc Although 36 percent of the timbcred arcnR wcre elassifieel as having no accclcmtrcl erosion (onditions arc still mthrl serious Sheet erosion OCCllrs on 55 pCJ(cnt of tho flrens light gully erosion 011 7 per(ent and howy gully erosion on 2 PPI((nL Browse and timbered arca arc murkedly less lC(essiblc thun thr pIpiously mentioned (ovor types MorcoVCl thc fomge genPlul1y SI)(Hking is less palatable to IhestoCk These (ontlitions hnTc Jtsldtt-d ill more moderate gm7ing und less loss of plnnt liLtpr nnd hutnus nnd Consequently lcss lC(tlcrniion of Nosioll ] 11 tll(l ticns(ll t illl 1)(1 stnnds even in the n bscnCc or hCllH1CC()US ypgdn tion thc qun 11 titmiddot of litter rcsulting from the tr(l(ls forms u wry eflecthmiddotc ng(lnt ill Contro1ling crosion

ARPEN

Thc aspen type inelucles n11 nlens in aspen woodlnnd Grmnium (Geranhlln spp) lnrgo mountnin hlollHgrns (BIOmU8 mOrfiIlUII1S) nnel snowbcrry nrc the predominating subordinn tr plan t The nspen is of little significance on this wntershcd Of tho fOll ft rpns totaling 322 aCros one wns without Nosion nnd three showed Mlklt erosion only NOlie of them wns gullied

gAIlO

1Itnclows nre rnT( in this seltiion infl(qucntly o(CuIling nlong strenms The vegptntion (onsisls mninl) of sCdges (eON sppJ ]liyc of the eight mendow nJ(ilS Jound middotele without e[oRion th( ollH1 thlrc with shret elosioll )011( or thllU wns gullied

DellS( LindH lind 1)Iush IlInd whilmiddot1I hll ( no grtlil1g yuhl 01

which hilP such 101 YlllutS (hilt t1H UIlllO[middot h( (IOnOllli(Hlly 1lsld 010 (lltssifi(d in till llongm7inv type Iltis condition Ilia) 1Jt dul to denseness tiLh(I or b1l1h 01 01 stunding 01 down Linlgtll 01 1() spalsenpsl of I(mgc grow1h ~1()Sti of (II( nOllglH7ing typ (011shy

sistld oj lti(nsc patch(s of sllowblush wOlthlrss fUl gllling 0111(1 Hrcns not strictlyin timiJ(f 0 brllsh nnd y(t so rough olinlC(psihll ns to mnlm (ntilel plOblelllnti(Ill their gm7ing u( (Ie inltiudrd in this (lnssifientioll Thrse 11(1S hHye th( l(nst (Iosioll of lnv of tho types ~4 p((((n t of UHlll b(ing lln(Iod(d FUll r( (pll 1)(1((11 (

Hle sheet-eloded onlmiddot ll1d light gully (Iosiol1 OC(lIlS on bul ~ 1l(lPllt

No ltIo(p gully lIosioll wns fOllnd rhil(of no imporlnl1( 101 grnshying this typo is highly middotnlunble 101 (on [rolling (he soil nnd pr(cntillg erosion The dcnse sIn ntis of 1 im bcl Ot brllsh prod u(( n gl(H ( qunntity of littel nnd this is ConsidNed the factor eiljelly responsible for the little (Osion Lowdermilk 10 has pointcd out the Y(IT glcnt vnlue of fOlest littel ill eheeking (Iosion

In gencrlll littrl (on[ is most lacking in thosc typcs whete ([osion is the greatest The qunntjty of littel nnd humus found on (fldl of the eight (oyel typrs (oIlesponded dose] to the orcPl in whieh they were croded EoI eXHmple the w(((t tY]l( whi(h is the mos( seriously rroc((l had Fjfj percent of its HlrnS luCking n litter till

Q L()OEIl~IlLK W C J~neE~n Clf t(lInST 1lTnH o~ 1lX-On IEHCOTIOX XO tHO~lOX JourForestry 28 H4-101 Blus 103Q

EROSION ON THE BOISE lUYER WATERSHED 2]

grass type had 46 p(rc(ut and 50 on to the 1(1L5 t (roded nongrnzing typc wh(Jc but 35 pcrccnt of the tlr(IU were lllcking in litter

enr(ful study of (rosion in rclation to plnnt type strongly indishyelltcs thot nlthollgh tllCle is n rola tion ])(fw(cn thrill to the cxtcn t thllt ((lItain types arc eroded more than otlllrs this is probn bly due more to the aetioll of oth(l factors tluUl to inher(nt proj)(rtils of the pliLllt typlS Fot cxample the weed and gm5S l1I(n8 which itwe the most S(YC1C (rosion hllxe glfLdicnts ehnmet(ristk of the mOle cIod(d HI(HS in g(nclul Fllrthcrl1lorl (x((pt 101 l1llndow ntcns the 01((1

in whiclt the typ(s nrc c1odcd follows (oslly the ordcr of a(((ss1bilit~ to JiY(sto(k 01 in othPl words the 01lt1(1 of intlnsitY of grftzing The (0 III pu t(d ynhll shows thnt 13l pcr(en t of the Yllrintion in (1OS1011 conditions is nsso(intcd lilt YIlIintion in ty[gt(

UI~SIlY O~middot nGIlAII()oI

TlIt (hit illfllltn(( of YPgetntioll on lIosion is S(tll ill its nbility to obshll(t rlll1-ofl jllOdll(( II litt( (on j)rprpnt the 1I((ullllllntio

J ~ fIe I i-tJ

~

- 43 -

11 ~6 iI__ _ ____J1

15middot20 25-30 35middot40 45-50 5560 65-70 75-80 RANGE VEGETATION DENSITY

oIimiddot) fP0ltIOti 0SHHT EROSION bull GUllf EROSIOII

Flf~n~l~ 11 1gt(l1~Jly (If ftlJ1C vcgctnthn aU1 dl~Jrc( or lroiion

oj U[( into stJaJl1lptH IIl1d (nus( I)( tin Htltilll1H tu drop Ihpi loads of silt 01 liUN Thus it is reasonable to Cxpp(t fhnt tI( d(nspr the (g-dation the JllOJC (([pdive it will be in pmiddotlYCntingerosion This liS founci Iuc in tIe pr(H(nt stud in the classes or grnllnhlp wgetlltioll nbon~ ~5-ao rhcre tho roycr wus less thun ao although the Crosioll Was 111 Heh ll1Oro P(ulet1 t and SPytJ( d i fJpJcn ((5 ill density as shown in figllr( 11) mucic less difleJpnrc ill the pP(cntllgl of uren l1odpd Thnt 30 p(rc(nt of the areas within the 5- () d(ngity Clns nre 11ll(IO((d is nccount((1 for in pnrt by the lnct that 12 alit of thc totnl of 18 HIlllS in this elnss huyo rocks holding the soil in place 01 timigtpr reproduction with heavy littcr (not included in the dcnsit~- ll(ordNI) and bcin~ only 65 percent ncccssible to Iivcstock nrc lightly grllzed The higher pcrccntnge of croclecl uren in the G5-70 dlllsity class ItS eompnred to the otlHnnse rcgulnr trcnd is a(count((l fot by tlip fnet tlHlt all of the gullied areas in tlli elnHil fnll 011 hllIsllY HrPlis on stock drivcwuys wliidl nre pxcessicl trailld and Lrnlllplcd hy sllllpmiddot

22 ll~(middotl-lN](l HULIJgllN j28 1 S j)l)Pl (W AWtlCULrUIU~

Thc lCllLtioll betwN1l erosion and pilln t dtnsiLics in ex(css of tilt 2i)-~O dnsl1 is fllltilct elllphnflized by the tv(rng( densities 101111(1 On the H 1(IlS lWing dill(I(I1 t degrees 01 (Iosion The fI (Illge d (naity t1li(ld iroJn 3j on tllens witholl t erosion to 27 wlwle the[e Was sh((t (Iosion onl~ to 21) on HIlH5 ligbtly gullied lind linnllY to 22 011 IlINIS

ith d(pp-glllly PI08ion It is signifiCll11t dso tlwl nlthough 71 I)Pr(Plll 01 u11 the l[NS ]ltlVC d(nsiti(s of 30 0[ less (tnble 7) onl 1(ii Oll t 01 322 U1(I()dNI n1(115 Or 52 prl(Put hn vc th(s( low ltlPl1si titS ng (olllpnlCd tl) 7X p(J((nt of the shcct-erod(d HlpnS S11)(ICCllt oj tll( lightly gulJi(d flnd un but] 01 th( 2~ ))(uTil gllllip(] n[Cns 111( linglp itPtI dh glllli((l ntNt wilh n dttlSLh or lUOI( than an WlIs mbkd to tx(ssiw tlHiling nnt tnllllpling

---~----~~--~ shy-lIullomiddot 1l~JIXltI ~lW~t1 )ll lty or nI(L hUll I I WilYprn~iolt (Iroslou i ~Illl~ Il rbull ~rnsion (rf)~i(J1J--_ shy

lIl11ba XII mba llmlJ(t SlImlfr SItIlIr i Jtrtfllt middotmiddottll ail 1middot ri 1m I~l 23

~ ~ tH 1

2~ 1) 2foO Ia III j 0~1 10J 1 middot1112 III ~~ u 12 I Il 115 1-1 i tl -~lfI W ~1 21 nJ jn l~ -

IfiO 11 ~ I I I 21f -~ 7f 11 a 2 II 11 I 11

middotu ~ 1 OJ 0 1) I

Tltmiddott a liIlII i II 11112 lIJ1I1l

11ffll1y p 1HIiItmiddot ~Irtmiddot JJPldp UI 11u- lit-III tHJJ~ 10 till IWar(sti 1pr(t~HL Itt tJI(Iaho( tahiti tJlt~t(J1IIs 1(0 )rlluJIfr b P ir

TIll fll that d( dlgl(( of (Iosion dews not HIV (oni~laquontly with ynlin j ions in dlllSi t llldlI ~() is n n j nell(alioll of Illpi Jl teJpln~ oj ntiwl itrtos TJJ( 1l1PIls with d(llsiti(i l(sH th1ll iO in(lllcln thow on which J)()tlt thp ytgt[lltioll IIIld foil JlIl( ]((11 JlClmiddotil~r dppld(d b~r 0(1shyWIillg TJlIori~innl plnnt(oYl1 hus h((11 thinlwd Ollt 11 lid (h(JllOII jltlllltllhlP plants JII1( JIllwl~ IlltPIl (Iimillllt(d nnd (1I1l no-l)( foumi ollly IlSlIJllIlHlllH 111 iHOIlli(d 01 lIotfc(Wj pIIWIS I11p iOlf()il Oil th JllHilljt~middot of tIllt Ill(lts with low d(llsiti(s 11n- disI1PIWIII(llnnd Ih([( js lit til if nny pInnt IiIlN Thr InwP] plnnt d(nRiti(s Jlntlllnll~ )((l1l

also on Ow thin (()tlIS(-ROilld fOIlOWlly CXPORUI(S (ul(uiu(iolls or illlt lln(ion hdwe(ll d(llSit~ of Y(gtlnin lind

rosiol1 101 10middot12 IlIPIlS indicat( thnt uS P(j(Pllt or tIl( nlJinlioll in (fusion is nss()ciutpd )lith lJnsity

1I01gt=I 1=[I~SIAll()-I

HOlti(l1tS lllJJllPlOIlS Ilml spnllllillg on lHnII~ SO PP)(PIlI of dl( BOls il(PS)Hd 1111( llndoulJ(NlIy bPNI [ltSIHlIlsihl( ro flO smull ]lHI( (If tlH pr(s(llt Nosioll holly d(pend(llt lIpon til( lHlbHl(OllS

llnns fUI tlwil 10011 supply thpi tlPllllTl(iollB IlllmbplB hnyp 1H111 Ill

important (olJiliIHltillg Judo Idong wiUt O(I~In7lllg by Ji(sloIJ tutltl unll1orablp di1llIlt ill d(piding thiS cO(ing twd thus hll ~INltly ltdu(d h prottfion nfold((llh soil Hlld ~uhj((middott((l it tllp ltJOIP to inlIPlls(d Rlr(lf ltosion g(n Ii~ht rnills Oil JOd(Il-illfCHtltd 1l[NIH 111( likl)Y to ftnlt (lIUjn~ wJlirh Jlln~ d(l(lop 1n(o dCBtlucth(middot gully ([O-iOIl h((lnISl of Ow IIl1l1ost inrlll((tin(( n(uJnulntioll 01 1Ullshy

ofl in tJw 1llYlind of blllTOWS llnd ilnl1JlIIs whirh i hest Ilnill)llls (011shyslllId jlls lilld([ (lJ slIlH( or (h soil

22 ll~(middotl-lN](l HULIJgllN j28 1 S j)l)Pl (W AWtlCULrUIU~

Thc lCllLtioll betwN1l erosion and pilln t dtnsiLics in ex(css of tilt 2i)-~O dnsl1 is fllltilct elllphnflized by the tv(rng( densities 101111(1 On the H 1(IlS lWing dill(I(I1 t degrees 01 (Iosion The fI (Illge d (naity t1li(ld iroJn 3j on tllens witholl t erosion to 27 wlwle the[e Was sh((t (Iosion onl~ to 21) on HIlH5 ligbtly gullied lind linnllY to 22 011 IlINIS

ith d(pp-glllly PI08ion It is signifiCll11t dso tlwl nlthough 71 I)Pr(Plll 01 u11 the l[NS ]ltlVC d(nsiti(s of 30 0[ less (tnble 7) onl 1(ii Oll t 01 322 U1(I()dNI n1(115 Or 52 prl(Put hn vc th(s( low ltlPl1si titS ng (olllpnlCd tl) 7X p(J((nt of the shcct-erod(d HlpnS S11)(ICCllt oj tll( lightly gulJi(d flnd un but] 01 th( 2~ ))(uTil gllllip(] n[Cns 111( linglp itPtI dh glllli((l ntNt wilh n dttlSLh or lUOI( than an WlIs mbkd to tx(ssiw tlHiling nnt tnllllpling

---~----~~--~ shy-lIullomiddot 1l~JIXltI ~lW~t1 )ll lty or nI(L hUll I I WilYprn~iolt (Iroslou i ~Illl~ Il rbull ~rnsion (rf)~i(J1J--_ shy

lIl11ba XII mba llmlJ(t SlImlfr SItIlIr i Jtrtfllt middotmiddottll ail 1middot ri 1m I~l 23

~ ~ tH 1

2~ 1) 2foO Ia III j 0~1 10J 1 middot1112 III ~~ u 12 I Il 115 1-1 i tl -~lfI W ~1 21 nJ jn l~ -

IfiO 11 ~ I I I 21f -~ 7f 11 a 2 II 11 I 11

middotu ~ 1 OJ 0 1) I

Tltmiddott a liIlII i II 11112 lIJ1I1l

11ffll1y p 1HIiItmiddot ~Irtmiddot JJPldp UI 11u- lit-III tHJJ~ 10 till IWar(sti 1pr(t~HL Itt tJI(Iaho( tahiti tJlt~t(J1IIs 1(0 )rlluJIfr b P ir

TIll fll that d( dlgl(( of (Iosion dews not HIV (oni~laquontly with ynlin j ions in dlllSi t llldlI ~() is n n j nell(alioll of Illpi Jl teJpln~ oj ntiwl itrtos TJJ( 1l1PIls with d(llsiti(i l(sH th1ll iO in(lllcln thow on which J)()tlt thp ytgt[lltioll IIIld foil JlIl( ]((11 JlClmiddotil~r dppld(d b~r 0(1shyWIillg TJlIori~innl plnnt(oYl1 hus h((11 thinlwd Ollt 11 lid (h(JllOII jltlllltllhlP plants JII1( JIllwl~ IlltPIl (Iimillllt(d nnd (1I1l no-l)( foumi ollly IlSlIJllIlHlllH 111 iHOIlli(d 01 lIotfc(Wj pIIWIS I11p iOlf()il Oil th JllHilljt~middot of tIllt Ill(lts with low d(llsiti(s 11n- disI1PIWIII(llnnd Ih([( js lit til if nny pInnt IiIlN Thr InwP] plnnt d(nRiti(s Jlntlllnll~ )((l1l

also on Ow thin (()tlIS(-ROilld fOIlOWlly CXPORUI(S (ul(uiu(iolls or illlt lln(ion hdwe(ll d(llSit~ of Y(gtlnin lind

rosiol1 101 10middot12 IlIPIlS indicat( thnt uS P(j(Pllt or tIl( nlJinlioll in (fusion is nss()ciutpd )lith lJnsity

1I01gt=I 1=[I~SIAll()-I

HOlti(l1tS lllJJllPlOIlS Ilml spnllllillg on lHnII~ SO PP)(PIlI of dl( BOls il(PS)Hd 1111( llndoulJ(NlIy bPNI [ltSIHlIlsihl( ro flO smull ]lHI( (If tlH pr(s(llt Nosioll holly d(pend(llt lIpon til( lHlbHl(OllS

llnns fUI tlwil 10011 supply thpi tlPllllTl(iollB IlllmbplB hnyp 1H111 Ill

important (olJiliIHltillg Judo Idong wiUt O(I~In7lllg by Ji(sloIJ tutltl unll1orablp di1llIlt ill d(piding thiS cO(ing twd thus hll ~INltly ltdu(d h prottfion nfold((llh soil Hlld ~uhj((middott((l it tllp ltJOIP to inlIPlls(d Rlr(lf ltosion g(n Ii~ht rnills Oil JOd(Il-illfCHtltd 1l[NIH 111( likl)Y to ftnlt (lIUjn~ wJlirh Jlln~ d(l(lop 1n(o dCBtlucth(middot gully ([O-iOIl h((lnISl of Ow IIl1l1ost inrlll((tin(( n(uJnulntioll 01 1Ullshy

ofl in tJw 1llYlind of blllTOWS llnd ilnl1JlIIs whirh i hest Ilnill)llls (011shyslllId jlls lilld([ (lJ slIlH( or (h soil

__

EHOSlO~ O~ THE BOISE 1U VEH WATEmHIEf) 23

On ol1(-thiJ(L of (h( HIPUS (()cJpd hy t11( sunpy inf(H(ntioll In 10cLcI1 Is wns JlHcii um (H hCIl y Pockpt gOplHIS C~homomJ8 fllseis fllR(U8) (1( by fnr the most nbulldnl1t 81)((]P1 IJ(Ulg fOllnd on 01 peJ(ent of nlllll(nH glOlllld squirlpls ((iMhI8 irIftO(lNis) el fOllnd Oil slightly 11101( thun 1 p(recut lind 14 PlI(pni of nil 1l1(IlS W(lt inf(stcd with hoth 1[wrics

In gtIl(Inl 11I(IlS hltdlv infrsLpd wiill lo(I(nts tllC fOllnd (() hI s(clrlv cmd(d 111( (lost (olldlltion il(t(tll lOdllt inp(Il(ioll and PI)sion is showll h)r tJw fn(t thut ollly 441)(I((n( of til( 1lI(I1S with 110 rodcnts W(IC Nodl(l hil(middot with SlI((lsi(middot illtIpost ill infpsttlshytion Uln figul( JUJIlps to 01 la nnd finally (0 ~~ IlPlpllt 101 light J1lCdiIlJll lind 11(IIYY infptntions lNqw((hpjy s ShOWll ill tuhlt ~ nnd liglll l~ glrlly lIosion wus likpwis( fOlllHL OJl It 11111lt11 glCIlItI

lCO I

~ oe0---~-------------________ shy-lt

~ f

~ ( It t

I

~ r

___L-r__J __L I r ___

HUlt

Dr LRX0r~ 0hllT ERj~lVN I GJLLI ERCSI~ lttl It J - Und(ut iur(~~loItiun and tCIIt1l uf lrrpUri

PIOPOltiOJI of firp IWIl-il) inr(middot~td 1I1(IIS tirlln 011 tho 111(11 Jll(JlI(Ishy1l(ly 01 light I in((pd

T JILl )iIiIJlllilltl t~r tlIIIi ill (([Ill erosioll IZlt IlCronUllfl [0 rod III iJlll lIlinl

011 Ii~hl1llIlIllIIrl

rut

Study 0 (Ilt tlntn 011 til( d(gl( oj IOdtllt inpstnlioll ill n1lntion to (lOsion 1101111 willi (ire ([u(1l 1llIlninillg to til( 0111(1 u(tOIS tl(t(lt1 ill this SUI(Y fUIlirN (Illipirnsilwd tire impoltnn(( of 1Oltilnlll HntI jlointld out I(sons 101 tll( llggnlyalNI llosion lIIHI(I ((Itnin oth(r conditions Fol (XlIllIplCin lh(middot diusion oj pnlltiiCnt it IS round tlllltwhih CJOSiOll lt1((1(11(lt1 IlIfllI IInifolmly with tOI(IlS( in glHlishypnts IInltl(I ~ii PPI(lllt still 10 ]gtPIc(ntof Ih(l((middot1 nlPHS whlll (lpgl(( of lojJt (oliid not hun ])((111 II Judol (Il tloded ThaI 1ud(Il(s

24 lECHNICAL BULLETI)f ij2S L S DEPT OF AGRICULTURE

hlty( 1)((11 Ult impoltnn t fl(tol in tilt lIosion of these IIreus is indicttted I bv the (net t1mt nIl of them Ul( mo((rntplv OJ heavilv infested while tflO IPllluininp 81 pPl((nt of the lPyellU(I~ls 1110 (ither uninfestod Qt ~ only lightly so 1n t11( Hlltllysis of the dlttu 011 infpstnLion on slopcs the trends do 110t diO(I from the p(lllltd tlrllltl towtlld increased (lrosion wllllc there is un inCl(uHe ill lod(lIt infrstntion

Tile ex(cssive erosion 011 sOlltherlY us (ompnl((] with northerly (XPOSUl(s is pnltiully (xpluill((l bT tho fn(t thut rodent infrstution is 111l1h1linlly PI(nt(l 011 thl JOIn1(I probably h((lluso of the wn1ll1ll situatiolt und b(cnus( th( plunt spli~s 11](1( Ille III 0 1( uttrnetivl to lod(l1ts thllll Oil th(IIOItlHIIY slopts It (Ull he S((11 thnt with lR pelCrn t of the (Olllblll((] lloltll Jllll 1I(ust a lid nOlth w(st (xpOSUI(S modemt(I) illflsi((I us (Oll1poIpd It) a() ]gtPI(lIt 01 the south sOlltilshyW(st nnd sOllth(lIst I1SI)(Iels nIld (j P(I(tlI~ h(lIyily infesltcl liS (Olll shy

pllnd to 10 pel((lIt II ill[(stnlion on south(Ily (IXPOSUIPS is lll1( shy

ti(nll twi( liS S((I( In itw 01 Uw d(tid(d (1(11(1 tonld ill(l(lIilmiddotd (losi()I witll infIlttIS( in Iodpn till f(station lodpnl 11 PP(UI tolmve bCn It (olltljigtllting 11(OI ill lil~ JlIndpdnllintioll of (tOsioll with nspltCt

I tis signilietlllt to not ill Illn 1(latioll of lotknt inftstntion to PIosion on Ill(tlsith ltINP littpI lind (]((P ioiJ tllat of till 4) (lotlld nreus of this des(Iiptioll onl i wns uninf(sl(d

jOdPlltS also flp[lnl to hun i1ncl lin illfiuIl(( on th( (losion in til( w((lt1 u nd l1()lIglO 7ing tYP(IS (ill JOInwI til( most s(Y(I(I~ (lo(IPd nnd til IllttlI til( 1(Ist (loltipd of tll ligltt plnnt tYI1t In nil of tho otll([ tI)(il til( Jlll(Pllt of tllpail hieJ Wl1( uninf(s(rd or only lipbtly illf(strd ltlngtd floll1 )0 to (iii while in the we(d type it was 20 und in tlte l1onglllzing typo ll jWI(pnt

I~xnlllillntioll of tlll datu 011 ]o(knt in f(itntion in relatioll to d(llsity of Y(gdlllioll nyelllltl 110 tnllds nlh(l tlWll thl on(s j)Ieyiousl) indi(lIt(ti i ( nIl ill(IlIIS( in (Osion with thp ltINleuse in d(nsity tlwL is IlsHo(ini(d with jll(IPIlS(d odtllt inr(slution lIo(yeI it did show tllllt no gully (Ioillll pitiJ(1 slJullow 01 dt(p WIlS JOlllld on alPIlS ith dlllsit(S glpatl1 (hUll middotW (X(ppt WhlI( tll(s( tlIeHS W(lIC inflHlltd witll IOdPlIts lllltii(lIting tlH illlpmtHIJ(C of lodpl1ts ill Cuusing gully (Iosioll nt lh(lil( hi~dlll dlllHiti( By (alltulntioll of tIl( Idio of hI nlliII)(( of til lIleans of th( glOIips [0 tll( lllilll((1 (If l11 tIl( glOllpS (Ollligtill(d Ih( Illintion in (Iosioll nss()(int(d with rulinlioll ill l(ldllltinf(slnion WIIS foulld to bp 40 jltItlnt

AClESSlJIlIITY TO lnESTOCK

The (hall~(s brought about by tl( (onlinu((1 lli( of a rangp 1I1(IL

btyol1d its ell pucity aro lIsllll11y PI gllId lIul II nel II t nII one time mny be impeleeptibl( In the (lid I lto~I thtHl (hanges mn)~ be profound Jt ttpPCHIS ObVIOUS on tIll BOIse H1(1 wu telsiJf1 thn t pnst exelssiYe llse hus ll1(tlsurnbly thinnrti tll( stand of plnnt species must yullluble for forngo---witiCh fr(j lien tly ale tht speCies most valuable for control of erosion-nnd in pinetls hns actually caused its replncement by n type less ynluable os fornge nntl much less effective in controlling soil erosion In this locnlity dllllllcterized by course loose soils gltlzing sufIiCitl1 L1Y ligh t llot to in tclf(le with the normal physiologicnl functions of till fomge spcCies mny still he henvy enough to sturt erosion Hllll to ng-~rnYnto (Josion alrelldy startpoundtl The y(nrly lell1oynl by gllllling of (Yl11 n pOIlion of the plnnt plOwth thnt othllshywise woulll (onllibute to thl litt(l (OPI is sj~lliIietlllt 100 paltitushy

21 glWlil)~ 0gt[ TIm HOIKE ml~1t WTKHHllI~1l

Inrly tit( h1(11 king II p nlld disptIsioll or [lit j)otl(t hmiddotp (()(~I of twig 1tIlVPS find othpldplld pg(lnl II1nttlitl by tlumpliug tOgPUItI with the I(compnnying distulbnn(p of the stllICtUIl of tlip filllfll(l soil l1ndoubtedly is of glcnt impoltnn(e in eluRing (108ion

] t wns pointpd out 1l1H1pl tJ1P dpSCliplioll or fjpld Jlwthods t11nt t11r nce(ssihility or nn nltn to lin8to(k Wllf consicip]NI to bc thc bCRt flTflilublc ciilc(t ])HnSUIp oi tlin (uillulntin ((lPc(j or glfling lIl nnd tllPldolc fin inltlillct inltlpx of till p(p( of gltltillg on PIosion lhnL this is tlllP is inltii(ntpd hy flip JueL thnt 011 tillt lYCIlgP the ll11t1od((1 HIcns nrc 03 l)(l(pnt fI(((sRihle in (()llilat to [lir (1O(p(( IIIPI1S which HIl flOIH 92 to 03 ])(gt1((1 t nc((ssi hk

TIl( PClc(lltngC or slH(( POsion wns round (oinCIPflS( fuil1 (()nshysis[pntly liS 111( 1I1(llslw(llllp IlHH( 1I(((ssihl( to Ihpst)k (fig 1~ nlld

T 100 rshy

-ltgtltt 40

~ ~ ~ 2() v-_ (

~ f

Igt

A~ M fy ~tfrltmiddotIf~middot

o~i f l ~ Q~(~1l

tHIlllt nl flom 1 PPI((llt Oil IIIP Itss l(((ssilgtl( HI(l1S to Oii pltlcrnt Oil

(host fully H(((ssiblt lh( il(IHI ill gull~middot (IOSioIl wm ns IllQ11011l1(pd

though pss l(gullil (xcppt in (1111( illstnIH(s 110 gully (IOSIOIl WlIS

round on IInIIS Ips thnn ])(1((11( HC((ssiblt In 11(( tlllpt (lS(S olhrl rnctnl llPIHtll to H(lIll( rot t1H -1111 (I(lsiOI1 IO 01 t1ll1l1

nlthollgh nt PI(Spllt ]lIn(ti(IlIl inll(((ssihJI to (ntll WII T)(iollslv ()PIWI1Pc nnc 11111111gt1(lt1 hy sliPlp TIi( otlwl lIl(I with SiNP slopts is 1Il1(ISNI by glllli(ls orifiIlUfillg llll hptiy 1111ld lind 1l101( n(c(ssihlll1(aslho(

~hIJlIImiddot 1)[[(1shy~hNt ~lIll~ lul(1-(011 prtmiddot1fu lJI4l1JIl

llI111(r Sumff Yu7II1lrr ~t111l1Itr ~1tm(r Pi tllt nmiddot~j 11I O 1 1 110 la I20middot1 ~$ 111 1 II 11 II wmiddotr~ 2 I ] iill -1 j(iG-85 II Ii I lOS UI8(1-100 _ (011 k3 20 i han 702

fIJt1 11f bull _~~ _____ Z I-~~

20 JECHNlGAl BU1LE11N rj~8 u S DEI] OF AGRIC1UIUnlltJ

EXlIluinution or datil l(cllling thn modiryillg influcllcc or aeecHsishybility 011 the cflect of other fnetors IUltiJ(1 illdicates why (1osion mny hnye b(on Ineking under ccrtain (onditions nnd so pronounced ul1(lelothcrs

As brought out under the discussion or grndifmt (l complete lCshy

YCIRnl of the no]mnl trend toward inclenscd c1osion with inc1cascd gIIHiitnt was found 011 alCIlS with gmdicnts in cx(css of 35 l)Icent 1t is nppUnllG thnt the grcatcr usc by liYeftock of the lowC] gludicuts is olle of the more important eauscs iI not the prin(ipnl cause of this condition That the stccpcr tho slope the glcntc1 is the ClOSiOll proid(d grnrinp also is the snme lit nil slopps ifgt bOllle ou1 hy the

_oj

I

73 1

middot1

1-___ bull_~-_--~ _11-~t_l_-1-_---~r_3---I 0-25 26-45 46-65 euroG +

GRADIENT (PERCENT)

oNO EROSICN 0 SHEET EROSION bull GULLY EROSION

F(nenE ll-Clmllrni nrHI degree of erosion 011 nrcas full) ncccssihie III liyelo~k

study of nrPlls fully fHC(ssibl( On such I1rea as shown ill tnble 10 find J1g11ItIJ- tlosion is plog1(IssiYely wOJse with inc1el1se in glndient

TUII 10-- TIt( relation o gradient to drgrcr o erosion on (rra~ fully (lCC(8~ibli 10 ihlsock

-------~----- --~-- ~~- -_-----XC) ~II t 18lttlluw-l IletI- 1

lt1p~ (percent) u ~lIl1r I Ilull) _11 orcas(lrnHon I ~rnSlOn ~ ero~j(u I (lrosion I

I

Percent o 2i ~~ ~ n2) Ji~~ _~_4~ ~_ 3a11 4ri-nL ~ ~_ middotWmiddotI 60+_ bullbullbull 3X

TutuL __ 1000

bull The glfting Iwtor is nlso closely nssodnled with Ull vtlying tlosion

(OIHlitions found 011 difrcrent aspects III gCnelnl the plnnts whieh ])JNlominnte on south slopes fire mOJe pnlntnble to livestock than tho brushy Y(lgctntion common Oil nortll(lly exposures The fn(t that south s10I)CS nrc 82 pCJ(ent flceCssiblc to liYCsto(k while northerly expOSUlPS nl( only 62 ptJCcnt flt((ssiblc iltii(ttcs the henviel dcgleo of usc to which tilCsc tllNlS havc beCll subJccted

lDROSION ON rIlE nOISE lUVER WNJEHSHED 27

It is also jndieatrd tImt hcnyy gmling hnH contdbul cd to th( rloHion OIl Hw various types The wrcd und gmss typcs wlwlCI the NOS ion has been the grcntrst uIe nPPloximatoly n3 PCI(CIll uccessiblC to jiyeshystoek while the l1ongrn~ing liype which hns bern 1cnst eroded is only 22 pClcCnt ncccssible

Arcns with vegctlltion densitics of 30 or less w(le found to bC cloclCC] ll1ueh more thllll nrrns with highcr densitirs Jhis difrrlC1Hr lIlily be du( in pnrt to the fILet that the aleus with 10w(1 drllsiticH lIJC -Ifi~cd and trailcd considerably morc sillee they am OIL tltc nYCmge 80 ]gt(1_

(cnt ucccssible to livestoek while Ulcns with dcnsitics in c-ccss of 80 nle on the nYCInge but 74 pel(cnt n((tsRibl(

The complltntions show 11)5 PCICllllt of the yurinnce in crosion to he IlSS0(jnt(middotd with neecssibility to livostoek A CorlcIntioll of Hll(h mngllitnde Oil molc than 1000 uIPHS iud iCl1tps thllt g1n~il1g by li estOt k hUH I)((n n highly impoltH 11 t fndol ill enusing NORion

DISCUSSION OJ RI~SUIrs

Tho YILrinn(o ill (1osion nsso(int(d with en ell of tho scyon Jndols ~xplesRod in P()((llt appenIs in ns(ltnltiing oldcr of ImpOltall(( Ilil JolJow

Parr litGradiCnL _____ gt ________ bull ____ bull __ bull 2 lRodent infpslution_ 1 0

Plunt dCn-it~_ Ii I)Aspect _______ _ 10 Ii-iuilcOlitiitiolls _______ _ _ _ _ __ __ 128Plant type___ ______ __ _ _ __ __ 13 middotl

CIlItllaih-c elimiddott of paHt gJILzing as CXllICSSPc Igt~ U((sHiI)ilit of Illllle toII-estock -- - __ -- - __________________ _ ___ ____ ___ __ _ _ _ _ _____ _ _ _ _ 15 3

1ICII (( tllPll(gt fnetors n(Count 101 npploximat(ly 70 ptJ(Cllt of thc YHlintionin Plosion hile some of the pelccntngps nrc quite 8I11n11 they HIC ill ltYPIY C1lte signifieunt rublc 11 is nil nnnlysis of the ytllinnce by tlw Fishtl 11lPthod plcyiousiy rcfc]lcd to The last colshylImll in this tablc pxprtsscs the ll1tio of cHch l11(nn SC[UnJO to UIO mcnn RQlll1lC of the I(siltiuul The lo(J limit 101 signifirHI1(C (lltld ht not J(middotss thall 4()j hOIlltP nil the 11((01- 111( d(1fillit(lv Hignifi(llIlt in thtil rrl(Ct II pOll CIOSiOIl

[lly Ill Fbhtf I1llfhl)lltpitillltl nil PJI 1IIIlIIrI IIJ

oounol l of nrinlluu J)(If(I(I of hllln Hnlin tn (rt[dulli dam i SIUaro residual

A(((s~hIII~middot _ middot1 U U720a (lUISOI 137 iiJInnt t~I)(O_ 7 (JOaH OOUH 1iU ~Hollcoll( IlIous i 07122 OI2~A~Jlecl _ r~~ 7 Oilii7 001 )hjIlnnL dcn~il~ 7 012111 (JOtHl ai nHodonl infeslnUlln _ a 1I22h7 ~ ()Of2 [is 2OrnelicnL J Ulfilill OOI7J 117HsiciulIl bullbullbullbull _ _ __IUiJ2 _HI1II OOIlJlI1 _J~~lotIlL i I lall I 17aSl i

1lIC ahon~ points to gll1~ing alld JllOIC pfutic1I1Hlly otlgrning nnd its nttpmlnnt cflcwts of dCplctioll of plnnt rOWl I1lld JittN find trn1l1pling of the soil n the most impOItullt fnetol (oJltlibllting to closi011 Howcycr ns nllefldy llHntiollcd tJWlC 1110 mnny intellpJnshytions bctwepn factors which when more criticnlly studiNl tend to

28 T1WIlNICAI BU[LElIN i2S U S DEPT Oli AGlUCUlJlUHE

minill1i~c ((rinill fndmiddotors nlld to (mphllsi~( th( impoltulw( of oth(Js These justify furthel discussion

It is very evident that gradient in spite of the importance which migh t he a ttached to it on first though t is largely significant as a factor in accelerated emsion only as it aJfllcts the influence of other factors Oth(r thing heing qual it mi~ht he expected that the st((p(r tho slope the more erosion there will be However the results of this study show that on the 11verage erosion increased with inerense in grndient only lip to 35-pereent slopes after which erosio1 decreased with inClNISe in gmdient Thele WIlR relntively ]CS closion on slop(s of 70 80 and flO percent thnn on slopes of 20 01 30 pelCent It is uppnrent thnt OY(I 11 loner period of yenls under nntlllul (ondishyLions II bnlllllcc is estnhliS]1(d lthetwccll plnn t (OY(I soil nne] (Iosion which tlLk(s illto 1I((Ollnt ynrious fU(tOIS ineillding gludiellL ]11lt stcepe] tlte slope ill (xccss of 35 P(I(CII t the I(ss IH(essihle it is to liwstoek TDlosion illlIells(s yely rapidly Oil tJl( slop(s in nX((SR of a5-p(fCell Ii gIudieIl t wh(lI th() ILIC fll Iy U(llssihlt to li psio(k Also 011 the slop(s 1IndpI 2() ]JlICent which on the lIlIUPP hno ItJli~d1 d(glft of I((ossibility Nosioll ill(I(lIs((1 with in(I(l1s0 in glflditril Iho (ollcl usions s(lm i lIls(upn hl( lltn t p1tIltiiell L is of Ill inOl i III portn neo liS fl fllcto) in 1I((1el(lIIt((l Nosion until the inOuenee of othrl fnd-ol is hrought into piny thnt gl[~ing is the (hief distulbing fnetor which OPllU trs in IIssoeintioll wi th slopp nnd thllt on grn~ed slopes e]osion inc]oHses rnpidly with in(Iellso ill glndiont These lend to the further conclusion Oint th( h(niel tho grnzing the gllntN the neeole1lltion of erosion with jHICnse in grndilnt

Rod(ntj inflslntion shows fl low ]gtlt]C(ntllgo of Ynrinno nssoeilltld wi t h Nosion i(YNIIIPlps i t is of 11111 i IIlportlll(p in fll( (Iosion pm bshykill h((ltIIsli t i OIW of thI few con t 101InhlC fn((ols ApPloximn tply foul-firths of thn n(Il SIIITtYN] WIIS inftstlltl with roltilnts ILpploxishymntdy OlH-thiJ( hnying I1llciiurn ol]H1nxy infpstnlion lvlo](oY(lthC inlpstn tion wns hlnYitst on tht sou thNly slo]1(s whieh nlo nlso t he most hlllyily gIlL~(d nnd which 1Ir1e the soil plant typ(s nnd dlnsities nntllllllly 110st flllS((ptible to a(((IlIatcd Nosion GIIl~ing nlso plllYS some pnlL in locilnL dnmng(llnny of Illl JUIlwnys of poe(t goph(rs nl( situnt(d within (i to S in(h(s of the 5U1ln(( Und(lthlso eonclitions liYlsto(k in pnssing OV(l the Innel trnlllplC nnd (nYImiddot in the runs which 111( soon cltnnlll Ollt agnill hy the rodrnts This (xtla digging IlIlthll in(J(ns(s the distulbnnee or titlt soil

Plnn( c(nsity oLh(l things lwing (qUill might br txprctN] to hnye nn 111YPISe 111lntioIl to f1c((lernt(d Closiol1 i ( thn grent(1 the plnnt dll1siLy tll( smnllltL thlt (1osion lW(IUISe of thr plOt(dion nOol(IPd by dlllse vlgltntioJl lind ]ittlI (oY(r AJthough this is undollbtedly trlle in the Ifllgel spnsC it seClllS nppnlent on the Boise 11ilt1 wntrshysllld that ns hl the (nse of grndicnt more or llsS of i1 bnlan(e b(comes estnblished under llnturnl (onditions hetween erosion Ilud the plnnt t

density nflordld by the normnl climute Evidlntly erosion is ncshycelernted only whtn the normnl density is disturbed by periods of unIavornblc clin1l1te severe rodent infestation 01 grn~ing On this watershed the plnnt density has been reduccd by It combinntion of these three fnetors but more especinlly hy oYClgra~ing nnd iIlcidental trnmpling by livestock

It is shown chllt nspeet has II high percent of vnriunce IIssocinted with accelerated erosion It is ILppnrel1t howcver thnt this is not

24 lECHNICAL BULLETI)f ij2S L S DEPT OF AGRICULTURE

hlty( 1)((11 Ult impoltnn t fl(tol in tilt lIosion of these IIreus is indicttted I bv the (net t1mt nIl of them Ul( mo((rntplv OJ heavilv infested while tflO IPllluininp 81 pPl((nt of the lPyellU(I~ls 1110 (ither uninfestod Qt ~ only lightly so 1n t11( Hlltllysis of the dlttu 011 infpstnLion on slopcs the trends do 110t diO(I from the p(lllltd tlrllltl towtlld increased (lrosion wllllc there is un inCl(uHe ill lod(lIt infrstntion

Tile ex(cssive erosion 011 sOlltherlY us (ompnl((] with northerly (XPOSUl(s is pnltiully (xpluill((l bT tho fn(t thut rodent infrstution is 111l1h1linlly PI(nt(l 011 thl JOIn1(I probably h((lluso of the wn1ll1ll situatiolt und b(cnus( th( plunt spli~s 11](1( Ille III 0 1( uttrnetivl to lod(l1ts thllll Oil th(IIOItlHIIY slopts It (Ull he S((11 thnt with lR pelCrn t of the (Olllblll((] lloltll Jllll 1I(ust a lid nOlth w(st (xpOSUI(S modemt(I) illflsi((I us (Oll1poIpd It) a() ]gtPI(lIt 01 the south sOlltilshyW(st nnd sOllth(lIst I1SI)(Iels nIld (j P(I(tlI~ h(lIyily infesltcl liS (Olll shy

pllnd to 10 pel((lIt II ill[(stnlion on south(Ily (IXPOSUIPS is lll1( shy

ti(nll twi( liS S((I( In itw 01 Uw d(tid(d (1(11(1 tonld ill(l(lIilmiddotd (losi()I witll infIlttIS( in Iodpn till f(station lodpnl 11 PP(UI tolmve bCn It (olltljigtllting 11(OI ill lil~ JlIndpdnllintioll of (tOsioll with nspltCt

I tis signilietlllt to not ill Illn 1(latioll of lotknt inftstntion to PIosion on Ill(tlsith ltINP littpI lind (]((P ioiJ tllat of till 4) (lotlld nreus of this des(Iiptioll onl i wns uninf(sl(d

jOdPlltS also flp[lnl to hun i1ncl lin illfiuIl(( on th( (losion in til( w((lt1 u nd l1()lIglO 7ing tYP(IS (ill JOInwI til( most s(Y(I(I~ (lo(IPd nnd til IllttlI til( 1(Ist (loltipd of tll ligltt plnnt tYI1t In nil of tho otll([ tI)(il til( Jlll(Pllt of tllpail hieJ Wl1( uninf(s(rd or only lipbtly illf(strd ltlngtd floll1 )0 to (iii while in the we(d type it was 20 und in tlte l1onglllzing typo ll jWI(pnt

I~xnlllillntioll of tlll datu 011 ]o(knt in f(itntion in relatioll to d(llsity of Y(gdlllioll nyelllltl 110 tnllds nlh(l tlWll thl on(s j)Ieyiousl) indi(lIt(ti i ( nIl ill(IlIIS( in (Osion with thp ltINleuse in d(nsity tlwL is IlsHo(ini(d with jll(IPIlS(d odtllt inr(slution lIo(yeI it did show tllllt no gully (Ioillll pitiJ(1 slJullow 01 dt(p WIlS JOlllld on alPIlS ith dlllsit(S glpatl1 (hUll middotW (X(ppt WhlI( tll(s( tlIeHS W(lIC inflHlltd witll IOdPlIts lllltii(lIting tlH illlpmtHIJ(C of lodpl1ts ill Cuusing gully (Iosioll nt lh(lil( hi~dlll dlllHiti( By (alltulntioll of tIl( Idio of hI nlliII)(( of til lIleans of th( glOIips [0 tll( lllilll((1 (If l11 tIl( glOllpS (Ollligtill(d Ih( Illintion in (Iosioll nss()(int(d with rulinlioll ill l(ldllltinf(slnion WIIS foulld to bp 40 jltItlnt

AClESSlJIlIITY TO lnESTOCK

The (hall~(s brought about by tl( (onlinu((1 lli( of a rangp 1I1(IL

btyol1d its ell pucity aro lIsllll11y PI gllId lIul II nel II t nII one time mny be impeleeptibl( In the (lid I lto~I thtHl (hanges mn)~ be profound Jt ttpPCHIS ObVIOUS on tIll BOIse H1(1 wu telsiJf1 thn t pnst exelssiYe llse hus ll1(tlsurnbly thinnrti tll( stand of plnnt species must yullluble for forngo---witiCh fr(j lien tly ale tht speCies most valuable for control of erosion-nnd in pinetls hns actually caused its replncement by n type less ynluable os fornge nntl much less effective in controlling soil erosion In this locnlity dllllllcterized by course loose soils gltlzing sufIiCitl1 L1Y ligh t llot to in tclf(le with the normal physiologicnl functions of till fomge spcCies mny still he henvy enough to sturt erosion Hllll to ng-~rnYnto (Josion alrelldy startpoundtl The y(nrly lell1oynl by gllllling of (Yl11 n pOIlion of the plnnt plOwth thnt othllshywise woulll (onllibute to thl litt(l (OPI is sj~lliIietlllt 100 paltitushy

21 glWlil)~ 0gt[ TIm HOIKE ml~1t WTKHHllI~1l

Inrly tit( h1(11 king II p nlld disptIsioll or [lit j)otl(t hmiddotp (()(~I of twig 1tIlVPS find othpldplld pg(lnl II1nttlitl by tlumpliug tOgPUItI with the I(compnnying distulbnn(p of the stllICtUIl of tlip filllfll(l soil l1ndoubtedly is of glcnt impoltnn(e in eluRing (108ion

] t wns pointpd out 1l1H1pl tJ1P dpSCliplioll or fjpld Jlwthods t11nt t11r nce(ssihility or nn nltn to lin8to(k Wllf consicip]NI to bc thc bCRt flTflilublc ciilc(t ])HnSUIp oi tlin (uillulntin ((lPc(j or glfling lIl nnd tllPldolc fin inltlillct inltlpx of till p(p( of gltltillg on PIosion lhnL this is tlllP is inltii(ntpd hy flip JueL thnt 011 tillt lYCIlgP the ll11t1od((1 HIcns nrc 03 l)(l(pnt fI(((sRihle in (()llilat to [lir (1O(p(( IIIPI1S which HIl flOIH 92 to 03 ])(gt1((1 t nc((ssi hk

TIl( PClc(lltngC or slH(( POsion wns round (oinCIPflS( fuil1 (()nshysis[pntly liS 111( 1I1(llslw(llllp IlHH( 1I(((ssihl( to Ihpst)k (fig 1~ nlld

T 100 rshy

-ltgtltt 40

~ ~ ~ 2() v-_ (

~ f

Igt

A~ M fy ~tfrltmiddotIf~middot

o~i f l ~ Q~(~1l

tHIlllt nl flom 1 PPI((llt Oil IIIP Itss l(((ssilgtl( HI(l1S to Oii pltlcrnt Oil

(host fully H(((ssiblt lh( il(IHI ill gull~middot (IOSioIl wm ns IllQ11011l1(pd

though pss l(gullil (xcppt in (1111( illstnIH(s 110 gully (IOSIOIl WlIS

round on IInIIS Ips thnn ])(1((11( HC((ssiblt In 11(( tlllpt (lS(S olhrl rnctnl llPIHtll to H(lIll( rot t1H -1111 (I(lsiOI1 IO 01 t1ll1l1

nlthollgh nt PI(Spllt ]lIn(ti(IlIl inll(((ssihJI to (ntll WII T)(iollslv ()PIWI1Pc nnc 11111111gt1(lt1 hy sliPlp TIi( otlwl lIl(I with SiNP slopts is 1Il1(ISNI by glllli(ls orifiIlUfillg llll hptiy 1111ld lind 1l101( n(c(ssihlll1(aslho(

~hIJlIImiddot 1)[[(1shy~hNt ~lIll~ lul(1-(011 prtmiddot1fu lJI4l1JIl

llI111(r Sumff Yu7II1lrr ~t111l1Itr ~1tm(r Pi tllt nmiddot~j 11I O 1 1 110 la I20middot1 ~$ 111 1 II 11 II wmiddotr~ 2 I ] iill -1 j(iG-85 II Ii I lOS UI8(1-100 _ (011 k3 20 i han 702

fIJt1 11f bull _~~ _____ Z I-~~

20 JECHNlGAl BU1LE11N rj~8 u S DEI] OF AGRIC1UIUnlltJ

EXlIluinution or datil l(cllling thn modiryillg influcllcc or aeecHsishybility 011 the cflect of other fnetors IUltiJ(1 illdicates why (1osion mny hnye b(on Ineking under ccrtain (onditions nnd so pronounced ul1(lelothcrs

As brought out under the discussion or grndifmt (l complete lCshy

YCIRnl of the no]mnl trend toward inclenscd c1osion with inc1cascd gIIHiitnt was found 011 alCIlS with gmdicnts in cx(css of 35 l)Icent 1t is nppUnllG thnt the grcatcr usc by liYeftock of the lowC] gludicuts is olle of the more important eauscs iI not the prin(ipnl cause of this condition That the stccpcr tho slope the glcntc1 is the ClOSiOll proid(d grnrinp also is the snme lit nil slopps ifgt bOllle ou1 hy the

_oj

I

73 1

middot1

1-___ bull_~-_--~ _11-~t_l_-1-_---~r_3---I 0-25 26-45 46-65 euroG +

GRADIENT (PERCENT)

oNO EROSICN 0 SHEET EROSION bull GULLY EROSION

F(nenE ll-Clmllrni nrHI degree of erosion 011 nrcas full) ncccssihie III liyelo~k

study of nrPlls fully fHC(ssibl( On such I1rea as shown ill tnble 10 find J1g11ItIJ- tlosion is plog1(IssiYely wOJse with inc1el1se in glndient

TUII 10-- TIt( relation o gradient to drgrcr o erosion on (rra~ fully (lCC(8~ibli 10 ihlsock

-------~----- --~-- ~~- -_-----XC) ~II t 18lttlluw-l IletI- 1

lt1p~ (percent) u ~lIl1r I Ilull) _11 orcas(lrnHon I ~rnSlOn ~ ero~j(u I (lrosion I

I

Percent o 2i ~~ ~ n2) Ji~~ _~_4~ ~_ 3a11 4ri-nL ~ ~_ middotWmiddotI 60+_ bullbullbull 3X

TutuL __ 1000

bull The glfting Iwtor is nlso closely nssodnled with Ull vtlying tlosion

(OIHlitions found 011 difrcrent aspects III gCnelnl the plnnts whieh ])JNlominnte on south slopes fire mOJe pnlntnble to livestock than tho brushy Y(lgctntion common Oil nortll(lly exposures The fn(t that south s10I)CS nrc 82 pCJ(ent flceCssiblc to liYCsto(k while northerly expOSUlPS nl( only 62 ptJCcnt flt((ssiblc iltii(ttcs the henviel dcgleo of usc to which tilCsc tllNlS havc beCll subJccted

lDROSION ON rIlE nOISE lUVER WNJEHSHED 27

It is also jndieatrd tImt hcnyy gmling hnH contdbul cd to th( rloHion OIl Hw various types The wrcd und gmss typcs wlwlCI the NOS ion has been the grcntrst uIe nPPloximatoly n3 PCI(CIll uccessiblC to jiyeshystoek while the l1ongrn~ing liype which hns bern 1cnst eroded is only 22 pClcCnt ncccssible

Arcns with vegctlltion densitics of 30 or less w(le found to bC cloclCC] ll1ueh more thllll nrrns with highcr densitirs Jhis difrrlC1Hr lIlily be du( in pnrt to the fILet that the aleus with 10w(1 drllsiticH lIJC -Ifi~cd and trailcd considerably morc sillee they am OIL tltc nYCmge 80 ]gt(1_

(cnt ucccssible to livestoek while Ulcns with dcnsitics in c-ccss of 80 nle on the nYCInge but 74 pel(cnt n((tsRibl(

The complltntions show 11)5 PCICllllt of the yurinnce in crosion to he IlSS0(jnt(middotd with neecssibility to livostoek A CorlcIntioll of Hll(h mngllitnde Oil molc than 1000 uIPHS iud iCl1tps thllt g1n~il1g by li estOt k hUH I)((n n highly impoltH 11 t fndol ill enusing NORion

DISCUSSION OJ RI~SUIrs

Tho YILrinn(o ill (1osion nsso(int(d with en ell of tho scyon Jndols ~xplesRod in P()((llt appenIs in ns(ltnltiing oldcr of ImpOltall(( Ilil JolJow

Parr litGradiCnL _____ gt ________ bull ____ bull __ bull 2 lRodent infpslution_ 1 0

Plunt dCn-it~_ Ii I)Aspect _______ _ 10 Ii-iuilcOlitiitiolls _______ _ _ _ _ __ __ 128Plant type___ ______ __ _ _ __ __ 13 middotl

CIlItllaih-c elimiddott of paHt gJILzing as CXllICSSPc Igt~ U((sHiI)ilit of Illllle toII-estock -- - __ -- - __________________ _ ___ ____ ___ __ _ _ _ _ _____ _ _ _ _ 15 3

1ICII (( tllPll(gt fnetors n(Count 101 npploximat(ly 70 ptJ(Cllt of thc YHlintionin Plosion hile some of the pelccntngps nrc quite 8I11n11 they HIC ill ltYPIY C1lte signifieunt rublc 11 is nil nnnlysis of the ytllinnce by tlw Fishtl 11lPthod plcyiousiy rcfc]lcd to The last colshylImll in this tablc pxprtsscs the ll1tio of cHch l11(nn SC[UnJO to UIO mcnn RQlll1lC of the I(siltiuul The lo(J limit 101 signifirHI1(C (lltld ht not J(middotss thall 4()j hOIlltP nil the 11((01- 111( d(1fillit(lv Hignifi(llIlt in thtil rrl(Ct II pOll CIOSiOIl

[lly Ill Fbhtf I1llfhl)lltpitillltl nil PJI 1IIIlIIrI IIJ

oounol l of nrinlluu J)(If(I(I of hllln Hnlin tn (rt[dulli dam i SIUaro residual

A(((s~hIII~middot _ middot1 U U720a (lUISOI 137 iiJInnt t~I)(O_ 7 (JOaH OOUH 1iU ~Hollcoll( IlIous i 07122 OI2~A~Jlecl _ r~~ 7 Oilii7 001 )hjIlnnL dcn~il~ 7 012111 (JOtHl ai nHodonl infeslnUlln _ a 1I22h7 ~ ()Of2 [is 2OrnelicnL J Ulfilill OOI7J 117HsiciulIl bullbullbullbull _ _ __IUiJ2 _HI1II OOIlJlI1 _J~~lotIlL i I lall I 17aSl i

1lIC ahon~ points to gll1~ing alld JllOIC pfutic1I1Hlly otlgrning nnd its nttpmlnnt cflcwts of dCplctioll of plnnt rOWl I1lld JittN find trn1l1pling of the soil n the most impOItullt fnetol (oJltlibllting to closi011 Howcycr ns nllefldy llHntiollcd tJWlC 1110 mnny intellpJnshytions bctwepn factors which when more criticnlly studiNl tend to

28 T1WIlNICAI BU[LElIN i2S U S DEPT Oli AGlUCUlJlUHE

minill1i~c ((rinill fndmiddotors nlld to (mphllsi~( th( impoltulw( of oth(Js These justify furthel discussion

It is very evident that gradient in spite of the importance which migh t he a ttached to it on first though t is largely significant as a factor in accelerated emsion only as it aJfllcts the influence of other factors Oth(r thing heing qual it mi~ht he expected that the st((p(r tho slope the more erosion there will be However the results of this study show that on the 11verage erosion increased with inerense in grndient only lip to 35-pereent slopes after which erosio1 decreased with inClNISe in gmdient Thele WIlR relntively ]CS closion on slop(s of 70 80 and flO percent thnn on slopes of 20 01 30 pelCent It is uppnrent thnt OY(I 11 loner period of yenls under nntlllul (ondishyLions II bnlllllcc is estnhliS]1(d lthetwccll plnn t (OY(I soil nne] (Iosion which tlLk(s illto 1I((Ollnt ynrious fU(tOIS ineillding gludiellL ]11lt stcepe] tlte slope ill (xccss of 35 P(I(CII t the I(ss IH(essihle it is to liwstoek TDlosion illlIells(s yely rapidly Oil tJl( slop(s in nX((SR of a5-p(fCell Ii gIudieIl t wh(lI th() ILIC fll Iy U(llssihlt to li psio(k Also 011 the slop(s 1IndpI 2() ]JlICent which on the lIlIUPP hno ItJli~d1 d(glft of I((ossibility Nosioll ill(I(lIs((1 with in(I(l1s0 in glflditril Iho (ollcl usions s(lm i lIls(upn hl( lltn t p1tIltiiell L is of Ill inOl i III portn neo liS fl fllcto) in 1I((1el(lIIt((l Nosion until the inOuenee of othrl fnd-ol is hrought into piny thnt gl[~ing is the (hief distulbing fnetor which OPllU trs in IIssoeintioll wi th slopp nnd thllt on grn~ed slopes e]osion inc]oHses rnpidly with in(Iellso ill glndiont These lend to the further conclusion Oint th( h(niel tho grnzing the gllntN the neeole1lltion of erosion with jHICnse in grndilnt

Rod(ntj inflslntion shows fl low ]gtlt]C(ntllgo of Ynrinno nssoeilltld wi t h Nosion i(YNIIIPlps i t is of 11111 i IIlportlll(p in fll( (Iosion pm bshykill h((ltIIsli t i OIW of thI few con t 101InhlC fn((ols ApPloximn tply foul-firths of thn n(Il SIIITtYN] WIIS inftstlltl with roltilnts ILpploxishymntdy OlH-thiJ( hnying I1llciiurn ol]H1nxy infpstnlion lvlo](oY(lthC inlpstn tion wns hlnYitst on tht sou thNly slo]1(s whieh nlo nlso t he most hlllyily gIlL~(d nnd which 1Ir1e the soil plant typ(s nnd dlnsities nntllllllly 110st flllS((ptible to a(((IlIatcd Nosion GIIl~ing nlso plllYS some pnlL in locilnL dnmng(llnny of Illl JUIlwnys of poe(t goph(rs nl( situnt(d within (i to S in(h(s of the 5U1ln(( Und(lthlso eonclitions liYlsto(k in pnssing OV(l the Innel trnlllplC nnd (nYImiddot in the runs which 111( soon cltnnlll Ollt agnill hy the rodrnts This (xtla digging IlIlthll in(J(ns(s the distulbnnee or titlt soil

Plnn( c(nsity oLh(l things lwing (qUill might br txprctN] to hnye nn 111YPISe 111lntioIl to f1c((lernt(d Closiol1 i ( thn grent(1 the plnnt dll1siLy tll( smnllltL thlt (1osion lW(IUISe of thr plOt(dion nOol(IPd by dlllse vlgltntioJl lind ]ittlI (oY(r AJthough this is undollbtedly trlle in the Ifllgel spnsC it seClllS nppnlent on the Boise 11ilt1 wntrshysllld that ns hl the (nse of grndicnt more or llsS of i1 bnlan(e b(comes estnblished under llnturnl (onditions hetween erosion Ilud the plnnt t

density nflordld by the normnl climute Evidlntly erosion is ncshycelernted only whtn the normnl density is disturbed by periods of unIavornblc clin1l1te severe rodent infestation 01 grn~ing On this watershed the plnnt density has been reduccd by It combinntion of these three fnetors but more especinlly hy oYClgra~ing nnd iIlcidental trnmpling by livestock

It is shown chllt nspeet has II high percent of vnriunce IIssocinted with accelerated erosion It is ILppnrel1t howcver thnt this is not

21 glWlil)~ 0gt[ TIm HOIKE ml~1t WTKHHllI~1l

Inrly tit( h1(11 king II p nlld disptIsioll or [lit j)otl(t hmiddotp (()(~I of twig 1tIlVPS find othpldplld pg(lnl II1nttlitl by tlumpliug tOgPUItI with the I(compnnying distulbnn(p of the stllICtUIl of tlip filllfll(l soil l1ndoubtedly is of glcnt impoltnn(e in eluRing (108ion

] t wns pointpd out 1l1H1pl tJ1P dpSCliplioll or fjpld Jlwthods t11nt t11r nce(ssihility or nn nltn to lin8to(k Wllf consicip]NI to bc thc bCRt flTflilublc ciilc(t ])HnSUIp oi tlin (uillulntin ((lPc(j or glfling lIl nnd tllPldolc fin inltlillct inltlpx of till p(p( of gltltillg on PIosion lhnL this is tlllP is inltii(ntpd hy flip JueL thnt 011 tillt lYCIlgP the ll11t1od((1 HIcns nrc 03 l)(l(pnt fI(((sRihle in (()llilat to [lir (1O(p(( IIIPI1S which HIl flOIH 92 to 03 ])(gt1((1 t nc((ssi hk

TIl( PClc(lltngC or slH(( POsion wns round (oinCIPflS( fuil1 (()nshysis[pntly liS 111( 1I1(llslw(llllp IlHH( 1I(((ssihl( to Ihpst)k (fig 1~ nlld

T 100 rshy

-ltgtltt 40

~ ~ ~ 2() v-_ (

~ f

Igt

A~ M fy ~tfrltmiddotIf~middot

o~i f l ~ Q~(~1l

tHIlllt nl flom 1 PPI((llt Oil IIIP Itss l(((ssilgtl( HI(l1S to Oii pltlcrnt Oil

(host fully H(((ssiblt lh( il(IHI ill gull~middot (IOSioIl wm ns IllQ11011l1(pd

though pss l(gullil (xcppt in (1111( illstnIH(s 110 gully (IOSIOIl WlIS

round on IInIIS Ips thnn ])(1((11( HC((ssiblt In 11(( tlllpt (lS(S olhrl rnctnl llPIHtll to H(lIll( rot t1H -1111 (I(lsiOI1 IO 01 t1ll1l1

nlthollgh nt PI(Spllt ]lIn(ti(IlIl inll(((ssihJI to (ntll WII T)(iollslv ()PIWI1Pc nnc 11111111gt1(lt1 hy sliPlp TIi( otlwl lIl(I with SiNP slopts is 1Il1(ISNI by glllli(ls orifiIlUfillg llll hptiy 1111ld lind 1l101( n(c(ssihlll1(aslho(

~hIJlIImiddot 1)[[(1shy~hNt ~lIll~ lul(1-(011 prtmiddot1fu lJI4l1JIl

llI111(r Sumff Yu7II1lrr ~t111l1Itr ~1tm(r Pi tllt nmiddot~j 11I O 1 1 110 la I20middot1 ~$ 111 1 II 11 II wmiddotr~ 2 I ] iill -1 j(iG-85 II Ii I lOS UI8(1-100 _ (011 k3 20 i han 702

fIJt1 11f bull _~~ _____ Z I-~~

20 JECHNlGAl BU1LE11N rj~8 u S DEI] OF AGRIC1UIUnlltJ

EXlIluinution or datil l(cllling thn modiryillg influcllcc or aeecHsishybility 011 the cflect of other fnetors IUltiJ(1 illdicates why (1osion mny hnye b(on Ineking under ccrtain (onditions nnd so pronounced ul1(lelothcrs

As brought out under the discussion or grndifmt (l complete lCshy

YCIRnl of the no]mnl trend toward inclenscd c1osion with inc1cascd gIIHiitnt was found 011 alCIlS with gmdicnts in cx(css of 35 l)Icent 1t is nppUnllG thnt the grcatcr usc by liYeftock of the lowC] gludicuts is olle of the more important eauscs iI not the prin(ipnl cause of this condition That the stccpcr tho slope the glcntc1 is the ClOSiOll proid(d grnrinp also is the snme lit nil slopps ifgt bOllle ou1 hy the

_oj

I

73 1

middot1

1-___ bull_~-_--~ _11-~t_l_-1-_---~r_3---I 0-25 26-45 46-65 euroG +

GRADIENT (PERCENT)

oNO EROSICN 0 SHEET EROSION bull GULLY EROSION

F(nenE ll-Clmllrni nrHI degree of erosion 011 nrcas full) ncccssihie III liyelo~k

study of nrPlls fully fHC(ssibl( On such I1rea as shown ill tnble 10 find J1g11ItIJ- tlosion is plog1(IssiYely wOJse with inc1el1se in glndient

TUII 10-- TIt( relation o gradient to drgrcr o erosion on (rra~ fully (lCC(8~ibli 10 ihlsock

-------~----- --~-- ~~- -_-----XC) ~II t 18lttlluw-l IletI- 1

lt1p~ (percent) u ~lIl1r I Ilull) _11 orcas(lrnHon I ~rnSlOn ~ ero~j(u I (lrosion I

I

Percent o 2i ~~ ~ n2) Ji~~ _~_4~ ~_ 3a11 4ri-nL ~ ~_ middotWmiddotI 60+_ bullbullbull 3X

TutuL __ 1000

bull The glfting Iwtor is nlso closely nssodnled with Ull vtlying tlosion

(OIHlitions found 011 difrcrent aspects III gCnelnl the plnnts whieh ])JNlominnte on south slopes fire mOJe pnlntnble to livestock than tho brushy Y(lgctntion common Oil nortll(lly exposures The fn(t that south s10I)CS nrc 82 pCJ(ent flceCssiblc to liYCsto(k while northerly expOSUlPS nl( only 62 ptJCcnt flt((ssiblc iltii(ttcs the henviel dcgleo of usc to which tilCsc tllNlS havc beCll subJccted

lDROSION ON rIlE nOISE lUVER WNJEHSHED 27

It is also jndieatrd tImt hcnyy gmling hnH contdbul cd to th( rloHion OIl Hw various types The wrcd und gmss typcs wlwlCI the NOS ion has been the grcntrst uIe nPPloximatoly n3 PCI(CIll uccessiblC to jiyeshystoek while the l1ongrn~ing liype which hns bern 1cnst eroded is only 22 pClcCnt ncccssible

Arcns with vegctlltion densitics of 30 or less w(le found to bC cloclCC] ll1ueh more thllll nrrns with highcr densitirs Jhis difrrlC1Hr lIlily be du( in pnrt to the fILet that the aleus with 10w(1 drllsiticH lIJC -Ifi~cd and trailcd considerably morc sillee they am OIL tltc nYCmge 80 ]gt(1_

(cnt ucccssible to livestoek while Ulcns with dcnsitics in c-ccss of 80 nle on the nYCInge but 74 pel(cnt n((tsRibl(

The complltntions show 11)5 PCICllllt of the yurinnce in crosion to he IlSS0(jnt(middotd with neecssibility to livostoek A CorlcIntioll of Hll(h mngllitnde Oil molc than 1000 uIPHS iud iCl1tps thllt g1n~il1g by li estOt k hUH I)((n n highly impoltH 11 t fndol ill enusing NORion

DISCUSSION OJ RI~SUIrs

Tho YILrinn(o ill (1osion nsso(int(d with en ell of tho scyon Jndols ~xplesRod in P()((llt appenIs in ns(ltnltiing oldcr of ImpOltall(( Ilil JolJow

Parr litGradiCnL _____ gt ________ bull ____ bull __ bull 2 lRodent infpslution_ 1 0

Plunt dCn-it~_ Ii I)Aspect _______ _ 10 Ii-iuilcOlitiitiolls _______ _ _ _ _ __ __ 128Plant type___ ______ __ _ _ __ __ 13 middotl

CIlItllaih-c elimiddott of paHt gJILzing as CXllICSSPc Igt~ U((sHiI)ilit of Illllle toII-estock -- - __ -- - __________________ _ ___ ____ ___ __ _ _ _ _ _____ _ _ _ _ 15 3

1ICII (( tllPll(gt fnetors n(Count 101 npploximat(ly 70 ptJ(Cllt of thc YHlintionin Plosion hile some of the pelccntngps nrc quite 8I11n11 they HIC ill ltYPIY C1lte signifieunt rublc 11 is nil nnnlysis of the ytllinnce by tlw Fishtl 11lPthod plcyiousiy rcfc]lcd to The last colshylImll in this tablc pxprtsscs the ll1tio of cHch l11(nn SC[UnJO to UIO mcnn RQlll1lC of the I(siltiuul The lo(J limit 101 signifirHI1(C (lltld ht not J(middotss thall 4()j hOIlltP nil the 11((01- 111( d(1fillit(lv Hignifi(llIlt in thtil rrl(Ct II pOll CIOSiOIl

[lly Ill Fbhtf I1llfhl)lltpitillltl nil PJI 1IIIlIIrI IIJ

oounol l of nrinlluu J)(If(I(I of hllln Hnlin tn (rt[dulli dam i SIUaro residual

A(((s~hIII~middot _ middot1 U U720a (lUISOI 137 iiJInnt t~I)(O_ 7 (JOaH OOUH 1iU ~Hollcoll( IlIous i 07122 OI2~A~Jlecl _ r~~ 7 Oilii7 001 )hjIlnnL dcn~il~ 7 012111 (JOtHl ai nHodonl infeslnUlln _ a 1I22h7 ~ ()Of2 [is 2OrnelicnL J Ulfilill OOI7J 117HsiciulIl bullbullbullbull _ _ __IUiJ2 _HI1II OOIlJlI1 _J~~lotIlL i I lall I 17aSl i

1lIC ahon~ points to gll1~ing alld JllOIC pfutic1I1Hlly otlgrning nnd its nttpmlnnt cflcwts of dCplctioll of plnnt rOWl I1lld JittN find trn1l1pling of the soil n the most impOItullt fnetol (oJltlibllting to closi011 Howcycr ns nllefldy llHntiollcd tJWlC 1110 mnny intellpJnshytions bctwepn factors which when more criticnlly studiNl tend to

28 T1WIlNICAI BU[LElIN i2S U S DEPT Oli AGlUCUlJlUHE

minill1i~c ((rinill fndmiddotors nlld to (mphllsi~( th( impoltulw( of oth(Js These justify furthel discussion

It is very evident that gradient in spite of the importance which migh t he a ttached to it on first though t is largely significant as a factor in accelerated emsion only as it aJfllcts the influence of other factors Oth(r thing heing qual it mi~ht he expected that the st((p(r tho slope the more erosion there will be However the results of this study show that on the 11verage erosion increased with inerense in grndient only lip to 35-pereent slopes after which erosio1 decreased with inClNISe in gmdient Thele WIlR relntively ]CS closion on slop(s of 70 80 and flO percent thnn on slopes of 20 01 30 pelCent It is uppnrent thnt OY(I 11 loner period of yenls under nntlllul (ondishyLions II bnlllllcc is estnhliS]1(d lthetwccll plnn t (OY(I soil nne] (Iosion which tlLk(s illto 1I((Ollnt ynrious fU(tOIS ineillding gludiellL ]11lt stcepe] tlte slope ill (xccss of 35 P(I(CII t the I(ss IH(essihle it is to liwstoek TDlosion illlIells(s yely rapidly Oil tJl( slop(s in nX((SR of a5-p(fCell Ii gIudieIl t wh(lI th() ILIC fll Iy U(llssihlt to li psio(k Also 011 the slop(s 1IndpI 2() ]JlICent which on the lIlIUPP hno ItJli~d1 d(glft of I((ossibility Nosioll ill(I(lIs((1 with in(I(l1s0 in glflditril Iho (ollcl usions s(lm i lIls(upn hl( lltn t p1tIltiiell L is of Ill inOl i III portn neo liS fl fllcto) in 1I((1el(lIIt((l Nosion until the inOuenee of othrl fnd-ol is hrought into piny thnt gl[~ing is the (hief distulbing fnetor which OPllU trs in IIssoeintioll wi th slopp nnd thllt on grn~ed slopes e]osion inc]oHses rnpidly with in(Iellso ill glndiont These lend to the further conclusion Oint th( h(niel tho grnzing the gllntN the neeole1lltion of erosion with jHICnse in grndilnt

Rod(ntj inflslntion shows fl low ]gtlt]C(ntllgo of Ynrinno nssoeilltld wi t h Nosion i(YNIIIPlps i t is of 11111 i IIlportlll(p in fll( (Iosion pm bshykill h((ltIIsli t i OIW of thI few con t 101InhlC fn((ols ApPloximn tply foul-firths of thn n(Il SIIITtYN] WIIS inftstlltl with roltilnts ILpploxishymntdy OlH-thiJ( hnying I1llciiurn ol]H1nxy infpstnlion lvlo](oY(lthC inlpstn tion wns hlnYitst on tht sou thNly slo]1(s whieh nlo nlso t he most hlllyily gIlL~(d nnd which 1Ir1e the soil plant typ(s nnd dlnsities nntllllllly 110st flllS((ptible to a(((IlIatcd Nosion GIIl~ing nlso plllYS some pnlL in locilnL dnmng(llnny of Illl JUIlwnys of poe(t goph(rs nl( situnt(d within (i to S in(h(s of the 5U1ln(( Und(lthlso eonclitions liYlsto(k in pnssing OV(l the Innel trnlllplC nnd (nYImiddot in the runs which 111( soon cltnnlll Ollt agnill hy the rodrnts This (xtla digging IlIlthll in(J(ns(s the distulbnnee or titlt soil

Plnn( c(nsity oLh(l things lwing (qUill might br txprctN] to hnye nn 111YPISe 111lntioIl to f1c((lernt(d Closiol1 i ( thn grent(1 the plnnt dll1siLy tll( smnllltL thlt (1osion lW(IUISe of thr plOt(dion nOol(IPd by dlllse vlgltntioJl lind ]ittlI (oY(r AJthough this is undollbtedly trlle in the Ifllgel spnsC it seClllS nppnlent on the Boise 11ilt1 wntrshysllld that ns hl the (nse of grndicnt more or llsS of i1 bnlan(e b(comes estnblished under llnturnl (onditions hetween erosion Ilud the plnnt t

density nflordld by the normnl climute Evidlntly erosion is ncshycelernted only whtn the normnl density is disturbed by periods of unIavornblc clin1l1te severe rodent infestation 01 grn~ing On this watershed the plnnt density has been reduccd by It combinntion of these three fnetors but more especinlly hy oYClgra~ing nnd iIlcidental trnmpling by livestock

It is shown chllt nspeet has II high percent of vnriunce IIssocinted with accelerated erosion It is ILppnrel1t howcver thnt this is not

20 JECHNlGAl BU1LE11N rj~8 u S DEI] OF AGRIC1UIUnlltJ

EXlIluinution or datil l(cllling thn modiryillg influcllcc or aeecHsishybility 011 the cflect of other fnetors IUltiJ(1 illdicates why (1osion mny hnye b(on Ineking under ccrtain (onditions nnd so pronounced ul1(lelothcrs

As brought out under the discussion or grndifmt (l complete lCshy

YCIRnl of the no]mnl trend toward inclenscd c1osion with inc1cascd gIIHiitnt was found 011 alCIlS with gmdicnts in cx(css of 35 l)Icent 1t is nppUnllG thnt the grcatcr usc by liYeftock of the lowC] gludicuts is olle of the more important eauscs iI not the prin(ipnl cause of this condition That the stccpcr tho slope the glcntc1 is the ClOSiOll proid(d grnrinp also is the snme lit nil slopps ifgt bOllle ou1 hy the

_oj

I

73 1

middot1

1-___ bull_~-_--~ _11-~t_l_-1-_---~r_3---I 0-25 26-45 46-65 euroG +

GRADIENT (PERCENT)

oNO EROSICN 0 SHEET EROSION bull GULLY EROSION

F(nenE ll-Clmllrni nrHI degree of erosion 011 nrcas full) ncccssihie III liyelo~k

study of nrPlls fully fHC(ssibl( On such I1rea as shown ill tnble 10 find J1g11ItIJ- tlosion is plog1(IssiYely wOJse with inc1el1se in glndient

TUII 10-- TIt( relation o gradient to drgrcr o erosion on (rra~ fully (lCC(8~ibli 10 ihlsock

-------~----- --~-- ~~- -_-----XC) ~II t 18lttlluw-l IletI- 1

lt1p~ (percent) u ~lIl1r I Ilull) _11 orcas(lrnHon I ~rnSlOn ~ ero~j(u I (lrosion I

I

Percent o 2i ~~ ~ n2) Ji~~ _~_4~ ~_ 3a11 4ri-nL ~ ~_ middotWmiddotI 60+_ bullbullbull 3X

TutuL __ 1000

bull The glfting Iwtor is nlso closely nssodnled with Ull vtlying tlosion

(OIHlitions found 011 difrcrent aspects III gCnelnl the plnnts whieh ])JNlominnte on south slopes fire mOJe pnlntnble to livestock than tho brushy Y(lgctntion common Oil nortll(lly exposures The fn(t that south s10I)CS nrc 82 pCJ(ent flceCssiblc to liYCsto(k while northerly expOSUlPS nl( only 62 ptJCcnt flt((ssiblc iltii(ttcs the henviel dcgleo of usc to which tilCsc tllNlS havc beCll subJccted

lDROSION ON rIlE nOISE lUVER WNJEHSHED 27

It is also jndieatrd tImt hcnyy gmling hnH contdbul cd to th( rloHion OIl Hw various types The wrcd und gmss typcs wlwlCI the NOS ion has been the grcntrst uIe nPPloximatoly n3 PCI(CIll uccessiblC to jiyeshystoek while the l1ongrn~ing liype which hns bern 1cnst eroded is only 22 pClcCnt ncccssible

Arcns with vegctlltion densitics of 30 or less w(le found to bC cloclCC] ll1ueh more thllll nrrns with highcr densitirs Jhis difrrlC1Hr lIlily be du( in pnrt to the fILet that the aleus with 10w(1 drllsiticH lIJC -Ifi~cd and trailcd considerably morc sillee they am OIL tltc nYCmge 80 ]gt(1_

(cnt ucccssible to livestoek while Ulcns with dcnsitics in c-ccss of 80 nle on the nYCInge but 74 pel(cnt n((tsRibl(

The complltntions show 11)5 PCICllllt of the yurinnce in crosion to he IlSS0(jnt(middotd with neecssibility to livostoek A CorlcIntioll of Hll(h mngllitnde Oil molc than 1000 uIPHS iud iCl1tps thllt g1n~il1g by li estOt k hUH I)((n n highly impoltH 11 t fndol ill enusing NORion

DISCUSSION OJ RI~SUIrs

Tho YILrinn(o ill (1osion nsso(int(d with en ell of tho scyon Jndols ~xplesRod in P()((llt appenIs in ns(ltnltiing oldcr of ImpOltall(( Ilil JolJow

Parr litGradiCnL _____ gt ________ bull ____ bull __ bull 2 lRodent infpslution_ 1 0

Plunt dCn-it~_ Ii I)Aspect _______ _ 10 Ii-iuilcOlitiitiolls _______ _ _ _ _ __ __ 128Plant type___ ______ __ _ _ __ __ 13 middotl

CIlItllaih-c elimiddott of paHt gJILzing as CXllICSSPc Igt~ U((sHiI)ilit of Illllle toII-estock -- - __ -- - __________________ _ ___ ____ ___ __ _ _ _ _ _____ _ _ _ _ 15 3

1ICII (( tllPll(gt fnetors n(Count 101 npploximat(ly 70 ptJ(Cllt of thc YHlintionin Plosion hile some of the pelccntngps nrc quite 8I11n11 they HIC ill ltYPIY C1lte signifieunt rublc 11 is nil nnnlysis of the ytllinnce by tlw Fishtl 11lPthod plcyiousiy rcfc]lcd to The last colshylImll in this tablc pxprtsscs the ll1tio of cHch l11(nn SC[UnJO to UIO mcnn RQlll1lC of the I(siltiuul The lo(J limit 101 signifirHI1(C (lltld ht not J(middotss thall 4()j hOIlltP nil the 11((01- 111( d(1fillit(lv Hignifi(llIlt in thtil rrl(Ct II pOll CIOSiOIl

[lly Ill Fbhtf I1llfhl)lltpitillltl nil PJI 1IIIlIIrI IIJ

oounol l of nrinlluu J)(If(I(I of hllln Hnlin tn (rt[dulli dam i SIUaro residual

A(((s~hIII~middot _ middot1 U U720a (lUISOI 137 iiJInnt t~I)(O_ 7 (JOaH OOUH 1iU ~Hollcoll( IlIous i 07122 OI2~A~Jlecl _ r~~ 7 Oilii7 001 )hjIlnnL dcn~il~ 7 012111 (JOtHl ai nHodonl infeslnUlln _ a 1I22h7 ~ ()Of2 [is 2OrnelicnL J Ulfilill OOI7J 117HsiciulIl bullbullbullbull _ _ __IUiJ2 _HI1II OOIlJlI1 _J~~lotIlL i I lall I 17aSl i

1lIC ahon~ points to gll1~ing alld JllOIC pfutic1I1Hlly otlgrning nnd its nttpmlnnt cflcwts of dCplctioll of plnnt rOWl I1lld JittN find trn1l1pling of the soil n the most impOItullt fnetol (oJltlibllting to closi011 Howcycr ns nllefldy llHntiollcd tJWlC 1110 mnny intellpJnshytions bctwepn factors which when more criticnlly studiNl tend to

28 T1WIlNICAI BU[LElIN i2S U S DEPT Oli AGlUCUlJlUHE

minill1i~c ((rinill fndmiddotors nlld to (mphllsi~( th( impoltulw( of oth(Js These justify furthel discussion

It is very evident that gradient in spite of the importance which migh t he a ttached to it on first though t is largely significant as a factor in accelerated emsion only as it aJfllcts the influence of other factors Oth(r thing heing qual it mi~ht he expected that the st((p(r tho slope the more erosion there will be However the results of this study show that on the 11verage erosion increased with inerense in grndient only lip to 35-pereent slopes after which erosio1 decreased with inClNISe in gmdient Thele WIlR relntively ]CS closion on slop(s of 70 80 and flO percent thnn on slopes of 20 01 30 pelCent It is uppnrent thnt OY(I 11 loner period of yenls under nntlllul (ondishyLions II bnlllllcc is estnhliS]1(d lthetwccll plnn t (OY(I soil nne] (Iosion which tlLk(s illto 1I((Ollnt ynrious fU(tOIS ineillding gludiellL ]11lt stcepe] tlte slope ill (xccss of 35 P(I(CII t the I(ss IH(essihle it is to liwstoek TDlosion illlIells(s yely rapidly Oil tJl( slop(s in nX((SR of a5-p(fCell Ii gIudieIl t wh(lI th() ILIC fll Iy U(llssihlt to li psio(k Also 011 the slop(s 1IndpI 2() ]JlICent which on the lIlIUPP hno ItJli~d1 d(glft of I((ossibility Nosioll ill(I(lIs((1 with in(I(l1s0 in glflditril Iho (ollcl usions s(lm i lIls(upn hl( lltn t p1tIltiiell L is of Ill inOl i III portn neo liS fl fllcto) in 1I((1el(lIIt((l Nosion until the inOuenee of othrl fnd-ol is hrought into piny thnt gl[~ing is the (hief distulbing fnetor which OPllU trs in IIssoeintioll wi th slopp nnd thllt on grn~ed slopes e]osion inc]oHses rnpidly with in(Iellso ill glndiont These lend to the further conclusion Oint th( h(niel tho grnzing the gllntN the neeole1lltion of erosion with jHICnse in grndilnt

Rod(ntj inflslntion shows fl low ]gtlt]C(ntllgo of Ynrinno nssoeilltld wi t h Nosion i(YNIIIPlps i t is of 11111 i IIlportlll(p in fll( (Iosion pm bshykill h((ltIIsli t i OIW of thI few con t 101InhlC fn((ols ApPloximn tply foul-firths of thn n(Il SIIITtYN] WIIS inftstlltl with roltilnts ILpploxishymntdy OlH-thiJ( hnying I1llciiurn ol]H1nxy infpstnlion lvlo](oY(lthC inlpstn tion wns hlnYitst on tht sou thNly slo]1(s whieh nlo nlso t he most hlllyily gIlL~(d nnd which 1Ir1e the soil plant typ(s nnd dlnsities nntllllllly 110st flllS((ptible to a(((IlIatcd Nosion GIIl~ing nlso plllYS some pnlL in locilnL dnmng(llnny of Illl JUIlwnys of poe(t goph(rs nl( situnt(d within (i to S in(h(s of the 5U1ln(( Und(lthlso eonclitions liYlsto(k in pnssing OV(l the Innel trnlllplC nnd (nYImiddot in the runs which 111( soon cltnnlll Ollt agnill hy the rodrnts This (xtla digging IlIlthll in(J(ns(s the distulbnnee or titlt soil

Plnn( c(nsity oLh(l things lwing (qUill might br txprctN] to hnye nn 111YPISe 111lntioIl to f1c((lernt(d Closiol1 i ( thn grent(1 the plnnt dll1siLy tll( smnllltL thlt (1osion lW(IUISe of thr plOt(dion nOol(IPd by dlllse vlgltntioJl lind ]ittlI (oY(r AJthough this is undollbtedly trlle in the Ifllgel spnsC it seClllS nppnlent on the Boise 11ilt1 wntrshysllld that ns hl the (nse of grndicnt more or llsS of i1 bnlan(e b(comes estnblished under llnturnl (onditions hetween erosion Ilud the plnnt t

density nflordld by the normnl climute Evidlntly erosion is ncshycelernted only whtn the normnl density is disturbed by periods of unIavornblc clin1l1te severe rodent infestation 01 grn~ing On this watershed the plnnt density has been reduccd by It combinntion of these three fnetors but more especinlly hy oYClgra~ing nnd iIlcidental trnmpling by livestock

It is shown chllt nspeet has II high percent of vnriunce IIssocinted with accelerated erosion It is ILppnrel1t howcver thnt this is not

lDROSION ON rIlE nOISE lUVER WNJEHSHED 27

It is also jndieatrd tImt hcnyy gmling hnH contdbul cd to th( rloHion OIl Hw various types The wrcd und gmss typcs wlwlCI the NOS ion has been the grcntrst uIe nPPloximatoly n3 PCI(CIll uccessiblC to jiyeshystoek while the l1ongrn~ing liype which hns bern 1cnst eroded is only 22 pClcCnt ncccssible

Arcns with vegctlltion densitics of 30 or less w(le found to bC cloclCC] ll1ueh more thllll nrrns with highcr densitirs Jhis difrrlC1Hr lIlily be du( in pnrt to the fILet that the aleus with 10w(1 drllsiticH lIJC -Ifi~cd and trailcd considerably morc sillee they am OIL tltc nYCmge 80 ]gt(1_

(cnt ucccssible to livestoek while Ulcns with dcnsitics in c-ccss of 80 nle on the nYCInge but 74 pel(cnt n((tsRibl(

The complltntions show 11)5 PCICllllt of the yurinnce in crosion to he IlSS0(jnt(middotd with neecssibility to livostoek A CorlcIntioll of Hll(h mngllitnde Oil molc than 1000 uIPHS iud iCl1tps thllt g1n~il1g by li estOt k hUH I)((n n highly impoltH 11 t fndol ill enusing NORion

DISCUSSION OJ RI~SUIrs

Tho YILrinn(o ill (1osion nsso(int(d with en ell of tho scyon Jndols ~xplesRod in P()((llt appenIs in ns(ltnltiing oldcr of ImpOltall(( Ilil JolJow

Parr litGradiCnL _____ gt ________ bull ____ bull __ bull 2 lRodent infpslution_ 1 0

Plunt dCn-it~_ Ii I)Aspect _______ _ 10 Ii-iuilcOlitiitiolls _______ _ _ _ _ __ __ 128Plant type___ ______ __ _ _ __ __ 13 middotl

CIlItllaih-c elimiddott of paHt gJILzing as CXllICSSPc Igt~ U((sHiI)ilit of Illllle toII-estock -- - __ -- - __________________ _ ___ ____ ___ __ _ _ _ _ _____ _ _ _ _ 15 3

1ICII (( tllPll(gt fnetors n(Count 101 npploximat(ly 70 ptJ(Cllt of thc YHlintionin Plosion hile some of the pelccntngps nrc quite 8I11n11 they HIC ill ltYPIY C1lte signifieunt rublc 11 is nil nnnlysis of the ytllinnce by tlw Fishtl 11lPthod plcyiousiy rcfc]lcd to The last colshylImll in this tablc pxprtsscs the ll1tio of cHch l11(nn SC[UnJO to UIO mcnn RQlll1lC of the I(siltiuul The lo(J limit 101 signifirHI1(C (lltld ht not J(middotss thall 4()j hOIlltP nil the 11((01- 111( d(1fillit(lv Hignifi(llIlt in thtil rrl(Ct II pOll CIOSiOIl

[lly Ill Fbhtf I1llfhl)lltpitillltl nil PJI 1IIIlIIrI IIJ

oounol l of nrinlluu J)(If(I(I of hllln Hnlin tn (rt[dulli dam i SIUaro residual

A(((s~hIII~middot _ middot1 U U720a (lUISOI 137 iiJInnt t~I)(O_ 7 (JOaH OOUH 1iU ~Hollcoll( IlIous i 07122 OI2~A~Jlecl _ r~~ 7 Oilii7 001 )hjIlnnL dcn~il~ 7 012111 (JOtHl ai nHodonl infeslnUlln _ a 1I22h7 ~ ()Of2 [is 2OrnelicnL J Ulfilill OOI7J 117HsiciulIl bullbullbullbull _ _ __IUiJ2 _HI1II OOIlJlI1 _J~~lotIlL i I lall I 17aSl i

1lIC ahon~ points to gll1~ing alld JllOIC pfutic1I1Hlly otlgrning nnd its nttpmlnnt cflcwts of dCplctioll of plnnt rOWl I1lld JittN find trn1l1pling of the soil n the most impOItullt fnetol (oJltlibllting to closi011 Howcycr ns nllefldy llHntiollcd tJWlC 1110 mnny intellpJnshytions bctwepn factors which when more criticnlly studiNl tend to

28 T1WIlNICAI BU[LElIN i2S U S DEPT Oli AGlUCUlJlUHE

minill1i~c ((rinill fndmiddotors nlld to (mphllsi~( th( impoltulw( of oth(Js These justify furthel discussion

It is very evident that gradient in spite of the importance which migh t he a ttached to it on first though t is largely significant as a factor in accelerated emsion only as it aJfllcts the influence of other factors Oth(r thing heing qual it mi~ht he expected that the st((p(r tho slope the more erosion there will be However the results of this study show that on the 11verage erosion increased with inerense in grndient only lip to 35-pereent slopes after which erosio1 decreased with inClNISe in gmdient Thele WIlR relntively ]CS closion on slop(s of 70 80 and flO percent thnn on slopes of 20 01 30 pelCent It is uppnrent thnt OY(I 11 loner period of yenls under nntlllul (ondishyLions II bnlllllcc is estnhliS]1(d lthetwccll plnn t (OY(I soil nne] (Iosion which tlLk(s illto 1I((Ollnt ynrious fU(tOIS ineillding gludiellL ]11lt stcepe] tlte slope ill (xccss of 35 P(I(CII t the I(ss IH(essihle it is to liwstoek TDlosion illlIells(s yely rapidly Oil tJl( slop(s in nX((SR of a5-p(fCell Ii gIudieIl t wh(lI th() ILIC fll Iy U(llssihlt to li psio(k Also 011 the slop(s 1IndpI 2() ]JlICent which on the lIlIUPP hno ItJli~d1 d(glft of I((ossibility Nosioll ill(I(lIs((1 with in(I(l1s0 in glflditril Iho (ollcl usions s(lm i lIls(upn hl( lltn t p1tIltiiell L is of Ill inOl i III portn neo liS fl fllcto) in 1I((1el(lIIt((l Nosion until the inOuenee of othrl fnd-ol is hrought into piny thnt gl[~ing is the (hief distulbing fnetor which OPllU trs in IIssoeintioll wi th slopp nnd thllt on grn~ed slopes e]osion inc]oHses rnpidly with in(Iellso ill glndiont These lend to the further conclusion Oint th( h(niel tho grnzing the gllntN the neeole1lltion of erosion with jHICnse in grndilnt

Rod(ntj inflslntion shows fl low ]gtlt]C(ntllgo of Ynrinno nssoeilltld wi t h Nosion i(YNIIIPlps i t is of 11111 i IIlportlll(p in fll( (Iosion pm bshykill h((ltIIsli t i OIW of thI few con t 101InhlC fn((ols ApPloximn tply foul-firths of thn n(Il SIIITtYN] WIIS inftstlltl with roltilnts ILpploxishymntdy OlH-thiJ( hnying I1llciiurn ol]H1nxy infpstnlion lvlo](oY(lthC inlpstn tion wns hlnYitst on tht sou thNly slo]1(s whieh nlo nlso t he most hlllyily gIlL~(d nnd which 1Ir1e the soil plant typ(s nnd dlnsities nntllllllly 110st flllS((ptible to a(((IlIatcd Nosion GIIl~ing nlso plllYS some pnlL in locilnL dnmng(llnny of Illl JUIlwnys of poe(t goph(rs nl( situnt(d within (i to S in(h(s of the 5U1ln(( Und(lthlso eonclitions liYlsto(k in pnssing OV(l the Innel trnlllplC nnd (nYImiddot in the runs which 111( soon cltnnlll Ollt agnill hy the rodrnts This (xtla digging IlIlthll in(J(ns(s the distulbnnee or titlt soil

Plnn( c(nsity oLh(l things lwing (qUill might br txprctN] to hnye nn 111YPISe 111lntioIl to f1c((lernt(d Closiol1 i ( thn grent(1 the plnnt dll1siLy tll( smnllltL thlt (1osion lW(IUISe of thr plOt(dion nOol(IPd by dlllse vlgltntioJl lind ]ittlI (oY(r AJthough this is undollbtedly trlle in the Ifllgel spnsC it seClllS nppnlent on the Boise 11ilt1 wntrshysllld that ns hl the (nse of grndicnt more or llsS of i1 bnlan(e b(comes estnblished under llnturnl (onditions hetween erosion Ilud the plnnt t

density nflordld by the normnl climute Evidlntly erosion is ncshycelernted only whtn the normnl density is disturbed by periods of unIavornblc clin1l1te severe rodent infestation 01 grn~ing On this watershed the plnnt density has been reduccd by It combinntion of these three fnetors but more especinlly hy oYClgra~ing nnd iIlcidental trnmpling by livestock

It is shown chllt nspeet has II high percent of vnriunce IIssocinted with accelerated erosion It is ILppnrel1t howcver thnt this is not

28 T1WIlNICAI BU[LElIN i2S U S DEPT Oli AGlUCUlJlUHE

minill1i~c ((rinill fndmiddotors nlld to (mphllsi~( th( impoltulw( of oth(Js These justify furthel discussion

It is very evident that gradient in spite of the importance which migh t he a ttached to it on first though t is largely significant as a factor in accelerated emsion only as it aJfllcts the influence of other factors Oth(r thing heing qual it mi~ht he expected that the st((p(r tho slope the more erosion there will be However the results of this study show that on the 11verage erosion increased with inerense in grndient only lip to 35-pereent slopes after which erosio1 decreased with inClNISe in gmdient Thele WIlR relntively ]CS closion on slop(s of 70 80 and flO percent thnn on slopes of 20 01 30 pelCent It is uppnrent thnt OY(I 11 loner period of yenls under nntlllul (ondishyLions II bnlllllcc is estnhliS]1(d lthetwccll plnn t (OY(I soil nne] (Iosion which tlLk(s illto 1I((Ollnt ynrious fU(tOIS ineillding gludiellL ]11lt stcepe] tlte slope ill (xccss of 35 P(I(CII t the I(ss IH(essihle it is to liwstoek TDlosion illlIells(s yely rapidly Oil tJl( slop(s in nX((SR of a5-p(fCell Ii gIudieIl t wh(lI th() ILIC fll Iy U(llssihlt to li psio(k Also 011 the slop(s 1IndpI 2() ]JlICent which on the lIlIUPP hno ItJli~d1 d(glft of I((ossibility Nosioll ill(I(lIs((1 with in(I(l1s0 in glflditril Iho (ollcl usions s(lm i lIls(upn hl( lltn t p1tIltiiell L is of Ill inOl i III portn neo liS fl fllcto) in 1I((1el(lIIt((l Nosion until the inOuenee of othrl fnd-ol is hrought into piny thnt gl[~ing is the (hief distulbing fnetor which OPllU trs in IIssoeintioll wi th slopp nnd thllt on grn~ed slopes e]osion inc]oHses rnpidly with in(Iellso ill glndiont These lend to the further conclusion Oint th( h(niel tho grnzing the gllntN the neeole1lltion of erosion with jHICnse in grndilnt

Rod(ntj inflslntion shows fl low ]gtlt]C(ntllgo of Ynrinno nssoeilltld wi t h Nosion i(YNIIIPlps i t is of 11111 i IIlportlll(p in fll( (Iosion pm bshykill h((ltIIsli t i OIW of thI few con t 101InhlC fn((ols ApPloximn tply foul-firths of thn n(Il SIIITtYN] WIIS inftstlltl with roltilnts ILpploxishymntdy OlH-thiJ( hnying I1llciiurn ol]H1nxy infpstnlion lvlo](oY(lthC inlpstn tion wns hlnYitst on tht sou thNly slo]1(s whieh nlo nlso t he most hlllyily gIlL~(d nnd which 1Ir1e the soil plant typ(s nnd dlnsities nntllllllly 110st flllS((ptible to a(((IlIatcd Nosion GIIl~ing nlso plllYS some pnlL in locilnL dnmng(llnny of Illl JUIlwnys of poe(t goph(rs nl( situnt(d within (i to S in(h(s of the 5U1ln(( Und(lthlso eonclitions liYlsto(k in pnssing OV(l the Innel trnlllplC nnd (nYImiddot in the runs which 111( soon cltnnlll Ollt agnill hy the rodrnts This (xtla digging IlIlthll in(J(ns(s the distulbnnee or titlt soil

Plnn( c(nsity oLh(l things lwing (qUill might br txprctN] to hnye nn 111YPISe 111lntioIl to f1c((lernt(d Closiol1 i ( thn grent(1 the plnnt dll1siLy tll( smnllltL thlt (1osion lW(IUISe of thr plOt(dion nOol(IPd by dlllse vlgltntioJl lind ]ittlI (oY(r AJthough this is undollbtedly trlle in the Ifllgel spnsC it seClllS nppnlent on the Boise 11ilt1 wntrshysllld that ns hl the (nse of grndicnt more or llsS of i1 bnlan(e b(comes estnblished under llnturnl (onditions hetween erosion Ilud the plnnt t

density nflordld by the normnl climute Evidlntly erosion is ncshycelernted only whtn the normnl density is disturbed by periods of unIavornblc clin1l1te severe rodent infestation 01 grn~ing On this watershed the plnnt density has been reduccd by It combinntion of these three fnetors but more especinlly hy oYClgra~ing nnd iIlcidental trnmpling by livestock

It is shown chllt nspeet has II high percent of vnriunce IIssocinted with accelerated erosion It is ILppnrel1t howcver thnt this is not

bull

EROSIO~ ON fHE BOISE RIVEIt WATERSHBD 29

clue to aspert per se but to tho fact that ((gtJtain of the otheL factors are more effective on certain aspects The reltLtively high clegree of erosion 011 southerly slopes is due in part to the fact that the soil on these slopes is characteristically shallow of coarse texturc and light in litter and humus cover-all conditions that are conducive to erosion The plant types most susceptible to erosion induclin~ weed grass sagebrush and browse predollunate on the southerly slopes Plant densities also are smaller there than on Ilortherl) slopes Rodents plefer the south slopes fhe lower grnchents Oil

these slopes indicate that normal geologie erosion hus proceeded at t morc rapid rate thnn on other slopes and suggest the probability tllllL factors whi(h indtl( ucCelpru ted erosion if brough t in to play would be most eil(ctiYe on the southerly slopes JhCy all 011 the t(rHgt moro accCssibl( to glHzing blcnuse of the 10wN gmclients and hfWl plant specils more pnlatable to livestock FurtiHrlllorl the soil and littl1 (onclitions on these slopls LIC more ensily distulbld by glazing Hnillutls and thev aro thlrefore more sllsceptible to dHn1l1gl by grnzing thnn 011(1 slob(s GrHzing (tspecially overgrazing) ~of dOll1esti~ liyestock Hnd dnlllnge by rodents mny be expected gnatly to Itccelllshyute erosioll 011 the sou th(lly aspeds

Inherent chnrnctllistie undoubtedly nccollnt for the large degree of (JosioJl nssociated with soiL fhe (ourse texturC pnu(ity of dny to hind tl10 (our( particlts together shallow depth nnd nntu1nllv ligllt littrr unci humus (OlI in many pll(ls nrc naturnl conditions on jlJ(~ Boie Hiwl wnt(lsll(d which account for high susc(ptibility to cloion (spleiully llpon introduction of disturbing fuetors Jhls( dlflrnctPlisti(s as will br evident an most likClv to be ltig-Itly ng-shyg-rn n tld by grazing O more espccilllly by oYcrgmzing and 1oc(gtn t cI nlllngl

Yegetn tion type hns lL fnidy high nssociation with llcceiern Hon of (rosion (ni1~ in pmt to the greater protection yulue of some kill(1H of plallt (on The weed nnd grnss t)pes for exnmple produce the leust Jitter sagpbrllsh nncl hrowse types nrc next highest the timhel tYVe is Jlext nnd tho nonglt1zing type in dense timber 01 brush is the l1ighest in quantity of litter 111l1ultnined Agnin the weed nncl grnss types huYe the glentest propoltion of theil nreas illfeted with 10shydellts iollowed h)r the sngeblllsh browse timber mendow und 1I0nshygll1zing Association of plnnt type with erosion occurs in the Sllme order It is It fuct also that (Ntnia of the plnllt types most sus(Cptishyblo to llosion such HS grass nnd sagebrush OCCUI morc cOlllmonly OIl the more Hccessibll shallow-soiled severe south nspCets whelells tho denslI timber lIlcL brush types nlc more JICctuCnt 011 the deepelshysoilld more humid lolthCr1y IIspects FurtlllllllorC the 111010 spverely eroded plnnt jyplS nrc composed of speCips mom pnilltlible to Iinstock J Lis difI1eult theleforc to weigh the Jpln tic importan(e of plant tY1W nlOJle in lelation to nc(elellded erosion but it is quite evident jhat althollgh some types nre inherently moro sllsceptible to erosion thlln others the secondary ulluenee of glllzing and rodent activity is of equal Ot greater importance thnn inherent quulities

Of aU the causes of Hccelerated erosion studied grazing stllllds out as by fnr the most important (1) because it is important in itself (2) because it is the one factor that most Ilccentuates the influence of nearly nll the olhl1 fnctors i nnd (3) because it is the one factor most susceptible of control

30 II~CHXl(L BFILETlN j~S middotU S J)EPT OF AGlUCULTllUJ

AIPLICA1ION OF IUJSmIS

Tht llRtJitR o[ the st udy ~(lTe u tL hnsiR f(f tht Istublishnllnt of ploleetin l11lnUI(s in(lllding til( ]egulntioll of gllldng on wutClslwd Innds nnd for plnnning siudiCs whi(11 will dCelop further irnproy(shyments in the mnnngltlllcnt of wattlshcd Innds similar to those on the tl1ltn dluil1Cd hv the Boise RiYcr

DEplltliol1 di[ulbnllclt uncI modilicntioll of the plnnt cover nnd SUl1[lcC soil b~ trumpling and ltxClssimiddotc glnzing of linstock ns l11 n- (OIlSlIHlptiolt 01 ngetntion nncl the (ollstruction of myrinds or burrows nlnlI~S nnd mounds hy Iodltnts dlstloy mnn~T of the proplltils of tJw 1101T1lni plullt lind lioil conditions which lCtnrd snrfa(( run-orr Hilt (IOSiOIl h is nppnlltnt thati IIndlt1 nOlmnL (olldishytion- SlIlflHC 11I11-0rr i d(lny(d nnd lIbsolbEd by the soil to n dCgnp sllfli(IPnt to [ll(Ylnt (ontilillul Jupid lIosioll rIHn thesE lIoJIllll (oJl(litiolls alc dillIrlHd the run-ofl is pcnnittpd qui(kly to gnthPl inln ~tl(illl1llt lldliei(nl tmiddoto ~p(Nl lip til( nOIIlIH PIO((SS ClIl( Iud I (d lllltIt ploion 1)((ol11(s n 111lIHHt I() ~[I(1I11l d (ypIOpnlllI t ror irrigntioll alld (JlltI pUlpOSCS lIlll to the (l[Hl(it or thn soil or tl1l It(Jllld (0 podllt (orngc uncl timbtI III yiCortlH palt pll~(d by plnllt (O([ 111lt1 SlIrJUO soil it is lppnlCI1L lhnt tJ 1 0 sloillg lip llId lIltilllatp elll(king or laquo(s[mclin (Iosioll ](sts plimllil~r on illlshyPI()(I1HIl( or pnllt lnd soil eOIlltiiliolls _Itifkinl harri(ls suh tis

gllll~ dum tplIWPS lIld silt hu~ins douhtlss han n pltHl in till solutiol1 or tllt plohhIll hilt it is (yicltnt in (ol1sicltring tho ltitgll( of pl1nt and soil dit IIll1nl1(o lI1cl dlplCtioll ulld (0[ of (onslluetion or (ontro] wOIks tlwt 1(s(ol1ion alld 1l1llinttIl1I1(( of nlOl( 11(llllshy1II(lltd lUlrnl( (undi(ioll 111( PllIUII10IIll(

Ih( ((PIII or iIllPIOPIllCnt olplnllt llld soil (onltiilion 11(((-1I~ 10 (011(1(11 l1Oiol1 Itr((ti(ly fol til( difl(J(llt (ulldiliolls of ugtct gnldiPllt plnnt typt plnllt dPllsitilS IIlId dgtp( of plant lIlIcl soil dlplptioll alld tll( jp( pnlltilC to follow l1l Iillllllknown 1[0shy( PI tit IlH1IP -CIIII (JI)ion It(J( plnn dplIsiti(s all 1Jllo ~() (Jllphnsil tlu 11((d of I(toling Ind Illlintuining a (0(1 in ex((s (If (llH( figtll( Condition on til( glollll(l illdi(al( tIl( possibility of goo(il(ults ill lllUIl pIn((s flom natulHl lfv(grtntiol1 of the Iluti( s(Hli(s wllich IllHlnrg(lI 1)( uc(umplisll(d 1hlollgh prop(J l(gltlatiol1 or gllIzillg Jtifiial Jls(ltding lnd ]Jlnuting undoubtNlly hun u plIC( III (11( plngltllll hilt JIIIIIHI stlld~ is 11((lpltl to linplop (()shylIolJlicd practirCs tlld 10 dtiPIllIillP II( pllII( (0 11(

ioltilIlI- sltould 11(1 (ol1llulled (0 lllillillliz( (Ii dnllHlgl lo uil alld ctta(iol1 JIOIlI tIIi gtOlllp

rll( ](lIih or lit -( Iidy do 1l0t l11011 1lit p(middot1Il1isi hlP (i(gJ(( of IItilizatioll 01 ollwl iniolllwtioll 011 tillt kind of Illtlllag(IlJ(ut to folio ill gluzing wltrsiltd- or IIII llwlu([middotPI studipd I(i pidpnf ho(pl Ihll IItilizHtioll IJIIIS he (onsis(pntly lightI nnd (hut glllzing III list hl mol( caleflllly nJanugltcl t hln hilS rOJIlI(riy hO(11 t bough L 1ll(Pssu IY The [Iil [ioll in ~lIs((ptibiIity to t((ploJll tld (JosioJ1 of (c[tlin nrlllS 1gt1(11 us south aspects W(Nt unci grnss [YPCs Igtt(gt(p H((ltssiblE iope nnd slll11low oils in (ompnrisoil to ilOJth HSPNls d(II(I timigtE1 typos inll((ERSibl( sloplts nnd deCplI soils poillts to til( J1(ld 101 (nl( in s(llcting thl grflzing pllletic( 101 llleh 10(111 (onditioJl SonH of til( s((gt(Igt(I tlin-soil(d molc badly dlplltted iUCilS should not be glnzltd al niL unttl better plnnt and soil condishy

30 II~CHXl(L BFILETlN j~S middotU S J)EPT OF AGlUCULTllUJ

AIPLICA1ION OF IUJSmIS

Tht llRtJitR o[ the st udy ~(lTe u tL hnsiR f(f tht Istublishnllnt of ploleetin l11lnUI(s in(lllding til( ]egulntioll of gllldng on wutClslwd Innds nnd for plnnning siudiCs whi(11 will dCelop further irnproy(shyments in the mnnngltlllcnt of wattlshcd Innds similar to those on the tl1ltn dluil1Cd hv the Boise RiYcr

DEplltliol1 di[ulbnllclt uncI modilicntioll of the plnnt cover nnd SUl1[lcC soil b~ trumpling and ltxClssimiddotc glnzing of linstock ns l11 n- (OIlSlIHlptiolt 01 ngetntion nncl the (ollstruction of myrinds or burrows nlnlI~S nnd mounds hy Iodltnts dlstloy mnn~T of the proplltils of tJw 1101T1lni plullt lind lioil conditions which lCtnrd snrfa(( run-orr Hilt (IOSiOIl h is nppnlltnt thati IIndlt1 nOlmnL (olldishytion- SlIlflHC 11I11-0rr i d(lny(d nnd lIbsolbEd by the soil to n dCgnp sllfli(IPnt to [ll(Ylnt (ontilillul Jupid lIosioll rIHn thesE lIoJIllll (oJl(litiolls alc dillIrlHd the run-ofl is pcnnittpd qui(kly to gnthPl inln ~tl(illl1llt lldliei(nl tmiddoto ~p(Nl lip til( nOIIlIH PIO((SS ClIl( Iud I (d lllltIt ploion 1)((ol11(s n 111lIHHt I() ~[I(1I11l d (ypIOpnlllI t ror irrigntioll alld (JlltI pUlpOSCS lIlll to the (l[Hl(it or thn soil or tl1l It(Jllld (0 podllt (orngc uncl timbtI III yiCortlH palt pll~(d by plnllt (O([ 111lt1 SlIrJUO soil it is lppnlCI1L lhnt tJ 1 0 sloillg lip llId lIltilllatp elll(king or laquo(s[mclin (Iosioll ](sts plimllil~r on illlshyPI()(I1HIl( or pnllt lnd soil eOIlltiiliolls _Itifkinl harri(ls suh tis

gllll~ dum tplIWPS lIld silt hu~ins douhtlss han n pltHl in till solutiol1 or tllt plohhIll hilt it is (yicltnt in (ol1sicltring tho ltitgll( of pl1nt and soil dit IIll1nl1(o lI1cl dlplCtioll ulld (0[ of (onslluetion or (ontro] wOIks tlwt 1(s(ol1ion alld 1l1llinttIl1I1(( of nlOl( 11(llllshy1II(lltd lUlrnl( (undi(ioll 111( PllIUII10IIll(

Ih( ((PIII or iIllPIOPIllCnt olplnllt llld soil (onltiilion 11(((-1I~ 10 (011(1(11 l1Oiol1 Itr((ti(ly fol til( difl(J(llt (ulldiliolls of ugtct gnldiPllt plnnt typt plnllt dPllsitilS IIlId dgtp( of plant lIlIcl soil dlplptioll alld tll( jp( pnlltilC to follow l1l Iillllllknown 1[0shy( PI tit IlH1IP -CIIII (JI)ion It(J( plnn dplIsiti(s all 1Jllo ~() (Jllphnsil tlu 11((d of I(toling Ind Illlintuining a (0(1 in ex((s (If (llH( figtll( Condition on til( glollll(l illdi(al( tIl( possibility of goo(il(ults ill lllUIl pIn((s flom natulHl lfv(grtntiol1 of the Iluti( s(Hli(s wllich IllHlnrg(lI 1)( uc(umplisll(d 1hlollgh prop(J l(gltlatiol1 or gllIzillg Jtifiial Jls(ltding lnd ]Jlnuting undoubtNlly hun u plIC( III (11( plngltllll hilt JIIIIIHI stlld~ is 11((lpltl to linplop (()shylIolJlicd practirCs tlld 10 dtiPIllIillP II( pllII( (0 11(

ioltilIlI- sltould 11(1 (ol1llulled (0 lllillillliz( (Ii dnllHlgl lo uil alld ctta(iol1 JIOIlI tIIi gtOlllp

rll( ](lIih or lit -( Iidy do 1l0t l11011 1lit p(middot1Il1isi hlP (i(gJ(( of IItilizatioll 01 ollwl iniolllwtioll 011 tillt kind of Illtlllag(IlJ(ut to folio ill gluzing wltrsiltd- or IIII llwlu([middotPI studipd I(i pidpnf ho(pl Ihll IItilizHtioll IJIIIS he (onsis(pntly lightI nnd (hut glllzing III list hl mol( caleflllly nJanugltcl t hln hilS rOJIlI(riy hO(11 t bough L 1ll(Pssu IY The [Iil [ioll in ~lIs((ptibiIity to t((ploJll tld (JosioJ1 of (c[tlin nrlllS 1gt1(11 us south aspects W(Nt unci grnss [YPCs Igtt(gt(p H((ltssiblE iope nnd slll11low oils in (ompnrisoil to ilOJth HSPNls d(II(I timigtE1 typos inll((ERSibl( sloplts nnd deCplI soils poillts to til( J1(ld 101 (nl( in s(llcting thl grflzing pllletic( 101 llleh 10(111 (onditioJl SonH of til( s((gt(Igt(I tlin-soil(d molc badly dlplltted iUCilS should not be glnzltd al niL unttl better plnnt and soil condishy

31 EHOSIOX O~ lHE BOISE RIYER WATERSHED

ions haye 1)(C11 ]estolCd These al(as alC of YNT minor glflzing Tillue allyn~ O(flzing ]l(obably l1Cccl 110t he 0lilllinntCd Oil oUH alcus ployi(ling du( (Hutioll is ohs(lvecL to preyent dCpJ(lioll of COCI nncl soil FUIUl(( illYestigatiol1 is 11(CCled to dCtCrmil1( the JI1f111I1(I and dCglc( of glnzing hi(h mw be followCd fOl HlP RC nlfl I pl(ililing (olHlitiollR wi (holl t serious inj llly to wlltpIhNL Yllill(S nlid until thCRe ll( d(t(lll1inNI nil gluzing should hC mOIC (ollsCLTnliC (0 illslI(( illllll((liu(C illlpIOCnlCl1t of pltll1(-(OPI (oIHli(iolls

J( -(llIIS Jogird to aSSllllle Ul1It III)difi(ttiolls or Ihp [llnll ((1(

atHl )-oillw ( lpd tH(d Ih( Cli pu(ify of (middothn 1111111(( soi I I) II bsolh LIIIH 11 Hwl bUl (olliriblllld [0 Ihe (lIrlilI flo or (Ilt B)isl Iinl IS IotllshyjHl[(d II) rOnJl(1 YltlIl Jr](I(Hslng till nhSlllp(ly( qlltlilips of fill oil -llOllld d(Il((tlllOllgt of Ill( 11l1L-oH jllfn -111gtLI((1 (hallll( llId 1I111P t grCul(t qll1l11titY of wufpt uHilnhlC JatC( ill till -paSUII dltlls([ plant (0(1 will lIPmiddot gLPotPI qlllln(i(ic of wHII hilt iI will nl till -11111( tilll I(dll(( til nrI(llIlltNL PlORioll lt111(1)(1 iIIYClishyglllion 11( 1 (((SIII) (0 dlitlIlline (he lcluti( illl[lOlfnIH( of fitp- (ollsilti(I1tiolJs (ntil ll10re of UIP fI((s llgmling titl infltllll(P of JIPlhnc(olls t IHI ~h Ill h (0(1 on lIsn hl( wn ((( yield 111 C I)((n dCtelshyIII ill (d (frolf should Ht 1C1t bC nlllt1( to I1lllilitnill n (OCI nltirquntC o dIP(] Plosioll sinc (Ill Closion 1I1CIII(C may b( PXIH((d 10 (onshytinll( or tmiddoto illel(Hs( ns long H plnt COY(I nnd soil condition nrc lin tifn ( tory

SUMlIAHY

TIH illigntpd lnnd of the Uoi( Plojl(t in -Outh(ln Idaho (oll1plis( one of till JIlOIP ynlu1bl( nglicultulnl 11(1 of t 1t -Itat( 11(( tiiOtHl 1(((- YHll1(d in Cxp(s of Si()OOOIH)O llJC wholl~T ci(pltnlti(lIt UpOIl th Hoil HiPI Im wntpI This vtiup i Iwing Cndllng(l(d by n(I(IIIO(ltI C1()ion in PlOgl(S on l(nrly tn-t hilds of til( pOltiolJ of thp 11(lsl](ltI ltxHlnin(d in this Slll(~T nil 11(11 oj iIgtI II(IltS

This stndy a Illn(h~ to dis(lPI jllt wltnt flldol itl( infllltll(pd till pnspnl (IOiOIl tite Iplati( illllwltalH( of (11lt11 of t1IP( raelnls and tfllough wltieit on(s if 11IIy tlH Cl()siol ll11~T ltI1llttiPly b( COIlshytllllpd TIt( pliucipul 1llationhips iIWolv(d ill th uso(inlioll of thn Ynljous 1n((ols to (IOSiOll arc SlIlllIHalizltd hliCf1y in thp followingpUlngrnphs

O(ritlIi-i(h OUICl fneto( pqunl 1IH 1I1l10unt find slY(Jitr of tlJ ()oinn u- found to yal)T tiilpdl wit it gmtitll ([tlnIly hOW((I tl)( ((OSiOll inICupd - IhC gmrii(lli illlI(1-ld onlT up (0

IIpplllilllntI gtii ppJI(lnt b(~oll(1 Ihis poillt 1)[(lltlS( o(h(1 f(ol t)(lIotmiddot ((Jlllli Oil -(PIHIlll(nS till pJ()sioll (1()(lSl- On IIH 1(1)(1 -lojlP 111(11 fa(lors litipJl lig-h(PIgl1zillg by linlo(k t1slIIIi(i(nlshyIy 1)()ItIIIII to ((plse (0 IIIJ))( I d thn tl(IHI totlld in(((llsld etoioll wi h iIHIlts(d gratij(lIl

middot~fH(middotI TIII~ cau-ps of Iosioll l1C foulld 1lt) Iw JIlI)L ol)(rnfiH 011

S()utit(riy u-Ptltts On nOlI itpriy (xpo-UIP dilr(IttH(S in (tlllpllIlI ure ILnd 1I10istmc (onltii lion glad lInlly hll nl blOugh Ii I bOll L IL vCgetatiOlI (OT(1 which is more ltirCcthe in its abili t to bold the soil and Pl(nl1 t (rosion lhis PfrPtu tioll in turn Hud to n frrt1 Cr extent tlUlTl 011 foutilCllv nspC(ts hilS ilUJloccI soil (onditions throufrh ndclitions to the lit(pl md orgnllic maUCI ~Iolp(JI tlH lllilint(llllHC of tb(sp illlPIOCt conditions on nOltltCdy IlSpC(ts has I)(cn inv)l(tI b~ ligi1tlJ rodenL inftlutiotls lnt less usc by livcstoek

32 TECHNICAL BULLETIN 528 1~ S DEPT 01 AGHIC(LIlUE

Soil-Bedous ]OS~tS of the topsoil han1 o(culIClL ovel extCnsiv( arens rith theil normally (Ollrsn t(gtxtUIC and cOlltpamtic luck of binding properties even the soils whero t1UlI top layer cun still be founel erode easily The loss of litter Bnd organie mattei through the removal of the top layer has still fUlthcr reduced the soils resistshyance to erosion and thelefore has aggnwated the efrect of the factors of steepness scant v(getation lod(llt infcstl1tioll l1tuL oyelgrHzing

Plant type-JilOsioll conditions difllL sltnlpl)- on th( valiolts range t~pes The WtNI and glHSS types ill pIltieulnr lut n suflel(d SlPlely Hnd ev(n in the sugllJllIslt b10 ( Hlld t iIllIHL lypls IlUIlt dnlllHgl hus b((n dOlll ] t i significallt tlmt the morn HPlioltsly lIod(d typli UI( those WltOHl soil (OIHlitiollS hat~ bll1l j hI must diiiurlHd by IOdell is 11Iltl grazing

Dellsity ()f lYj(aiull-A ypgptutioll (0([ of J(iS tllllll 30 ptI((I1l appeHIS to hu ( jj ttJ( H PPI((in hlP p(((t i11 Ipttlnlillg Iosiol1 HineC this setll1t (on I fuul1d 011 I1lOle thull oll(-hnll of tll( wal(lsllCd thl Y(~dntioJl in its prpsllIt d(pl(((d (ondiliol1 is Jngplv 11I(fl(cti( ill tli( PIPv(l1tioll or control of (losiol1 Ali th( (irIliity oj lite (g(tlltion illshy([(tlSPS nbo(W 1)(1((11 t the el08ioll Ill pid Iy (((I(IlHIH ulid Hppnl(11 tty n CO([ 0110 1)(Il(PIlLis sufieilnt to PIPPllt gully (IOioll 1II1ci(lIolml1 cOllditiollS of glzillg ust TII(i( fnets illtlictl( t itt ]I(((sit in ortiPl to SlellJ(~ full dl(clinlltsi oj tlte (over of mllilltllining n yegetation dlllsity or 10 PPI((l1t Ol llOle ~

HUrfltts- RodplltS UpPlIll to hIp bl(11 111 lInpoltunt fndol (ontrihuting to the Hc(pllltrt(d tIosiull TIl(sl llllilllnli hI( pnrtinUy d(plet((1 tht Pgttu liol1 nlid d iH( II r1wd til( soil 0(1 fOIIl-fi ft hs of t h( IlIPH studi(d In ndditiol1 tl1(il (flp(t upon (IOiioll hlli pmbabJy b((11 i(I(IlS(ltI by tlHillwhili of cOI1((l1llltioll Oil soutit(rly (xpoilIrcs alld 0111(1 HnllH hich HIC IHuil glHzpd h linstock

1((~ibiitl ill illt(ck The IOSiOIl u foulld to uly dilPcUy with thl dpgllp to whi(h thp Y(glItlioll (011 hui hePH d(pl(ltd and tl( sUlftcl conditions diMurlwd bv tlll gllzing of ]iesto(k Almost without (x((pliol1 til( t1l(1S wlti(1t 1111( b((i) gluz(ld mOHjll(I-iJv a(~ fxumpl(s oi till most S((I( PIOSiOll On Ull lIlln with the stNP slops JOOSl (OIlIH( soil tlld S(UI1I Ylg(tntioll chn1lctPIistic of this wuttlslJ(d tll( dlglPp of IIS( hy liPHtock HPplllli to bp of 1111 moll importanee in iti (11((( IIpon (J()sioll tlllln nny otlJ(l of the fnctols stlldiCd

Tlw H1II(~~ 11l1s blOught to light tlll s(tiousllCss of thl (toiion on t vuluublc uttlsll(d nnd II kllowl(cigp of the (I(OIS which unc(J thp COlic i(iOIlS peclIlill to tile WI ((1811(lt1 hl ( IgtN11 Chi(fly I(spol)si hi ( To I (hp tIOSiOIl 1h( IPmlts point to (ill illlll1(dilt(I1(((ssi(~middot of 1(storing Ill( pIn 11 t co V(l to II d(llsi tv of 1 t JPllHL middotw PPI(PII t I ltciucillg the pxc(ssiY( rod (11 t po pula lion und ini (in ti Ilgi 1ll1)JO (l1lpn ts in Ill Il(c nnd liY(stock I11HIll~(IlIlnt which willl(i(c (oIHlitiow 011 IlI(HS pnltilushylurl slls(pptibl( to IOHio1l TIJ(Y lIlso i1ldieutc the dil(([ioll detuiitd studips should tul( in thc d(j(millu(ioll of Iltullng(Il)(lIt pluclies which willlltiJiz( thc range nsoltl((S without ([Himgelillg ttt(tshct ntiues

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