C H A P T E R

Streams andDrainage Systems

Stftrrc i, the LadsupeErosio, b! Ruaing Watel

ceorew ol stftane

Dytani$ ot sn o,qtouFrtots in stftd'nfouChtnges D@Btrean

The C d.n SbanIflg*SeL Chang6 in Eq"llibtiuh

Ita Sbenk Load

Conpetene and Capacity

D@,stt&n Chdnga ih Gtuin SiaFrctoE lnfuucing Sedindtt fieLd

D.positioiat EatuE€ oJ sE.aflsIbanphins r L.@d

Dnitdg. S!.r6sDtuindg. B6ihs dhd Ditides

E@lttion ol DtuinaSeStftan History

E6sa!: Cdt6trophi. Eloo& and th.Ctoweled Sceblord

Inportant Words ot l Teffis to

Que.Eo6 tot Reaitu

i eG a14e 'nhr tu. ht l|\tuy h4d Rr(4r@ {!16 rk 3@!.i6altrc.ba rdh pt6htat4 rah

eib\ tt44 ot he Hivhw i ttu dnkts.

213 Prftrs$ rh shp tre E'ri1s!rl(

STREAMS IN THE LANDSCAPE

Almod inywhcr wc taveloverthe Eanhk hndsurlae we.an scc c dcnc.ofthexorkorrunninBwit.I' Even ]n P|ace\ wher no rives l]oa'iodal,we aie likely ro find dcposiis and landloms rharrcll us I'arer h:s been in*tunenbl in shapinS thclind$pd. rvlo{ ol rhese leducs.an be reLated t,rlre rdiviry oI *rcanrs that ar part or .omple\drai'ugcsyftns. A sft",'is: body.rwaier rhar.irn.s rock prnichsrnd dhsolve'l subnan.cs, andfloss d.$n a slope alon8 a dcrly dcfincd prthIh. parh is thcnr.im! di,//,:nd rherock pariicles ..dsiirlte Ihe bulk or iis r,,4 thc mdenal

st€ams playin imponintrolej. ou! lilei Theyare

inpoiini sou(. of rvder ror hrman and,nduinrL consumprjon Mant iivere are avcnucsor tansponauon. Thcy rlso hrve Bre'r s.enicandrccrcihonil vilue The flo.n.fnrcrn vall€ys arcgenerrlly renik, rnd building on thcm iseasybe.ause ihe teiriin E Scntlc As a a!n, they iendio inrite la$? popubhons which rhen n$r taceth. d.n8er ol dimigc by floods rs lell as the ne.essiy otcontollidg n€m pollLiion liom thc dn.

In add,6.. b thdir innnediate prach.al ind evtheri. inponaf .., nrcams irc virrr seobgi. :3dn6

1� stea'ns.ajry mod ol ihc Micr thd goes i..nhnd b sea, aod n):ft m es*nrial patol th.

2. Evcry vcar ircrms tansPoi billiotrs oI tons oI

and .an uuinatcll become pit of rhe r..k re

3. Sftims shrFe the surra& dr the !.ntinenbl.ni

valleys sepa.ared brr hiBhar gmlrl and arc iheresdlt.r weaiherinS, masy*ashng, ind steamerosion rorkjng in .ombmahon (Fig r0]t

ERO�TON AY RfNNING W,{TEII

[mdon by wdcr hsins even be|.r 3 dktin.r sh.amhas bcu f.fred. Ii od.uA i'r iwo ways: bv mpacris raindtups hitrheSrcund, and byshe.isorsarerflowing oler th. sround duniS hevy rains Asoind.ops {rike biip Eround they ddodge smllparticlcs ol loose !oil, sp*reringthem in illdne.ftins On : dope ihe rcsult is ner disphcn€nt

$dh ro ioh thr cans6 RNd h 'oi 'hqn hd6 fte

downhill one ni'rtlrcp has lide effed, but thenumber oI Eind!.ps is so Brear thar rogcihcr tlreyon a(omplish a lar8c amountolerclon

Th. avcragc rnnurl iinr'll on rhe arca oI iheUnitcd Si:tes h eqrilalenr ro i layer oI laicr 76.d thi.k $venn8 rhe enine lind surfi.e. Otih,slayer,4t.n rctoms to ihe inosphercby avapoEiion a.d hansprarion (FE. r r3), and r .m in-liltaies rhc grcund, rsharBrng rh€ grcundwaretihe rema,nii830.m rorns runoff wecan sub'ii-vide rhe ilion inb ourodlo4 themokmedor runoll in brcad shccs or grouFs.I shall, inrerconn€criry rilk, and sftr,n/lor4 the now of su.rae w*er in a wel d€nnedchanncl whilesream'fiow is vc4 obvious, ovdnrnd flo! h les $ Usulyovenand now o..us ody rhDush sho(dinan.es

*rc:ns su.h ilok rakes pla.e wherver rainrall is3rcdei ihan ihe.apacity or rh€ Sround to absodit.Thccrosionpc omed by ovcrlind nowiscalled

1heerre.6vene$oIraindops,nd.venand fl.vin emding ihe land isEreatly dininishe'i bya pm-

rdiw @ver of v%ebrion. A.e l6ffi md bEn heoI ftes bEak rhe fo(. ol laling raind$Ps anddshion their inpa.t upon the 8ound, More im-potuily, th€ iniriole n€h{dk of r@ts fofrs adght meeh ihatholds.oil in plae, Br6dy Educingsosion. Tne mot neturl als holds warer, lei€ngit peml,te slowly down tn@Bh th€ $

b€neath.As a @nseqnetu€, in vegeraied .Eas l* warer

In plie3 wh.E doP3 aE grcM, lhe slrtd isordimrly bat durinS part of each '€ar. on un-wgebed, slairy fields, paslrlB llEtd b doelyEE*4 ud M pla ed {irh widely sp6.ed @pssuch as om, 6tes ot eosi6 .an be higt. rvi*larnes tfteElore Edue ares of baE $il bo a nin-inm md pftv.nr th€ Fass sver on ?astur€s frcnbeing *e.*oned by ov€€ding (Fig. 10.2). Ifcrcpssuch ae cm, loba@, and otlon nusr b€ planredo. a slope, ships oI such mps aE ofi€n .lr€datedwilh sh'ips of 81a$ trsis'lar plant tnat Fsisr sieet

u.d€r etuin mhGI ondiiionb ihe Bpl$h ofraindbps .nd the work of sheet ercsion are soeffective ihar rhey snbine io Emove l,rge vol-unes of fine rNk padid€s. In sone subbopicarSnssl'n& aI tne ninfau ft .ondhated within asi4le 6iny season. Durin8 the long dry seasm,evaporarion so depl€b $il noistue ihat 81a$

nsured ove Idr '€6 at 8diny, Msoun. fte ld Ldly'doP€L4's,andannudEh6ni91000tru'n!

st@tu nd Dnirqa stsas 219

EG!ru{3El'ecbol'c|eBtd,h€eteciono!asilty

sldae h* ben lowend abode d h lh lassydB,sindiodbylhe€xPo*dftemdlbdMEmnfboI d\€ dli3rn:i srdd $*a€.

beomes spae, .overing no more ihan 40 io 60p€runt ol the 8rflnd. Altho!8! tept bare by mbu.l .auses, lhe sil is as wlnerable b eEsim as$il laid bare by ranins (rE. r0.3).

CEOMETRY OF STREAMS

A skm's channel ie designed as an eltuient on-duit lor orryinA wara. Tte lisrt 4!, d quanfiryoI watu that pase d Siven pont h the ch$nelpei lnn nme, vari6 both.lmg the.hdnnel and&rcud tine. ln resp.tue, n6t .hannels aE selradjustirg, ontinually nodiEms lhen sh.pe rd.hanging @nd ions. Tne Biz. of any panicular.hffel m$ stion Ef,ets the typi@l siEan.onditiore ar thlt pl.e. Howder, ft my noi b€laee aough b carry xceprional ,loas whjdoatoP the sh€am bant6 and spEad aaos theadjoininsfoor'r'Irii-rh€ pan or my shean valleythai is inundat€d duing floo&.

A sftan chann€l itPiolly is rcunded in (:IG seclion. very snal shams may be as deep as lheyde wid€, wneM *ry lalg€ steams suany tuvewidths mny limes geae th.n then deprhs (Fig.10.4). Ir fonows dEt along .ny shcan .hannel rhentio oI widrh b depth G l&ely ro.h,nge dl)M-st€ah as rhe volme oI warer inftaes. It aiecha$6 .s the vobme and chdacrer of the load

IN t'Mn rtu shqa ttt E dr s sufi-

(a lin€ d6w. along ihe surf.e of a stream ftomi$ source to fts nouth) h eendally a dpe rharde@* in Sradi6t downshean (Iis. 10.s).H ever, it j3 nol a pede.ily snootn cum b€cuseof iftgularilies alon8 the channel. A locl cha$rin gradient my mM, for exaiple where a channel pa$es lion a beft or nsisbi m.l i.ro one thatis more erodiblq or wheE a l.ndslide or lava nowIorns a remporary d.n. A han-nade dan sini.larly intudu.es m iftellarity in the long pn6leof a sftan chrnnel, uslaly cEaiing an utensiveeseivot rpst€m liom ihe obsh.tion. whereabrpr dEig6 in L\e Id€ psfiie (@r, wahi hndsro flow nore rapidly and rudulenrly through astetch of 6pids, or it nay plun3. over a steeP

The flow ol warer within a channel is rci mirorm.Veldity ded€ases loward the bed ed the cnamelwalls becaGe ol ireasiry iiiciionar resistan . bnow. In lar8e sinnNs riveB, the nuinun veleirtin a skaight €endt of channel js ai d near &e

bends, tne zone of highesr velooty swings rowadrhe outside of ihe .hann€l (Fig. 10.6).

=...-Z

---�" . 1 " .

3d rhat th€L sidihs (w) ae d rhe ene €6re. h 8€neEr,rhe widE rhe chinnel, rhe ldgd rhe ntio or widrh rodgrth. (sd/d: Anr L€opord d r., ]ea.)

The jradr'dt (or slop4, wnich is a neasuE of theveitiGl drop over a giv€n horizontal dtuirne, may

whereas near rhe mourh ol a la$r nver ir ndy be0.1 na,km or *en l€$. the avsaSs Siadienr of adver deftases downstreatr, and so ib /"arDfr.

@. sii,-

E

in8tyPig|dowd@n.henseingE

of rhe channel (in Frcnrhc56) i€ m$uEd h n!6 pq dome6 (tu) 6rN$s nlhq sbdily dorchn {s@dj

s t . t I r t ! . , I t , t , 1 n n D 1

.-l! siruou! dlrtri (L$8is or &^\* hdfts (irvs[o{!do.i]$) i ic?on.otfishsr !.h.rr 1ni {oe)

shce rhelhanoei15 Ehdvdy ncishi G{riDr r ind

o!.iba,,r i id l,ps beldr ihe sn&i$dion5 rand 5t.

Er.epr whee ihe lards.ape is {rDngly infllen.adby ioinb or fiulG, nrai8ht chann.l scrqmcnc d.ruft. cendlall! thdy o..!r Io..ily btui *rethesbclorc tlrcy hm snuous. closc c\imindion or lnraighisegmcniof.hinnrlm ihe 6eld shows thatit his miny of th. ferturt\ ofsnuous.hinn.ls.]\

call.,l thc !rdr.r& typi.inl doc nor rollo$ r inigh(pdhequidni,nrton rhe binks, buiuandea bi.(and foih a.ro$ the chrnnal (ris. l0 7a) whaieth€ rhalwe8 *lings ro on. side ol i dunncl, trd.post ofalluuun (i rnr) tends to r..unNlit onrhr opFos*.ldr whsrvdo.tunroyq 3( srrhe thalw+ n \inuous br.\ rltcmne on oppo

nel ihplies neihar : \ymndd.al, on$dngjngdrcannrd nor : nmighi thaL$c8.

Th.padsrr.Id'.{*rdm.k a seies of !nd.th, kn)Fl*e bends nrat rc siDrildin sz. Sudr i rooplikebefd ora nipi,n.hd.neis !i[d,r : ,nr@d' lfnm ihc Mcndcrcs Rirer i']sourhlre{ern Turkey lL,bn = Merndert, nortd Iorrs wifding couse). r{arnd-s dtu.or i(dcniiLrhey o(ur mod commonl! in .h:niar\ hAhrjSenueSn.iienbin fine gE,ncJ aruyn,m, d th.v

mcafderi'r8 pafle.n tuIre.b rhc ray in nhi.h i

enerFy as unirormlv as posiLne abng iG ou.seri ha F'r.m oi equihbnum

i) {di[ru, tb) fr 4^dsiig;,f d (o br,] d{l

"r),/C'.,', .:;

222 P a{! nd shr r! !i, d, ! s{ ii{,.

Ml|rrtr,i ,l rldtr/Itr 'lhe

neinr' (od,nuousshift ormigrabon of i me,nd.ris :(.nPlirhedb!$oson on theourerbrdksorn$nderb€dds ALd,Eihr i.ner side orer.h mdiddr ldrF, $h€ru \'atarh nrlbNp{ af.l rclo.ity is lo\-cn, .orsc scdimcnrs i<unulare b nrm . d,*hdid torr td

slumping ol ih. nrcim binks o.o's mo! rrcqucntly ilong th. dowo*'eim !'le ot ! n€nderbmd. This,s Hh.re ihe ih:lweg, rid the highd$.urft.r \rl..itt, impinEes .i

: tusulr, nea.ders rend to DriSnre sLoNlv doLrrrhe valle), n'btactin8 rrcn,, i.d idding to, rarioustle(es ofreiLenie ilons thc banks Thi\ on{:ntshifiinrjof lind from onebriktuihd.rher!:. leidb lesaldrsFutsorer p(,p.il line.)nd a\e. ovft

l,ldr/f cd,,ll: rhe behifo, or lreins ,n hb,oratr.I drndph du\r rl'I jr the brdl+dinentu unirorn, D,e der:r slinn'ebi.al rnd migntadownvall.l,ar rh. srmc rite. Ho(erer, rhe mdenil or mrunl t'anks scn.mlb F not unilonn!\rherver rlt Joln{Gam rimb ora neander cn

nigcinro !n be doe edlin'b, migrarinB Nya rapidL!, DD) i'n*sed rnd.utinto th€ sloseFmoyi'rs limb (ris. 10.34. rhus,thc .hinncl byp.s.s thc loop b.tr!.cn tlr. lnohmbsiodihccun,ffrNf is (fr dcd intui.rncd

thcrc and th. {r.am L.n8rh c shoncm.l (Fi8 10.3b)N.ir y 600 knr of rr NrississiFti Rnu.hrmrL

h3s been ablnJoncd ihruu8h ebtrs 5in.. r776.HoNevar Iha n\erbrs n.tbeed lh.rtaned )ppre

hare beer L:lrned bv lentthe.irgas.thE d'rad

watar in a brafiad +ran flo*s tlmugh [o ..

n red b t r ba6 o r i s ra rd r lF iE .10 7q r f i d . sa i runrble ro ninspon ill rhc ivijlibe load, rt miydepositrhed.a6e*+dime.rasabrrhi.h ld:lildirL.lcs thc fiow a.d.on.cntdcs ii ir ihc d.!per

As thc br builds up, irnr] enclgc abovc ihc surfi.c as in ina.d ind

Lirsc bri,dcd rivcrs tvpi.illt hire nrmc'ous

-1<::-g;3

Frf n,!q Pohr thtrh! n$r, rr{r(.hinod hid i

iedinientldr lFirl r0 eJ

mDr. IDn r0 percenr or rhe hidih of ihe enbn.hinnclsr{.m, r'i lhin a si',gle +anrd rll r mo!df ihe \urfacc ldimrnr mr} bc rtnorkcd by itr.

Thp bdidad rljfteh rend5 b tum in sr.imshavhg hiShry rariable dis.ha+e and €rnly eodibLr binks rh* an suppLy itrund:nr sedi,nenr r.trdri the.hr.nelsy$en. lfa mrindcnn8 drean isunabre ro mole rrl rrrar.:d ir h hn\podnsrhrcushi .ertrin chinnrr s$m.nr, i .hingc ro I bnidedritrcrn wllippirc.ily i'rcase Ihe ibil$ or rheei,adn.hr+€ r. f.\e: sreicrloid. This is pos

snnu. Ntd Dflta* svtdn. rt3

Five basic ra.toG onlrol the manner in which apa dicular s rEa m behaves: O ) the ct ,,,a, dt,.,ri0,r(width and .tepth), expre$e'i in nereB (n), {2) rhe3'4di.'r, eipr€esed in meiec pe! kironerer (mam);(3) the ru'tr8. drtu, expressed in mee^ per ftond (m/s), (4) the d'sr'4l84 expBed in dbic ne.i€re per sec.nd (mi ), and (5) lhe rdd, onsistjnsof roc* pa*icles plus mall€r in solution, expEsscdin meiii. rons p€i cubi. nehr {m.t.h:). Unlikeo.k parrides thai consijhE ihc mcchaniGl load,diselved ma(er 8en€ralry males riide dnfer€nceto thc behavior of thc sbcan

A sfta6 sFten n chara.ienzed by i coniinualini€rplay among these facto6. M.duFfrens otnaiurar sreans show rhar as dis.ha*e changetv€loc y and channel shape also.hrnS€. The rlarionshipcn be eipre$ed by the fdmula:

q = u x d x ,

(hr)

sy$eh be.omes greaier and rhe slope lmuy in-crcas.6 (Fig. 10.3). The braidcd patem, thspfop,may repesentan adjusrnentbywhich a sbeah isable ro tnnspod a la4er ldd mor erri.ienily

DINA]TIICS OF STREAMF LOW

Depih vades.ontnuously aco$ the stidrm, andvdociry diffes at every poini in any .nss s{tion.Th.eror., rhese valfts are dprssed ,s avetges,which arc difficult io obbin a.curai€ly. when dis-cha4€ chan8es, .s it do* coniinually, one or norcol rhe orher three terms nu$ change ror balan.eto be mainhined wirh increased discha'ge, th.relo.ity al$ in r*A. The dpan esds and enhrs6 ns channeli Gpidlyifnflows on 'lluium,much nore slowly f it nows on bedrocr. Thc in-ccased ioad is.aried away

-fhis continues unril

rhe in.eased dis.haiSe Gn b€ arommodated in alar3€rchanneland byraier now. In mntasr, whendis.harge dedeases, somc ot rhe load is dmpp€d,deftaling ihe .h:nn.l deprh and widrh, and rheveldry is r€duced by increascd friction. ln theraays width, depih, and v€lo.ity are c.niinuallyr€adjusted to.hansins discha€e.

A dranah. enmplc ol.hanges in sftah facto6can be seen when fl6ds o.dr. Dunng 19S, thechannel of the Colondo Riler at Lees Fe.ry, Anzona, qp€rienred a naFr ctunse in din€NioNas dis.na€€ in.€$d and rhen dedin€d (Fis. 10 10).ftior to rhe flood, ihe .hannel avecgsd about 2 hdeep and 100 n wide. As discha€e increased inlaI€ spri$, rh€ warer rop in the channel and ercsion soured ihe bcd und ar peak f,ow the .hannelwas about 7 n deep a.d 125 m wide. Togeth.rw h m increase in vel6ity, the enlarsed channel

dischalge and .arry a gEater led. As diehaeerell, the sheam wae rnabl€ to tanspod as much

Thechann€lsotmostnatuialskdns.onsisrpa lyor wholly ol sdiment. As steans move rhis ma,r.dal from phce io placs, iheir chamels are con-iinuany being alrerud. Because st€am and .n:nnelare closely ielared and ar everrhangingi theyshodd be ennhed roaerher as an ini€mrai€d sye

224 Pt@% rtut sro\ thr bdr s st4rcl

ar8e hqakd tum February b tun€, the

rhe b:irs. Dudng rhe hlline wder ph s,reprh.{soru: Afier L€opold et d.,

sedin€nt, and $e sice$ load wrs dropped in ihc.rruner, cudry ib nooi ro rise. Ar th€ same iine,the water lev€l fell, thereby reMing the cm$se.iional arta to iG preflaod din€nsions.

Thus, a steam and iis chann€larc related inh,hately. we cm rhini( or rh€n as a stngle sysbn.The channel js so fspmsive ro ch.nses in dis.cna4r that the slskn, ai my point along rhe sftam,is continually close io a balaned condfiion

Traver4 down a nver 6on ib hed ro iis mourh,one can see that oderly adiu*nenb o(ur aronSit. ro. example, (1) discha4e increases (Fig. l0 s),(2) widrh and deprh of ihe chann€l inrease (Fig.10.1t); (3) v.locity in.ras€s slishily (FE. 10.r1)jand (4)gEdient deeases (Fiss 10sand 10.11).

Trle fad dDr v€lejty indea* doMsham eems

rush6 tub,ljendy down seep ndnrain srop6 andnows snoothly over neany nat bwlands. However the physical appe&ance ol a steam is nor atue meas!re ot its velocjtj?. D3cha$e is low in rh€h€adward iea.h€e of a s6ean, $ avenge vetociiyn a,so low. Discha€e inaeaps downdream askibuhnes inroduce moie saier To a@hn.darthe Starer lolun€ of waier, velo.ity increases ac.onlingly, roge&er wjth the .o$ 6edionil are. oI

A5 a sr€m flows downsrope and enrers rhe sea,ils potenhal energ Lus b zro md it no lon8eihas tne ability lo deepen iis channel. The finiiing

level below which a stuin crmot €rcde rh€ landis .a\ted is base ].ut, the rltihrfi bde lro.l f6nod srreans is Slobal sea level, projecred inlandas an inasinary suirace (Fis r0.12).Exeptionsaieshans rhar dnin inro dosed inhnor b,sins hav-jng no oudet b thc sca. where the noorola iecionicauy downrauned basin ries berow s6 rev.r (roiexample, Death Valley, C.lifomi4 or the basin olihe Dead S.a in rhe Middle Ea$), such sbeans .anemde tneir channels well below ihe level of lhe

For a dEan ending in a lak€, d\e level ol rh€lake acts as ioral rre t@.1, Ior the skean cannotdode beiow it{Fig. t0.12). Such lo. base l€v€hp a han b ihe *rcamk abiriiy io erode down-$ard. sur if ihe ra*e is dedmyed by erosion at irsoutlet, the *rcam, having a.quired addiional pGtential ene4y, would ihcn bc $le to deepen ib.hannel. Bydoingsoitworldadjlstnsbngpofileb the change'l condiiions

Th.practi€olbuildinsanifiGrdamsadossnvediheft byceahnga rcsdonupsft anIrcm ihedan(a loel basc level), his b€en widespread in many.ounries. some of rhe d,ns iake po$ible rhegeneraiion oI hydroel€cric power, and rhey aleredu.e sesonal noods by allowiry lowered resedots to fiil dlring times ol flood. Because iheese*oin ar€ adificial lak€q rhey tup nearly allrh€ edifent rhar the nver fomerly cadcd unin-temptedly ro the o.can. tlle a(umulating sedimenr wil evendalry fi[ the Fewons, nu].in8 rhemEle$ However, rhe *dimenradon pEe$ is slow,

stafthd Dntilst sestms lL'

m dircdion rlons a 8tu slsM Dis'.hnse inae*, I mw 6bubn4 Ft

doGlup or drkh.lge b cimm' qdrh and depth, to verc'y, dd 'o sldP€ I

edinnGte€itwjllbeatleasrsdemlhunde't qPended in rhe nov€ment of waler and s€diment

rraE betoE resefloirs are filled vfth sedinhi. along tts course FEquddy, this involv.6 6Lr8eent ol rhe chamel fts stion bv dcion, as in

ne kmple of rhe Coloiddo Riwr nmd' or rc_dudions or ft dincn'ioB rhneh depocition Tt€

l dju5hng ro. .Hgcs,1dis. hd8- dd e'!db,lN overix Fn'lPncf 6 roward a 'noorhIonBp'olilFoi ft bed a sftam modihes i6 ch,nncl .o thrt d ps6le ol eqirFgul,riric. dF 'miniad dnd rh. lmq h.€) u a sble ol 6alre. Ceol%rt4 hdw long used se

IIE

a b a lml ba* l4el (a bke) rrone

226 P@s rtnt shap n ea* utlu,

iemfrr& in rclediry ro a str€am that has achievedsuch a balance. A fnded sr..d js one in whichthe slope has become $ adjusted, lnder condiiionsof available discharge and prsailing chamel chr.acierisrics, rhar rhe sheah is just abre ro hmpodthe sedinenr lud avanabh b ii. II any oI dE contolling fa.tos.han€e, th6 ihe sftam wil adjn*b absorb the chary€ and rcstore an equilibriln

h actuariry, ii is unrik€ly rhar a ronditjon of peFIed eqrifibn!fr i3 flerachieved in natunl sftamsFtens. In ihe ,lrainage basin ot a typi.al nverichan8€. aE condanrly bking p1a.e rhar +ser ihebalanG. A pa$ing nin cloud my sudde'rly in-crease rhe discharee in one hibuhry, collapee 01 abmk nay lmxy inhod!@ an exess of edimenrio the chamel, or ihe drean my abopdy .n,ounier a le$ erodible rck along s couse. Ad-ru3hflb ta*e prace, bur €ach eveni pertorbs thesystem and leads ii away fron a srai€ ol per'edbalance. For this rcason,

is nde apFopnab bthin* or a srpan as reaching a condirion of ap-pronmte equilibium jn which adjustnents aE

Ldrg.-seb ahges in Eqnilibritn

signilicanr chanS€s in dE equitibnum ondition oIa sbeam sydem nay rcqui€ mlch longer Fiodsotad'ushenr ror esnpr€, a maioi srod 6n in,imdue a sdden incfase in discharg€ Elluirings$sbntiil chamel adiustunr ftough a laBe panof the dram sysien. A longiem .hange in cli-m.re can arso have dran3tic effe.rs on a sbean ifit resuhs in a charye in n€an annual discharge, inthe seasonal dishiburion of precip aiion. or in rhev*eration sver and rerared dres of runoIf. Ftuc,batift of world sea I*el may lead to major dr$6in river sydems as siG:ms adjus their long po,files to , rise or lall oI base l{el. T{bnic adivityGn ako .a! se sheans tjo chanSe course, ro h€mm€ponded, or tio erode doMward d build up iheirch.mek in Fsponse 60 local or Fgional crutalnovenenb. ln each oI rhese ca*s, b.ih lona-i€madjusrnenb or dninaSe sysiems and shoneremadjusknenb elakd ro *aenal, 1oGi, or sml{€le

The seaenai disribuiion or rainfan eues 6anyst€ams b ns. s.asonally in ned. This i3 dischaBeEEar enough ro €u* a stEm io overfl@ ib bar*!Gig. r0.t3). Pspl€ a{ecred by doods are rie

rrcuRE 10.f Mekons Rivq h knpuchea (iomerlycanbdh)? sworrcn by no$on nins and 6lord bduy i i h i t s l cdo f j h ' v l aga 'bu tmPo lsmdPerchedon rhe hrghdt paft d 6e he6, irc s'dnded by

quently surp*rd and even outaaed at whar iherampagjng stiean ha6 dde io ihen, but geologidsbd ro vis fl@ds as nomd and expetable ddb.

As dischaBe increases dudnga tlood, e doesvelo.iry. 1"ni3 nas rhe double €lled or enablinB a*rcam to drry nor only a €rdter load, but akolarger partides. The .olapse oI rh€ rarye st. FrancisDan in 3outhem Califomia in 1923 pnvides ane$tn. example of the ex.eptional lore ol doodwakE. As rhe dah gav€ way, th. ware' behind iitushed doM rhe valley, novin€ blmks ol6n etewe*hing as much as 9000 netic tons rh$ugh di*ranes oI nore thm 750 n. seuse mhnl floodsaje al5o .apable or movins very la4e objecb aswen as grcai volnmes of sedin€nt they are ableid acomplish comid€nbl€ g€ologic wdk.

Major n@ds en be diesho* *nt3, ausinaboth l6s ot lite and dbnsiw propedy damg€craue 10.1), so

murd be hisNy desrabre 1o beable ro pEdict iheir omrene. By aMlyzing iherreqrcncy or odnen@ of past flood3 .t difteanr

227

size, we Gn edabtsh dE pnbable inre'al, in yea6,betueen floods of. given dagnitlde This int€rualteded 'he z.Dd.e ti,u 14 is lound by plortinson a Fobability Sraph ihe f.equenct or noods o{different naenitldes lhar a steam has experienceddlnng a pedod ot rc.onl. The resulting rufle isrhen used ro €{imare how lrequendy a flood oI a.etuinmagniiudeislikelytoKur. InFi€uel0 l{,for exrmple, a flood havinS, dG.hary€ or 1750 m'/sis lirely b recur once in every 10 yeas, wheFas ,larg€r flood of 2500 nrk wiU probably rccur only

Ex(eptional floodFwe0 oubide the skansnornai nrye m.ur infreguently, only on.e inmany decades or even @ntfiei A larg€ nood thatrcd6, Ior esmple, only on.e in evcry r00 yearis refeftd b as a l0cy6! fl@d. Duii4 such doodsthe B€ologj. woik a(onplish€d my be pbdi'gious. Nev€rthele$, iheir lonSrem effe.ts on thelandrape may be le$ than rhe cumulative errecrof annual floods over rhe same inrewal.

TEE STREAM'S LOAD

qcUREt,xcuflcof'lood;IqFicyfolskykomGhRjver d cdld Bar, w*hjnsrd4 plotred on a prchabiliry

yeas c rhere hkely ro be a nood ol50 m1s (s4rclD*afionU's.GfulogiG|sldey;:lt!Dunreddko

nor in .onsran I moiion. Inslead ihey move disonri.uonsly by rollin8 or sljding. wn€re roices aFsufli.ienr to lifr a panid., n may move shoi disr es by srrrtrnl a motion rhar is inrem€diarebebreen slspension and olling or sliding. lt in-volves the p@8esjve, rofl,rd moven.nt of apartide i. a senes or short inhrnirrenr jtrmps alonsadate Paths. Salbhon wiu ontinue is long as.urrenb are ruibulenr enoLSh ro lin partides andpemit them b havelsome djsran€ doMsneam.

fte bed 1Gd Eeneraly anounk to beseen 5and 50 p*.entofrhe to|ll load of nost sheams,

A sheant load oI solid p'frjdes .onsisk lagelyor oae padicles rhar move along or dop id ihedftarbed (he t?d /,4tl) d fine panicles that :esuspended in the sftam (&e s/spdd?d rood).wh€r€ these $lid panicles are deposited, they mn.titute alluviun. In addition b solid pdid*,sblans 6rry dksolv€d sub*ances (the dissolr.droad) rhar aru chi€f,y a prcdud 01 .heniol oeath

Trle a vsage ate or novemenr or bed l6d parttdesis le$ than rhar oI the warer, for rhe particles ap

ua PN6es rtut sn\ tt ht 5 sr4a1

The muddy .haracter of nany nreans is due roth€ prcsence oI Iine paiiid€s ol silr and clay movingin suspension (Fig. 10.13) Thc re]bw River (HuM8H€) of china is ye[o, hecaGe of rhe Sreat l@d ofyeusish silt it erodes and hspoa *awdd tomvidesFead deposis of colian *dimenr ihai un-

Be.alse lpwa.d froving drenb within a tuFbulenr srcam exe€d rhe rero.fv ai whi.h partidesorsiltand clry.an setle toward thebed underihepuu of 8nvny, su.h parti.res rend ro rcmain insuspension longer rhan rhey wourd in nonrrrbuleni wate$. They cm s€tl€ ind be deposiied onlywh.re velo.ity decrases and turbul€nce c€apsi ason a floodplain, in a lake, orm ihe sea.

Mod of rh€ suspended load in steams is derivedfiom fine Srai.ed regorirh vashed trcm aE.s un.pmt{r€d by vegeraiion and fmm sediment erodedand rcworked by the steam Imn ib own ba.rs.

Ev.n ihe clear.st shahwater contains dssolved.henical subdanfts ilrai .ondiiuie pan oI iis lmd.Only s.vcn ions compns. ihc bulk of the dissohedcontent of mo* rive*. These aF hcarbonie, .al'.iuh, sulrare, .hbnde, $diufr, fragnesiui, andpotassium. Alihoughsolved l6d day rEpresent only. Iew perc.nt ofthc ioral load, in oiheB it amounb to morc thanhalr Steahs rh,r receive lar8e .onhiburions ofSmundwaierSeneranyh:vehiSh*dissolved roadsrhandrosewho*wars.onesmainryfiomsu*ace

Conpatae dna Capacit!

when a .lear, 8€niry nowinS *ran is banslomcdinroa roreniof muddywaierdunngflood*ason,iis abirity io bansport sedimeni.an ind.as. d'a-ratiGlly. Nomally this ability is el€Rd to in i€msof a sheam s o,a&rc and .nptr jry.

'n'e sia or panicld a srcrm.an ransportund€ri given set of hydroroaic condinds is a mesure.lls.o,,J,.rd,d,exPle$edasthcdiameeJofthe|argest sedineni lhal can be fovad :s bed lcdconperen.e depends nainly on veloc y This iswhy a major floo,l can move very lal8e bouldes,o! even obie.b li*e nilrod Io.omorives, whil€ Ln

der awraSe flow mnditions rhe same $rc,m maybe able b banspot only nne gnv€j.

A stean s .4p..ify is rhe pohnhal load ii ff cry,measuFd as rhe rclume of s€dimeni pa$ing a Sivenpoinr in ihe channel p€r unir.f iime. ri dependsespecially on dhcha4e, channel gradi€ni, and thecharactei of rhe load. Nuneous field n€asure-menk of narural sreans sho! rhar suspended sedinent load tends ro indease w h incrc$ing dis-

Dibttzan Cncnges in 6nh Size

B{ause conp€ienft is mainly rclared ro lelo.iry,one highi dxpect the alera8c size ot sediment toincrcase in rhe downsieam diecrion as verociyincrcases. In ract, the oppos € is tuq sedin€ntnormally dea€ases in coaEene$ down$rcam. ln

;

t_Bi

rh€ ,lishi'se lor res2. lsad: Afirt r?opold er al., rB.)

mountainons headwatere of large nve6, bibutirysrrcams m osrly fiow thmu8h .ha nnek noond with.cne anvel ihar may include bouldcE is hlge rs

iseasily move'1, even by $rcrms hNing low dis'.harAe, ii is reidily canied away by smau mountain*reamr leavrnS the .oaser sedinent behind.Thtuueh time, th..oase bed lcd isgraduallyrc.du.ed in size by abrasion and irpadas it movesslowlt, along. when ihe dFam cvcntually rcachesihesea,nsbedloadniyonsisrhainlyoraltuviur

Fo.ton Inften.int seninctr vieLlSome*Eanstund6rnearlyallthctimc,wher.:sothers aI€ con*anily nuddy :nd are qu c ob-viouslrr tan sponin8 a sizable scd jmen I bad. smhcontu$s suffe$ thit some hnd rreas aie bein8ercded more mpldly thai orher. The dilrcrenccsarc rclaicd ro a.ofrbin'iion of 8eolo8i., dimahc,and topogaphn fa.toG, including rc.k ryPe andstuctotu, lo.al.lirare, and relicl and sloPe TheselactoB .ontol the sedinenr yield rsm a drainase

CLmri. innuen.es erosion in sevcml ways Onemirghr exp(i that ihc sEakr rh€ piecipirarion, theEeare! ihe erosion. How.vcr, in humid re81ons,rhe nearly coniinuous ve8eiahon .ovej tends toinhibit erc6ion In smh areas with hiSh a!er,8epre.ipitation, therelorc, erosion mts may tct!allybe less rhan in som€ dry rcgions ihai lack: ..ntinuo$ covcr ol vc8chhonsusge* rhar rhe grcaiest scdimcntyields:f fmflintlsapes hansnnJnal ba$een fulld.sci.ondjiions:nd grasland (Fi3 10.16) With in@asinghumidiry and ihedevclopment Df rorestmvei, *d-imenr ),ields i€nd to declind.

The hiBhes neasured scdiment yields ar rrcmbains thd dnin nounbin@s ftAons haviry $ccpslopesand highelief. Raiesarcalsohigherinareasundenain by endible dadic sediments or sedimenrary rc.rs, or by low-sade mebmorphi. ncks,rhanraruasrhcre.rysallin.orhishlypermeabldcarbonate D.ks .bp otrt. Stucruml ldos alsoplaya rcle, ror rocks that mc mor highlyjoinredor fractured arc more su*eptjble ro eiosion than

sr4n* 'd Ddtli3r srFr' 229

Human activiry, cspmially the deanng or rorcns,dcvclopment of duivat€d land, dammin8 of*ieams, and consbu.tion of ciiies, 'ls. 'fl..b ension rares and sedihentyields in rh€dninageba$ins where ihey o.dr. Someiines the resulb ardramati.. ln patu ol the eascm United Siates, ,ras.learcd ror.onstucrion produ.e behveen l0 and100 times mop pdimeni than comparable rural ornator:l areas thrt re v+ebrd. on rhe orh€r hand,in urb ized areas scdiment yi.ld tends ro be lowbe.ause thc land is almon.omplerely coverd bybuildings, sidewalks, aid {ads thar pmi{r iheundcrlying rdks and sedinents rrcmerosion.

DEPOSTTIONAL FEA7URES OF STREAMS

when a ileam ris.s in nood, it may ovedow irsbank an.l inundatc ihc floodplain (Fig. l0 r4. Manysheamsare hrdered by mtonlleves brm,l,lowrid8es olnne alluvium builtrlong both ndes orasheam channel by e'rer rhar sprcads out of thc.hannel duiing floods. The alluviun ol Nhich lev'ees 3r .omposed b€mn€s shl1 finer iwat from thenverand glades inio a thin.over ofsilt:nd d3yover rhe rcst of rhe floodPl,in.

E D

yield ddrns. (s.rd, Ar& L.nsbeb aDd schumm, re3.)

230 Ptds rtut stupt tu tudh 1 sr4r.

Natml lev6 ar€ buili, and aF sndnnany addedro, o,rly .luring noods so high dEt rhe doodPlainj3 onErted esenlidllt into a la*e deep enaugh tos!bmer8! the levees, As dE waber flws olt of theslbmereed channel dlring a flNd and a@$ theadjaent submeBed floodplair deph, velEit', andrurbulence 'lm.se abruprly .i ihe cftannel naFejns. The ded€*e nsdk in sudda, spid depGsftion oI rhe oaRr pan of the suspended ldd(6ually 6ne end .nd 3ilt) .long the na€ins orlhe .hannel, Farth€r away tom lhe channel, finersilr and clay *tlle out in the quiet warer,

MGr sftan valeF ont in tm6, ,hich areabandoned flaodphins fomed when a sheanflowed at a level above that of its present channeland floodplajn {F*. 10.14, fteir pl*n.e indi-er* rhat a cha$r in tfte equiDbnum dndiiion oIrhe sftan h6 odred. Tene€s lom as a sb€me$de downwad thsugh ils deposits to a newhvel. A r€n4 ray b. unddlain by sdimnb, bybedr.&, o. by boti. ln other wo'ds, a t€rae is aIandlm and is distind fmn rhe natdials rhat

T?Ercs nay oor ar many laelt implyinS a @m-pld hi3biy of 3b€m evenh. Terace Emanrs onopposite 5id* of a v.I€y dEt lie ar ihe sn€ levelaE lened /dhd td.* Ft.10.13a). A ser oIpaied ren .er inpliee an infrval df depGfiion(also calle.l ,A&zLtm) ro pmdu.e a sedinenbry

, rollowed by e €pisode of dohdtting (akocaled dq"and,br). A series oI such rdac therIore poinb ro a 3uGsion ol a#rad.tional and

Temes on opposit€ sides of a skeam that do noinarch ar€ cal€d rdr'aiEd read@i (FB.lo$b)and nu* dillbr in ag€. Ior a sream 6mot trfr atdinerent l*ls sinulbnedsly. They en r€f,ecr asinSle ?i8ode of d$radation as a srem shifrsbhrany ton ore side of its valley lo the otherwhne ohina dmnward. Many tsne yqu€nesinclude exdpl€s of both paied ud .mpanedtyp6, naling intdFetation of shem hisrory dif-

Fcw n.r E$mpr6 or (.) paircd rnd (b) nonpaiEd drudd @a!. A 3ua.,h@ cu$s oi 3tun @odidon (rchation 1o desEdatio), {h€ms rhc no!.

p:[€d &me Fqren.e inchkd nqdnd a i$le cha$e (trm assradatun'o d€Edadon) c 'he sftrr lhifbd r

when a srftam flowing through a *frp highlandvalley.omes out suddenly onro a neaily level val-ley floor or plain, ji expedenes m abrupr d*aseof slope md a conesponding de.rease jn .omp€ten.e.'Ihedoie, it deposjis the pait of irs load rhar.annot be tansPo ed on the Sentler slope.

As sedinents are d€posihd, rh€ {rcam channelshilts heraly roward low* grcund. Through onsbnt shiftinS of rhe .hannel, rh€ deposit takes ihclorm of an ,lhral laa defned a6 a fan*hap.dbody of alluviun typically built ,heie a strcamleavca a steep mounrain valley (Fig. t0,l9l Thepolile of the fan, ton top to base in any dne.iion,has the $ne ored lorm characrerisri. oi the lon8proliles oI *rcams. Tne exrd lom of rhe Pofilddep-"nds chiefly on discha€e and on th€ diamctcEof padicles in the bed load. Hence, no iwo lansarc exa.dy alik.. A snall shan odying a lMd of.orGc pdrides build.: 6ho er, sieeper fan fiana lalger *Ean carryine a load or finer Padicles.

Theareaof a tun generallyiscloselyruhedbihesize of the arca lpsrieam rom {hich ns s€dimenrs

A 6n n onEiMIy l@lired by a d€@& or slope.As soon as ih tong Folile has bcmne smooth,luihq deposihon o.d B a s wa l€r is redishibutedihrcu8l a netuork of spreading channels, resrltingin net reduchon in di$hai8f, velGiry, and conperence in each.hannel. Deposjrion my also ortuas warer percolaies down into thc underlying poFous fan sedin.nts, theieby €du.in8 surrac disrharge and competen.e. ln ene c.*3, such PeFohtion will cause a sbean lo disappe,r near thetop of a la4e lan, only to ieapp€ar agrin near ihe

As the wais oI r shan ente$ ih. standin€ waierof the se. or i l.*e, ,ts speed dops rapidly, il losesborh ompeten.e and capaoiy, and it deposib nsled. Th. sedimenrary deposii ihai rsulrs may d€-

x2 eft36 nat stftp. tlE Ern|s st4e

velop a tudely hianglh. shape like rhe Crek let-ler della (A), from which the deposit denves nB

D.l.a Typ6. Delras built by sft.m bmspot-ing oak sedinenIs are or two 9pe5. G'avel-ichdel|is fomed where an alluvial fan G buildin8 o!t'ward inro a dandins b.dy or warer aF called t ,,.rto, (Fis, r02ra). They 9Tnally oeupy basinsadh€n oamounbiJrho . sftm{haffd,sherdood, and debn$flow sedinenis characieristic 01aUnvi:l lans iom the upppr pais of ihese d€p6ih.Such sedinenis display widene of highly vanabhdftnt' and abtupt chan8es of fa.ies, ,rrrd dr}rsare coaBe€Iained deuas .onstud€d by braidedsneams rh.i pr%rade (build ousad) inr,o, stand'ing body or warer lFig.l0.2ra). Their upper padsdisplay leaiue .haracteristic oI bEided steans.Snch dehas aF esp{ialy conmon, for emple,where braid€d gl.cial neleakr sheans ndw into

tdr' S.dtrr'rs. As rhe stream enten sbndinAwater, particles of ihe bed lGd are depos ed tui,in ordr of de@asi$ weighr. In€n ihe s$pendod*dimenh prde ont. A lawr apresenring one dep-osiiioml event Guch 6, ,insle trood) is sorkd,Siadins lron 6arse sediment at the sftan hourhb nner sedifrent offshore. Ihe a(unulation ofnany so.€ive layers a€ahs an emhnkneni Lhatsows pEslsively outudd GE. 10.21a). affierhick, s@ply sloping part of a deposiiiorol unit ina delta i3 a ldtu r Lrza rrac€d away r.om theshoft, rhe same un

be.omes Gpidly ihinner andfins, .ovenng the botbn over a widc aFa. ftisgendy slopin& nne, ihin pai of a depositional $iiia a dEltajs a bottotut |r!d.

As depdition proeeds, the oaEe roEsei laye$pr%Essi*ly overlap the bodomsei laye*. Thesteam Sndualy exiends ouead over th€ 8nw-ing delta, so that its coue n lengihened. C@Eecnann€l deposiis and tiner inErhannel deposikr%ether fon toleer l4y.r6, derin€d as rhe layasof sheam *dimeni that overlie the foret layec

5o6e ot the world's greatest dves, a6ong themrhe GaryesBrahmpuba, the Huang He, the Am'azon, and the M$issippi, have buih nasive del'tas at then noldr. Each delra has its Nn P<ul

ianties. These are deiemined by such factoG asthe sb€ant diehai3€, the charader and volumeof ic ldd, rhc shapc of ihe bdrcck oadlincrhe detb, rhe ofshor€ bp%raphy, and ihe inhn-siiy and dneciion ol ldngshoE turents and waves.Most mjor nves tanspod larye quantitis or tineslspended sedihent, the bulk of which is cartied

sali water at th€ odt. The tine sedin€ni th€n se!tl€s oui b lom th€ gendy sloping rront ol a miinedelb. Whef cftnk and wave a.tion aft $ shorgthat host sedimenr r€aching ihe.mst is rcworked,d€lh lomarion my h€ inhibited However, iI ih€rare ol sedinenr supPly ex.eeds rhe nte of rdov.lby eosion almg the or*, lhen a delra will b. bliltseamrd. fte Mi$isippi Riv€r deliwG such r la4pl6d to the Gull or Mexi.o rhat lonA fingatre bod-ies of sedin€ni aE depciEd along and abunddndbuiary channels 60 lom a conplex delia tent(Fig. 1.15). The cdced sdimenr ljes along ihechamel, while tner sedinenr Eaches the front of

FTGURE 10.a Mlin fcduFs of de[* (a) A kaid derb b 1r inb a bb dLpby5

; buirdbs od hb rhe dy o' wde! (b) Prt ofa hlge fine.8nined dexa buik

b ron' and beyond. (r4ui Pr[y aficr

rh€ delta and also a(unulahs beeeen disftibu-r.ry.nimeh durin8 fies ot oledank ioodmS.TnereulrEacmp|s nktun8ugof famslFiB,

stdn dad Dnnns. sgsnns X\

In North An€ii.a, ihe huge drainage basin oI theMssissippi River en ompass an aFa that exce?ds40 per€ni ol the area ot rhe conti8lols Unitedshles. Not surpnsingly, ihe aFas of drainage baiiro bear a dos-a relationship to borh rhe l€n8th andnean annual discharge ol rhe $mams ihai dFin

'Ihe ananaen€nr and dindsions or 5b.an5 in ad.ainaS€ brsin r.nd to be oderly. This can be ve.in€d by exanininS a sftam sysrem on a map andnunbenng the obhved 3km s$menb arord-inA 60 rhet position, ot ord4, in th€ sy*en. Thesmlesr segmenk lac* tibnt:n€s and are cla$ilied

DRAINAGE SYSI:EMS

DraiMSe Bashs tutI Diti.les

E!e'y 3h€an or segnenr ofa sream is su'dndedby s drraSe bffi4 the rorat ae that onbibureswarer lo the 3ftam. The line rhar sepaiates adja-cenr drainag€ basin6 is a dilir'g, DraimSe bashsanSe in size fron l6s than a sqlare kjlohetF tovasr a rea3 of subconiinental dinensjon (Fig. I0.23).

24 Pilsr lpt 9tupt th Endh 5Elo4

mourhs (sor..: Anq Evans, a3r )

wherc ko n6t{rdsr strans ioin; thcy have nE!orde. tribuhn.s Thiid orde! str6ms are romedby ihe joining of tvo seond'odcr shcrms ind .inhave liGt{rder and second order bibulanei rnd$ Iorth for slcce$ively hi8her stream oders (Figl0 23).Irthe numb& orsegnenk or each order istabluai€d,

can guickly be srn ihai for any drcansysiem the nrmber ol s$menk in.ieases wiih decrcrsing skan order. ln orher $ods, a sftrmsynei n sonewhatliker t€d, Njth a ttunk (ihemin sr€m) and nunsoG bmn.h6 (ih€ ribFrarieq This ordeniness is lj*c th inheEni in askan s long prclile, in which Eradient deseasessy$emafiolly fron headcharye, velo.ity, andchanneldimensionsinaease.All thes€ relationshiFs imply rhar in r€sponse ra agiv€n quanrry ol runolt snam sydems d.velopwith jus ihe size and spa.ing ftquned b moveihe sarer off ea.h pafr of th. land wnh geatest

A sydem oI dreans does not neessrily rcquiremuch tine io d€vclop, as indicarcd by the lollo$-ing exanple. In August 1959, m eaihquake oc

.urred ar He4en Lake, near wei Yerowione,Monrana The movemenr rilred the reqain in sucha way rhat a lar8e area oI sili an.l snd, tomenypart oI rhe lakebed, emerged and was subjeded iolunorr. sfrall d.ainage sy*ens b+an ro developinmediately Sampl€ aruas le€rc surey€d andmapped om and tuo ycas afrcr ihe caihqua*eo(uEd. The results showed ihe $nd basic sFomerry ihai charadeiizes much laqer an.l oldersystens. The shall, newly romed valleys, togeth.rwilh ihe aleas behr€€n them, were disposing ofihe availablc runot in : highly systematic way, .ndall w hin a penod ot hd yeas aher the sufi.ehad endBed rron benearh the lake.

As a dnina8e sydem develops, derails ot ns pd-tern.hange New tibuhnes areidded, and someold tiburalies arc lost due ro starr .,pto- (or,,im.y), rhe mtrrcprion rnd divsion of one sftamby another sirean rhar h erpanding irs basin byeosion in the headward dt€.ijon. In the prcc€sssone steam sqn€nb are l€ngthened and oiheBare shortened ,!st as the hydranlic r:ciors lnhina skan are onnantly adjustins to chanEes, soroo k rhe drainaa€ slsren consbndy changing andadjushng as it grcws. L&e the sterm chmnel, iin a dynani. systeh tending rowad a ondihon of

-l\**,stdrc tnd Dtain\. sykn\ 23t

I

+-,1_"..d:

i

'*,

shams Gn b€ .la$ified inlo e€ral skgonB ftarftnet dGhn.tive hisbn6. By an yziry rhe r€ra-hon3hip of sreams to rh€ n.k unih a.oss khichtney flow, an expeided geologid may leam a€t€ar deal abou he structlf and e€ologi. hkrort

A colsrtl,t srr.d t one whose patrem is d€-ljemined solely by the diFdion or slope of rhe land(FE. t0.24a). conseguent stuam orren m foundin resiv€ o! gstly sloping rc.ks.

A e/rs.4!ni stu r is a sream whose .our* hrsb€.on€ adjusted $ rhar it mopies b€iis or weakm.r n orhs 3€logi. sd!.tue (Fig.10.2ab). wtentu h b€lb m lory and sh,8ht, $bsequent itr€nsrollowing thd ar€ ale shEht.

An ,rirad.rt st rr is one rhar h:s maint inedib coue aft$ an a@ of rhe tu* thai wa3 rais€dacnss irs parh by loldi.S or lauriing (Fig. r0 24.).the nane on6 troh dE frci that the sft.n isanisedent ro (older rhan) rhe upliried srrudure,sn.h sh€ans aF olhn re.ogniable beuse iheym$ topo8raphicly high nd8es thmu8h d€ep90Ig6, Ether rhan taking a noF obvious patharound th€ end of the uplift.

A flr'4os?d sk , was l€r dowD o! superposed,Iiom mrlying sbata onro buied bedrocr havinSa ridrloSy or srutue ur ik€ that of rhe ov.dngshb (Fjs. 10 24 d). Mst superposed s@ans be3m as oGequenr shans on rhe sude€ of covering skata. Their initial patk, theEfoft, wae nor.onholed by lhe toc*s on whiclt they aE now

zt6 PNs fh,t skP: ttu ban 3 sa4at

unde4ng i.L studF pdde hfdrudd !bdu' 3tu hLbly. G) a 6n*gued sfrin td* d6M 6e rop. or lt6dy dr&d sbb. (b) fte 6ue ofi sbequmr dean ha bloru .djudcd b rhs fordcd nrudrc or undsdtnsmck by nNhs:lons a %[€y bek€i adjaen' panusl iolds. {.) tu an'eed.ir

ave been upli,bd am$ ib pdh. (tl) A

daBd oow rb, h 'b undsrFE ,sn@u E&.

EssaycAlArIRorHK ,-OODS AND THt CHANNTLTD 5LAB-AND

Mosr oI the columhia Piver Basin in tne mih-wesim U.iied Stab i5 underlain by *n-sive b6sa} nows thar co edively lom rhe Ccllntta Plabea!. A nch t,opeil ovenying ihebasalt mak€s the plahan a prine wheaEproducing region-ht not aI oI it. A glane ar aerel e inrge of ihe pheau in easr.d Wash-inerd Bho* an afty of dark .hannel-likeIeaes wiep hva li€s ar rh€ su.Iace, stippedof tuilile topsoil (Fig. 810.1). Alihough rheyEtuble . Iar8. bEided shan By8td, theclunn€ls ar€ nN n6dy dry.

In tbe 1920s, geolqisr J Haden BEL begana dudy oI dis dnous landscapp, which he

naned the Channeled S.abland. BreE.are'tully dmunmhd rhe chai&er trd distibution of an affiblae€ ot Iandsdpe featuFetiat provid€d aid€ne about tne ongin oI thesobland. The6e induded dry coul€s (on',rns) wilh abrup1.iifis marl-ins romei h!8e€hFd ststens, plmge pools, po$o16, deprtrl basiE crwd in $e basalt, ll]Aiw g €lba$ .onbining enofrous b@lde$, depositgol grawl in the Im of giganri. drenr dp-ples, and upper linib oI wareFe@ded bnathat lie hundre& ofnetds.bde v.lky ne$.

Although Bclz @Gidered albemanve hy-p.thes6 bo qplain th& amy or rahFs, he

8j{;j 'u]dwdcFstiPFdd{}'.ovsolr$hl

Y . ,* '

$is re.r inscp:bry b.on.rude rhd rhcl.ouldor )r bc icounied lor by a carasbphi. e(enra huL)r g,gantic nood, faj larBer l|Dn any hnroncnood A implccilculaiion poided roanenomDus\lruheorwder rhesourc olwhi.h

tincnhl i.p shedt lrknn8 we$em crnadidunns rhr liigli.iirion ha.r adva.ced a.rossrhe clark Fork Rrvff ind damnRr a hugerakain ihe vi.id v or Mi$outi, Monrrna. cla.irlLake Missouh .onb;ned bei{een 2000 ind

dam was *able trhmcvcr ihe gla.ier rctmated orbe3an b fr.rr in rherning tatc, rhcdam railcd, an.r mief ,!:s rera:*J 'apidtffrom ihc basin, as rhrcu8h : ph8 had beenpolldd rrom r sisinh. b*hrub The olny pos

a.d down rhe corunbrr Rrvcr ro rhc searniiiall)r rhere wrs nu.h re!*an.e to rhc

rlood hvpoihcsk, blr ausrnarivp ides I-4edis.rrded one by onc is cvidence neadilva.cunulaied Fuiher*ud] ihroushoutrh3corumbk Rivcr Brsin has Senarared n*v rnr

Senftarry asrecd thar manv noo.rscrcsed ihe

8e.r%ic dffads of rhere evd.\ h:ve v4 ro be

The lan.llrms prc.lued bf ilre neing !vde6providc ducs rtroui rhc ntriur€ oI rhe noods.

rully mcasurcd Thcn hcight and wiLlh hasbeen tular€d b rlnndr waar deFrh :n'i q?tersurta.c slope, as rccon*ru.te'i rron ri-cld measuremensolthe highencvidcnc.of flood icrjvity. sbndard equrhons used by hydritrli.dngi.eaR ihdn pefriiied otihares io be n'de

sulrs indicde tlDi the Siaftipplas formed inwierdepthsof 12to 150 m whcrt. the rratcrsun:ce sloped 13 b5 6 h/kh, an,l underrverase nolv vero.iries of e r. 13 frh (32 6 65

Su.h mrcd,gahons hold pronisc Ibr gain.in8 r norclrmpleta trndeabndinSorrhedynamjcs ol ota$rcphtr 0oodjns and the man.ner n, nhi.h8ia.r noods.rn iadi.allvalreralandsipc. Althor8h ihc prchkbft SoLiandfloods rrcr or cx.cptionil ma8nih'dc, ninvorher exanpres of nood wrptuBl enin nakeir appiicnt rhat su.h .ahnrcphic gcolo8i.ev€nb have plrled a l..rlly impo{:nr tule in