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<br />',122
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<br />CALlPORl'llA FISH AND GAlrlE
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<br />T~-~ffiHERY OF THE wwiR coi~~~" ;-iviit=--.:....::':~c:' f23i:=i=';:"1-~~
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<br />"alleys and this has requiredext~nsive'leveeingto protect airi:' '-',:':;:J,~=
<br />limds. The depth of its channel has also varied greatly depend"" '... -~-.:~:.':.:
<br />'nthe rat~ of flow and the deposits of silt. At the Yuma gaging=~:::::-~:"--'-4::;:=:
<br />~:lor eXample, such average depths as 1.9 feet (at a flow of 2,020:
<br />'d31.1feet (at 89,600 c.f.s,) have been recorded by the United.
<br />'~ogica1 Survey: _ - ':.- , ';--. =' _ -:- .'~ u :'.-
<br />ts' .nurmal gradient from Topock to Yuma is about 1.5 feet to 'the
<br />.=11 i,s higher above and lower below this section. At Yuma such
<br />S~parated mean velocities' as 6.40 and 0.07 feet per second have
<br />'~ured. These do not represent extremes.
<br />" ere, the river cuts through rocky spurs one finds narrow-sided
<br />. , f4-:Danks-iandlll!teepenedgradienLJl~r~jts co~~,~ subject ---.
<br />ange. But in its alluvia.l ba.Sins~ of recenUinconsolidateifSiff; .=- ',. .:, '-
<br />u.els have been abandoned for new. Sloughs, lagoons, oxbow
<br />-~:ap:peared and diSlippeared; On the bottom land there has
<br />r;)greSSivedciwnstream movement of the meanders' so that wide
<br />j~ been-worked over by the river, with continuous destruction
<br />~.,llD.d tnarginal vegetation" and' equally continuous deposition
<br />",Ji,nd growth of new plants: All rivers change, but some only
<br />:the'Colorado one is impressed by the ephemeral character of
<br />," natural features-the effects of normal lateral cutting, of
<br />'(J.plant succession, and of flOod-stage erosion. ' .
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<br />Flow
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<br />_oW in the Colorado usually reaches its peak in June, diminishes
<br />;'August, and is very low from September to February. How-
<br />il.ries greatly from year to year and even from day to day.
<br />~.el"c~ction of Boulder Dam, the usual discharge at this point
<br />pm-:3c;OOO to 150,000 c,f.s. (Anon., 1941, p. 45.) But there have~..
<br />.greater extremes here and further down the river. It has been'
<br />.,-for example, that in 1884 there was a flood of about 384,000
<br />;~~es. (Weymouth, 1930.) At Yuma, a maximum flow of
<br />:M-s. (Jan. 22, 1916) and a minimum daily flow of only 18 c,f.s.
<br />.' 27,1934) have been recorded,6
<br />. tributing to the unpredictability of its run-off have been the
<br />~~~ilash" floods (usually in the late summer and winter) when
<br />'c~ter have come coursing down the Bill Williams, the Gila, or
<br />~., rollS washes. The Colorado has been a rampaging torrent; it
<br />'~ & sluggish creek. And, until recently, man ~as had but little
<br />e1"its whims.7
<br />~pletion of Boulder Dam in 1935 has enabled the storing of
<br />", tities of flood water; the entire average flow of the river can
<br />'ekfor two years. With release during the dry season, it is
<br />e to maintain a lUore or less constant flow in the stream below
<br />.>~:number of factors (natural ones, and the changing demands
<br />;and water) make it impossible to predict the future flow in
<br />':r~yer with accuracy. Both Weymouth (1930) and Stevens
<br />. . ested that the mean annual discharge might be around
<br />
<br />,:,'-~ water above Yuma and Inftowfrom the.Glla afCects the river here, of
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<br />, 'n ttng (albeit a bit fanciful) account of man's struggle against the
<br />ury (19'41).
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<br />dl Boat LandlIlg' Feb. 1942,
<br />FIG. 54, A bay In Lake }la.va.su below Neees ' ,
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<br />, " for renting and docking boats.
<br />on the lake, ,,'ith a store, Il few cab:s ln~d ~~~l;~~~~ Ilnd the rocky Mohave Clll!yon
<br />About 30 mile~ abo'\"e Parker ~am e a eo ock region. There may be slUall b;lYs
<br />!WIDe 10 miles long, sepa!ates ltd fr?cf ~~ed~e~ent from thut of the lower lake,
<br />here, hut the water lS sw1ft and eel e ~
<br />
<br />Topoek to Bould~r Dam (112 miles)" , .es of m'nr-"'" an,j
<br />he there is an extenslve sen ' .."
<br />~bovp. the narrOW!; of Mo aye anyon 'en Throughout the,river botl.,m art'
<br />a larg~ silting basin where the water le'\"el has ns f trees and "tules," . ,
<br />manv sl.)ughs and potholes a~d gener~us st.~ndt~: fourth on the river. Fifteen.l\ul:
<br />, TherE' i~, a hi:;:hway bn~ge at t;:f:st real town for hundreds of miles, t \lll;~~
<br />above Topock lS the town of NeedleSd th' ersists until one nears Boulder Dam, ,
<br />by the ri,ver muddies th'l stre~mhan , t IS,~ 'clear and c<,ld, (See Moffett, 1M:!. 1..' 3
<br />nbout 25 miles b~low t~e d:lm t e Via er 1.
<br />description vf thl~ section.)
<br />
<br />PHYSICAL AND CHEMICAL CONDITIONS INFLUENCING
<br />
<br />THE FISHERY
<br />
<br />t 1 d This is mostly plain (.r
<br />The lower river runs through a ~e~er t' an f only about three in~br.
<br />low country with a 1Il:ean annual preClpIta ~o~h~re are almost no \latUTlil
<br />and a high evapora~lve r.ate? conseque?-tlh{O'h forested country, a\ld lh~
<br />tributaries. The GIla, WIth Its s.ource :n, ':'tant uantities of water ~i
<br />Bill Williams rivers may contr~b~te lm~OIds theqtrunk of the Colora(}c:
<br />times b\1t the other streams .dralDl~ tov,;b~~ore reaching it. Its norllla.
<br />are"\Ost rivers" usuall~ dlsappearmg -off in the upper basin. .;
<br />fiow is derived almost .entll'elY fr~m s~X~~f the lower river has \"~r:,~
<br />Under normal dlscharge, t e ~~ '1 At flood stage it has IIlUJl
<br />from a few hundred feet t) about ha amI e. . ., "b-!":
<br />the California-Nevada boun"J.":0 t....'"
<br />. The section studied In 1942 tero;:~~~e~ ~~IIt1ca.l boundary and there ,. '
<br />12 miles above Needles. , However,
<br />change In the river at thIS point,
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<br />.... .....~~~:::-~~-,:.::oril'-:ef:"'?!.-:"::~:'
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