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.. BUS 5! HYDROLOGIC TE~QUES t'I.) ~ Q t:.n type in the upper area. Another 20 percent of the water. shed has a siltv-c1av soil deri'-ed from Cody Shale. Rootspenetrat; thi; sOil nbout 1 foot. This' area is co,-ered with Xuttall saltbrush and bottlebrush squirrel. tail (Sitanilm hY8triX). The ,-emaining 10 percent of the watershed is comprised of high, grass-covered plateaus and of bottomlilnds co.-ered with greasewood (Sarcooat1l8 t'61'miclIliztU8), .\.\'erage annual precipita- tion is estimated to be about 10 inches (~, J. King, oral commun., 1969). Runolf occurs '.from snowmelt and rains in the spring, and from occasional torrential sum- mer storms (Peterson, 1961). Additional hydrologic information, induding a16-yearrecord of sediment yield through July 1968,. was obtained from King (1959) and from X. J. King: andG. C. Lusby (written commun., 1969). . RESULTS ANO OISCUSSION Figure 2 shows the relatio.nship of estimated sedi- ment yields obtained iith the PSLI..C method to measur=ed sediment vie Ids for three sets of watersheds. In all three sets, ';ith the exception of the low-sedi- ment-yielding watersheds in '\\)~oming, the estimates tend to be lower than resen-oir ,-alues. as most of the points lie above the 1 :1lines1in figure 2~ Also. themean sediment.yield estimate.. for aU sites is L. acre. feet per square mile, and the mean for the reservoir records is l.i3. .. . The tendency for the estimated sediment yields to be 10w.er tlian. reser,'oir records is attributed to the author's bias in rating .someof the factors lower than they shou.ld havebeen,butn6factor \\,{IS.conSciously rated consistentl)' low. After the watersheds had been rated,it '~aS apparent thai the channel erosion and sediment transport factor had not been rated high enough for some of the steeper watersheds ha ,'ing. ra'" g-ullies. The ratings "'ere accordingly in~reased for some of the Badger ""ash and Xew :\Iexico watersheds, resulting in smnller dit!'enmces between the estimated and measured sediment yielcls. The correlation of mens. \1l~d runoff with values for the runoff factor in the method was rather poor: the coeflicient of correlation (r) was n.M. Xo objective means of adjusting ,'alues for the runoff factor was found. The correlation of watershed ~rea with the difference between reser\"Oir measurements and the estimates was very poor (I' = 0.13). App.vrently. on "erysmnll '~ater' sheds, the PSL~C method sufficiently accounts for ex. pected lnrl'er sNliment yields per unit aren caused by greater a \'crnge slope, intense storms co'-ering the whole watershed, nnd small transit losses. This indi. cates that the method may ha,.e application in the de. , . ~ I r::tO,9-4 I . ....1 ,,..-:... : /' / -. /~ . ~ ,," / "," 3- ~ '" .. i ..: -! w a: ~ I o 0 '" Q: 5; w .. ~ w w .., w '" 'i ;!: o - ~ SO .. .., ~ Z ~. :> is u "' Q "' :: Vi < w :> , ~ o 5. .- (::=0,7'& 3- /' I / . -/ / / . I . I ,. /. ~ . 2- c 0:.0" 01 Z 3' S 6 ESTIMATED SEOIMENT 'YIELD. IN ACRE-FEEl "'EIt SQUAItE MILE i-'IGl'ltE ~.'-Grapbs sbo\Ting i'e-ID.tioDSbip_ of es;ti. muted sediment yields to Dl_easured sedlme,nr yieldS. der€'rmined b[ thE> P:J.ciftc Southwpst Inrer.A.gen~.r Committee wl'tbOd. .tor re:o:erl"Qirs in tb~ Sf'ts ot n.utf'rsheds: .:1. Badger ".a~h. Colo.: B. N't'W' ),[esico; C. WYQmlog. All rorn- laUoD cOt?ffidents If) are sj~niticant at the ]. [)el"C'E'nt lef'~J. ThE' solid lines nrf> IinE'~ ot equnlit\" u'hetf tbE' estimatE'd sediment yield!' e-qual 'th~ mE"BSurtd ~dituent ripld~. ThE' dllsbed IiD~ are ~lon lines fitted to thE" poJnt!l. !'ign of structures for small watersheds and in proposals for land treatment. in add,tion to its US<' for mnkil' , broad scdiment classifications of larger arens. In applying' this method. good records from gaged :lrcas. "'here :l\'ailable. should be used to check the est.i. mates. If the estimntes and records do not reasonably > .