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, ,>",,'.;,1 . ,.- ~ '-~ where f-/=.::hannel VJidth, in feet; Dgo=grain size of bed material at the 9C~h ~e~centile fraction, in millimeters; u=mean velocity, in feet per second: S=slope of the water surface; and D =effect!ve grain size, in IT!ill;meter~, m The velocity, depth, and ,.:idtb offlm" fora c;i'ien discharge .."i,ere selected from discharge meaSUrei'lents made at the ga;i.rg st2tions.The bed-rilaterial size pa:-ameters \"ere conputed'from sieve-'"'ai:ah'sis of a composite bed-material sample collec~.....-pt eachC~gaging station. The vJater-.surface slope '.';as measured over a reach of channel, at least 20 channel v,idths in length and including, the'gaging-station cross sectior, He mean bedload-transport-rate versus water-discharge relation was determine~ ~y visual fit of the approxi- mately 10 computed points. The total-sediment-discharge versus wate~-~ischarge relation, shown by a dashed 1 ine in figure 2, was determined b~ summing the suspended- and bedload-sediment relations. I,./ith the rea-. relation bet\r-Jeen daily total- sediment load and daily water discharge e3tabl ished, the average-~nnual sediment load at the gaging stations ray be calculated from the average- a~nual frequency of daily mean water discharges (Hiller, 1951). Discharge-Duration ~e;ations The cumulative frequency of dai ly mear d;scnarges observed at a gagj~~ station may be represented by a flow-turation curve (fig. 3). The flow- duration curve shows the percentage of time a s:ecific discharge was equaled or exceeded in the per i od of record used. ',,'hen severa 1 yea rs of record are used, the flow-duration curve describes the 2!erage or probable frequency of various ranges of water discharges during 2 year. The gaging stations in the Yampa RiVEr ~a~in have been operated at ~if- ferent times and durations since October l?J~ (:able 1). Therefore, the dai- ly water-discharge records are not concurrent 2nd cannot be compared direct- ly. In order to obtain an estimate of the p:Jssible variations in the flO\'i- duration curves due to variable times arj ~eciods of record, flow-duration curves for the Yampa River at Steamboat S:ri~g5 we:-e computed for differert periods of record. A comparison of the flcw-ju~ation curves based on several sub records with the flow-duration curves bcse= en ~he entire recorc indicates variations of less than 5 percent. BecaUSE ::h's value is less than tr.e errors in the total-sediment-load versus di3c~arge relation, no attempt was made to synthesize daily water discharges for a standard period of record at all gaging stations. 9