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<br /> <br />'002520 <br /> <br />where <br /> <br />W=channel width, In feet; <br />Dgo=grain size of bed material at the 90th percentile fraction, <br />in millimeters; <br />u=mean velocity, In feet per second; <br />S=slope of the water surface; and <br />D =effective grain size, in millimeters. <br />m <br /> <br />The velocity, depth, and width of flow for a given discharge were selected <br />from discharge measurements made at the gaging stations. The bed-material <br />size parameters were computed from sieve analysis of a composite bed-material <br />sample collected at each gaging station, The water-surface slope was <br />measured over a reach of channel, at least 20 channel widths In length and <br />including the gaging-station cross section. The mean bedload-transport-rate <br />versus water-discharge relation was determined by visual fit of the approxi- <br />mately 10 computed points. <br /> <br />The total-sedlment-dlscharge versus water-discharge relation, shown by a <br />dashed line in figure 2, was determined "by summing the suspended- and <br />bedload-sediment relations. With the mean relation between dai ly total- <br />sediment load and daily water discharge established, the average-annual <br />sediment load at the gaging stations may be calculated from the average- <br />annual frequency of daily mean water discharges (Miller, 1951). <br /> <br />Discharge-Duration Relations <br /> <br />The cumulative frequency of daily mean discharges observed at a gaging <br />station may be represented by a flow-duration curve (fig. 3). The flow- <br />duration curve shows the percentage of time a specific discharge was equaled <br />or exceeded In the period of record used. When several years of record are <br />used, the flow-duration curve describes the average or probable frequency of <br />various ranges of water discharges during a year. <br /> <br />The gaging stations In the Yampa River basin have been operated at dif- <br />ferent times and durations since October 1904 (table 1). Therefore, the dai- <br />ly water-discharge records are not concurrent and cannot be compared direct- <br />ly. In order to obtain an estimate of the possible variations in the flow- <br />duration curves due to variable times and periods of record, flow-duration <br />curves for the Yampa River at Steamboat Springs were computed for different <br />periods of record. A comparison of the flow-duration curves based on several <br />sub records with the flow-duration curves based on the entire record indicates <br />variations of less than 5 percent. Because thi~ value Is iess than the <br />errors In the total-sediment-load versus discharge relation, no attempt was <br />made to synthesize daily water discharges for a standard period of record at <br />all gaging stations. <br /> <br />9 <br /> <br />!t'. <br />