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<br />Grams and Schmidt 7 <br /> <br />typical pre-dam hydrograph was dominated by spring snowmelt-runoff and low fall and <br />winter baseflows. The pre-dam mean annual flood was 334 m3s.1 and has been reduced <br />by about 63 percent to 139 m3s-1 since dam closure (Fig. 2). The volume of total annual <br />runoff and the mean annual discharge have not been affected by the operations of Flaming <br />Gorge Dam. <br />The change in hydrology due to operations of Flaming Gorge Dam downstream <br />from Echo Park is mitigated by the unregulated Yampa River which has the same mean <br />annual runoff as the Green River. The mean annual flood of the Yampa River is <br />unchanged for the period of record and is similar to that of the Green River prior to <br />construction of Flaming Gorge Dam (Fig. 2). The combination of regulated and <br />unregulated flow from the Green River and the Yampa River, respectively, results in a 26 <br />percent decrease in the mean annual flood at the gaging station near Jensen, Utah, 46 Ian <br />downstream from Echo Park. <br />Sediment transport has also been significantly affected by closure of Flaming <br />Gorge Dam. Sediment sources downstream from the dam are limited to the bed and banks <br />of the river and ungaged tributaries upstream from the Yampa River. The largest <br />tributaries, Red Creek and Vennillion Creek, enter the Green River 18 Ian and 70 km <br />downstream from the dam, respectively. The only site with a long-term record of <br />. sediment transport near the study area is about 150 km downstream from the dam at the <br />Jensen, Utah, gage. The mean annual load of suspended sediment has been reduced by <br />about 54 percent at this site, from 6.28 x 106 Mg to 2.91 x 106 Mg (Andrews, 1986). <br />5. METIIODS <br />5.1 Channel Cross sections <br />We measured 67 channel cross sections at approximately 1-km intervals to <br />characterize channel geometry. These cross sections were surveyed in 1994 during low <br />discharge using a geodetic total station and depth-recording echo sounder. Additional <br />water surface elevations were ~urveyed at each cross section during peak flow in June and <br />