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/r f ' r r When the minimum streamfiow hydrograph criteria is combined with discharges In excess of 20 percent of the peak f I ow for that year, a sediment balance results that exceeds the sediment load that could be transported at Mathers Hole by only 4 percent. The average annual depletion from the Yampa (Maybe) I) is 77,000 AF for this run. Within the accuracy of this analysis it would probably be feasible to deplete up to 100,000 AF from the Yampa River on an average annual basis. Larger depletions from the Yampa without equivalent depletions from the Little Snake would probably result In some sediment storage In the canyon over the long term. It should be noted that including a percentage of the peak flows in the minimum streamfiow hydrograph is sufficient for this type of analysis of historical flows, but would not be easily administered for future water resource management. An acceptable method would be to identify the upcoming wet, dry or average year and assign a peak flow condition that would repl icate the f orementi oned flow criteria. The Yampa River channel in Dinosaur National. Monument exists In a tenuous morphological ba l?an_ce between the bed material, channel sI oQe and the water discharge and sediment it conveys. This equilibrium exists because the I arge sediment I oad carried by the L ittl a Snake I s assi sted i n transport through the canyon by the larger discharges flowing In the Yampa River. The steep slope Is the key physical attribute which insures sediment transport in the canyon under historic flow conditions. Reductions in the streamf low as a consequence of water regulation with upstream water management, storage or diversion will have an impact on the riverine environment In the Yampa Canyon. From the results presented In this study, sediment storage w i l l occur i n the Yampa Canyon L the average annua I depl eti on from the Yampa River exceeds 10000 AF_whi l e thellttle_:Snake remains essentially unO minished. The effect of this storage may ] im°F? die w i ab I I -i?ty ©??critica ( ha of the endangered fish species which use the cobble bed reaches of the canyon for spawning. c?orm I ete water and sediment routing investigation of each reach. The Yampa River--has adjusted to basin conditions to be able to transport the sediment yield from the watershed. Both too little and too much sediment load in the canyon is construed as a negative impact when It varies from historic nditlons. This report clearly demonstrates concepts that previously had only been Inferred. The sediment load investigation reveals some of the consequences and long term impacts of f I ow depletion from the Little Snake and Yampa Rivers. To definitively address site specific im acts would require a 20