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Flow patterns An important aspect of fish reproductive life history is adaptation to flow timing patterns created as tributary streams interact to build the downstream hydrograph. For example, review of annual Green River system flow patterns shows that the Little Snake River drives the early peak of the Yampa River and the Yampa River drives the early peak of the Green River at Jensen. The flow of the mainstem upper Green River (Greendale) usually peaks after the Yampa River and provides duration of high flow below their confluence. The Yampa River flow includes the combined Yampa and Little Snake rivers (Figure 11). Changes in flow pattern and reductions in peak and duration (post 1963) are evident (Figure 12). Upper Green River sediment discharge pattern altered Sediment discharge on the upper Green River decreased following closure of Flaming Gorge Dam (Andrews 1986). Supply from the upper Green River as measured at Greendale was estimated to decrease by 3.6 million tons per year (reduced to 0 at the Greendale gage). Impacts on channel morphology were rapid. Fine sediments were scoured from the river bed near the dam. Channel widths decreased below the dam to Browns Park about 70 km upstream from the Yampa River. However, sediment input from Vermillion Creek and Red Creek in and above Browns Park, respectively, remained a significant source of sediment to the Lodore Canyon reach located downstream. Studies by Merritt (1997) have shown that geomorphic change in Browns Park since Flaming Gorge Dam regulation have proceeded in a series of complex responses rather than simple channel narrowing. These responses progressed from initial channel narrowing through vegetation encroachment; to channel shape change from a classic well graduated meander bend shape to a steep- banked, trapezoidal shape; channel widening; and island formation. 23