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(approximately bankfull flow) and 50 cubic meters per second in model simulations. Local scour in the primary and secondary channels during bankfull flow conditions was accompanied by deposition on the bar surface. At 50 cubic meters per second, deposition occurred in the primary and secondary channel, while the top of the bar was emergent. At 275 cubic meters per second, the approximate discharge at which the baseline topographic data were collected, little bar evolution was evident. Graf (1980) demonstrated that the influence of major dams may extend far downstream in describing changes in river rapid sections of the Green River in Utah and Colorado downstream from Flaming Gorge Reservoir following dam closure. He found an increase in the number of rapids which were stable under post-dam flow conditions. Background Research by Others Williams and Wolman (1984) summarized the observed changes in several alluvial rivers downstream from reservoirs in the semiarid Western United States. Flood peaks frequently decreased following reservoir completion, but changes in other water discharge characteristics varied. Suspended sediment loads decreased for long reaches below the reservoirs studied. The majority of observed channel degradation below the dams occurred during the first decade or two after dam closure. This observation supports the conclusions of Langbein and Leopold (1964): quasi-equilibrium conditions are reached rapidly compared to slower processes such as uplift or general land degradation. Graf (1977) described responses in geomorphic systems to disruptions in which the systems initially approached new steady states very rapidly. The rates of change slowed over time. He developed a system to assess eroding gullies to provide a general framework for prediction and comparison of changes in geomorphic systems following perturbation. From these studies, Graf concluded that the time required for geomorphic adjustment after disruption is not the same for all geomorphic systems, but the same model - the rate law - provides a framework for prediction and comparison. Graf further stated that a good fit to a negative exponential form equation by field data suggests a system that is influenced by a negative feedback mechanism, resulting in a decreasing rate of change that approaches a steady state. In a dynamic equilibrium situation, a steady state condition is not approached and a linear or power curve may best fit the data. Geomorphic thresholds, as used by Bull (1979), attempt to explain the relationship between process and form in fluvial systems. Bull concluded that stream channels tend toward a stream power threshold because of the interaction of bed slope change and deposition. At the stream power threshold, a reach of river will respond to changes in climate, base level, or changes induced by man by establishing a new stream power threshold. These changes may affect stream and/or critical power, resulting in aggradation or degradation. 2