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Introduction Trout require clean gravel in which to deposit their eggs during the spawning process (Reiser and Wesche 1977). Spawning gravels which remain downstream from dams may become imbedded with fine sediments recruited from bank erosion or downstream tributary inflow, thereby reducing survival of the emerging embryos (Hausle and Coble 1976 and Young et al. 1991). The removal of these fine sediments has become an objective of many flushing flow studies (Reiser et al. 1989).
River channel maintenance below regulatory structures can be accomplished with instream and flushing flows. A flushing flow is a controlled release of a high amount of water over a relatively short period of time whose purpose is to remove accumulations of fine sediment in the gravel by temporarily mobilizing the bed. Among the methods available to evaluate the effectiveness of flushing flows are measurements of bed material composition, bedload and suspended load transport, amount of intergravel fine sediment, and channel geometry (Reiser et al. 1985).
Flushing flows have been implemented and evaluated on two rivers in Wyoming, the North Platte River and the Big Horn River. This paper will present a portion of our findings.
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