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width). The Simons report indicates that mean velocities associated with the 100~year flood are not great enough to cause incipient motion for 50 percent of the bed material measured between Debeque and Cisco. Also, geologic controls and armoring have resulted in a channel larger than would normally be associated .with the present mean instantaneous peak flow. Lyons (1986) confirms that conclusion through inspection of aerial photographs taken in 1954, 1980 and 1986. No significant changes were noted in spite of large flow events in 1983 and 1984. Bank erosion on the north bank has been balanced with island formation to maintain overall channel width and depth dimensions. Therefore, channel degradation would not be expected from reduced peak flows. Channel Flushing W~ll the reduced flows caused by transmountain diversions and , evaporation result in siltation of the interstices between gravel/cobble substrate? Areas confirmed as Colorado squawfish i spawning sites in the upper Colorado River basin have the common characteristics of gravel, cobble and boulder substrates forming rapids or riffles associated with deeper pools or eddles. rt has , been hypothesized that a stable, clean substrate is necessary for spawning. These substrates are swept clean of fine sediments prior to the spawning period and maintained clean throughout the spawning and incubation periods. Simons (1983) indicates that the sediment transport capacity of the stream with the present flow regime g~eatly exceeds the available sediment supply. Even so, there ~re flows below those capable of transporting the majority of sediment that still allow fine sediment moving over the bed material to become entrained within the armor (Einstein, 1968). Periodically it is necessary to flush the fine sediment from the cobbles to enable successful spawning. 3