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Draft FInal Completion Report to UDWR for Contract #93-1070, Amendment 3 11 EXECUTIVE SUMMARY The Geomorphic Basis of Colorado Squawfish Nursery Habitat in the Green River near Ouray, Utah by Cynthia L. Rakowski and John C. Schmidt The purpose of this research project was to evaluate the ~eomo1Jlhic basis and to measure annual changes in the distribution of nursery ~t for age-O Colorad~~~~~ (Ptychocheilus /ucius) near Ouray. Utah. Unlike previous efforts to quantify nursery habitat in the green Riv~r (Pucherelli and others, 1990), this research integrated geomorphic and fisheries data collected at several spatial scales between 1992 and 1994. This research demonstrated that ~ 'lallow and deep nursery habi~ts are formed by different geomorphic processes and the suite of formative . processes differ in relation to the magnitude of flooding. Mandated base flows should vary in relation to the average elevation of bars in the Ouray reach. Many researchers (for example, Ligon and others, 1995; Hill and others. 1991) have shown that scientifically-defensiblejJ9w recommqidations for the purpose of maintaining aquatic habitat need to include a suite of flows and should not solely focus on the magnitude of base flows. The development of flow recommendations of this type must therefore be based on integration of physical and biological data. and the detail necessary to evaluate some processes mandates that multiple spatial scales be evaluated so that the applicability of data collected at detailed study sites can be confidently extrapolated to longer river reaches. The suite of flows that are needed to address fisheries habitat maintenance on sand-bedded rivers include periodic high flows of sufficient magnitude and duration to mllinrain channel width. scour in-channel vegetation, and rebuild channel topography. They also include base flows which maximize availability of optimal habital Development of flow recoo1ll1eJldations that consider the processes that form in-channel habitats as well as the flows that optimize their availability at low flow has not been attempted for the Green River. Age-O Colorado squawfish use habitats that occur within the active channel. These larval fish arrive in the vicinity of Ouray in July or August, after recession from the annual snowmelt flood. Thus, flow recommendations need to consider (1) the characteristics of high flows that create nursery habitats. and (2) the discharges that maximize their availability at the time they are needed by Colorado squawfish. Development of flow recommendations for the Green