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<br />2(") <br /> <br />r... <br />t'- <br />'P"'/ <br />(;") <br />C.:; <br /> <br />Summary <br />Habitat availability at different flow levels is relatively well understood for the San Juan River. The <br />river is generally run dominated, especially at high flows, and as flows are reduced lower velocity <br />habitats increase in abundance but still represent only a small percentage of the total habitat <br />available. Although additional fine tuning by collection of additional data will continue in 1996 and <br />1997, for the most part this objective has been completed. <br /> <br />5.2.4. Model Flow and Habitat Relationships. <br /> <br />Studies by Bliesner and Lamarra (1993, 1994, 1995) investigated development of a model for flow <br />and habitat relationships. Conceptually, habitat modeling took two tracks: (1) hydraulic modeling <br />of key features was used to predict formation of spawning and backwater habitat and (2) empirical <br />modeling was used to develop relationships between habitat and flowrate. <br /> <br />In 1992 channel geometry in representative secondary channels was measured with the intent of <br />utilizing the HEC-2 water surface profile model to determine the flow at which secondary channels <br />begin to flow. Model testing was completed to determine data requirements and assess predictability <br />(Bliesner and Lamarra 1993; R. Bliesner 1995, pers. cornm.). Since some secondary channels form <br />backwaters at lower stages, HEC-2 modeling will be used to assess hydraulic conditions necessary <br />to maintain these habitats (R. Bliesner 1996, pers. cornm.). <br /> <br />HEC-2 modeling and sediment transport analysis are being used to study spawning habitat <br />development and maintenance. Spawning sites were characterized in terms of channergeometry <br />and substrate characterization. The' characteristics found at known spawning sites are used to <br />identify other areas that would be suitable for spawning. HEC-2 models of each of these sites will <br />be developed to predict flow conditions necessary for creation and maintenance ofthe sites (Bliesner <br />and Lamarra 1995; R. Bliesner 1995, pers. comm.). <br /> <br />, Empirical models of flow-habi~at ,relationships (surface area of specific habitat as a function ,of <br />flowrate) are being developed to assess flow conditions necessary to optimize specific habitat during <br />· specific times of the year. Preliminary relationships, which have already been developed, indicate <br />that TW A increased with increased flow (Bliesner and Lamarra 1994, 1995). Also, the area of <br />backwater habitat appeared to be inversely related to flow at low to medium discharges but <br />demonstrated a direct positive relationship as flows increased from medium to high discharges <br />(7,000 cfs). Additional data collection to refine habitat flow relationships is ongoing. Year to year <br />variability in the relationship between flow and discrete habitat parameters indicates that the <br />relationship for some habitat types may be influenced by antecedent conditions. Based on results <br />of additional data collection, it will be determined whether these relationships can be described <br />statistically or mathematically (R. Bliesner 1996, pers. cornm.). <br /> <br />Ultimately, flow-habitat modeling efforts should provide a meaningful representation of flows <br />required for endangered and native fishes and projections of various types of habitats (e.g., spawning <br />sites and backwaters) that will be provided at different flows. <br /> <br />San Juan River Recovery Implementation Program <br />Summary Report <br /> <br />21 <br /> <br />17 January 1997 <br />PR-576-2 <br />