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37 peak spring discharges to the Green River and thereby contributes .to a more natural hydrograph in lower portions of the Green River. Additionally, the extent of the contribution tributaries provide towards meeting the biological and physical needs of the four endangered fish of the Green River is being addressed in ongoing Flaming Gorge studies, and by the RIP. In order to assess the impacts of flow reductions on listed species one should understand that the listed fishes are relatively long lived. This adaptation allows the fish to take advantage of good hydrological conditions when they occur and to endure poorer years when flows are not at the right stage or temperature to optimize spawning, recruitment, or movement.. Depletions in the Duchesne River have substantially altered the annual hydrograph resulting in reduced peaks and base flows. The cumulative impact of these alterations have artificially created more "dry" years, at a higher frequency of occurrence. The Service provided preliminary (interim) flow recommendations (Table 2) for the Duchesne River in a January 23, 1995, letter to the Central Utah Water Conservancy District. In a March 9, 1995, memorandum to John Hamill a modification to the earlier letter was provided from the RIP. Recommendations were further augmented with additional information from a workshop held during the Duchesne River Hydrology and Water Availability Study (CH2M Hill, 1997). Due to limited biological and physical information specific to the Duchesne River, flow recommendations were based exclusively on hydrology data. Hydrologic data used for the preliminary recommendations were developed for each month using exceedance values of 75, 50, and 25 percent. These exceedance values represent dry, average and wet years based on the premise that remaining water in the system may need to be legally protected and delivered to mimic a natural hydrograph in order to avoid the likelihood of jeopardy and/or destruction or adverse modification of critical. habitats. In addition to monthly values the Service also recommended channel scouring and maintenance flows for the Duchesne River. The recommended channel scouring flows are 2,800 to 3,000 cfs fora duration of 2 weeks, and should occur (on average) once every 4 years. The recommended channel maintenance flows are 1,500 to 1,800 cfs in the other 3 years. During the development of these preliminary flow recommendations future studies were identified as a necessity to fill data gaps and refine existing recommendations for the Duchesne River. On February 27, 1997, a final Scope of Work, entitled Duchesne River: Assessment and Refinement of Instream Flow Needs, was submitted and approved by the RIP. The study was funded and initiated in the spring of 1997. This 3 to 5 year study will test hypotheses and assess and refine the timing and quantity of water needed that will restore and maintain, to the extent possible, the ecosystem components and functions of the