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e e e Reviewing the operating history of Flaming Gorge five distinctive operational phases were identified for further analysis. Pre dam 1951 to 1952 when project planning was in progress. The 1963 to 1966 period represents the period when Flaming Gorge Reservoir was filling. The first full year of "normal" operation began in 1967. Data for the 1967 to 1978 period represents the pre-multi-level outlet hydrology. During this period there were few operational constraints on the dam and reservoir. The only constraint on releases was the 800 cfs minimum release to establish and maintain the trout fishery in the Green River below the reservoir. The 1979 to 1984 period of operation represents the pre-multi-level hydrology. During the previous period it was established that cold water releases from the dam were detrimental to the food base and trout growth. Subsequently, the dam was fitted with a multi-level outlet which allowed warmer water to be withdrawn from the reservoir. Post multi-level outlet operations conditions were evaluated from 1979 to 1984. The multi-level outlet system improved water temperatures by allowing warmer water to be withdrawn nearer the reservoirs surface and passed through the power generation units. The increased water temperature by several degrees C and contributed to a blue ribbon trout fishery developing below the reservoir. The 1985 to 1988 period reflects the hydrology when the interim flow agreement was in place to protect nursery habitats for endangered fish in the Green River downstream of Jensen, Utah. The interim releases provided for maximum releases of 100,000 acre-feet in August and September with daily fluctuation at the dam between 800 and 2,400 cfs. The releases were based on releases observed in 1985 which produce good habitat conditions and promoted survival of endangered fish. Reclamation also changed the operating criteria for the dam in 1985 to avoid spill which occurred in 1983 and 1984. These changes were in place during the 1985 to 1988 as were numerous flow tests from the dam for studies related to the preparation of the Flaming Gorge Biological Opinion. Complete daily and monthly hydrological data set have been developed for each of the five periods. Monthly data and graph are displayed in Appendix 1. Mean daily hydrographs for each of the periods are displayed in figures 3-1 to 3-15 at Greendale, Jensen, and Green River, Utah [5]. Comparing pre and post development periods, the reduction in peak flows is evident as well as the increases in base flows during other months. The distinct peak at Jensen is evident only because the Yampa River is virtually unregulated. Figures 3-16 and 3-17 compare pre and post development flows at Greendale and Jensen on the Green River and at Deerlodge Park on the Yampa River [5]. The changes in magnitude and duration of the peak as well as changes in base flows are quite evident. The influence of the Yampa River in maintaining the natural hydrograph is also clearly evident when comparing the pre and post development hydrographs. 3-7