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I I I I I I I I I I I I I I I I I I I Flood Insurance Study, Town of Vail, Colorado FEMA prepared a Flood Insurance Study for the Town of Vail, Colorado that is dated November, 1982. Their report acknowledged that the hydrologic and hydraulic analyses were prepared by GAl. The report contained a summary of the computed peak discharges for selected frequencies used in the hydraulic analysis. The report stated that regression equations were developed from snowmelt events to predict 10-, 50-, 100- and 500-year discharges as a function of drainage area. The discharge-drainage area curves were then modified to include the effect of rainfall events on the smaller drainage's using a synthetic unit hydro graph approach. III. NEW HYDROLOGIC STUDIES FOR THIS "LMMP" TASK ORDER Basin Description A map of the Gore Creek drainage basin is shown on Figure 1. A metric USGS topographic map (Quadrangle Sheet: Vail, Colorado, 1980) to the scale of 1: 1 00,000 and 50-meter contour interval was used to prepare this map. The map also illustrates the location of stream gaging stations in the basin whos{: annual peak flow records were analyzed. A short description of the drainage basin is provided to assist in interpreting basin runoff characteristics. The source of flows in the Gore Creek basin start at about 13,000 feet elevation where the tributaries drain the westem slope of the Gore Mountain Range. The Gore Creek basin has a total area of 102 square miles at the mouth where it has its confluence with the Eagle River about two miles Northwest of Minturn. Stream slopes vary from over 700 feet per mile on tributaries in the upper basin to approximately 70 feet per mile in the Gore Creek channel at Vail. Two small storage dams are located near the upstream basin boundary of Black Gore Creek, just below Vail Pass. The mos.t upstream structure, Black Lake Dam, controls an area of only 0.6 square miles. Black Lake No.2 is approximately 1.25 miles downstream and has a total drainage area of only 1.82 square miles. These structures are small and control such a small portion of the total drainage area that they have an insignificant effect on flood flows in the study area. The basin map shows that many of the northbank tributaries contain a few small lakes in their upstream reaches. Development in the basin has been confined to the valley floor because the terrain is steep and the Forest Service owns much of the land. Land use in most of the drainage basin will not change so development should not have a significant effect on the magnitude of discharges for a given probability. Imperviousness from development could increase runoff from small local drainage areas. However, restrictions in the floodplain along Gore Creek and tributaries can have a significant effect on water surface profiles computed using specific flood discharges. 4