FLOOD09514 - Laserfiche WebLink

Home Browse Search

I I I I I I I I I I I I I I I I I I I B-3 6. Ability to discharge based on status of other reservoirs (Willow Creek, Williams Fork, Green Mountain) and natural flood flows occurring be- tween Granby and Gore Canyon. 7. Irrigation diversions between Phase 2 and Granby Dam. B. AVAILABLE DATA Available data for estimating flood flows are as follows: 1. River flow stream gauge records, "YMCA" gauge located just downstream from Phase 2. The years of record are 1908-1911, 1933-53, and 1961-Present (May-September only). Granby Reservoir was closed in 1949. 2. USBR records for 1983 & 1984 of reservoir depth, inflows, discharges, etc. 3. USBR operating plan for dealing with flood inflows. 4. USBR summary of probable maximum flood flow calcula- tions. 5. USBR reservoir information for gate discharge curves, storage vs. elevation, etc. 6. Field observation during 1983 & 1984 of water depth in the Phase 2 vicinity at times of high flow. C. DISCUSSION OF VARIABLES 1. Natural snow melt flows: The data base of the YMCA gauge for the years prior to 1949 provide a reasonable base from which to project peak "natural" flows into Granby Reservoir. For simplicity, it is assumed that the peak flows projected are essentially snow melt related and are referred to hereinafter as the "snow melt" flows. HRS Water Consultants, Inc. projected the various return frequency flows using the Log Pearson Type III and Gumbel Extreme Value Methods. A copy of their report is attached. The peak flows are sum- marized as follows: LOG PEARSON GUMBEL EXTREME VALUE 100yr 50yr 20yr 10yr 4380cfs 4064 3734 3272 4650cfs 4230 3700 3200