Laserfiche WebLink
<br />. <br /> <br />the Una dam site was estimated as being approximately 70,000 <br />cfs. In addition, the above-referenced report, based upon the <br />annual peak flood frequency curve computed by the USGS using the <br />Cameo gage record and standard Water Resource Council <br />guidel ines, establ ished the 100-year and 500-year return period <br />flood peak discharges at the Una dam site as approximately <br />39,000 cfs and 44,000 cfs, respectively. Prorating these values <br />upstream using the ratio of the drainage areas yields values of <br />37,000 cfs for the 100-year flood event and 41,800 cfs for the <br />500-year flood event at the Webster Hill site. <br /> <br />. <br /> <br />F. INFLOW DESIGN FLOOD (IDF) <br />1. Genera 1 <br />The flood used for design against dam failure is termed the <br />"inflow design flood" (IDF), and in most, but not all, instances <br />will be equal in magnitude to the "probable maximum flood" <br />(PMF), defined as the largest flood that can reasonably be <br />expected to occur on a 9iven stream at a selected point. The <br />IDF selected for the Webster Hill project was the 500-year flood <br />event. <br /> <br />2. <br /> <br />Webster Hi 11 Reservoir Hydrometeoro logic Conditions Appl icab le <br />to IDF and PMF Estimate <br />The IDF and the PMF estimates for the Webster Hi 11 Reservoir <br />site were based on data and methodology contained in <br />the previously referenced Una Reservoir project study by R.W. <br />Beck and Associates (1982). The following information is <br />exerpted from their report. <br /> <br />. <br /> <br />The PMF estimate for the Una Reservoir Project is <br />based on a 1981 detailed watershed calibration and PMF <br />analysis conducted by Beck for the Tri-County <br />Reservoir Project on the Gunnison River near Lazear. <br />The Upper Colorado River Basin has watershed <br />characteristics similar to the adjacent Gunnison River <br />Basin. .. By considering differences between the two <br />basins in terms of drainage area, area-elevation <br />distributions, snowpack depths, and the Probable <br />Maximum Precipitation (PMP), the results from the Tri- <br /> <br />3686-a/5 <br /> <br />1-9 <br />