Laserfiche WebLink
<br />.. ," ~ <br /> <br /><.: <br /> <br />(greater than 9000 feet) and the fact that recorded annual peaks <br />are snowmelt (late spring and early summer) the rainfall portions <br />of the frequency curves were determined to be insignificant to <br />the 10-, 50-, 100-, and 500-year flood flows. This study <br />therefore analyzes the snowmelt peaks. <br /> <br />Lake Creek <br /> <br />For Lake Creek flood flow frequency analyses of streamgage <br />records using the procedures outlined in WRC Bulletin 17 were <br />used. The first analysis consisted of analyzing streamgage <br />information at gage 07084500 located 3.0 miles downstream of the <br />study site for the period 1946-1980. The streamgage information <br />included all diversions into the Lake Creek Basin through Twin <br />Lakes Tunnel No. 1. <br /> <br />The second method utilized the streamgage records and <br />corresponding Tunnel flows to develop a frequency curve for <br />unregulated conditions (useful for comparison purposes with other <br />basins) . To this frequency curve for unregulated conditions <br />maximum capacity tunnel flows were added to develop the regulated <br />frequency curve. Although the streamgage and Tunnel are located <br />7.0 miles apart, no adjustments were made for attenuation between <br />the gages since available Tunnel records indicate that diversion <br />flows normally remain constant for several days on and prior to <br />the date of the peak flow at the streamgage site, thus minimizing <br />any attenuation effects. <br /> <br />Comparing the results of the two frequency studies, it was found <br />that the second method produced discharges from 7 - 11% higher <br />than the first method. Review of the Tunnel flows show that <br />these flows have increased, on the average, 26% since 1971, as <br />compared to the period 1946-1970. <br /> <br />The Tunnel flows are now approaching the maximum Tunnel capacity <br />of 625 cfs. This indicates that the second method which includes <br />the 625 cfs diversion is the preferable method of the two <br />analyses. <br /> <br />Knowing the flood flows at the gage site, the discharges were <br />transfered to the study site using the transfer equation from <br />TM-l: <br /> <br />Qsite <br /> <br />=~ <br /> <br />~O. 79 <br />site X Qunregulated + 625 <br />gage <br />o gage = 75 sq. mt) <br /> <br />The exponent of the equation was substantiated by previous work <br />by the Bureau of Reclamation. (See Other Studies Section in <br />Appendix). The peak discharges calculated at the study site are <br />as follows: <br /> <br />-4- <br />