Laserfiche WebLink
<br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br /> <br />Discharge at that point represents only 56 percent (36.6 sq. miles) of the <br />modeled watershed, and historic records indicate that larger flood magnitudes <br />usually occur from Fourmile Creek. Therefore, these flood estimates should <br />not be used as a representative measure of the flood magnitude at the mouth of <br />the canyon. <br /> <br />Flood frequency analyses have been performed in several other studies. <br />The final hydrology study by the U.S. Army Corps of Engineers that is accepted <br />by both UDFCD and the City of Boulder is referenced in Boulder Creek Flood <br />Ha7.ard Delineation, January 1983, by Muller Engineering Company, Inc. The <br />flood frequency magnitudes that are accepted for Boulder Creek at the canyon <br />mouth are: <br /> <br />500-year = 21,200 cfs !(, ~) tI " <br />~ .' <br /> , . <br />100-year = 11,600 cfs <br />50-year = 8,000 cfs . ~(Ic <br />\e <br />10-year = 2,000 cfs <br /> <br />COMPARISON OF MODEL TO FLOOD FREQUENCY RESULTS <br /> <br />The model was run for both the 10-year and the 100-year rainfall and for <br />antecedent soil moisture at field capacity (DTHETA =0.25). That soil moisture <br />would represent the condition to be expected after the watershed had been <br />thoroughly wetted and then allowed to dry somewhat due to gravity drainage and <br />evapotranspiration. This would be representative of the watershed in early <br />summer. The flood peak estimates using the model under those conditions are: <br />100-year = 9,735 cfs <br />10-year = 1,570 cfs <br />These compare favorably with the accepted values that are listed above. <br /> <br />The model was run for the 100-year rainfall under four conditions of <br />antecedent soil moisture. These four conditions and resulting peak discharges <br />are summarized below: <br /> <br />5 <br />