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<br />PRELIMINARY <br /> <br />COMMUNITY OF WELDONA <br />MORGAN COUNTY, COLORADO <br /> <br />Hydrologic Summary for Schaefer Draw near Weldona <br />1997 Flood Event <br /> <br />Date of Flood: July 29/30,1997 <br /> <br />Duration of Rainstorm: 4 hours <br /> <br />Maximum Rainfall Depth near Basin Centroid: 4.2 inches <br />Rainfall depths obtained from NWS Radar data. Radar estimates of rainfall amounts were <br />calibrated to ground-truth data from the Fort Collins and Pawnee Creek storms. <br /> <br />Estimated Return Period for Rainfall Event: > 1 OO-year <br /> <br />Antecedent Moisture in Basin: Moderate <br /> <br />Estimated Maximum Peak Flow: 1,300 cfs <br />Peak flow estimated by CWCB staff based on surveyed cross-sections, high water marks, and <br />channel slopes. Several flow estimates were obtained and averaged at locations on the <br />stream above irrigation canals, reservoirs, or any significant man-made features. The <br />drainage basin above the observed location is essentially natural, unregulated, and <br />undeveloped rangeland. Drainage area above flow estimate location is approximately 5 <br />square miles. <br /> <br />Computed Peak Flows for Schaefer Draw <br />Using Various Hydrologic Methods <br />(Drainage Area = 5 square miles) <br /> <br />. .. . <br />.. .' - <br />co., ,,',,"'. . . "", <br />."s'~lI~ce'Qfi~timat~~."J)!Jow <br /> <br />CWCB "Guidelines for Determining 100-year Flood Flows for <br />Approximate Floodplains in Colorado" (1997) <br />USGS "Analysis of the Magnitude and Frequency of Floods in <br />Colorado" (Vaill, 1996 draft)* <br />USGS/CWCB "Manual for Estimating Flood Characteristics of <br />Natural-Flow Streams in Colorado" (1976) <br />SCS TR-55 methodology <br />UDFCD "Colorado Urban Hydrograph Procedure" ** <br />Actual Flood Event <br />* Eastern plains regression equations to be revised by USGS <br />* * Simplified single basin CUHP analysis using recommended infiltration parameters <br />*** Flood-frequency not assigned <br /> <br /> <br />lOO.~earP~akFI!!w <br />'(lIfs) <br />2,030 <br /> <br />3,060 <br /> <br />5,460 <br /> <br />1,310 <br />1,180 <br />1,300** * <br />