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<br />$= <br /> <br />- <br />" <br /> <br />Colorado Water Conservation Board <br />Department of Natural Resources <br />721 Centennial Building <br />1313 Sherman Street <br />Denver, Colorado 80203 <br />Phone: (303;, 866-3441 <br />FAX: (03) B66-4474 <br /> <br />STATE OF COLORADO <br /> <br />I) <br /> <br />July 9, 1997 <br /> <br />Roy Romer <br />Governm <br /> <br />Mr. John Liou <br />FEMA Region 8 <br />Denver Federal Center, Building 710 <br />Denver, Colorado 80225-0267 <br /> <br />James S. Lochhead <br />Executive Director, DNR <br /> <br />DariesC. Lite, P.E. <br />Director, eWeB <br /> <br />RE:Hydrology for Clear Creek County <br /> <br />Dear John: <br /> <br />The CWCB staff has reviewed the available hydrologic information for upper Clear Creek <br />County. The attached table provides a summary of peak discharges for Clear Creek at Silver <br />Plume, Colorado. As shown in the table, the Corps of Engineers proposed value of 1,400 cfs is <br />considerably higher than the values obtained using other methodologies. It appears that the <br />Corps' hydrology results from the Lawson gage downstream are reasonable. <br /> <br />The CWCB staff reviewed the Corps hydrology analysis and performed a regional regression <br />analysis based on published data for select lOO-year flow values in the mountains region of <br />Colorado. In addition, the staff reviewed the equations of the USGS publication entitled <br />"Analysis of the Magnitude and Frequency of Floods in Colorado." This publication, which is <br />still in draft form, has been developed by J.E. Vaill of the USGS. From our review, it appears <br />that a 100-year discharge of approximately 1,000 cfs is reasonable for Clear Creek at Silver <br />Plume. <br /> <br />The CWCB would support the study contractor's use of the new USGS regression equations to <br />obtain peak flow values in the upper Clear Creek watershed (upstream of Lawson). We would <br />also support the use of regionalized flood-frequency relations using a statistical analysis of <br />representative gaging station data within the mountains region. The USGS methodology can be <br />easily and quickly used to estimate peak flows for the 2, 5, 10, 25, 50, 100,200, and 500-year <br />recurrence intervals. Please instruct your study contractor to proceed with revising the <br />hydrology. <br /> <br />If you have any questions or need additional information, please give me a call. <br /> <br />Sincerely, <br /> <br /> <br />~.. <br /> <br />LarrY F. Lan .E. <br />Chief, Flood Control and Floodplain Management Section <br /> <br /> <br />c :\seca\projects\clr -crk\liou-I.doc <br />