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III IIIIIIIIIIIIIIII <br /> — TUConsu ltants f TTLE APPLEor Land and U GAT rce VeINC� �% � <br /> January 30, 1992 JAN 3 <br /> 0 1992 <br /> �^ MinQCf <br /> Card <br /> Mr. Berhan Keffelew , <br /> Mined Land Reclamation Division <br /> 1313 Sherman Street, Room 215 <br /> Denver, CO 80203 <br /> RE: Idaho Creek Resource; Channel Design <br /> Dear Berhan: <br /> On Wednesday, January 29, you asked for back-up information and <br /> computer input used in the relocated channel design. Attached with <br /> this letter is a copy of the USGS map used to determine the <br /> watershed contributing flow to Idaho Creek above the subject <br /> property. Also attached is the computer printout from the TR55 <br /> program which identifies the input parameters and the resulting <br /> output. <br /> Two assumptions were made in determination of the input parameters. <br /> First is the three ditches that lie upstream of Idaho Creek capture <br /> the runoff from the upper watershed. This assumption was based on <br /> the fact that the design storm being analyzed was the 10-year <br /> storm. It is very unlikely the irrigation ditches would have been <br /> designed to spill over during a 10-year storm. Therefore, the <br /> watershed is limited to the area above the Idaho Creek at the <br /> subject property and below the Boulder and weld County Ditch. <br /> The second assumption is that the flow to Idaho Creek is not <br /> restricted by the abandoned Burlington Northern Railroad. This is <br /> most likely a conservative assumption because any possible <br /> restriction along the railroad would delay the runoff, increase the <br /> time of concentration, and in turn reduce the peak flow. <br /> The subject property owner has not seen. Idaho Creek overtop its <br /> banks in the past 18 years, which would suggest it is likely the <br /> railroad does indeed restrict flow to Idaho Creek or divert the <br /> flow downstream of the subject property. <br /> Riprap will be placed along each of the bends of the new channel. <br /> The riprap will have a mean particle size of nine inches. <br /> Specifications for the riprap will be those outlined in CDOT <br /> standards for a mean diameter equal to nine inches. <br /> 11990 Grant Street, #410 Telephone: ( 303 ) 452-6611 <br /> Denver, Colo-ado 80233 Facsimile: ( 303 ) 452-2759 <br />