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<br />/ <br /> <br />. <br /> <br />. <br /> <br />. <br /> <br />Ti3, C:::~n <br /> <br />December 7, 1991 <br /> <br />MEMORANDUM <br /> <br />TO: <br />FROM: <br />SUBJECT: <br /> <br />R. H, French, Ph.D., P,E. <br />Tom Browning/Mark Glidden <br />West Ranoe Wash Diversion Dike - Sediment TransDort Analvsis <br /> <br />PurDose <br /> <br />The purpose of this memo is to describe the procedures used in sizing the West Range Wash <br />Diversion Dike for the City of North Las Vegas, Nevada. <br /> <br />Summary <br /> <br />The U.S. Army Corps of Engineers HEC-6 model was used for the analysis. The necessary <br />input parameters for channel, hydraulic, and sediment characteristics were estimated by the <br />methods outlined below, Based upon the results of this study, the width and height of the Dike <br />were determined according to the sediment carrying capacity of the channel and the resulting <br />deposition and scour along the proposed design, <br /> <br />Bed Material <br /> <br />Grain size samples were taken on the alluvial fan and along the proposed alignment of the <br />Diversion Dike. The variation in grain size distribution of the samples on the fan was not <br />significant and therefore, an average distribution was used. The same was true for the samples <br />taken along the proposed Dike alignment. Attachment 1 shows the grain size distributions <br />used for the bed material gradation cards in the HEC-6 model. <br /> <br />Inflowino Sediment <br /> <br />The volume of sediment yielded by the drainage basin, above the fan and design area, was <br />adopted from the estimates contained in "Western and Eastern Tributaries of Range Wash - <br />Flood Control Facility Plan" (Plan) Boyle 1991. The average annual sediment yield was <br />estimated to be 16 AF, This value is consistent with regional estimates as described in the <br />Plan, The ratio of 100-year to average annual sediment yield is in the range of 4 to 7 as <br />described in the Plan. For the purpose of determining the inflowing sediment rate at the apex of <br />the fan to be used in the H EC-6 model, a 1 OO-year sediment yield of 112 acre-feet was used (7 x <br />average annual). <br /> <br />The inflowing sediment rate was estimated from a generalized power function equation as <br />shown on Attachment 2, The resulting sediment rating curve used in the HEC-6 model is <br />shown on Attachment 3, <br />