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Loadout Area Hydrology Map, (Map 17a). This temporary diversion ditch <br />• and culvert are designed and constructed to safely pass the peak flow <br />resulting form a 10-year, 24-hour precipitation event as follows: <br />Drainage area <br />10-year, 24-hour event <br />Runoff - Curve ri90 <br />Peak Flow - Curve q90 <br />Flat Slope <br />Type II Storm <br />Western Colorado <br />Channel Type <br />Side Slopes <br />Channel Gradient <br />7.445 acres <br />1.6 inch storm <br />0.76 inches <br />7.6 cfs/inch runoff or <br />5.78 cfs <br />Trapezoidal <br />2:1 <br />Less than 2Ye <br />By trial and error using the U.S. Department of Transportation's <br />"Design Charts or Open Channel Flow", the appropriate channel width to <br />carry the peak flow at less than the critical curve velocity is <br />determined as three (3) fee with riprap bottom. <br />Channel Width 3.0 feet <br />Depth of Flow 0.42 feet <br />Velocity of Flow 3.3 fee/second <br />Critical Velocity 3.4 feet/second <br />Figure 23-24, Typical Channel Cross Sections shows the configuration <br />of this temporary diversion. <br />The culvert was designed according to procedures set forth by the U.S. <br />Bureau of Public Roads. Figure 23-11 illustrates the procedures used <br />to size the culvert. Using a HW/d of 1.0, an 18-inch culvert with a <br />cross-sectional area of 1.76 square feet is required to safely pass the <br />runoff from the 10-year, 24-hour event. For design purposes, it was <br />conservatively assumed that the bottom two-thirds of the existing 48- <br />• inch culvert is filled with fines. Under these conditions, the cross- <br />sectional area of open pipe is approximately 3.6 square feet which is <br />23-160R Revised - November, 1991 <br />