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2.4 CULVERT DESIGNS <br />All culverts are designed to safely pass the peak flow from the 10-year, 24hour storm event. Culverts <br />DA and DA2 are designed to safely pass the peak flow from the 100-year, 24-hour storm event. <br />The 100-year, 24-hour peak flow for Elk Creek is 107.Ocfs (using a conservative CN of 60). The <br />methodology and assumptions used to determine the peak flow are included in previously approved <br />submittals (refer to Section 2) <br />The culverts were sized using the U.S. Bureau of Public Roads nomography. The culvert nomography <br />can be found in the culvert design section. The culverts were designed assuming a <br />headwater/diameter ratio of 1.5. A summary of inputs and results are shown on the following Tables. <br />Culvert inlet protection will consist of a durable geotextile underlay, covered by riprap extending to <br />the highwater level (1.5 feet above the top of culvert). Small sumps may be constructed at the <br />entrances of culverts if OMI determines no under-cuttting will occur. Straw bales will be placed up- <br />stream of culvert entrances, when appropriate, to limit flow velocities and to control sediment. <br />