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eh <br />ESPEY, NUSTON 6 ASSOCIATES, 1NC. <br /> <br />We feel that 299 cfs design flow is a conservative estimate of the <br />10-year 24-hour storm flow crossing the road. <br />3.5.1.3 Culvert Sizing Sta 31+50 <br />Due to the limited available head, heavy wheel loadings and cost factors, <br />a group of 12 gauge 36-inch round CMP culverts was found to be the most economical <br />structure for this drainage crossing (see Exhibit C-14). <br />Placing the road surface 1.5 feet above the top of the culvert, and <br />allowing 0.5 feet of fzeeboazd, the design head is 4.0 feet. <br />Assuming the condition of Inlet Control, each 36-inch CMP culvert, <br />with mitered ends, kill carry 43 cfs with 4.0 feet of head at the inlet (culvert <br />• capacity was derived from Chart No. 5 of the Bureau of Public Roads Hydraulic <br />Engineering Circular 1~Io. 5). <br />To pass the required 299 cfs, 7 such culverts aze required. For an <br />additional factor of safety and to help prevent clogging of the inlet, an aditional <br />culvert was installed. <br />To prevent the flow from running down the west side of the road before <br />the 4.0 feet of head would develop, an earthen berm was placed just below the <br />culverts at the inlet azea. <br />\J <br />C-46 <br />