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<br />Two corrugated metal culverts installed at the road access to the <br />substation (at ditch station 3+75) must be checked for their <br />ability to pass 116 cfs, or 58 cfs per culvert. <br />Fill above culvert or allowable headwater is 2.8 feet. <br />Culvert slope, S is 4$. <br />Culvert length is 29 feet. <br />Diameter is 36 inches. <br />Roughness factor is .025. <br />Critical depth (dam) of each culvert is 2.99 feet. <br />de 2.99 <br />- - _ ---- _ .83 <br />D 3 <br />Critical slope (Se) = 2.7~. <br />Since culvert slope of 9t is greater than the critical slope of <br />2.9i, the culverts are inlet controlled. From standard nomograph <br />charts for culverts, HW/D is found to be 1.96. Therefore, the <br />• necessary headwater to pass the flow is 1.96 x 3 = 4.38 feet. <br />The allowable headwater is only 2.8 feet, which results in a flow <br />on the road surface of approximately 1.58 feet at its lowest <br />point. The sketch on the following page shows a cross-section of <br />the culvert installation. <br />C~ <br />.y/a~'~i <br />