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<br />Q = 1.49 R %AS % <br />n <br /> <br />(10) <br /> <br />where: <br /> <br />Q = outflow in cfs <br />n = Manning roughness coefficient, typically .025 - .045 <br />R = hydraulic radius in feet or area divided by the wetted <br />perimeter <br />A = cross sectional area in square feet <br />S = slope of energy grade or outflow channel <br /> <br />3.2.2. TRAPEZOIDAL AND OGEE SPILLWAYS. The available energy <br />head for flow over a spillway can be computed as: <br /> <br />h. = h - (L . * h) <br />h 0 <br /> <br />(11 ) <br /> <br />where: <br /> <br />h. = energy head in feet <br />h = head in feet or water surface elevation minus <br />spillway crest elevation <br />L. = approach loss for design head <br />h 0 = design head in feet or difference between normal <br />maximum pool elevation and spillway crest elevation <br /> <br />Pier and abutment energy losses can be computed by interpolation of the <br />data in Table 1, based on the ratio of the energy head to design head. These losses <br />can be used to adjust the effective length of the spillway crest as follows: <br /> <br />L E = L - 2 * h * (N * K + K ) (12) <br /> . p. <br />where: <br />L E = effective length of spillway crest in feet <br />L = total length of spillway crest in feet <br />h. = energy head <br />N = number of piers <br />Kp = pier contraction coefficient <br />K. = abutment contraction coefficient <br /> <br />7-78 <br />