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be recomputed with the upstream depth thus found as a control depth and proceeding in an upstream direction. The downstream depth (less than critical) is determined by finding the depth corresponding to the momentum flux for the constricted section at critical depth. The downstream depth thus found is used as a control depth to continue water surface computation in the downstream direction as far as downstream flow conditions permit. (5) Weir flow is computed by the weir equation: CLH3/2 where, Q = e - coefficient of discharge (see exhibit 2) L = effective length of weir controlling flow H - difference between the energy grade line elevation and the roadway crest elevation Q - total flow over the weir The approach velocity is included by using the energy grade line elevation in lieu of the upstream water surface elevation for computing the head, H. The coefficient of discharge "e" should not be greater than 3.1 for critical depth control, and in actual practice should be around 2.5 to allow for losses caused by bridge railings, etc. Where submergence by tailwater exists the coefficient "e" is reduced by the computer program according to the method indicated in reference (c). The total flow, Q, 1.5 computed by dividing the weir flow into subareas, computing L, Hand Q for each subarea and summing all subareas. (6) Pressure flow computations use the orifice flow equation of U. S. Army Engineering Hanual 1110-2-1602, "Hydraulic Design of Reservoir Outlet Structures", August 1963 (reference e): Q _ A72~H where, H = difference between the energy gradient' elevation upstream and tailwater elevation downstream K - total loss coefficient (see exhibit 2) A - area of the orifice g - gravitational acceleration Q - total orifice flow 11