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<br />striction. The downstream depth and the depth in the bridge are computed <br /> <br />by the momentum equations based on the momentum flux in the constriction <br />and the upstream depth. <br />Pressure Flow. The pressure flow computations use the orifice <br />flow equation of U. S. Army Engineering Manual 1110-2-1602, "Hydraulic <br />Des i gn of Reservoir Outl et Structures," Augus t 1 963 (reference h): <br /> <br />Q = A ~ 2t <br /> <br />where, <br /> <br />H = difference between the energy gradient elevation ups tream <br /> and tailwater elevation downstream <br />K = total loss coefficient <br />A = net area of the orifice <br />g = gravitional acceleration <br />Q = total orifice flow <br /> <br />The total loss coefficient K, for determining losses between the cross <br /> <br />sections immediately upstream and downstream from the bridge, is equal <br /> <br />to 1.0 plus the sum of loss coefficients for intake, intermediate piers, <br />friction, and other minor losses. The section on Loss Coefficients pro- <br />vides values for the total loss coefficient and shows the derivation <br />of the equation and the definition of the loss coefficient. <br />Weir Flow. Flow over the bridge and the roadway approaching the <br /> <br />bridge is calculated using the standard weir equation: <br /> <br />Q = CLH3/Z <br /> <br />where, <br /> <br />C = coefficient of discharge <br />L . effective length of weir controlling flow <br /> <br />9 <br />