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<br />. <br /> <br />Cy2W <br />l:1y=- <br />gr <br /> <br /> <br />where <br /> <br />Ay = superel.euatiDn <br /> <br />c = coefficient whose value depends on channel shape and type of l!urve <br /> <br /> <br />v = mean channel velocity <br /> <br />w = channel width at elevation of center-line water surface <br /> <br /> <br />g = acceleration of gravity <br /> <br /> <br />r = radius of channel center-line curvature <br /> <br />. <br /> <br />(4) Energy head losses in channel bends lU'e a function of the Froude number. The <br />increase in channel resistance is attributed to the free surface waves produced by flow <br />In the bend. Scobey (2) recommended that Manning's roughness coefficient, "n," be <br />Increased by 0.001 for each 20 degrees of curvature per one hundred feet of channel, up <br />to 0.003. <br />Horton (4) recommended that the roughneu coefficient be multiplied by 1.15 for a <br />channel having an appreciable degree of meandering, and by 1.3 for a l!hannel having <br />severe degree of meandering. The increase in Manning's "n" can be computed manually <br />then incorporated Into the HEC-2 input. <br /> <br />(5) Air entrainment should be considered in rapid-flow channels where the Froude <br />number is eqUal to or larger than 1.6. This phenomenon may result In bulking of flow <br />and increased depth. The Increase In depth can be expressed manually by the following <br />equation: <br /> <br />y2 (Fr)2 <br />m=-= - <br />200gd 200 <br /> <br />where <br /> <br />m = air to water ratio <br />v = average flow velocity without air <br />d = flow depth including air <br /> <br />. <br />