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<br />(Dam I.D. 120106). Values of Qp, and T are as previously calculated on <br /> <br /> <br />Worksheet W-l (Dam failure discharge). The length of the reach, 3,000 feet, <br /> <br />is the distance from the dam to the section of interest. We have judged this <br />to be the first critical section downstream of the dam. The slope(s), channel <br />roughness (n), and typical cross sectional shape are average for the reach as <br />determined by field reconnaissance and/or topographic maps. These parameters <br />are the basic data needed for the routing procedure. <br />The time required for the flood hydrograph to traverse the distance between <br /> <br />the dam and the critical section is referred to as the "Travel Time". Travel <br /> <br />time is a function of the reach length and the average flow velocity. The <br />Equation in the Form <br /> <br />average flow velocity may be calculated by using Mannings <br />Shown in Equation 2, or 3.[3] <br />Q = k D/f~ S~Z <br />n ' <br />OR <br />Q = /.:/" AA '7"3 Sill.. <br /> <br />Equation 2 <br /> <br />.,'i <br /> <br />Equation 3 <br /> <br />Where: <br /> <br />Q = Channel capacity, cfs <br />D = Depth of the flow, feet <br />Cl1.ecw.-vL <br />S = Slope, feet per foot <br />n = Manning's Roughness coefficient <br />K = Geometric coefficient of the channel shape <br />A = Cross sectional area, Ft2 <br />R = Hydraulic radius, ~ ' unitless <br />P = Wetted perimeter, feet <br />Equation Z can be used for trapezoidal, circular, or parabolic cross <br />sections, Equation 3 is general and applies to any cross-sectional shape. <br /> <br />11 <br />