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Diversion Ditch Design Methodology <br />Peak flow through the diversion ditthes was calculated for a 25-year, 24-hour <br />event, using the SCS method described in "Procedures for Determining Peak Flows <br />in Colorado - Technical Release No. 55." Ditches were sized using a typical <br />drainage area length of 1400 fee[ and varying the vertical spacing from 25 feet <br />to 100 feet. <br />Ditch dimensions were calculated using the modified Manning equation: <br /> <br />where D = design flow depth (f[) <br />q = design flow (cfs) <br />n = roughness coefficient <br />K = discharge factor <br />S = ditch gradient (ft/ft) <br />The discharge factor (K) is a function of ditch geometry and is discussed in [he <br />"Civil Engineering Handbook" edited by Urquhart, Chapter 4. <br />Peak flow velocity was calculated using the Manning Equation: <br />V = (1.49/n) R2/35112 <br />where V = velocity (fps) <br />n = roughness coefficient <br />R = hydraulic radius (ft) <br />f S = ditch gradient (f[/fC) <br />• A summary of diversion ditch design for various vertical spacings is shown in <br />Table 3.6-13. Figure 3.6-6 shows a typical diversion ditch cross-section with <br />all applicable dimensions. <br />HHH/jsb <br />12/7/84 <br /> <br />3-151 a REI/t~rOiV <br />APPROVED <br />GATE 9 a9-8'7 <br />/17~J -Teitn~ <br />REVISED ~ AUG 2t~'87 <br />