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<br />. <br /> <br />. <br /> <br />. <br /> <br />DRAINAGE CRITERIA MANUAL <br /> <br />RUNOFF <br /> <br />Step 2. Using the procedure for calculating normal depth described in <br />2.2.3 of "Major Drainage", Vol., II, USOCM, calculate normal <br />depth and velocity for reach A-B usi ng the peak flow of the <br />hydrograph. Check against the criteria in Table 4-2. <br />(Qn)/(Sl/2b8/3) = (156 x 0.04)/((.006)1/2(5)8/3) = 1.lO <br /> <br />From Table 2-1 of "Major Drainage" @ Z = 4, <br /> <br />y/b = 0.526 <br /> <br />y = 0.526b = (.526 x 5) = 2.63 ft <br /> <br />Area (A) = (5 x 2.63) + 4(2.63)2 = 40.8 ft2 <br /> <br />V = Q/A = 156/40.8 = 3.82 fps <br /> <br />F = V/;J Ag/T; where T = water surface wi dth <br /> <br />T = (2 x 4 x 2.63) + (5) = 26.0 ft. <br /> <br />F = 3.82/ V 40.8 x 32.2/26.0 = 0.54 0.80 <br /> <br />Use V = 3.82 ft/s since it is less than 6.0 ft/s recommended as <br />a maximum for a grass lined channel and results in a Froude <br />Number less than 0.8. <br /> <br />Step 3. Find the time of translation using the velocity calculated in <br />Step 2. <br />tA_B = L/(60V) = 5500/(60 x 3.82) = 24.0 minutes <br />Round off tD the nearest time increment and use tA_B = 25 <br />minutes. <br /> <br />5-1-84 <br />