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<br />ORAINAGE CRITERIA MANUAL <br /> <br />RUNOFF <br /> <br />Step 4. Enter the hydrograph at A into Column 2 and the hydrograph A . <br />lagged by tA_B = 25 minutes in Column 3 of Table 4-4. <br />Step 5. Enter in Column 4 the sum of local hydrographs (i.e. Basin 2 at <br />B and Basin 3 at B) for reach A-B. <br />Step 6. Add to the hydrograph in Column 3 the total of local <br />hydrographs (i.e. Column 4). Enter results in Column 5. <br />Step 7. Repeat step 2 for reach B-c using criteria for natural <br />waterway. <br /> <br />(Qn/Si b8/3) = (272 x 0.45)/((.008)i(20}8/3) = .0454 <br /> <br />From Table 2-1 of "Major Drainage" @ Z = 3, <br /> <br />y/b = .112 <br /> <br />y = (.112 x 20) = 2.24 <br /> <br />Area (A) = (20 x 2.24) + 3(2.24)2 = 59.8 ft2 <br /> <br />. <br /> <br />v = Q/A = 272/59.8 = 4.54 ft/s <br /> <br />T = (2 x 3 x 2.24) + 20 = 33.4 ft <br /> <br />F = 4.54/ V 59 x 32.2/33.4' = 0.60 ~ 0.95 <br /> <br />Use V = 4.5 fps since it is less than the recommended maximum <br />of 8.0 ft/s and has a Froude number less than 0.95. <br /> <br />Step 8. Repeat Step 3 for reach B-C. <br /> <br />tB_C = 3000/(4.58 x 60) = 10.9 minutes <br /> <br />Round off to nearest time increments and use <br />tB_C = 10 minutes <br /> <br />Step 9. Repeat Step 4 for reach B-C. <br /> <br />. <br /> <br />5-1-84 <br />