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<br />be developed for each subbasin. This is generally the case for basins exceeding 500 <br />square miles. The runoff hydrograplls resultin9 from Ule application oj rainfall to eacll <br />subbasin will be rou':ed and combined. <br /> <br />b. Calculate the values of Time in percent cf (L9 + 0.5D) for multiples oj unit duration. <br /> <br />c. From appropriate table for region from 1/(19+0.5D), determine q. <br /> <br />d. Determine the unit runoff volume for the tlasin. V', in day cubic feet per second This <br />is generally 1 inch of runoff over the entire basin converted to day-cfs units. <br /> <br />e. Rearranging Eq (\15) <br /> <br />qV' <br />Q <br />(g-,-6:-515 <br /> <br />(V-6) <br /> <br />Determine 0 for each time step. <br /> <br />f. Plot the ordinates Q and draw a smooth curve tt',rou911 the points. <br /> <br />For a complete description of this method refel' to Bureau of Reclamation's Flood <br />Hydrology Manual, '1989. <br /> <br />._1- <br /> <br />- <br /> <br />-_.~- <br /> <br />Example 7.4- Determine the synttletic: unit hydr09raph using the Bureau's dimensionless <br />technique given the following basin characteristics: <br /> <br />Basin Area = 6.2 square miles <br />L" 3.22 miles <br />L" " 0.95 miles <br />S ~ 0.030 Wit <br /> <br />Solution: <br /> <br />Finure 7-9 <br />1.) LL,,/S 5 = (3.22)(.95)/0.30.5 = 19.3 = '-9"" 1.5 hours <br /> <br />2.) Duration = 1.5/5.5 = .27 hours say .25 clours or 15 rni'lutes <br /> <br />3.) Lg + 0.5D = 1.5 + .5(.25) ~ 1.63 hours <br /> <br />4.) V' = 3.7 mi2 1 in 640 Ac 43.560 1\: <br />mi' Ac <br /> <br />91!Y <br />86,4CO sec <br /> <br />fL 167 day.cls <br />12 in <br /> <br />5.) Calculate ordinates Q: <br /> <br />Colorado Flood <br />Hydrology Manual <br /> <br />}-53 <br /> <br />fRI'FT <br />