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<br />Qp = qp x area of basin = 264 x 19.47 = 5140 cfs <br />where Qp = unit hudrograph peak rate runoff In cfs <br />Tp = 60 tp + 0.5tu = 60 x 1.21 + 0.5 x 10 - 78 minutes <br />where tu = time of unit rainfall duration in minutes <br />tp = time from beginning of unit rainfall to peak of hydrograph <br />in minutes <br /> <br />Utilizing the above calculative values and the general guidelines <br /> <br />from the Criteria Manual, the storm hydrograph for the basin was <br /> <br />drawn (See Plate 111-2). <br /> <br />The volume of runoff was determined by plan- <br /> <br />imetering the area under the hydrograph curve and by the calculation, <br /> <br /> <br />volume = area of basin in acres x 1/12 (one inch of rainfall), The <br /> <br /> <br />resultant volumes of 1033 acre-feet and 1042 acre-feet respectively <br /> <br /> <br />are within the recommended five percent of one another for each of the <br /> <br /> <br />pr8viously selected points along the channel. <br /> <br /> <br />After separate unit hydrographs had been computed ill 3 manner <br /> <br /> <br />similar to the above example, the remaining hydrology calculations were <br /> <br /> <br />computed utilizing VTN's electronic computer and the ][EC-l Flood )lydro- <br /> <br /> <br />graph Package developed by the Hydraulic Engineering Center, U.S. Army <br /> <br />Corps of Engineers, Sacramento, California. <br /> <br />Runoff volumes and peak <br /> <br />rates of storm runoff were determin8d for the 100-year storm under exist <br /> <br />lng developed conditions and for 10, 25, and lOO-year frequency storms <br />for fully developed conditions for the Big Dry Creek Basin. The peak <br />runoff determined from a 6-hour storm produced the greatest pe:,k clis- <br />charge. The 6-hour hydrograph for the peilk runoff was used to determine <br />the volume of runoff. <br /> <br />':>1- <br />