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<br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br /> <br />5 <br /> <br />The 1973 study used the UDM"CD Quldellnes in effect at that time. This rainfall event <br />had a totallOo-year depth of 3. 15 inches distributed over a 4-hour period with 2.25 <br />Inches of rain occurring during the first hour. <br /> <br />Whl1e the two rainfall depths are approximately equal, the current duration of <br /> <br />rainfall Is only half as long, resulting in a more intense rainfall event. This, in <br /> <br />turn, results In a greater volume of runoff and a hIgher peak discharge rate. <br /> <br />CUHP. The CUHP uses several parameters associated with the physical character- <br /> <br />istlcs of the watershed to generate a hydrograph from each individual subbasin <br /> <br />located within the total watershed. <br /> <br />These parameters include, for each subbasin, Its drainage area in square miles, <br /> <br /> <br />the length of Its main watercourse in ml1es, the length to the center of the area in <br /> <br /> <br />miles, the slope of the main watercourse in feet per ml1e, the percentage of the <br /> <br /> <br />subbasin which is Impervious, infiltration rates for the pervious portion of the <br /> <br /> <br />subbasin in inches per hour, and Initial losses for both pervious and Impervious <br /> <br /> <br />areas in inches. <br /> <br />The subbasins included in the Big Dry Creek watershed upstream of the Walnut Creek <br /> <br /> <br />confluence with Big Dry Creek are shown in Figure 2. The drainage areas of each of <br /> <br /> <br />these subbasins in square ml1es and acres are listed in Table I. <br />