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<br />Method of Calculation: Table 111-1 (100~year frequency storm- <br /> <br />projlosed land use) <br /> <br />Column 1: A rainfall interval of 10 minutes and a total time oC G <br /> <br />hours were selected. <br /> <br />Column 2: <br /> <br />These values were taken Cram the RainCal1 Dejlth-Duration- <br /> <br />Frequency Graph. <br /> <br />Column 3: <br /> <br />The incremental precipitation was determined hy Column 2 <br /> <br />(20 minutes) minus Column 2 (10 minutes) etc, <br /> <br />Co]unm 4: <br /> <br />Incremental precipi tation amounts Crom Col llnm 3 were re- <br /> <br />arranged into a realistic storm hydrograph pattern. <br /> <br />Colunm 5: <br /> <br />A constiJnt maXImum infiltration rate of one~hnlC inch per <br /> <br />hour was used as discussed previou~ly. <br /> <br />Column G: <br /> <br />The total detention and depression storage is detenni ned rrom <br /> <br />Tahle 2-2 of the Criteria Manual and shown as a total at the hot tom ur <br /> <br />Colunm G. <br /> <br />For each time period the detention and depression storage in <br /> <br />Col umil G is found by subtracting infi I tration, Column 5, Crom precipi tn, <br /> <br />tion, Column 4. <br /> <br />If the result is negaLL\le, there is no excess Cor this <br /> <br />period, and Column G and Column '7 and zero. <br /> <br />If the result is positive, <br /> <br />the amount is entered In Column G as tlw detention and clep,'esc ion stornge <br /> <br />for the time period. <br /> <br />When the cumulative amount in Column G equals the <br /> <br />total shown at the bottom of the colullln, the detention storage is Cui Iy <br /> <br />used and all remaining values arc zero. *Note that the last val110 of <br /> <br />detention storage is less thun Column '!minus C:OIUIlIll 5 and wa~; detel'lllin0d <br /> <br />by the difference between tbe total amollnt and the amount accumulated <br /> <br />-27 <br />