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I I I I I I I . I I . I I I I t I I I 2-year 5-year 10-year 50-year 100-year 1.10 1. 57 2.07 '2.61 2.85 4 TABLE II Drainage Basin Parameters Area Future % Roughness Coeff. (n) Slope Subarea (Acres) Impervious Impervious Pervious .(Ft, /Ft. ). 1 24.3 5.0 .016 .200 .0300 2 39.1 5.0 .016 .200 .0300 3 8.7 5.0 .016 .200 .0300 4 22.6 5.0 .016 .200 .0300 5 33.5 40.0 .016 .300 .0300 6 9.4 5.0 .016 .350 .0300 7 4.6 5.0 .016 .350 .0300 8 16.7 5.0 .016 .350 .0250 9 13.3 5.0 .016 .350 .0300 10 31.2 30.0 .016 .300 .0300 11 37.2 5.0 .016 .350 .0250 12 10.4 5.0 .016 .350 .0250 13 17.5 40.0 .016 .300 .0250 14 23.0 25.0 .016 .300 .0170 15 35.6 5.0 .016 .300 .0200 16 40.6 13.0 .016 .350 .0300 17 19.1 50.0 .016 .250 .0300 18 74.5 40.0 .016 .200 .0150 19 5.0 5.0 .016 .200 .0180 20 109.0 40.0 .016 .200 .0150 21 46.0 10.0 .016 .200 .0300 22 13.2 5.0 .016 .250 .0180 23 41.1 70.0 .016 .250 .0150 24 21.1 40.0 .016 .250 .0300 25 20.6 20.0 .016 .250 .0100 26 69.8 35.0 .016 .250 .0160 27 74.6 40.0 .016 .250 .0180 28 34.5 5.0 .016 .250 .0180 29 92.9 40.0 .016 .250 .0150 30 18.5 12.0 .016 .200 .0250 31 35.5 40.0 .016 .250 .0200 32 72.1 40.0 .016 .200 .0300 33 35.4 35.0 .016 .200 .0250 34 23.9 40.0 .016 .250 .0120 35 22.1 40.0 .016 .200 .0300 36 36.4 30.0 .016 .250 .0300 37 39.6 40.0 .016 .250 .0300 38 52.4 40.0 .016 .250 .0300 39 44.1 40.0 .016 .250 .0300 TABLE I Rainfall Data Storm Frequency Rainfall Depth (Inches) For a Three-Hour Storm Losses The following losses were applied to the SWMM computer simulation in order to estimate flood runoff. 1. Infiltration Losses: Maximum infiltration rate, 1.8 in./hr. Minimum infiltration rate, 0.5 in./hr. Infiltration losses are estimated using Horton's equation: Infiltration loss f + (f. - f )e-oct o ~ 0 where f. and f are the maximum and minimum infiltration rates, respec- ~ 0 tively; t is the time from the start of rainfall; and is the decay rate (0<.=0.00115 is used in this study). 2. Detention and Depression Storage: Impervious area, O.l-inch Pervious area, 0.4-inch Drainage Basin Parameters The drainage basin parameters used in this study are listed in Table II. A total of 38 subareas were considered, and are shown on Drawing No.3 of 12.