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I I I I I I I I I I I I I I I I I I I Sub- Basin 1 2 3 4 5 6 7 8 9 10 11 12 13 14 Are~ (mi ) .34 .18 .42 1.07 .30 .68 1.05 .18 1.03 .48 .21 .38 .47 1.05 L (mi) .83 .57 .85 1.74 .61 1.21 1.67 .55 1.67 1.23 .70 .95 .99 1.69 L (ffif) .42 .34 .47 1.10 .40 .64 .78 .28 .95 .61 .42 .53 .47 .95 TABLE II DRAINAGE BASIN PARAMETERS FOR CUHP TODD CREEK I * -a- 43 40 53 52 58 37 41 53 60 47 40 40 37 38 Slope (ft/ft) .032 .037 .022 .016 .016 .017 .016 .034 .019 .022 .027 .024 .015 .011 Detention Stg. Perv. Imperv. f. (in) (in) (inlhr) .35 .35 .35 .35 .35 .35 .35 .35 .35 .35 .35 .35 .35 .35 Depression and detention storage values were obtained from the USDCM. Values of pervious detention were estimated at 0.35 inches and impervious detention varied from 0.05 inches to 0.1 inches. Infiltration loss rates were estimated based on a preliminary inventory of soils prepared by the U.S.D.A. Soil Conservation Service (Reference 11). Infiltration losses were based on Horton's Equation: (i~9hr) (s~-l) .05 .05 .10 .10 .10 .05 .05 .10 .lO .05 .05 .05 .05 .05 3.50 4.00 3.75 3.00 3.00 3.75 3.75 4.00 3.50 3.50 3.00 3.75 3.50 3.75 .50 .60 .55 .50 .50 .55 .55 .60 .50 .50 .50 .55 .50 .55 * I - percent impervious area for future basin conditions a upon a time distribution of rainfall recommended by the manual. Areal reducti ons of rai nfa 11 were appl i ed to the most intense 15-mi nute peri od of the desi gn storms based on Area-Depth Curves developed by NOAA. Table IV shows typical design storms used for hydrologic modeling and includes the areal rainfall adjustments. .0018 .0018 .0018 .0018 .0018 .0018 .0018 .0018 .0018 .0018 .0018 .0018 .0018 .0018 f = fo + (fi - fo)e-oct whe re; infiltration rate in inches/hour initial infiltration rate in inches/hour final infiltration rate in inches/hour decay coefficient in per second units t = time in seconds f < = f. = , fo = oc = The hydrology modeling results in Table I are also summarized in the form of discharge probabil ity profiles (Figures 3 through 5) and 100-year flood hydrographs (Figures 6 and 7). Hydraulic Analysis A hydraulic analysis was completed along the channel of the studied streams to determine the water surface elevation for the lOO-year runoff event. This hydraulic analysis was completed using the HEC-2 Water Surface Profi 1 e Computer Program developed by the U.S. Army Corps of Engineers (Reference 9). 6