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I I I I I I I I I I I I I I I I I I I FIS WOBS 9,48* 2.52 from Previous Re rts, ~i~I~~~.JI_JllII~~i 10lyiilifl&~yii'.. ' 3500 6600 8600 14500 2850 * Includes Windmill Gulch drainage basin area 6.3. Hydrologic Analysis little Johnson/Security Creek drainage was analyzed using the TR-20 model (Ref, 6,2), This model was obtained from the Little Johnson/Security Creek Drainage Basin Planning Study and modffied to include overflows from Windmill Gulch at Canal #4 and Grand Avenue, Both the 24- and 2-hour storms were used for this study, Windmill Gulch peak discharges were modeled using a TR-20 data deck obtained from Wilson & Company (Ref, 6,3) and modified to reflect conditions relatively consistent with the Little Johnson/Security Creek model. The output hydrograph from Windmill Gulch overflows were then added to the Security Creek hydrograph within the TR-20 model, Table 6.2 summarizes the peak discharges for the key locations shown in Figure 6,1, Since this is a limited detail study, peak discharges are only shown for the 100-year flood, The 24-hour storm was recommended by EI Paso County for floodplain delineation in order to remain consistent with drainage basin planning studies. This conclusion appears reasonable given the very slight differences between the results. The increases in flows on Security Creek are due to: (1) inflows to the basin from Windmill Gulch at Canal #4, (2) Grand Avenue and (3) overflow due to the additional inflow from area west of Grinnell. Area' (sq,ijli.) 24-hour storm cfs 2-hour storm cfs 38 0,31 100 160 39 0,72 300 370 40 0,80 440 500 91 1.90 2130 2220 41 2,20 2690 2710 45 2,61 3,350 3370 1 Note: Basin areas do not include the Windmill Gulch drainage basin area of 3.38 are miles, 6,3 Resource Consultants & Engineers, Inc,