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<br />1 <br /> <br />4.55 <br />3.12(3) <br /> <br />2,795 <br />2,868 <br /> <br /> <br />I <br /> <br />exIst will outfall to the main channel at various points along <br />its course. <br /> <br />I <br /> <br />I <br /> <br />Two previous hydrologic studies were available for review. The <br />most recent is the FEMA tL'li!. Revision for Spring Run (Chevenne <br />Meadows Drainage !;hannell (LOMRFC) (Reference 14). The second <br />is not a formal report; it is the analysis performed by the <br />Colorado Department of Highways for the design of the culvert <br />under Interstate 25 (HWYFC) (Reference 15). <br /> <br />I <br /> <br />5.2 <br /> <br />Previous Studies <br /> <br />I <br /> <br />The LOMRFC was conducted using a draft of the current DCM <br />requIrements. They evaluated both the 2-hour and 24-hour storm <br />events under distributions described in Section 1.0 of this <br />report and used the same 2l,-hour rainfall depth shown in Table <br />1.1. In deviation to the current DCM requirements, AMC II <br />condItions were assumed for both storm events. In addition, <br />the derived rainfall depth of 2.88 inches for the 2-hour storm <br />is less than the 3.05 Inches presented in Table 1.1. <br /> <br />I <br /> <br />I <br /> <br />The Colorado Department of Highways used the SWMM computer <br />model for obtaining their design hydrology. They used a 2-hour <br />storm event under fully developed conditions. <br /> <br />I <br /> <br />I <br /> <br />Results of both studIes are shown in Table 5.1. It should be <br />noted that the peak dIscharge location for the LOMRFC is at <br />Loomis Avenue and for the IllNFC is at Interstate 25. <br /> <br />I <br /> <br />TABLE 5. 1 ~_ SUMMARY OF FC PEAK DISCHARGES FROM PREVIOUS REPORTS <br /> <br />I <br /> <br />REPORT <br /> <br />LOMRFC(1 ) <br />HWYFC (2) <br /> <br />DRAINAGE AREA <br />~I~ miles) <br /> <br />PEAK DISCHARGES ~ <br />10 YR 50 YR 100 YR 500 YR <br /> <br />I <br /> <br />(1) The peak discharge location for LOMRFC is l.oomis Avenue. <br />(2) The peak discharge location for the IIWYFC is Interstate 25. <br />(3) This areH does not include the subbasin above Curr Reservoir. <br /> <br />I <br /> <br />5.3 Hydrologic Analysis <br /> <br />I <br /> <br />Review of the recent LOMRFC study concluded that their <br />hydrologic parameters were reasonably defined and could be used <br />as the basis for this study. Basin areas 1, 2, and 3 in Figure <br />5.1 are the same as presented in the l.OMRFC. Basin area 4 has <br />been added to complete the watershed down to Interstate 25. <br /> <br />I <br /> <br />I <br /> <br />The LOMRFC assumed full development for the watershed even <br />though they projected that it would be fIve years In the future <br />before this occurred. A slight adjustment of the CN values was <br />made to account for existing conditions at the present time. <br />The change Is not very sIgnificant. The Tc values were used <br /> <br />I <br /> <br />25 <br /> <br />R€~OURC€ CON~UlTI\NT~ INC <br /> <br />I <br />