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<br />Re:" Bums, P.E. and Bob SII P.E. <br />Final Repon - Hydrologic Aruuysis of the Cooper Slough Within Larimer COUllJ.)', Colorado <br />Page 2 <br /> <br />A copy of the Boxelder Creek LMMP Flood Insurance Study (FTS) report was obtained to <br />determine the peak 100-y,~ar overflow discharge at the followin.g fivt~ locations along 1-25. <br /> <br />· Larimer-Weld Canal <br />· "me Drive <br />. Low point of highway south of Vine Street <br />" C&S Railroad <br />· S tate Highway 14 <br /> <br />The map on the following page shows the approximate location of these overtopping areas. <br /> <br />Only the lOa-year peak overtopping discharge values could bl~ dett:rmined from the FrS report. <br />In order to update the 1n7 SWMM model not only are the peak overtopping discharges of each <br />storm event was needed, but also the runoff hydrographs for each of these storm events must be <br />input into the SWMlv! model.. <br /> <br />The peak overtopping discharges for the 10-, 50-, arld 500-year S1:Orms were obtained from a <br />meeting with Mr. Geralc. Shultz of the USBR. Mr. Shulr.z prepared the Boxelder Creek <br />hydrologic analysis and de~:ermined the overtopping discharges. The following table lists the peak <br />overtopping discharges fer each of the storm recum:nce intervals at each of the overtopping <br />locations. <br /> <br /> TABLE 1 <br />PEAK OVERTOPPING DISCHARGES INTO <br /> TEE COOPER SLOUGH BASIN (cl's) <br />- Location IO-vI' 50-vI' IOO.-vI' SOO-vI' <br />Larimer-Weld Canal" 57 258 258 258 <br />Vme Street 191 930 1450 2430 <br />South ofVme Street 18 68 104 158 <br />C&S Railroad" 47 74 94 132 <br />State Highway 14"" 275 530 726 1136 <br /> <br />"The canal and railroad flows actually go through underpasses Ullder 1-25. <br />"Flow down highway median is not subtracted. Refer to the following section. <br /> <br />OVERTOPPINGANAl.YSIS AT STATE IDGHWAY 14 <br /> <br />At all of the locations Iist~d above, except at State Highway 14, the USBR determined the <br />amount of flow that goes down the 1-25 median and subtracted that amount from the total flow to <br />determine the amount of flow that crosses over the southbound lanes into the Cooper Slough <br />basin. At State Highway 14, the USBR determined the peak ovedlclw that leaves the Boxelder <br />