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<br />Flood Insurance Study Repolt Data <br />Flood Insurance Study. Cooper Slough, Larimer County, Colorado <br />Page 9 <br /> <br />at the point where they join the 100-yr floodplain of the Cooper Slough. Boxelder <br />overflows from the Larimer Canal and Vine Street were added to section P at Vine <br />Drive. An analysis of the ditch along the west side of 1-25 indicates that the Boxelder <br />overflow south of Vine S'treet travels south to the cas Railroad, west along the north <br />side of the railroad embankment and overtops the railroad at a point approximately <br />900 feet west of 1-25 joining the Cooper Slough bank overtoppings at section G. The <br />Boxelder overflow under 1-25 at the cas Railroad travels south and spreads out to <br />join with the Boxelder overflow that has overtopped the railroad thus creating a <br />continuous zone of shallow flooding from the 100..year floodplain of Cooper Slough <br />to 1-25, and from the C&S railroad to State Highway 14. Ttlis analysis was field <br />verified. Boxelder overfk)ws at State Highway 14 were added at section B. <br /> <br />Initial HEC-2 analyses 01 the Overflow from State Highwa1l14 to its confluence with <br />Boxelder Creek indicated that the flow spills out of the floodplain of the Overflow <br />between sections A and E. These flows leave the Overflow floodplain at Lake Canal <br />and travel southeast in t1e low area between Lake Canal and the Cache La Poudre <br />Reservoir Inlet, eventuallv joining with the Boxelder Creek floodplain. To model this <br />split in flow, Section 35 was placed within the Boxelcler Creek floodplain (i.e. <br />downstream of the study limits and just downstream of the split flow) and given a <br />fixed water surface elevation as reported in the 1981 SU~ report. Split flows from <br />sections A to E were returned to the floodplain at section ::15. Elased on recent aerial <br />photography (Reference 11) several buildings were incorporated into the model. <br />These buildings are shown on the maps presented with tllis rE~port. <br /> <br />Figure 1 is a schematic of the Cooper Slough study area with the locations and <br />quantities of incoming and outgoing (spill) discharges in addition to the discharge at <br />selected locations along the flow paths. Table 4 lists the discharge calculated at <br />each cross section alonu the Cooper Slough. Locations of selected cross sections <br />used in the hydraulic analyses are shown on the Flood Pmfiles (Appendix E). <br />Because the water surface elevations for the storm events at Sherry Drive are similar, <br />only the 100-year water Burface elevations are shown. <br />