FLOOD05049 - Laserfiche WebLink

Home Browse Search

Flood Insurance Study Report Data Flood Insurance Study - Cooper Slough, Larimer Coun1y, Colorado Page 3 distribution of flow in the Cooper Slough Basin. This restudy of the Cooper Slough basin was authorized to describe the impact of these inflows. Tile limits of study for Cooper Slough determined in the initial CCO meeting am from it's confluence with Boxelder Creek to the crossing of East Vine Drive apprOJ<imately 2.1 miles upstream. However, the Cooper Slough channel does not tie into Soxelder Creek directly. At State Highway 14 only a small portion of tIle ponded flow from major storm events passes under the highway through the Cooper Slough culvert. This flow joins with Lake Ganal approximately 700 feet downstreiam of State Highway 14. It then overtops the canal and flows south along Shemy Drive. At a low point east of Sherry Drive, it overflows to Prospect Road. At Prospect Road, tllis flow merges with the backwater from Boxelder Creek. Tt,e majority of the flow ponded at State Highway 14 from major storm events overtops the highway at a low point approximately 1225 feet east of the Cooper Slough channel and flowl; south to its confluence with the Soxelder Creek floodplain. Because this flow is not hydraulically connected to the Cooper Slough channel flow, this overflow was analyzeid as a separate floodplain. Therefore, the HEC-2 models and their limits of study for this LMMP are: Cooper Slough from State Highway 14 to Vine Street ("Main Channel"); Cooper Slou~~h from Prospect Drive to State Highway 14 ("Sherry Drive"); and thiS State Highway 14 overflow from Boxelder Creek to State Highway 14 ("Overflow"). 2.2 Community DescriPtion (no change from FIS dated March 18, 1986) 2.:3 Principal Flood Problems Floods in the study area are usually caused by general rain storms and cloudburst storms from May through September. Floods resulting from heavy rainfall over the watershed are characterized by high peak flow of moderate volume and duration. The cloudburst storm is characterized by a high-intensity, short-duration rainstorm which produces a flood of high peak flow, short duration, and relatively small volume of runoff. Peak runoff will usually occur within a few hours after a single storm. The Cooper Slough floodplain is predominantly flat. Channel capacity is limited in places promoting overbank flows and divided flow conditions. Channel flow is restricted by relatively small culverts at Vine Drive, the Colorado and Southern Railroad, and at State Hi~lhway 14. Due to an undersized culvert at State Highway 14, a ponded area will form north of the highway, and eventually overtop the highway