FLOOD04080 - Laserfiche WebLink

Home Browse Search

I I I I I I I I I I I I I I I I I I I CHAPTER II - GENERAL STUDY AREA DESCRIPTION AGENCY CONTRACT INFORMATION PROVIDED Regional Transportation Di strict A. Danaher RTD Detention Pond Data A. Study Area State Engineer's Office J. VanSciver Henry's Lake Data D. Method of Analysis Henry's Lake Basin lies within the southwest portion of the Denver Metropolitan area. The upper end of the basin is located just immediately west of Kipling Street at Quincy Avenue. The confluence with Bear Creek is located just east of Pierce Street. The basin location and boundary are shown on Figures 11-1 and 11-2. The sequenti a1 process and methods of ana 1ysi s ut i1 i zed in thi s study were based upon the termS of the contract, the Urban Storm Drainage Criteria Manual, current codes and regulations of the City of Lakewood and Jefferson County, and analytical procedures developed by WRC. Henry's Lake drainageway lies within basin number 1-31-55-1-01 as described in the Project Reuse "Drainage Basin Descriptions" (Reference-I). The study classifies the basin as being rural, large lot residential, and as having no definitive channel. Subsequent to the initial data gathering and field reconnaissance work to establish basin boundaries and existing storm drainage features, the study area was divided into separate sub-basins within the major watershed. The physical parameters (i.e., area, length, slope, and percent imperviousness of each sub-basin for future development conditions) were then defined and the design storm hydrographs developed for the 10- and 100-year recurrence interval storms. The design rainfall information was obtained from the UD&FCD and the 1 hour NOAA rainfall depths (Reference-4). The flood hazard area delineation (FHAD) for Henry's Lake Basin under the initial contract, extends from Bear Creek to the outfall from Henry's Lake located north of Quincy Avenue. The area of the basin tributary to Bear Creek is 1.45 square miles (930 acres). The drainageway lies entirely within the City of Lakewood and Jefferson County. A small portion of the watershed south and east of Henry's Lake lies within the City and County of Denver. The combining of the hydrographs, channel routing, and routing of the flood hydrographs through Henry's Lake and existing pondS were performed using the Storm Water Management Model (SWMM, Reference-6). The model was ca1 ibrated usi ng the Colorado Urban Hydrograph Procedure (CUHP, Reference-2). The resulting hydrographs were used to define the future basin development floodplains for the 10- and 100-year recurrence interval storms by util i zi ng the Army Corps of Engi neer' s backwater computer program (HEC-2, Reference-7). After preliminary hydrologic analysis of the study area was completed, a major flow split was identified in Academy Park just upstream of the culvert beneath Hampden Avenue. The nature and extent of this flow split is discussed in Chapter III. The original FHAD contract waS amended by Addendum No.1 to evaluate the flow split (and the tributary local runoff) from the point of origin at Academy Park northeasterly to Bear Creek. The flow split combines at Pierce Street and Hampden Avenue with the local runoff from a right bank direct flow area (A = 0.20 square miles) tributary to Bear Creek (see Figure II-2). A majority of the direct flow basin lies within the City of Lakewood, with the area immediately adjacent to Bear Creek lying within the City and County of Denver. The Henry's Lake Basin drainageway from Bear Creek to Hampden Avenue is generally urbanized. Approximately 50% of the area is fully developed with single -2-