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HYDROLOGY III. I I I I area is located entirely on the property of Camp George West The Pleasant View Tributary was not included in the previous Master Plan. This reach has remained relatively unchanged. Hydrologic analyses were performed for Upper Lena Gulch above Maple Grove Reservoir to aid in the development of alternative plans for management of storm runoff These analyses were conducted in accordance with the procedures outlined in the Urban Drainage and Flood Control District's (UDFCD) "Urban Storm Drainage Criteria Manual" (USDCM). These analyses update previous studies performed as part of the Lena Gulch Drainage Master Plan. June 1975 prepared for the UDFCD, the Cities of Golden, Lakewood and Wheat Ridge, and Jefferson County. General Pleasant View Tributary from the discharge point of the improved channel to the start of the improved channel upstream of Orchard Street P-2 I The channel as it presently exists has been constructed to have capacity for the 100-year flows. Numerous erosion control structures serve to stabilize the grass-lined channel. The two bridge crossings at Nile Street and Orchard Street have adequate capacity for the 100-year flows without overtopping. I I the Colorado Urban Hydrograph IS Modeling Methodology The currently accepted approach for computing urban runoff in the Denver area Procedure (CUHP) which is outlined in the USDCM. upstream of Orchard Street to the end of the Study area above Pike Start of improved channel Street P-3 I Because the peak flows for ultimate future basin development estimated in the 1975 Master Plan have been adopted as regulatory flows, it was necessary to calibrate a model developed using the updated methodology to these peak flows. Estimates of percent of impervious area for ultimate future land use conditions were projected using land use and zoning maps provided by Jefferson County, the City of Golden, and the City of Lakewood. Peak discharges were computed which reflect projected ultimate future basin development This portion of Pleasant View has no well-defined channel. Stormwater flows overland through undeveloped lots adjacent to single family homes to reach the improved channel downstream. No improvements have been constructed in this reach. I I The study area was divided into seventy-seven sub-basins ranging in size from 30 acres to 145 acres. Figure 3 presents the sub-basin delineation. Sub-basin characteristics such as percent impervious, infiltration, area, length, length to centroid and slope were determined from available sources. I Runoffhydrographs from each sub-basin for the 2-,5-, 10-,50-, and 100-year recurrence interval storms were generated using the computer program CUHPE/PC. The program used the one-hour rainfall to develop a two-hour design storm, computed excess precipitation, and developed runoffhydrographs for subsequent combination and routing. A detailed description of the computational procedures used in CUHPElPC may be found in the USDCM I I 10 The basin runoff hydrographs were combined and routed to develop discharge hydrographs from each basin using the UDFCD computer program UDSWM2/PC. A complete description of the UDSWM2/PC program's capabilities and limitations may be found in the program's user manual available from UDFCD. Figure 4 presents a schematic diagram of the hydrologic modeling structure for the 1992 existing conditions with the Denver West ponds built into the model. More detail on the hydrologic modeling for the Upper Lena Gulch basin can be found the Phase A Report. I I I Input Specific input parameters used in modeling runoff from the basins include: basin area; length of the longest water course; length along the water course to the sub-bas in's centroid; weighted basin slope; percent impervious area; pervious and impervious interception losses; initial and final infiltration rates, and the infiltration rate decay exponent. Table I summarizes the input parameters to CUHPE/PC by sub-basin for future land use conditions Model 6 I I I