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I I I I I I I I I I I I I I I I I I I SANDERSON GULCH FLOOD HAZARD AREA DELINEATION reported in this study, werep~epared by Gingery Associates, Inc., under contract with the Federal Insurance Administration. The hydraulic analyses for the remainder of the study reaches were completed under the Agreement with the Urban Drainage and Flood Control District. - PREFACE - Authorization This report was prepared for use by local officials in developing a program of floodplain management and for the general information of the public. The 100-year floodplain limits are shown on the topographic mapping (Sheets 4 -19) throughout the study reach. The corresponding water surface profiles (Sheets PI - P8 ), showing the elevations for the 100-year flood event, are also provided. A floodway defining the high hazard area during large flood events was prepared for the study reach of Sanderson Gulch in Denver. The floodway, based on a criterion of 18 inches of depth, is described in Table 5. This study was authorized by the Urban Drainage and Flood Control District as part of their continuing program to identify flood hazard areas along stream channels within their jurisdiction. The study was completed by Gingery Associates, Inc., Consulting Engineers, under an Agreement with the District dated October, 1978. The floodplain analyses were completed during January, February and March, 1979, and reflect channel conditions existing along Sande~son and North Sanderson Gulches at that time. Purpose and Scope This report was prepared to redefine the limits of the lOO-year floodplain in the Sanderson and North Sanderson Gulch basins following extensive channel improvements over the past several years. These channel improvements have been the direct result of Major Drainageway Planning by the Cities of Denver and Lakewood and the Urban Drainage and Flood Control District. - STUDY AREA DESCRIPTION - The Sanderson Gulch basin is a long, narrow drainage area sloping in an easterly direction from South Union Boulevard above Smith Reservoir toward the South Platte River (Figure 1). This basin was largely undeveloped prior to 1940. The upper basin was largely agricultural, as evid~ by numerous irrigation storage reservoirs, many of which still exist today. The study limits for Sanderson Gulch extend from the South Platte River confluence to Smith Reservoir. On North Sanderson Gulch, the limits are from the Sanderson Gulch confluence to Garrison Street (Sheet 1). The study area on Sanderson Gulch from the South Platte River to Sheridan Boulevard is within the City of Denver. Sanderson Gulch upstream of Sheridan Boulevard and the total length of North Sanderson Gulch are within the City of Lakewood. Sanderson Gulch is a tributary to the South Platte River with the confluence a short distance north of West Florida Avenue. The basin drainage area is approximately 7.6 square miles. North Sanderson Gulch is the only significant tributary drainage channel in the basin. It drains approximately 1.4 square miles. This floodplain analysis was completed in conjunction with the Flood Insurance Study for the City of Denver. The hydraulic analyses fo~ Sanderson Gulch within the City of Denver, as Development in the lower basin below Sheridan Boulevard generally occurred between 1940 and 1960. The downstream reach between the South Platte River and Mariposa Street is primarily a light industrial area. The remaining lower basin is mostly single family (1)