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-j, i . .;'c' n:_',~i i', 2.t;-S{; V\(;:~l ~~,;. /,' I. '". ,,,,-,\ Denver, COiOkJ0 GUll DRAFT SECTION III RIVER HYDROLOGY Drainage Basin The South Platte River drainage basin at Littleton includes approximately 4.850 square miles extending from the Continental Divide in the Rocky Mountain Range to the high plains and foothills of eastern Colorado as shown on Figure Ill-I. The characteristics and hydrologic impact of the mountainous region and the high plains and foothills region are quite different. The mountainous western portions of the basin produce heavy snowmelt runoff during late spring. On the other hand. the high plains and foothills portions of the basin are more susceptible to high runoff during summer thunderstorms. The metropolitan Denver area is heavily developed and outlying areas are sparsely developed. The mountainous areas are generally unsuited for dense developmen t and will probably remain sparsely developed. The foothill and high plains areas are more likely to develop but not to the extent of the existing metropolitan area. Existing development in the metropolitan area consists primarily of residential and commercial areas with minimal indus- trial regions. The river flow hydrology at the Columbine Valley river reach is strongly con trolled by Chatfield Reservoir. For that reason this analysis is pri- marily for the portion of the South Platte River approximatly two miles downstream from Chatfield Reservoir. The hydrology of the South Platte River is closely related to the uses of the river and its floodplain area. A review of the tabulation of uses shows that peak flood flows. reservoir releases. average flows. low flows. water rights. return flow from lawn irrigation and other non-point discharges. and sewage effluent are all hydrologic factors which affect the flow of the South Platte River. .