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General flooding resuRed along the South Platte River. Flood of 1973, SnowmeR runoff from the lower mountain area ofthe-South Platte River basin began about the middle of April, Rainfall amounting to as much as 6 inches, which was the major causative factor of the flooding in the South Platte River basin, began on 5 May, Sharp increases in flow as a resuR of the rainfall runoff were recorded at all gaging stations along the South Platte River from Littleton to the Colorado-Nebraska State line, The rainfall runoff was augmented by mountain snowmeR runoff which was also increasing during this period. The resuR was general flooding throughout the South Platte River basin; flooding was characterized by high, sharp hydrograph peaks from the rainfall runoff followed by a slow recession because of the continuing mountain snowmeR runoff, Bankfull discharges were experienced along portions of the main stem of the South Platte River for most of the month of May and on into June, Major South Platte River tributary streams that experienced flooding or that contributed to flood flows on the South Platte River are Bear Creek, Cherry Creek downstream from the dam, Clear Creek, St. Vrain Creek, Big Thompson River, and Cache la Poudre River, 4.1.2 PLUM CREEK BASIN Flood Historv, The following accounts illustrate flood potential in the Plum Creek basin, Flood of Seotember 1933, On 10 September 1933, a cloudburst occurred over the South Platte Paver between Denver and the foothills, wnh the center over Plum Creek, Little Dry and Big Dry Creek basins, ARhough information on tributary flows is limited, it was estimated that the Plum Creek peak discharge below the confluence of the East and West Branches was about 30,000 cubic feet per second attenuating to about 5,500 cubic feet per second at the mouth, Flood of 16-17 June 1965, The flood of June 1965 is wnhout questions the most disastrous flood event in tenns of dollar damage that has ever occurred in the South Platte basin, The flood was the resuR of runoff from heavy intense rainfall occurring on the evening of 16 June, centered over the high plains area of the Plum Creek and Cherry Creek basins, Runoff from the Plum Creek area produced a major disaster not only the tributary nsett, but also along the South Platte River through Denver, beginning at the point where Plum Creek empties into the South Platte and extending downstream through Denver and on below through the rural area along the South Platte River, 4.1.3 LITTLE DRY CREEK BASINS Flood Historv. Descriptions of two floods occurring on Little Dry Creek in Arapahoe County are representative of the effects of severe storms in an area of extensive urban development. The September 1933 flood is an example of a severe storm extending over Colorado Flood Hydrology Manual 4.4 ffiI!FT