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I I I I I I I I I I I I I I I I I I I HISTORY OF FLOODING 4 June 1949 - On 4 June 1949, Lefthand Creek had overbank flooding as a result of heavy and prolonged rainfall during late May and early June and the runoff from an unusually heavy snow blanket. The prolonged high flow on Lefthand Creek caused minor damages to irrigation headworks, bridges, and farmlands. The gaging station near Boulder, Colorado recorded a peak discharge of 1,140 cubic feet per second during the flood period. Scattered data from unofficial sources and limited records indicate significant flooding occurred in 1864, 1876, 1894, 1921, 1938, 1949, 1951, 1969, and 1973 (Reference 1). The following are descriptions of some these floods. A detailed flood history of the county, prepared by Boulder County, will be published in the near future. That publication will contain more detailed information than given here. 3 August 1951 - During the afternoon and night of 3 August, a heavy rainstorm occurred over the front range and foothills east of the Continental Divide from the vicinity of Boulder to near Fort Collins, Colorado, a distance of approximately 50 miles. One of the storm centers was in the Lefthand Creek basin near the town of Niwot,' Colorado. At this storm center, total precipitaton was unofficially reported to have 2 - 6 June 1921 - This storm produced general rains over the South PI atte Ri ver bas i n with the greatest amounts a long the foothi 11 s. The storm covered an area of approx imate ly 520 square mil es and 1 asted fi ve days. The maximum recorded rainfall was 5.29 inches and the greatest recorded rainfall intensity was 4.3 inches in six hours at Longmont. This flood was produced by a combination of rainfall and snowmelt. Although this storm caused overbank flooding, neither discharges nor damages were recorded. been over 6 inches. The runoff from this storm caused flooding on St. Vrain Creek and on its tributaries, Dry Creek and Lefthand Creek. Overbank flows occurred along most of the length of Lefthand Creek. Bridges, roads, crops, and irrigation structures were damaged. 3 September 1938 - During this storm, showers were general over the Lefthand Creek basin accompanied by isolated cloud bursts along the foothills and the lower elevations. A maximum peak discharge of 812 cubic feet per second was recorded at the U.S. Highway 287 gaging station near Longmont, Colorado. This gaging station was not in operation during the 1949 and 1951 floods. 4 - 8 May 1969 - Heavy rainfall with a relatively long duration occurred from 4 May unt il 8 May. The storm covered an area along and near the eastern slopes of the Rocky Mountains and extended into portions of the high plains. The heaviest amounts were centered 25 miles southwest of Denver and extended in a bank along the foothills of the Rocky Mountains northward to Estes Park. Rainfall amounts to 7.60 inches were reported at Boulder, Colorado. 4