FLOOD06857 - Laserfiche WebLink

Home Browse Search

longer duration, Because of the steep stream slopes, the flood peaks travel down the valley with such rapidity that little time is available to warm or evacuate residents. A general description of the last four major floods occurring on Left-Hand Creek is provided to illustrate the flood potential, Heavy damages were not recorded for these floods since the flood plain was rural in nature, Flood of 2-6 June 1921. This storm produced general rains over the South Platte basin with the greatest amounts along the foothills. It covered an area of approximately 520 square miles and lasted 5 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. Flood of 3 September 1938, During this storm, showers were general over the Left- Hand Creek basin accompanied by isolated cloudbursts 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. This gaging station was not in operation during the 1949 and 1951 floods. Flood of 4 June 1949. On 4 June 1949, the Left Hand 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 Left Hand Creek caused minor damages to irrigation headworks, bridges, and fannlands. The gaging station near Boulder recorded a peak discharge of 1,140 cfs during the flood period. Flood of 3 August 1951. During the aftemoon 'and night of 3 August. a heavy rain stonn occurred over the frontal range and foothills east of the Continental Divide from the vicinity of Boulder to near Fort ColOns. Colorado, a distance of approximately 50 miles . One of the stann centers was in the Left-Hand Creek near the town of Niwot At this stonn center, total precipitation was unofllctally reported to have been over Inches. The runoff from this storm caused flooding on St Vrain Creek and on Irs tributaries, Dry Creek and Left-Hand Creek. OVerbank flows occurred along most of the length of Left-Hand Creek. Bridges, roads, crops, and irrigation structures were damaged. 4.9 BOULDER CREEK Flood Historv, Floods in the Boulder Creek basin are produced by intense rainfall during either isolated or general storm systems. In addition, there is nonnaily an increase in flows during the mountain snowmelt period in May and June which is frequently augmented by rainfall runoff. Large floods in the basin were reported in 1864, 1876, 1894, 1914, 1923, 1938, and 1969, Colorado Flood Hydrology Manual 4.13 fR'lFT