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<br />, <br /> <br />Boulder and South Boulder Creeks. The gaging station at Orodell recorded a peak <br />discharge of only 1,220 cubic feet per second. In Boulder, however, local inflow increased <br />the Boulder Creek peak to an estimated 3,000 cubic feet per second. The peak discharge <br />on South Boulder at Eldorado Springs was 1,690 cubic feet per second. Flooding below <br />the confluence of these two streams extended over large portions of the flood plain. <br /> <br />,. <br /> <br />4.1.9 LEFT HAND CREEK <br /> <br />Flood History. Left-Hand Creek floods are most frequently produced by intense rainfall <br />during thunderstorms. Snowmett runoff combined with runoff from spring rains of long <br />duration also produce high streamflows. The former arB characterized by a high peak <br />discharge of short duration. The latter usually have lesser pBak discharges and are of <br />longer duration. Because of the steep stream slopes, the flood peaks travel down the <br />valley with such rapidity that little time is available to warm or evacuate residents. A <br />general description of the last four major floods occurring on Left-Hand Creek is provided <br />to illustrate the flood potential. Heavy damages were not recorded for these floods since <br />the flood plain was rural in nature. <br /> <br />Flood of 2-6 June 1921. This storm produced general rains over the South Platte <br />basin with the greatest amounts along the foothills. It covered an area of approximately <br />520 square miles and lasted 5 days. The maximum recorded rainfall was 5.29 inches and <br />the greatest recorded rainfall intensity was 4.3 inches in six hours at Longmant. This flood <br />was produced by a combination of rainfall and snowmett. Although this storm caused <br />overbank flooding, neither discharges nor damages were recorded. <br /> <br />Flood of 3 Seotember 1938. During this storm, showers were general over the Left- <br />Hand Creek basin accompanied by isolated cloudbursts along the foothills and the lower <br />elevations. A maximum peak discharge of 812 cubic feet per second was recorded at the <br />U.S. Highway 287 gaging station near Longmont. This gaging station was not in operation <br />during the 1949 and 1951 floods. <br /> <br />Flood of 4 June 1949. On 4 June 1949, the Left Hand Creek had overbank flooding <br />as a resutt of heavy and prolonged rainfall during Late May and early June and the runoff <br />from an unusually heavy snow blanket. The prolonged high flow on Left Hand Creek <br />causBd minor damages to irrigation heaclwOrkS, bridges, and farmlands. The gaging <br />station near Boulder recorded a peak discharge 011,140 cis during the Ilood period. <br /> <br />~ <br /> <br />Flood 01 3 Auoust 1951. During the aftemoon and night of 3 August, a heavy rain <br />storm occurred over the lrontal range and foothills east of the Continental Divide from the <br />vicinity 01 Boulder to near Fort Collins, Colorado, a distance 01 approximately 50 miles. <br />One of the storm centers was in the Left-Hand Creek near the town of Niwot. At this storm <br />center, total precipitation was unofficially reported to have been over inchesc The runoff <br />from this storm caused flooding on St. Vrain Creek and on it's tributaries, Dry Creek and <br /> <br />. <br /> <br />Colorado Flood <br />Hydrology Manual <br /> <br />4.13 <br /> <br />CFIFr <br />