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<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 />4.1.9 LEFT HAND CREEK <br /> <br />Flood Historv, Left-Hand Creek floods are most frequently produced by intense rainfall <br />during thunderstorms, Snowmen runoff combined with runoff from spring rains of long <br />duration also produce high streamflows, The former are characterized by a high peak <br />discharge of short duration, The latter usually have lesser peak discharges and are of <br />longer duration, Because of the steep stream slopes, the flood peaks travel down the <br />valley wnh such rapidny 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 wnh 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 Longmont. This flood <br />was produced by a combination of rainfall and snowmen, Although this storm caused <br />overbank flooding. nenher 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 resun 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 />caused minor damages to irrigation headworks, bridges, and farmlands, The gaging <br />station near Boulder recorded a peak discharge of 1,140 cfs during the flood period. <br /> <br />. <br /> <br />Flood of 3 AUGust 1951. During the afternoon and night of 3 August, a heavy rain <br />stonn occurred over the frontal range and foothills east of the Continental Divide from the <br />vicinity of Boulder to near Fort Collins. Colorado. a distance of 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 inches, The runoff <br />from this storm caused flooding on St. Vrain Creek and on it's tributaries. Dr)! Creek and <br /> <br />Colorado Flood <br />Hydrology Manual. <br /> <br />4,13 <br /> <br />a:w=r <br />