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66 FLOODS IN COLORADO miles west of Franktown the Weather Bureau record showed only . 0,25 inehes. A slope-area measurement of Bayou Gulch was made at a favorable point 1 mile above the mouth in sec. 23, T. 7 S., R. 66 W" and a peak discharge of 8,670 second-feet obtained. This represents 456 second- feet per square mile from an area of 19 square miles. An attempt was made to make a slope-area measurement of Cherry Creek in sec. 4, T. 6 S., R. 66 W., at the. lower end of the. area of heavy precipita- tion, but conditions were so unfavorable that the computation of 17,000 second-feet discharge cannot be considered more than an esti- mate. Above this point the drainage area affected by the storm was .87 square miles, and the estimated unit runoff was 195 second-feet per square mile. N ear this point the creek started to rise at 4 p. m. and was at maximum stage from 4:30 to 5 p. m, By 8 p. m. it had fallen 3 feet, and by the next morning it could be forded easily. From these data the total discharge was estimated at about 4,000 acre-feet. At the point where Cherry Creek was measured, in sec. 4, T, 6 S., R. .66 W., a loeal resident stated that the flood of July 14, 1912, reached practically the same stage as that reached in 1922. But in 1912 the storm was closer to Denver, and therefore caused a peak flow at Denver estimated at 11 ,000 second-fcet, as contrasted with the peak flow of about 6,000 second-feet in 1922. The flood of August 2-3, 1933, the largest of reeord on Cherry . Creek, was caused by the failure of Castlewood Dam, about 35 miles upstream from Denver. The storm eausing this failure was confined to the 175 square miles of drainage area in the upper part of the basin :above the reservoir, at altitudes between 6,500 and 7,500 feet. Had it not been for the sudden release of about 2,500 aere-feet of water stored in the reservoir, the flood crest would sOOn have been reduced to a stage at whieh it would have caused little damage. No precipita- tion stations are maintained in Oherry Creek Basin above Castle. wood Dam, but local residents measured the precipitation at several points in improvised rain gages. R. I. Meeker, consulting engineer of Denver, visited this area shortly after the storm and obtained the information presented in the following table. , Precipitation in Cherry Creek BastOn, during nioht of Aug. ~-3. 1933 Location Preelpi. Method 01 measurement tn.t1on TIme (Inches), - 8eo.19. T. 9 S.. R. 6& W ____nhn . Ducket with vertical sIdes_.. 6 p. m. to 3 a. m. SEW sec. 19, T. 9 e., R. 85 w..~__ 3 .~~~J~~~~::::::::::::::::::: 9 to IOp.ID.; rain very heavy. Sec. 33. T. 9 S., R. 85 W~__....__. . 6 p. m. to 1 a. m.; rain hardMt Sees. land 2, T. 10 8.0..:-' 08 W U. .__..do.._.__.__.h.......____ from 9 to 10 p. m. 7 Bee. 4. T. 10 S., R. 66 ____Hu__ . ID-gallon milk can Jmeas. urement correot lor shape of can). T . MAJOR FLOODS-SOUTH PLATTE RIVER 67 Ivan E. Houk, an engineer in the Bureau of Reclamation, made an investigation of the failure of the dam. He found that the flood reached the reservoir about midnight, and within 45 minutes had raised the water level 11 feet, to a point 5 feet over the spillway and 1 foot over the top of the dam itself. The overflow washed out a large part of the dam, and the reservoir level dropped 18 feet within a few minutes. On this basis, the average inflow, disregarding spillway discharge, was computed as 30,000 second-feet, and the discharge over the spillway and the dam itself just before failure was computed as 5,000 second-feet." The inflow of about 35,000 second-feet represented a unit run-off of 210 second-feet per square mile from 167 square miles above the reservoir, or 350 second-feet from the 100 square miles chiefly affected by the storm. Assuming that the reservoir level dropped 18 feet in 15 ninutes, the computed rate of discharge at the dam was 126,000 second-feet duriug that period." With no inflow below the dam, the channel and valley storage reduced the peak discharge to 34,000 second-feet at Kenwood dam site, about 23 miles downstream, as shown by slope-area determina- tions made by the Office of the State Engineer. Between the Ken- wood dam site and the mouth in Denver, a distance of about 12 miles, the peak was further reduced to 15,000 second-feet, as deter'llined by the increased discharge of South Platte River at the gaging station just below the mouth of Cherry Creek. At this point the flood Wag of short duration, its peak la.sting only a few minutes. The sudden release of the stored water above Castlewood Dam resulted in a veri- table wall of water rushing down the valley of Cherry Creek, flooding the bottoms to an extent greater than during any other flood of which dcfinite information is available. By the time the flood reached Denver, the advaricing front had a height of about 8 feet. As the peak which reached Denver at 8 a. m. August 3 originated at Castle- wood Dam about 12:30 a. m., it traversed the intervening 35 miles at a rate of 4.6 miles per hour. Although this flood had a discharge con- siderably greater than the flood of 1912, the stage at the Denver tramway car house was only about 7 inches higher thnn in 1912, ac- cording to the Corps of Engineers, United States Army." This is due to the greater capacity of the channel. The total damage is esti- mated at $1,700,000, of which $960,000 represents damage above Kenwood Dam. Subsequent to the flood of 1933 the city constructed a detention reservoir 0{1 Cherry Creek 7 miles above Denver, designed to protect the city from a flood with a discharge of as much as 70,000 second-feet, J4 Western Construction N@ws and Highways BuDder, San Franclsco. S@pt. 1933. II Idem. " Cberry Crook and tributaries: 76th Cong., 1st sess., H. Doe. 426, p. 18, 1939.