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<br />due chiefly to the very heavy rains on the north side of the river, Throughout the area <br />affected the ground was very hard and dry and had been grazed so closely that practically <br />no vegetation remained, These conditions were conducive to an extremely high <br />percentage of run-off, and it is believed that as much as two-thirds of the 6-inch rainfall <br />reported appeared immediately in streams. On the north side of the river the water was <br />reported to have 'flowed away in a perfect sheet, overspreading the whole country and <br />running into the river chiefly below the Amity Dam at Prowers, causing a very rapid rise'. <br />This run-off reached Holly sometime before midnight, October 19, and reached a stage <br />of 9.8 feet on the gage at Holly. The flood was prolonged by the arrival of flood waters <br />from Two Butte Creek and smaller tributaries from the south, and had only receded half <br />a foot the moming of October 20 when the second flood arrived. <br /> <br />The second part of the flood was caused chiefly by floodwaters from the Purgatoire <br />River. It reached a peak stage of 11 feet at Holly at noon, October 20, At 7 a.m. October <br />21 it had receded to 4.6 feet, and at 7 a,m. October 22 it was 3.0 feet. <br /> <br />The peak discharge at Amity Dam, half a mile north of Prowers, was estimated at <br />more than 100,000 cfs, and at Holly a slope-area measurement made by the Amity Land <br />Co. gave a discharge of 136,000 cfs. The discha,rge at Holly in 1908 was slightly greater <br />than during the flood of 1921. <br /> <br />Flood of 1921 - Above the mouth of the Purgatoire River no damaging flood <br />occurred after 1894 until 1921, when the general storm that covered the State June 2-5 <br />was concentrated in a series of cloudbursts between Canon City and Pueblo. These <br />covered two separate areas. The larger area, roughly elliptical, extended from the northern <br />boundary of Pueblo County to the top of the Wet Mountains near Beulah, a distance of 30 <br />miles, and from a point a short distance above the mouth of Rush Creek nearly to Pueblo. <br />a distance of 15 miles. The smaller area covered the south slope of the Pikes Peak uplift, <br />which forms the northern part of the mountain valley, and extended from a point above <br />Skaguay Reservoir to a point 3 or 4 miles south of the river, a distance of 25 miles, and <br />from Oil Creek to Beaver Creek, a distance of 11 miles. The two areas together comprise <br />550 square miles. <br /> <br />The progress of the storm down the valley caused the resulting floods on many <br />of the tributary streams to reach Pueblo at nearly the same time, bringing about there the <br />greatest flood of record. The Geological Survey made an investigation of this flood, and <br />published a detailed report. The peak discharge at Pueblo, as determined by slope-area <br />measurement, was found to be 103,000 cfs, and the total discharge of the main flood at <br />that point, less than 90,000 acre-feet. <br /> <br />After the flood of 1921 the Stale Legislature enacted the Conservancy District law, <br />which enabled various interests in the Arkansas Valley to organize the Pueblo <br />Conservancy District. This district constructed a detention reservoir 10 miles above <br />Pueblo, which was designed to reduce a discharge of 100,000 cfs. Channel changes in <br />Pueblo were designed to carry, without overflow, a flood discharge of 125,000 cfs and thus <br />to provide for a flood flow of 25,000 cfs originating below the reservoir, <br /> <br />Colorado Flood <br />Hydrology Manual <br /> <br />4.25 <br /> <br />fRtff <br />