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<br />'"' <br />,;. r\.... ~low in the Arkansas River upstream from Pueblo Reservoir is regulated <br />~by several major and minor off-stream reservoirs. At the Arkansas River at <br />Canon City (station 07096000), the average streamflow for 96 years (1888-1984) <br />was 725 ft'/s (Ugland and others, 1986). From 1975 to 1982, the annual aver- <br />age streamflow of the Arkansas River was 654 ft'/s at Canon City and 657 ft'/s <br />at Portland (station 07097000). During this period, about 80 percent of the <br />annual streamflow at Portland was estimated to be native flow, and about <br />20 percent was estimated to be transmountain flow. The streamflow-gaging <br />station at Portland is the farthest downstream streamflow-gaging station in <br />the upper Arkansas River basin and is approximately 10 mi upstream from Pueblo <br />Reservoir. From 1983 through 1985, the annual average streamflow was <br />1,280 ft'/s at Portland, indicating that almost twice as much water was <br />available for storage in Pueblo Reservoir during this period than from 1975 <br />to 1982. <br /> <br />During the 1985 water year (October 1984 to September 1985), the daily <br />mean streamflow at Portland ranged from 356 ft'/s during March to 7,010 ft'/s <br />during June, and the mean for the water year was 1,270 ft'/s. The summary of <br />minimum, mean, and maximum monthly streamflows (fig. 2) indicates that the <br />smallest monthly mean streamflows occurred during September, December, and <br />January. The largest monthly mean streamflows occurred during May, June, and <br />July. During these months, the average streamflow was 2,780 ft'/s due to <br />snowmelt runoff, transmountain diversions to the Arkansas River, and reservoir <br />releases in the upper basin. <br /> <br />DESCRIPTION OF PUEBLO RESERVOIR <br /> <br />Pueblo Reservoir is the farthest downstream eastern-slope storage <br />facility of the Fryingpan-Arkansas project, a multipurpose water development <br />authorized by Public Law 87-590. The chief purpose of the project is to <br />divert unappropriated water from the western slope of the Rocky Mountains for <br />use on the more populated and water-short eastern slope. Pueblo Reservoir <br />derives almost all of its contents from water entering through the Arkansas <br />River, which is comprised of native and transmountain flow. The reservoir is <br />formed by a concrete and earth-fill dam on the Arkansas River approximately <br />6 mi west of Pueblo. The climate at Pueblo Reservoir is characterized by <br />small annual precipitation with periodically intense thunderstorms, large <br />evaporation, moderate-to-high wind movement, low humidity, and a large daily <br />range in temperature (Phillip E. Flores Associates, Inc., 1975). <br /> <br />Pueblo Reservoir is a multipurpose facility which can be described <br />by its space allocation. The reservoir has a total storage capacity of <br />357,678 acre-ft; 30,355 acre-ft of dead and inactive capacity, which com- <br />prises the recreation pool; 234,347 acre-ft conservation pool, which is used <br />in regulating transmountain and native water for municipal, industrial, and <br />irrigation uses; 65,952 acre-ft joint-use pool, which must be vacated and <br />available for flood control from April 15 to November 1 each year; and <br />27,024 acre-ft of exclusive flood-control capacity. The top of the exclusive <br />flood-control pool is the crest of the spillway at an elevation of 4,898.7 ft. <br />The crest of the dam is 26 ft above the crest of the spillway and would tem- <br />porarily hold an additional 131,500 acre-ft of flood flows. <br /> <br />8 <br />