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<br />0"'1'/.'1 <br />u. ".. <br /> <br />CHAPTER IV--WATER RESOURCES EVALUATION <br /> <br />SURFACE WATER <br /> <br />Major streams in the vicinity of Coal Creek Basin are Boulder, South <br />Boulder, and Coal Creeks. Records of runoff for these streams began in <br />1887, 1888, and 1959, respectively. The average annual runoff of the <br />streams for the period October 1941 through September 1977 are: Boulder <br />Creek, 60,718 acre-feet; South Boulder Creek, 49,651 acre-feet; and Coal <br />Creek, 3,069 acre-feet. Monthly distribution of runoff for these <br />streams is shown in figure 1. The critical low runoff occurred in <br />1954-1956. Previous studies identified 1954 as the most critical runoff <br />year of record. <br /> <br />Runoff is primarily from snowmelt, and approximately 65 to 75 percent of <br />the annual runoff occurs in May, June, and July. Coal Creek runoff <br />peaks in May because of its lower elevation. Boulder Creek is regulated <br />primarily by Barker Reservoi r, South Boul der Creek by Gross Reservoi r, <br />and Coal Creek is unregulated. Water is imported to South Boulder Creek <br />from the Colorado River Basin through the Moffat Tunnel and delivered to <br />the city of Denver. These creeks are subject to irrigation diversions <br />and, consequently, may be severely or completely depleted in their lower <br />reaches during the late summer. <br /> <br />Recorded discharges for Boulder Creek ranged from 2,500 ft3/s in June <br />1921 to 1 ft3/s during January and February 1933. South Boulder Creek <br />experienced no flow in October 1932, and has freQuently been near zero <br />during winter periods. The maximum discharge of 7,390 ft3/s for South <br />Boul der Creek was recorded in September 1938. The maximum recorded <br />discharge for Coal Creek was 2,060 ft3/s in May 1969, and in most <br />years the creek experiences many days of no flow. <br /> <br />Major floods on Coal Creek occurred in 1876, 1891, 1921, and 1938, and <br />minor floods occurred in 1935, 1949, and 1969. Major floods on Boulder <br />Creek were reported in 1864, 1876, 1894, 1914, 1923, 1938, and 1969. <br />The largest historic flood on Boulder Creek occurred in 1894 and peaked <br />at about 11,000 ft3/s. The only major flood reported OF] South Boulder <br />Creek occurred in 1938, with a peak discharge of 7,390 ft3/s. <br /> <br />The quality of water from Coal, South Boulder, and Boulder Creeks is <br />generally suitable for municipal and industrial use, although concentra- <br />ti ons of iron and manganese exceedi ng Envi ronmental Protecti on Agency <br />(EPA) secondary drinking water standards have been measured in Coal <br />Creek.' Broomfield and Westminster obtain a portion of their water <br />supply from Coal Creek, and the city of Boulder uses Boulder Creek <br />runoff for much of its needs. Lafayette, Louisville, and Erie presently <br />use South Boulder Creek as the sole source of their water supply. <br /> <br />25 <br />