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<br />2.2 <br /> <br />, <br /> <br />2.3 <br /> <br />Boulder Creek was studied in detail while the tributaries <br />were studied through approximate methods. Although South <br />Boulder Creek does not actually flow inside the Boulder <br />corporate limits, flooding from the creek can occur within <br />the corporate limits. South Boulder Creek was, therefore, <br />studied by detailed methods. <br /> <br />Community Description <br /> <br />The City of Boulder, population 66,879, is located in <br />Boulder County in north central Colorado. A population <br />increase of 77 percent since 1960 indicates strong growth <br />pressures at Boulder and, in part, reflects the growth of <br />metropolitan Denver. Boulder is just upstream of the <br />confluence of Boulder and South Boulder Creeks. Boulder <br />Creek flows easterly through the center of the city, while <br />South Boulder Creek lies to the south and east. Boulder <br />is bounded on the west by the foothills of the Rocky <br />Mountains and on the north, east, and south by broad <br />plains. <br /> <br />Principal Flood Problems <br /> <br />Floods in the Boulder Creek basin are produced by intense <br />rainfall during thunderstorms. Typically, the floods <br />occur in the spring and early summer when snowmelt runoff <br />is highest. Usually, several days of moderate rainfall <br />combine with the snowmelt runoff to saturate the valleys <br />and fill the streams. Then, when an intense rainstorm <br />occurs, flooding is produced. However, intense rainstorms, <br />often referred to as cloud bursts, can by themselves pro- <br />duce flooding. <br /> <br />Large floods have been reported in the Boulder Creek <br />basin during the years of 1864, 1876, 1894, 1914, 1923, <br />1938 and 1969. The largest historic flood occurred in <br />1894. <br /> <br />2.4 Flood Protection Measures <br /> <br />Barker Dam and Reservoir, located on Boulder Creek near <br />Nederland, has no significant effect on flood peaks at <br />Boulder. Gross Dam and Reservoir, on South Boulder Creek <br />about 7.7 miles upstream from Eldorado Springs, would <br />have some effect on flood peaks that originate in the <br />upstream portion of the basin. <br /> <br />The City of Boulder has adopted flood plain regulations <br />for all water courses within the city based on approxi- <br />mate lOa-year flood outlines. <br /> <br />3 <br />