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<br />. <br /> <br />. <br /> <br />. <br /> <br />STUDY AREA DESCRIPTION <br /> <br />Community Description <br />Gilpin County is located in central Colorado just on the east side of the Continental Divide and is <br />bordered by Boulder County on the north, Jefferson County on the east, Clear Creek County on the <br />south, and Grand County on the west. Central City is the County Seat of Gilpin County, and serves <br />as one of the two main tourist attractions for limited stakes gambling in the county. Central City is <br />approximately 30 miles southwest of Boulder and 30 miles west of Denver. The Gilpin County <br />population was 4,058 as estimated by the Department of Local Affairs in July 1997. Highway 119 <br />is the major highway that serves the county's population centers. The area studied for the FHBM is <br />the unincorporated areas of Gilpin County as of June 10, 1977. <br /> <br />Watershed Description <br />Gilpin County is situated at the headwaters of the South Platte River basin on the eastern slope of <br />the Continental Divide. North Clear Creek, South Boulder Creek, and Ralston Creek are the major <br />tributaries within the county. The headwaters of North Clear Creek and South Boulder Creek <br />originate at the Continental Divide with elevations in the range of 12,000 feet. Ralston Creek has <br />its headwaters at elevations as high as 10,000 feet north of Blackhawk, and joins Clear Creek in the <br />Denver area. The only recording USGS streamflow gaging station within the county was located on <br />South Boulder Creek at Rollinsville. <br /> <br />Mining between the mid. to late 1800's disturbed portions of the natural watersheds. Except for the <br />major stream courses and valleys, the terrain is generally steep and rugged. The basins are <br />vegetated with a typicallight.density subalpine covering consisting of Douglas fIr, lodgepole pine, <br />ponderosa pine, a sprinkling of aspens, and grasslbrush ground cover. <br /> <br />Floodinl! Problems and Floodinl! History <br />Floods in the subject watersheds normally occur during the months of May through August and are <br />caused by intense localized cloudbursts or thunderstorms. The combination of intense <br />thunderstorms and the steep, narrow topography results in floods having high peak discharges with <br />low volumes over short durations. There is typically a very short window of opportunity for flood <br />warning and evacuation once a major storms hits the area. Less damaging floods can also result <br />from rapid melting of mountain snowpack in the spring and early summer months, especially on the <br />larger drainageways. A combination of rainfall and snowmelt can sometimes prove to be the worst <br />flooding scenario for Colorado's mountain streams. <br /> <br />There is a well documented history of flooding on North Clear Creek and its tributaries in the <br />vicinity of Blackhawk and Central City. Floodwaters and debris flows have wreaked havoc on <br />citizens and infrastructure during intense thunderstorms. Documented floods have happened in <br />1864, 1881, 1883, 1898, 1910, 1942, 1975, and 1998. Other than the 1998 flooding, very little <br />technical information is available for the previous flood years. <br /> <br />Floods on Boulder Creek and Ralston Creek within the county are either minimal or undocumented <br />due to hydrologic characteristics and sparse population in those watersheds. <br />2 <br />