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<br />. <br /> <br />. <br /> <br />e <br /> <br />HYDROLOGIC ANALYSIS <br />FOR COAL CREEK AND OAK CREEK <br />IN THE VICINITY OF FLORENCE, <br />FREMONT COUNTY, COLORADO <br /> <br />PURPOSE OF STUDY <br /> <br />The purpose of this study is to determine peak discharges and frequency relationships for <br />Coal Creek and Oak Creek and their tributaries at various concentration points within the watersheds <br />as requested by the Colorado Water Conservation Board (CWCB). The values will be used to <br />determine flood-prone areas and to promote prudent flood plain management. This study was <br />prepared under authority of the U.S. Army, Corps of Engineers Flood Plain Management Services <br />(FPMS) program, Section 206 of the Flood Control Act of 1960 (PL86-645), as amended. <br /> <br />WATERSHED CHARACTERISTICS <br /> <br />The city of Florence is located in south-central Colorado in the eastern portion of Fremont <br />County approximately 38 miles southwest of Colorado Springs, Colorado. U.S. Highway 115 passes <br />east-west through Florence. The area has a semi-arid to arid continental climate. The large <br />variations in altitude create considerable variations in the average temperatures. The temperature <br />varies from a mean minimum of 200F in January to a mean maximum of 900F in July. The mean <br />annual precipitation for Florence measures 12 inches of which 8 inches fall between May and <br />September. In the mountains south of Florence, the mean annual precipitation is 20 inches. While <br />slopes are steeper in the upper drainage basins, the dense vegetation in these areas serves to reduce <br />rainfall runoff. The sparse vegetation of the foothills and pasture land at the lower elevations permits <br />a greater percentage of runoff. <br />Coal Creek originates in the upper portion of the San Isabel Forest and discharges into the <br />Arkansas River within the city of Florence. The Coal Creek watershed is elongated with an area of <br />approximately 18 square miles at the confluence with the Arkansas River, a length of 12.3 stream <br />miles, and a weighted slope of212 feet per mile. For the purpose of this study, the Coal Creek <br />watershed was divided into 10 subareas. Exhibit 1 shows the watershed boundary and subareas for <br />Coal Creek. <br />Oak Creek originates in the Wet Mountains in Colorado at elevations over 14,000 feet and <br />discharges into the Arkansas River within the city of Florence. The Oak Creek watershed is <br />extremely elongated with an area of approximately 72 square miles at the confluence with the <br />Arkansas River, a length of 30.3 stream miles, and a weighted slope of 119 feet per mile. For the <br />purpose of this study, the Oak Creek watershed was divided into 20 subareas. Exhibit 1 also shows <br />the watershed boundary and subareas for Oak Creek. <br />Economic activities of the area include cattle ranching, tourism, and some small-scale <br />mining, primarily for coal. A prominent tourist attraction is the Royal Gorge. The narrow gorge, <br />1,055 feet deep, is spanned by the world's highest bridge. In addition, the world's steepest incline <br />railway travels to the bottom of the gorge, and an aerial tram glides across this spectacular chasm. <br /> <br />1 <br />