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<br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br /> <br />SECTION II <br />BASIN DESCRIPTION <br /> <br />II-I <br /> <br />GENERAL BASIN DESCRIPTION <br />Ralston Creek, a tributary of Clear Creek in the South Platte River Basin, <br />has a drainage area of 91 square miles. The basin originates in Gilpin <br />County at an elevation of over 10,000 feet. The creek flows in an easterly <br />direction about 25 miles to its confluence with Clear Creek at an elevation <br />of 5,250 feet. The creek has two major tributaries, Van Bibber Creek to <br />the south and Leyden Creek to the north, Van Bi bber Creek ori gi nates in <br />the mountainous areas west of the hogback and flows in an easterly direc- <br />tion paralleling the mainstem of Ralston Creek. The westernmost part of <br />the drainage basin are characterized by rolling, grassy meadows, surrounded <br />by lodgepole pine forest, intermixed with lesser stands of spruce, fir and <br />aspen, Soils are typically moderately permeable with moderate water hold- <br />i ng capacity. <br /> <br />6,000 feet to 5,250 feet. Soil permeability is typically low and water <br />holding capacity high in this area. The mainstem of Ralston Creek crosses <br />three major irrigation ditches and numerous roads and streets. Development <br />in the upstream portions is mainly rural with urban residential downstream <br />in the City of Arvada. <br /> <br />The downstream area of the Ral ston Creek drainage basin, from Cl ear Creek <br />to the Ralston Creek confluence with Leyden Creek is highly developed with <br />residential and commercial/industrial areas. In many cases, specifically <br />upstream of Garrison Street, development has encroached into the floodplain <br />and constricted flow severely. During flood events damage to these proper- <br />ties would be extensive. <br /> <br />The more eastern portions of the basins west of the foothills contain rug- <br />ged mountain terrain with average ground slopes of about 50 percent. Soils <br />are shallow and permeable, but average water holding capacity is low. Most <br />of the soils are in Soil Conservation Service (SCS) hydrologic classifica- <br />tion C and D. The part of the basi n between the hogback and the foot of <br />the steep front range contains soils that have rapid permeability and high <br />water holding capacity. <br /> <br />LEYDEN CREEK <br />The Leyden Creek drainage basin begins at the foothi 11 s just south of Rocky <br />Flats and extends to the confluence with Ralston Creek. Elevations range <br />from 7,500 to 5,400 feet with upstream ground slopes averaging about 15 <br />percent. Soils, permeability and development of the Leyden Creek basin are <br />simil ar to those described earl ier for the Ral ston Creek basin east of the <br />hogback. The drainage basin is largly undeveloped with the exception of <br />development occurring at the extreme lower end. <br /> <br />RALSTON CREEK <br />Ralston Creek, downstream of the <br />from foothills to high plains, <br /> <br />hogback, is characterized by a transition <br />The elevations in the basin range from <br /> <br />The downstream port ion of Leyden Creek, just upstream of the Ral ston Creek <br />confl uence, is developed with res i denti al properties. Upstream of the <br />development, to Leyden Lake, the channel is small but clearly defined and <br />more closely maintains its natural state. There are areas where the chan- <br />nel is steep and velocities are high as well as areas where there are sub- <br />stantial channel meanders across an undisturbed floodplain. Leyden Lake is <br />the upstream limit of the study on Leyden Creek. Leyden Lake is currently <br />a water storage facil ity owned and operated by the Farmers Highl ine Canal <br />and Reservoir Company of which the City of Westminster is the largest <br />stockholder. The cities of Thornton, Arvada and Westminster along with <br />Adolph Coors jointly own the majority of the stock. <br /> <br />Three reservoirs exist on the <br />Ralston Reservoir owned by the <br />owned by the Ci ty of Arvad a, <br />Creek. <br /> <br />creeks studied. On Ralston Creek there is <br />Denver Water Department and Bl unn Reservoir <br />Leyden Lake is on the mai nstem of Leyden <br />