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<br />INTRODUCTION <br /> <br />1. Purpose <br />The purpose of this report is to present the <br />methodology, assumptions, and results of the hydrologic <br />analyses of Ralston and Leyden Creek drainage basins, located <br />in north central Colorado near Denver, Colorado. This <br />information is prepared for a joint Corps of Engineers <br />(CaE) /Urban Drainage and Flood Control District of Denver, <br />Colorado (UDFCD) feasibility study that will present a <br />mutually acceptable solution to flood problems along Ralston <br />and Leyden Creeks. <br />Objectives of the hydrological study are listed as <br />follows: <br />1) Determine discharge-frequency relationships for 10-, <br />50-, 100-, and 500-year events for future without-project <br />conditions without Leyden Dam in place. <br />2) Perform a dam-failure analysis on Leyden Dam. <br /> <br />2. Scope <br />The scope of this study is to provide feasibility level <br />detail for the hydrology of Ralston, Van Bibber, and Leyden <br />Creeks. This includes application of a hydrologic model for <br />those basins to derive the discharge-frequency relationships. <br /> <br />BACKGROUND INFORMATION <br /> <br />1. Basin Description <br />Ralston Creek drains a 91-square-mile area northwest of <br />Denver in Gilpin and Jefferson Counties. It emerges from the <br />Front Range of the Colorado Rocky Mountains and continues <br />eastward across the high plains, passing through the city of <br />Arvada to its confluence with Clear Creek near the <br />Adams-Jefferson County line. The creek has two major <br />tributaries, Van Bibber Creek to the south and Leyden Creek to <br />the north. <br /> <br />a. Dimensions <br />The Ralston Creek drainage basin, as shown in Figure 1, <br />is approximately 24 miles long and averages 4 miles in width. <br />Slightly more than one-half of the drainage area is located in <br />the mountains. Elevations in the mountainous area range from <br />10,000 to 5,900 feet mean sea level (m.s.l.) in the foothills. <br />The elevation at the mouth is 5,250 feet m.s.l. <br /> <br />b. Reservoirs <br />Three reservoirs and several small lakes exist in the <br />basins studied. Ralston Reservoir, owned by the Denver Water <br />Board, is located on Ralston Creek on the east edge of the <br /> <br />1 <br />