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<br />2. EXECUTIVE SUMMARY <br /> <br />The following discussions summarize the principal findings <br />of this study. <br /> <br />2.1 Alluvial fan Ch~racteristics <br /> <br />1. Three types of depositional landforms. fans. washes, and <br /> <br /> <br />aprons. are often confused. Each has different flooding <br /> <br /> <br />characteristics. The focus of this study is on fans. <br /> <br />2. Alluvial fan morphologic, hydrologic, and hydraulic <br /> <br /> <br />characteristics vary widely between fans. Consequently. the <br /> <br /> <br />exte~, severity, and behavior of floods on. fans depends <br /> <br /> <br />heavily on individual characteristics. <br /> <br />3. Key watershed and Lan characteristics which influence <br />fan flood behavior are: <br /> <br />. watershed slope; <br />. watershed soil type and vegetation; <br />. forest fire frequency; <br />. rainfall intensity and duration; <br />. fan slope and topographic shape; <br />. existence of an entrenched channel; <br />. apex discharge (hydraulic) conditions; <br />. fan sediment type and vegetation; and <br />. the location, density, geometry of development <br />on the fan. <br /> <br />4. Development pressures are substantial on many <br /> <br /> <br />the western and southwestern parts of the U.S. <br /> <br /> <br />adjacent to urban centers are already experiencing <br /> <br />fans in <br />Fans <br />rapid <br /> <br />14 <br />