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<br />development. Hence, <br />flood damages on fans <br /> <br />the potential <br />is high. <br /> <br />for significant future <br /> <br />5. A recommended approach to identification of key fan <br />characteristics is suggested: <br /> <br />. perform a field survey; <br />. develop detailed topographic mapping; <br />. obtain geologic and flood histories of the fan; <br />and <br />classify the fan <br />characteristics. <br /> <br />. <br /> <br />according <br /> <br />to the <br /> <br />key <br /> <br />2.2 Flood Dynamics <br /> <br />,. 'All watercourses on fans are ephemeral. with severe <br />flash floods occurring spo.ddicalll'. Channel patterns and <br />inundation zones often chonge with each flood. Sediment <br />erosion and deposition, occur rapidly during floods and <br />quickly alter channel geometries. <br /> <br />2. Three hydraulic zones can be identified on many fans: <br /> <br />. channelized zone, near the apex, where a single <br /> <br /> <br />definable channel exists; <br /> <br /> <br />. braided zone, a transition area where the <br /> <br /> <br />channel becomes unstable and multiple sinuous <br /> <br /> <br />flow paths form; and <br /> <br /> <br />. sheet flow zone, where the flow spreads <br /> <br /> <br />laterally and is very shallow. <br /> <br />3. Two time scales are of importance in fan flood dynamics: <br /> <br />. <br /> <br />geologic time (millenia), <br />paths wander across a fan <br /> <br />during which the flow <br />and the fan aggrades <br /> <br />15 <br /> <br />