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<br />D <br /> <br />~ <br /> <br />Numerous factors affect the spatial and temporal response of a stream channel. These <br />factors enccmpass various aspects of geomorphology and fluid mechanics and include <br />fluid properties, sediment characteristics, discharge, sediment transport, channel <br />geometry, and fluid velocities. The behavior of these variables depends on the time scale <br />under ccnsideration: short term, long term, and very long (geologic) term. For example, <br />channel geometry can be ccnsidered relatively constant in the short term of a few weeks <br />but highly variable in the geologic time frame, <br /> <br />u <br /> <br />D <br /> <br />o <br /> <br />For most practical applications. engineers are interested in phenomena that take place in <br />the short and long term; thus, certain variables can be ccnsidered independent. For <br />instance, in the geologic time frame, valley slope is a function of geology and climate; <br />however, short- and long-term channel formation processes occur at a much faster rate, <br />and valley slope can be ccnsidered independent in many instances. For short and long <br />term analyses, it can be assumed that the discharge regime and sediment supply are the <br />driving variables that act on channel boundaries and vegetation to produce changes in <br />channel cross section, longitudinal profile, and alignment. <br /> <br />D <br /> <br />(J <br /> <br />o <br /> <br />m <br /> <br />m <br /> <br /> <br />r. <br /> <br />D <br /> <br />~ <br /> <br />m <br /> <br />o <br /> <br />Mobile home destroyed after bank collapse in Flamingo Wash during the July 8, 1999 ftood in <br />Las Vegas. Nevada, Photograph courtesy of Leslie Sakumoto. <br /> <br />D <br /> <br />D <br /> <br />m <br /> <br />6 <br /> <br />m <br /> <br />. <br />