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<br />24 <br /> <br />,... <br />W' <br />"'l <br />C)I <br /> <br />targeted as primary agents of erosion in previous studies, the entire <br /> <br />channel system is actively expanding and downcutting in the area. <br /> <br />Consequently, efforts to reduce natural levels of erosion must be <br /> <br />directed towards the overall channel network as opposed to only rills <br /> <br />and tributary basins. <br /> <br />Twenty-three of the three largest channel types cross the High- <br /> <br />line Canal or intersect at close proximity to it. Of them, three are <br /> <br />upland channels, 13 are cliff channels, and seven are piedmont channels. <br /> <br />Where they cross the piedmont, the upland channels have the lowest <br /> <br />gradient and the piedmont channels have the highest gradient. <br /> <br />Due to their large size, the first three channel types were ex- <br /> <br />amined with the aid of topographic maps and aerial photographs, and <br /> <br />only general characteristics were observed. The characteristics include <br /> <br />the ,channel gradients and the analogies to rill development mentioned <br /> <br />above. The main channels and several major tributaries were measured <br /> <br />in eight tributary basins (Fig. 5.2) for the purpose of identifying <br /> <br />inter- and intrabasin channel relationships. <br /> <br />Of the measured basins, Basin T is a tributary of an upland <br /> <br />channel (West Salt Creek), Basins N, P, and Q drain into a piedmont <br /> <br /> <br />tributary of a cliff channel (Leach Creek), and Basins A, R, S, and <br /> <br />U are tributaries to piedmont channels (Fig. 3.1). As expected, the <br /> <br />tributary-basin channels have greater gradients than the channels <br /> <br />into which they drain. Consequently, where channels start on or flow <br /> <br />over the piedmont, average channel gradients increase from Type 1 <br /> <br />upland channels, to Type 6 rills. <br /> <br />The flow in nearly all channels in the area is ephemeral, flowing <br /> <br />in response to high intensity summer thunderstorms. The only <br />