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<br />nature are selected herein to illustrate how the significant spatial <br />variation in width is related to river channel's adjustment toward uniform <br />power expenditure. This example will also show why the regime approach may <br />not be employed to simulate river channel changes. <br /> <br /> <br />Fig. 1 Streamwise variation in wiClth dunng stream channel adjustment <br />toward establishing straight water-surface profile, San Diego <br />River at Lakeside, California <br /> <br />Fig. 1 shows a short reach of the San Diego River at Lakeside, Califor- <br />nia on February 25, 1981 during the initial stage of a storm. The estimated <br />discharge of 600 cfs persisted for several subsequent days. Prior to the <br />storm, this sandy streambed was graded, due to sand mining, to a wavy <br />profile. ouring the initial period of flow, the water-surface profile was <br />not straight because its gradient was steeper over higher streambed areas <br />than over lower areas. Gradually, these higher streambed areas were scoured <br />while lower places filled. Small widths formed with streambed scour whereas <br />large widths developed with fill as shown in the figure. The width develop- <br />ment in this case was rapid in occurrence in the sandy material, its signi- <br />ficant streamwise variation is depicted by the natural streamlines visible <br />6 <br />