CHANNEL INCISION ON THE LOWER AMERICAN RIVER, CALIFORNIA, FROM STREAMFLOW GAUGE RECORDS

Channel incision along the lower American River from 1905 to 1995 is i nvestigated using channel cross-section plots and statistical analysis of stage-discharge data from two streamflow gages located at three si tes. Channel incision lowered thalweg elevations at rates of up to 8.2 cm yr(-1), and flow stages decreased at rates of up to 4.3 cm yr(-1) for periods lasting several decades. Al a critical flood risk location in Sacramento, flow stages lowered 2 m from 1924 to 1970. Channel inc ision was the result of channel recovery from aggradation due to hydra ulic gold-mining sediment and was exacerbated by sediment storage behi nd dams. Prolonged erosion and transport of historical alluvium in thi s river suggest that G. K. Gilbert's symmetrical sediment wave model i s inappropriate for the lower American River and may not adequately al low for the importance of sediment storage and remobilization in fluvi al systems.