Channel incision on the lower American River, California, from streamflow gage records

Abstract

Channel incision along the lower American River from 1905 to 1995 is investigated using channel cross-section plots and statistical analysis of stage-discharge data from two streamflow gages located at three sites. 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. At a critical flood risk location in Sacramento, flow stages lowered 2 m from 1924 to 1970. Channel incision was the result of channel recovery from aggradation due to hydraulic gold-mining sediment and was exacerbated by sediment storage behind dams. Prolonged erosion and transport of historical alluvium in this river suggest that G. K. Gilbert's symmetrical sediment wave model is inappropriate for the lower American River and may not adequately allow for the importance of sediment storage and remobilization in fluvial systems.