Regulation of the Feather River by Oroville Dam and reservoir in northeast California (beginning in 1967) changed the streamflow and sediment discharge downstream from the dam. Changes in channel geometry to adjust to the new regimen were still in process in 1975. Streamflow and sediment concentration and discharge had decreased. Median streamflow at Feather River near Gridley and Feather River at Yuba City, 27 miles and 49 miles downstream from the dam, had not changed, although the frequency of flow rates less than median increased and the frequency of flow rates greater than median, and which transport most sediment, decreased. Sediment-transport data indicate an increase in sediment yield from the 1965-67 period to the 1968-75 period in the basin downstream from Gridley to Yuba City , although the quantity of sediment transported was reduced owing to removal of sediment by Oroville Dam and to reduced streamflow. The increase in yield, assuming no change in tributary inflow, may be attributed partly to channel erosion accelerated by the clear-water releases and to the change in frequency and magnitude of flow rates.
