Channel Evolution During Drawdown of Iron Gate and Copco I Reservoirs, Klamath River, CA

This study used the world's largest dam removal on the Klamath River to investigate channel evolution in unconsolidated silt and clay sediment during reservoir drawdown. Timelapse imagery revealed retrogressing rotational slides and flowslides as key sources of sediment to the re‐emerging channels. The majority of bank failures, channel adjustments and peak turbidity occurred during drawdown. Sediment consolidation, saturation, and valley morphology were the primary factors governing erosion. Rotational slides were more common along shallow hillslopes and deep deposits of Copco I reservoir, while steep hillslopes and shallower deposits of Iron Gate reservoir promoted flowsliding behavior. Four pulse flow releases of annual recurrence interval did not create appreciable geomorphic change but did mobilize fine sediments and produce moderate turbidity peaks.