Mechanisms of river incision into bedrock: Implications for Grand Canyon formation

Abstract: Bedrock erosion in a river channel is commonly proposed to be proportional to stream power, the rate of energy expenditure of a flow (stream power model). However, laboratory experiments have demonstrated a non-linear relationship between sediment supply, grain size, rock tensile strength, and bedrock erosion rate (saltating bed load model). By relating the stream power model to bedrock incision in the Grand Canyon, we determine that channel slope must have adjusted to accommodate changes in incision rate. By comparison, the saltating bed load model allows an additional degree of freedom for channel adjustment; the Colorado River may have changed bed rock exposure to accommodate changes to incision rate, sediment supply, or bed rock tensile strength. We discuss the implications of the saltating bed load model for bedrock incision and future changes to sediment supply in the Grand Canyon.