Many of the standard conceptual models developed for alluvial rivers do not adequately describe bedrock channels, which have a greater threshold of erosional resistance and longer response time to a change in driving forces. Improved understanding of bedrock rivers is important because: portions of the drainage network formed on bedrock exert a disproportionately large control on drainage basin evolution, and effective construction, modification, and removal of dams requires knowledge of bedrock channel form and process. The proposed research will systematically investigate relations among bedrock substrate, channel geometry, movement of coarse sediment, and flow hydraulics along bedrock channel segments in order to test the existence of a consistent threshold discharge for substantial channel change among bedrock channel segments of differing substrate and geometry. Results from the research will provide insight into key questions of bedrock channel dynamics regardless of whether the data support the existence of a threshold discharge. Field work will be conducted along the Ocoee River of Tennessee and the Gauley River of West Virginia, each of which includes a bedrock canyon with downstream variations in rock type and channel geometry. Flow along each canyon segment is closely controlled by a dam upstream so that flow is reduced to a minimum and then released at higher discharges on a regular schedule. This will allow us to characterize channel geometry and substrate in detail during low flows, repeatedly measure hydraulic variables under various discharges, and relate hydraulic variables to substrate and to coarse sediment movement and deposition. Field measurements will include: channel geometry and coarse-sediment distribution; substrate in terms of joint geometry, rock-mass strength, lithology, and relative resistance to abrasion; and hydraulic variables (water-surface topography, mean velocity, degree of flow separation) at varying discharges.
