Morphodynamics of Bedrock Rivers

Landscapes are shaped by the interaction of tectonics, climate, and rock erosion dynamics. Active incision in bedrock rivers sets the pace of landscape evolution because river incision cuts deep valleys and canyons into bedrock, transporting that material to the sea. This unburdens Earth's surface, allowing uplift of majestic mountain peaks in tectonically active settings. Bedrock-bound rivers, where the banks and bed are mostly bedrock, are hard points in the landscape that set the upstream base level of drainage basins and that must be vertically incised to lower landscape elevation and balance erosion against tectonic uplift. There are four distinct bedrock-bound channel morphologies that do not occur in alluvial channels—constriction-pool-widenings, rapids, overfalls, and waterfalls—each of which has a distinct flow structure. Our ability to predict bedrock-bound channel morphodynamics is nascent, but the discovery of mechanistic lateral bedrock erosion models, coupled with existing vertical incision models, allow prediction of bedrock river geometry and adjustments due to changes in water flux, sediment supply, and regional uplift. ▪ Coupled lateral and vertical erosion models reveal that the geometry of bedrock rivers is dominantly controlled by sediment supply, not discharge. ▪ Coupling observations of nonuniform flow structures and erosion models confirm that bedrock-bound channels are loci of intense erosion along a river's profile. ▪ Prediction of the 3D shape of bedrock-bound rivers is possible by combining models for flow, sediment transport, and bedrock erosion. ▪ Morphodynamic predictions are limited by poor understanding of nonuniform flow structures, flow resistance, and sediment transport in bedrock-bound channels.