River incision or diversion in response to bedrock uplift

Contrary to the popular belief that stream power determines whether a river incises through or diverts around an evolving bedrock uplift, we propose t hat river sediment nux and tectonic uplift rate are the most influential va riables. We construct a simplified theoretical model of an equilibrium allu vial river system responding to local bedrock uplift by coupling a diffusio n model describing the alluvial river with a kinematic wave model describin g the incising bedrock river. The initial uplift reduces local river gradie nt, causing the river to deposit sediment in the accommodation space create d upstream. At the same time, the river incises into the uplifting bedrock, starting from a knickpoint at the downstream edge of the uplift. The sedim ent aggradation must keep pace with the uplift rate until the incision has propagated through to the upstream edge of the bedrock block; otherwise the river will divert to another course. We use geometric arguments to identif y sediment flux and uplift rate as the controlling variables of the system.