KNICKPOINT MIGRATION AND LANDSCAPE EVOLUTION ON THE ROAN PLATEAU
As a first exercise, we use a stream power model to predict the locations of the knickpoints. This model reduces to one in which the recession rate of the waterfall is proportional to water discharge, and to rock susceptibility to erosion. We test variants in which a threshold power, and hence discharge, is allowed. We impose rapid incision of the Colorado River at a specified time to initiate knickpoint propagation. Models of the Parachute drainage (11 knickpoints) show the expected rapid initial propagation, which declines as tributary junctions are passed. The present locations of knickpoints can be reasonably predicted with a single rock susceptibility, with minimal erosional threshold. Tradeoff between rock susceptibility and timing of Colorado River incision makes the susceptibility constant ambiguous. To constrain independently the timing of initiation of incision, we are attempting to use the cosmogenic burial method to date a Colorado River terrace gravel deposit 200 meters above the Colorado River on Battlement Mesa, just south of the Plateau.