Modeling of knickpoint retreat on the Roan Plateau, western Colorado

Abstract

The Roan Plateau in western Colorado constitutes a natural experiment for studying landscape response to a drop in base level. Late Cenozoic incision of the upper Colorado River led to elevational isolation of the Plateau and initiation of a wave of incision into its southern edge. Knickpoints (oversteepened reaches that contain waterfalls 60–110 m in height) mark the upstream extent of this headward propagating wave. That this incision has occurred in a laterally extensive, well‐stratified, and essentially flat‐lying bedrock and in an area with relatively uniform climate, implies that it should serve as a good test of existing knickpoint propagation models. We predict the locations of knickpoints by using a stream power‐based celerity model, in which knickpoint recession rate is a power function of drainage area and is proportional to rock susceptibility to erosion. Models of the Parachute and Roan drainages (17 and 16 knickpoints, respectively) show expected rapid initial knickpoint propagation rates, which decline as drainage area decreases stepwise at tributary junctions. The modeled positions of knickpoints match well with observed features, using a single combination of parameters to model retreat in both drainage basins. We compare our celerity model results with past studies and explore how longitudinal profile analysis may be used to derive independently the exponent on drainage area in the celerity model.