Hillslope-derived blocks, erosion thresholds, and topographic scaling in mountain rivers

This is a poster presented on May 24th, 2017 at the Community Surface Dynamics Modeling System (CSDMS) annual meeting in Boulder, Colorado, USA. It presents a numerical modeling study exploring steady-state erosion rate-slope relationships in channels influenced by hillslope-derived blocks of rock. It uses the numerical model of Shobe et al (2016; Geophysical Research Letters).

Delivery of large blocks of rock from steepened hillslopes to incising river channels inhibits river incision and strongly influences the river longitudinal profile. We use a model of bedrock channel reach evolution to explore the implications of hillslope block delivery for erosion rate-slope scaling. We show that incorporating hillslope block delivery results in steeper channels at most erosion rates, but that blocks are ineffective at steepening channels with very high erosion rates because their residence time in the channel is too short. Our results indicate that the complex processes of block delivery, transport, degradation, and erosion inhibition may be parameterized in the simple shear stress/stream power framework with simple erosion-rate-dependent threshold rules. Finally, we investigate the effects of blocks on channel evolution for different scenarios of hydrologic variability, and compare and contrast our results with those of more common stochastic-threshold channel incision models. We show that hillslope-derived blocks have a different signature in erosion rate-slope space than the effects of constant erosion thresholds, and propose characteristic scaling that could be observed in the field to provide evidence for the influence of hillslope-channel coupling on landscape form.