Modeling overland flow-driven erosion across a watershed DEM using the Landlab modeling framework.

Abstract:

Many traditional landscape evolution models assume steady-state hydrology when computing discharge, and generally route flow in a single direction, along the path of steepest descent. Previous work has demonstrated that, for larger watersheds or short-duration storms, hydrologic steady-state may not be achieved. In semiarid regions, often dominated by convective summertime storms, landscapes are likely heavily influenced by these short-duration but high-intensity periods of rainfall. To capture these geomorphically significant bursts of rain, a new overland flow method has been implemented in the Landlab modeling framework. This overland flow method routes a hydrograph across a landscape, and allows flow to travel in multiple directions out of a given grid node. This study compares traditional steady-state flow routing and incision methods to the new, hydrograph-driven overland flow and erosion model in Landlab. We propose that for short-duration, high-intensity precipitation events, steady-state, single-direction flow routing models will significantly overestimate discharge and erosion when compared with non-steady, multiple flow direction model solutions. To test this hypothesis, discharge and erosion are modeled using both steady-state and hydrograph methods. A stochastic storm generator is used to generate short-duration, high-intensity precipitation intervals, which drive modeled discharge and erosion across a watershed imported from a digital elevation model, highlighting Landlab’s robust raster-gridding library and watershed modeling capabilities. For each storm event in this analysis, peak discharge at the outlet, incision rate at the outlet, as well as total discharge and erosion depth are compared between methods. Additionally, these results are organized by storm duration and intensity to understand how erosion rates scale with precipitation between both flow routing methods. Results show that in many cases traditional steady-state methods overestimate discharge and incision by orders of magnitude when compared to the hydrograph method. This suggests that the choice of flow-routing method can significantly impact evolving topography, especially if extrapolated across centennial-to-millennial timescales.