Modeling The Effects Of Bed Topography On Fluvial Erosion By Saltating Bed Load
Huda, Shahen A. 1 ; Small, Eric E. 2
1 University of Colorado at Boulder, Dept of Geological Sciences
2 University of Colorado at Boulder, Dept of Geological Sciences
Abrasion by bed load is a dominant erosional mechanism of fluvial incision into bedrock. The foremost saltation-abrasion model states that erosion rate is linearly dependent on the flux of impact kinetic energy in the vertical direction and on the fraction of the bed that is not covered by alluvium [Sklar and Dietrich, 2004]. Results from this model show that erosion is maximal in moderate flows with medium-sized grains. However, the saltation-abrasion model is only applicable to smooth, flat beds, which almost never appear in nature. Despite the fact that the floor of most bedrock channels are sloped and sculpted into rough topography, this model has been applied in numerous studies to model streams and landscapes. Here, the saltation-abrasion model is modfied for bed load transport over simple bed topography by accounting for kinetic energy flux normal to topography. Averaged over the entire domain, erosion rates can increase by orders of magnitude depending on grain size and flow strength. This erosion is focused on flow-facing slopes, and is corroborated by experimental and field observations. The amount of erosion enhancement is greater for smaller grains and stronger flows, even if the topography is small and low-angle. This is in direct opposition to the findings of Sklar and Dietrich [2004]. Therefore, bed topography should be considered when attempting to estimate erosion rates in bedrock channels.
Sklar, L. S., and W. E. Dietrich (2004), A mechanistic model for river incision into bedrock by saltating bed load, Water Resources Research, 40, W06301, doi:10.1029/2003WR002496.