Date of Award

Spring 1-1-2013

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Geological Sciences

First Advisor

Eric Small Tilton

Second Advisor

Robert S. Anderson

Third Advisor

Gregory E. Tucker

Abstract

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 greatest 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 floors of most bedrock channels are sloped and sculpted into rough topography, this model has been applied in numerous studies to model evolution of streams and landscapes. Here, the saltation-abrasion model is modified 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.

Share

COinS