T36 Over the Hills and through the River: The Mechanisms of Change in Bedrock River Influenced/Controlled Landscapes

Sunday, 9 October 2022
1:30 PM - 5:30 PM
406

LATERAL EROSION OF BEDROCK CHANNEL BANKS BY BEDLOAD AND SUSPENDED LOAD

Paper number: T36-3
Program: Technical Sessions
Time: 1:55 PM – 2:10 PM

Authors

Abstract

Those who have seen the turbid and turbulent flow of a flooding mountain river know that bedrock rivers transport vast quantities of fine sediment in suspension. Could these tiny but energetic particles be responsible for eroding bedrock river banks and thus govern the width of actively incising channels? Surprisingly, this question has not yet been investigated mechanistically. Here we developed a mechanistic model for erosion of bedrock channel banks by impacting bedload and suspended load particles that are advected laterally by turbulent eddies (advection-abrasion model). The model predicts high lateral erosion rates near the bed, with rates decreasing up to water surface. The model also predicts greater erosion within the suspended load layer than the bedload layer for the majority of sediment supply and transport conditions explored. We compared the advection-abrasion model with a previously derived model for lateral erosion of bedrock banks by bedload particles deflected by stationary bed alluvium (deflection-abrasion model). Erosion rates predicted by the deflection-abrasion model are lower, except within limited conditions where sediment is transported near the threshold of motion and the bed is near fully covered in sediment. Both processes occur in bedrock rivers at the same time, so we combined the advection-abrasion and deflection-abrasion models and found that the lateral erosion rate generally increases with increasing transport stage and relative sediment supply for a given grain size. Application of our combined-abrasion model to a natural bedrock river with a wide distribution of discharge and supply events, and mixed grain sizes, indicates that finer sediment dominates the lateral erosion on channel banks in low sediment supply environments and can be as important as coarser sediment in high sediment supply environments.

Geological Society of America Abstracts with Programs. Vol. 54, No. 6

doi: 10.1130/abs/2022AM-377736

© Copyright 2022 The Geological Society of America (GSA), all rights reserved. Permission is hereby granted to the author(s) of this abstract to reproduce and distribute it freely, for noncommercial purposes. Permission is hereby granted to any individual scientist to download a single copy of this electronic file and reproduce up to 20 paper copies for noncommercial purposes advancing science and education, including classroom use, providing all reproductions include the complete content shown here, including the author information. All other forms of reproduction and/or transmittal are prohibited without written permission from GSA Copyright Permissions.