Satomi Yamaguchi
Jonathan M. Nelson
Takuya Inoue
2017
<p><span>Previous work has shown that the bedrock erosion rate </span><i>E</i><span> because of collisions of saltating bedload can be expressed by </span><i>E</i><span> = </span><i>βq</i><sub><i>b</i></sub><span>(1-</span><i>P</i><sub><i>c</i></sub><span>), where </span><i>q</i><sub><i>b</i></sub><span> is the sediment transport rate, </span><i>P</i><sub><i>c</i></sub><span> is the extent of alluvial cover, and </span><i>β</i><span> is the abrasion coefficient. However, the dependence of the abrasion coefficient on the physical characteristics of the bedrock material is poorly known, and in particular, the effects of wet-dry weathering on the saltation-abrasion bedrock incision has not been specifically characterized. Observation suggests that the typical wet-dry cycling of exposed bedrock in river beds gives rise to cracks and voids that are likely to alter the incision rate of the material when subjected to impacts of moving sediment. In this study, flume experiments are performed to develop an understanding of how wet-dry cycling affects the rock tensile strength and the bedrock erosion rate. To represent the physical effects of weathering, boring cores taken from natural bedrock channel are exposed to artificial wet-dry cycles. The experimental results suggest the following: (1) the abrasion coefficient for fresh bedrock is estimated by </span><i>β</i><span> = 1.0 × 10</span><sup>− 4</sup><i>σ</i><sub><i>T</i></sub><sup>− 2</sup><span>(</span><i>d</i><span>/</span><i>k</i><sub><i>sb</i></sub><span>)</span><sup>0.5</sup><span>, where </span><i>σ</i><sub><i>T</i></sub><span> is the tensile strength, </span><i>d</i><span> is the diameter of colliding gravel, and </span><i>k</i><sub>sb</sub><span> is the hydraulic roughness height of bedrock; (2) the tensile strength of the bedrock decreases exponentially as a result of repeated wet-dry cycles, </span><i>σ</i><sub><i>T</i></sub><i>/σ</i><sub><i>T</i>0</sub><span> = exp (-</span><i>C</i><sub><i>T</i></sub><i>NW</i><sub><i>a</i>0</sub><span>/σ</span><sub><i>T</i>0</sub><span>), where </span><i>σ</i><sub><i>T</i>0</sub><span> is the initial tensile strength, </span><i>W</i><sub><i>a</i>0</sub><span> is the initial normalized rate of water absorption., </span><i>N</i><span> is the number of wet-dry cycles, and </span><i>C</i><sub><i>T</i></sub><span> is a constant; (3) the erosion rate of fresh bedrock depends on the inverse of the square of tensile strength, but the erosion rate of weathered bedrock depends on the − 1.5 power of tensile strength.</span></p>
application/pdf
10.1016/j.geomorph.2017.02.018
en
Elsevier
The effect of wet-dry weathering on the rate of bedrock river channel erosion by saltating gravel
article