Document Type
Thesis
Abstract
I examine variations in channel width across variable rock resistance in rockbed channels in the upper James River basin, Virginia. Fluvial bedrock erosion is a primary geomorphic process driving landscape evolution, and a key component of landscape evolution models. However, relatively little empirical data is available on how and why channel geometry, particularly channel width, varies in rockbed channels. If a river is to maintain an equilibrium profile, erosion rates must be uniform, and therefore, unit stream power must vary in response to spatial variations in rock resistance and/or uplift rates. Variation in unit stream power is accommodated through changes in river discharge, width, and/or slope. In this study, I focus on how width varies in rockbed rivers crossing rocks of variable resistance, and the relative importance of slope and width in controlling unit stream power. At roughly 200 rockbed stream cross-sections in the upper James River basin, I have obtained channel width during the 100 year flood from FEMA Flood Insurance Study maps and channel slope from profiles constructed from USGS 7.5’ quadrangles. Combined with estimates of the 100 year flood discharge made using drainage area above each cross-section, we calculate unit stream power for each crosssection. Measured channel widths vary from 60 m to 200 m, and bedrock lithologies include sandstone, limestone, shale, and granite. Assuming erosion rates are similar in each cross-section, stream power may be used as a proxy for resistance, allowing us to examine the extent to which stream width varies as a function of bed rock resistance. We will also examine the relative importance of width and slope variations in determining unit stream power along stream reaches. Stream power varies by roughly a factor of six from the least resistant shale lithologies to the most resistant granite lithologies. The relative importance of changes in width and slope varies between lithologies. On shale, changes in width are more important for adjusting unit stream power than on the other lithologies. Over granite and sandstone, changes in slope are more important. I believe that the relative importance of changes in width and slope relates to the process by which the river erodes the bed.
Date Awarded
2004
Department
Geology
Advisor 1
Gregory S. Hancock
Recommended Citation
Craddock, William Howard, "How do Channel Width and Channel Slope Vary Across Differing Lithologies in Rock Bed Rivers?" (2004). Geology Senior Theses. William & Mary. Paper 129.
https://scholarworks.wm.edu/geologyseniors/129
