Date of Award

Fall 2023

Document Type

Open Access Thesis

Department

Civil and Environmental Engineering

First Advisor

Enrica Viparelli

Abstract

Downstream changes in river planform can be associated with changes in geologic controls and often signal changes in channel geometry, bed slope, or bed material grain size. While previous studies documented downstream trends in channel geometry and planform for a variety of rivers, there is a gap in the literature on spatial and temporal trends in channel geometry on the fluvial part of Coastal Plain rivers, i.e., the not-tidally influenced part. The literature highlights the existence of crevasse splays in natural levees that allow floodplain inundation below bankfull conditions as unique feature of channels and floodplains in the Coastal Plain. Although sub-bankfull inundation has been well documented, the relationship between channel morphology and sub-bankfull inundation has not been thoroughly investigated. This study presents a geomorphic analysis of the Congaree River, SC, an 80 km long fluvial Coastal Plain River beginning at the Fall Zone, with channel data spanning from 1880s to present. Congaree River channel morphology is described by using one historical hydrographic survey, aerial photos, LiDAR data and modern field surveys. The study reveals that despite a history of urbanization, logging, and damming in the watershed, there is no significant change in Congaree channel geometry and planform in time, but there are noticeable spatial changes in channel morphology. In particular, channel sinuosity and migration rate increase downstream, though bed slope remains nearly constant. The Congaree River channel experiences a downstream reduction in cross-sectional area and width, with mean channel depth remaining near constant. Natural levees are found along the entire study reach, though only certain reaches of the Congaree River floodplain experience sub-bankfull inundation. Field data collected over a 138 long time interval suggest that the reduction in channel area and width is associated with the streamwise reduction in channel flow caused by sub-bankfull inundation of the floodplain. This streamwise discharge reduction notwithstanding, mean bankfull depth is unaffected. Consequently, channel transport capacity per unit width of sediment as bedload and suspended load does not change downstream, though overall sediment transport capacity decreases because of the reduction in channel width.

Rights

© 2024, William Nicholas Logan

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