Date of Award

2018

Document Type

Open Access Thesis

Department

Geography

Sub-Department

College of Arts and Sciences

First Advisor

L. Allan James

Abstract

Anthropogeomorphic changes in response to destructive agricultural practices followed the arrival of European settlers into the Americas. The southeastern Piedmont physiographic region of the USA was severely affected by erosion and sedimentation following settlement in the 1700s and farming up through the 1930s. Deep floodplain aggradation formed uninterrupted alluvial deposits that extended many km. This research examines anthropogenic impacts of land-use change on valley bottom sedimentation in the Chicken Creek Watershed of South Carolina. Abrupt contacts between pre-settlement floodplain soils and a thick overburden of legacy sediment are common throughout the two-km study reach and provide clear evidence of extensive post-settlement sedimentation. Soil stratigraphic and sedimentologic evidence are presented to contrast pre-settlement and post-settlement sediment characteristics and thicknesses. LiDAR-based spatial analysis is used to examine patterns of legacy sediment delivery, deposition, and floodplain storage and the environments in which this occurred. Legacy sediment 2 to 4 m thick rests on top of exposed pre-settlement soils throughout the stream corridor, with the pre-/post-settlement contact ~1.5 m above the stream channel on average. Linear regression analysis shows that legacy sediment thickness is controlled by valley width and proximity to tributary sediment sources. Thin pre-settlement alluvium over bedrock suggests modest erosion and sedimentation rates prior to European arrival. Pre-settlement geomorphic stability is supported by the presence of a buried Ab soil epipedon on pre-colonial floodplain surfaces. Mean grain-sizes are similar between the pre- and post-settlement alluvium, but substantial contrasts in the degree of stratification and bulk density document differences between pre- and post-settlement sedimentation environments and post-depositional changes. Channel adjustments since the time of maximum aggradation include incision at least as low as the pre-settlement longitudinal profile and widening that is on-going.

Rights

© 2018, Tyler L. Dearman

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