River systems respond to natural and human-induced disturbances by adjusting the shape and slope of their channels. In the case of channelization, a prevalent form of human-induced disturbance, changes in channel shape and slope occur when there is an increase in erosion in some parts of a watershed that occurs simultaneously with increased sedimentation in other parts of the same watershed. Adjustment processes occurring in channelized tributary streams of the Lower Hatchie River in west Tennessee are resulting in accelerated sedimentation in the Lower Hatchie River. Spatial patterns and rates of change for channel shape, channel slope, and erosion/sedimentation adjustments in river systems are not entirely understood. Existing studies do not focus on system-wide changes and often do not analyze changes in sediment behavior over time. This study aims to identify and explain spatial and temporal patterns of changes in channel shape, channel slope, and erosion/sedimentation in response to historic channelization in three sub-watersheds of the Lower Hatchie River by: (1) examining channel shape throughout each sub-watershed using standard surveying techniques, (2) measuring contemporary rates and locations of erosion and sedimentation throughout each sub-watershed to construct a budget of sediment inputs, outputs, and storage, (3) analyzing core samples of floodplain deposits to reconstruct historic erosion and deposition rates to compare with contemporary erosion and deposition rates, (4) using the data collected to develop a geographic information system to examine spatial variations in channel shape, locations of erosion and deposition, and to determine if the presence of artificial levees and/or dredging activity in some reaches affects adjustment process, and (5) comparing the spatial patterns identified using the geographic information system to spatial patterns predicted by existing models of channel shape, channel slope, and erosion/sedimentation adjustments to test the applicability of these models in channelized tributary streams.
The results of this dissertation research will address theoretical and applied questions of river system response to human disturbance. Existing studies concerning river system response to disturbance lack spatial and temporal detail. This study applies a more spatially and temporally comprehensive approach by examining changes in channel shape, channel slope, and sediment processes (historic and contemporary) on a stream reach basis for entire sub-watersheds. Results will help determine if current estimates for rates of river system recovery after disturbance are grossly underestimated and if physical processes integral to recovery after disturbance have been overlooked. The Lower Hatchie River is prized for its biological diversity and hardwood bottomland habitat. An understanding of adjustment processes and rates will aid restoration projects planned by national, state, and non-profit agencies for tributaries of the Lower Hatchie River, as well as restoration projects in other disturbed rivers. Consideration of adjustment processes in resource management decisions would result in greater success for restoration projects because the focus of such plans should no longer be the symptoms of change but the underlying processes and causes of change. As a Doctoral Dissertation Research Improvement Award, this award will also provide support to enable a promising student to establish a strong independent research career.
