Date of Award
Doctor of Philosophy
Carol P. Harden
The processes involved in fluvial geomorphic adjustment to human-induced change are not well understood, despite an increasing and global prevalence of human disturbance to rivers. This doctoral dissertation research examines spatial and temporal patterns of geomorphic adjustment processes in three tributary streams of the Lower Hatchie River Basin, in west Tennessee, which are adjusting to historic land clearance and channelization. This dissertation examines (1) the types and spatial pattern of geomorphic adjustment processes in a total of 34 tributary reaches located in Richland, Jeffers, and Dry Creeks, (2) the applicability of an existing model of geomorphic adjustment for use in tributary streams with multiple episodes of disturbance, (3) sediment dynamics at the reach scale, including floodplain and channel re-coupling, and (4) the connections between reach-scale processes of sediment dynamics and systemwide geomorphic response. Results from this dissertation research suggest that after an initial period of down cutting, channel widening involving bank failure and bank undercutting are the dominant adjustment mechanisms, and create asymmetrically-shaped channels. Bank failures in the study tributaries are common and are produced by progressive bank undercutting related to redirection of flow towards banks by well-developed bars and berms deposited in the channel. The lifetime of channel bars and berms appears to be long, enduring beyond seven months of monitoring. The common occurrence of asymmetric channels and well-developed bar and berm deposits throughout each of the three study tributaries lends field-based support for the operation of bar-bend processes of lateral migration. These results highlight the important role of lateral adjustment processes postchannelization and sediment storage in determining the location of geomorphic processes and potentially initiating system-wide lateral migration. Applicability of the Channel Evolution Model may be liInited in tributary streams with mUltiple periods and/or locations ofchannelization because it focuses on the area of maximum disturbance, and it lacks explicit incorporation of lateral migration processes and sediment dynamics. Field-based sediment monitoring and simulation of sediment connectivity using channel morphometrics and Multi-Response Permutation Procedure suggest that sediment dynamics remain in a state of adjustment, lacking suitable long-term storage of sediment due to floodplain/channel de-coupling and irregular sediment transport. Analysis of a core taken from one re-coupled floodplain in Richland Creek suggests that re-coupling is possible but, in this instance, required more than 50 years to occur. This indicates that sediment will continue to be stored in the channel well into the future, potentially prolonging channel widening and lateral migration processes. Finally, results from this research suggest that spatial and temporal patterns of geomorphic adjustment depend upon reach-scale processes of sediment dynamics and flow deflection. The dominance of reach-scale dynamics in the tributaries calls into question the applicability of numerical models developed on a watershed-based approach and demonstrates the need to understand reach-scale controls ofsystem-wide response in fluvial systems.
Boulton, Mary A., "Spatio-Temporal Patterns of Geomorphic Adjustment in Channelized Tributary Streams of the Lower Hatchie River Basin, West Tennessee. " PhD diss., University of Tennessee, 2005.