Spatio-temporal patterns of geomorphic adjustment in channelized tributary streams of the Lower Hatchie River Basin, West Tennessee.

摘要

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. In particular, this dissertation examines (1) the types and spatial pattern of geomorphic adjustment processes, (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 system-wide geomorphic response.; Results from this research suggest that spatial and temporal patterns of geomorphic adjustment depend upon reach-scale processes of sediment dynamics and flow deflection and may initiate system-wide response, such as lateral migration. Channel widening processes involving bank failure, bank erosion, and long-term sediment storage as channel bars and berms are the dominant adjustment processes. Bank erosion and sediment storage processes may be initiating bar-bend processes of lateral migration and offer field-based support for the involvement of bar-bend processes in the onset of lateral migration in straightened channels. Applicability of the Channel Evolution Model may be limited in tributary streams with multiple periods and or locations of channelization because of its emphasis on pinpointing the area of maximum disturbance, and the model lacks explicit incorporation of lateral migration processes and sediment dynamics. The dominance of reach-scale dynamics in the study tributaries questions the ability of numerical models developed on a watershed-based approach to be used in adjusting, tributary streams, demonstrates the need to understand reach-scale controls of system-wide response, and for better incorporation of sediment dynamics in conceptual and numerical models of geomorphic adjustment in fluvial systems.