TRIBUTARY REACTIONS TO THE DAMMING OF A COASTAL PLAIN RIVER IN SOUTHEASTERN TEXAS

Within southeastern Texas, an opportunistic geomorphic experiment arose when the Trinity River was impounded. The dam represents a marked moment and place of a system perturbation. Impoundments and dams influence downstream geomorphology and hydraulics by altering discharge and sediment dynamics. These downstream effects, by extension, influence water resources, riparian land use, and stream ecology, and through coupling processes effect tributaries to the impounded trunk stream. While the downstream impacts of dams have been discussed widely in the literature, little attention has been given toward the tributaries downstream of a dam. The purpose of this study is to describe and explain tributary changes within the lower Trinity River basin, Texas, downstream of Livingston Dam. While a dam will often influence both flow and sediment in a stream, the extent of the impact depends upon many factors. Within the Trinity system, flow has been minimally affected, while the sediment regime has been altered for nearly 60km below the impoundment. Geomorphological effects of the lower Trinity River tributaries were investigated through five different types of data: analysis of published discharge and sediment load data, examination of alluvium, planform change as measured from aerial photographs, resurveys of bridge cross-sections, and field mapping of indicators of geomorphic change. Results suggest that the dam may have minimal impact on the downstream tributaries. Overriding system factors may provide greater control on geomorphological changes in the lower Trinity system.