Year of Publication


Document Type



Arts and Sciences



First Advisor

Jonathan D. Phillips


The purpose of this study is to describe and explain tributary changes within the lower Trinity River basin, Texas, downstream of Livingston Dam. 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. 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 geomorphic indicators of change. Since closure, Lake Livingston has reduced sediment supply while minimally affecting the discharge regime. Channel scour is evident for about 60 km downstream. All the tributaries studied are located within this reach. Currently, there is no model that directly addresses the morphological response of a tributary streams confluence downstream of a dam. Therefore, the Confluence Effects Model is developed to predict the resulting geomorphological impacts within a tributary streams mouth with varying changes in trunk stream discharge and channel morphology. When applied to two confluences of the lower Trinity River, the Confluence Effects Model successfully predicts the resulting geomorphological changes. Within the lower Trinity River basin, the tributaries are reacting in a nonlinear and complex manner. Delayed or lagged responses are illustrated through sediment budgets for two tributaries which suggest a large amount of sediment is in storage within the tributary basins. Applying the unstable hydraulic geometry model, thirteen qualitatively different modes of adjustment with respect to increases, decreases or lack of change in width, depth, slope and roughness were observed within the tributary systems. The nonlinear and complex reactions of the tributary systems mask the effects of the impoundment beyond the confluences with the Trinity. The geomorphic characteristics of the tributaries are largely dominated by Holocene sea level change and the response to extreme events, such that dam effects become relatively localized. While this study considered a coastal plain fluvial system perturbed by human modifications, other earth surface systems may draw comparisons between emergent responses, response times and landscape sensitivity to a disturbance within a system.