Evaluating Channel Migration of the Lower Guadalupe River: Seguin, TX to the San Antonio River Confluence

On Earth, rivers are found meandering across the landscape. To accommodate dynamic flow regimes and sediment loads, rivers are in constant adjustment within the channel and adjacent valley. Extreme floods as well as base flows alter the course of the river at different rates. Geomorphic characteristics control the extent of adjustment of a river over time. Numerous geomorphic and watershed characteristic variables influence the course of the river at different spatial and temporal scales. Each river is unique, and each reach of river is different from another, thus, the mechanisms driving, and the rates of changing the course of one river reach may not be the same for another. This study addresses the change and driving mechanisms on a 380 km reach of the Guadalupe River, from Seguin, TX to the confluence with the San Antonio River. The following questions are addressed: (1) at what rate does channel migration occur along the lower Guadalupe River, and (2) what are the driving mechanisms controlling channel migration? To determine the answers, a Geographic Information System (GIS) analysis was performed using data from 1960 to 2014. An analysis of the 380 km reach was performed as well as a sub-reach analysis of seven reaches. Statistical analysis was performed for the entire reach and the sub-reaches and shows that the channel is relatively stable. For the 380 km reach, lateral rates of migration range from 0.11 to 1.65 m/yr with a mean of 0.36 m/yr. To understand the drivers of lateral migration, sub-reach analysis concluded that presence of vegetation and high silt-clay soil composition relate to lower rates of migration. Each zone varied significantly from one another. The highest and lowest average rates of migration occur in adjacent zones, the Upper and Middle Deltas (UD, MD) and the Belmont Fault zone (BFZ) and Upper Coastal Plain (UCP). Several dams outside of and within the study reach influence the BFZ and UCP, whereas an active zone of subsidence in this area contributes to migration in the UD and MD