Using Time‐Lapse Lidar to Quantify River Bend Evolution on the Meandering Coastal Trinity River, Texas, USA

Abstract

AbstractTime‐lapse airborne lidar on the coastal Trinity River in Texas, USA, shows profound downstream variability in point bar growth and cut bank erosion resulting from a historically large flood that occurred in 2015. The difference map generated from two surveys covers 55 river bends and captures the transition from quasi‐uniform flow into backwater flow. In the upstream portion of the survey, reach‐averaged deposition is greater than erosion, with high local variability between the two due to the occurrence of bend cutoffs. Point bars shift laterally up to 3 times as much as cut bank retreat in this area. In the backwater zone, cut bank erosion consistently outpaces deposition on point bars and cut bank retreat exceeds the lateral shift of the point bar. Edge‐to‐edge channel width, measured from active scroll bar to outer bank, increases for all bends. This widening is often partially due to point bar widening and movement of the scroll bar away from the channel. The combination of net erosion and limited lateral movement of point bars within the backwater zone implies that during large sustained floods, bank pull instigates channel migration in this area. Farther upstream, net deposition and the high ratio of point bar to cut bank lateral motion imply bar push is more important. Patterns of deposition and erosion within a single bend suggest that channel migration was dominated by downstream bend translation with little bend deformation. Results from this study help to deepen the understanding of coastal river system morphodynamics by connecting changes in the geomorphology to changes in river bend kinematics, hydraulics, and sediment transport.