Characterizing Bank Erosion Style Along Two Bends of a Sand-Bedded Meandering River with Monthly Lidar Surveys

Earth's big rivers can erode their banks at a rate of several meters per year, modifying channel width and changing the planform shape of channel bends. The processes controlling when and how river banks erode are difficult to quantify because precise, repeat survey data of steep bank topography is hard to collect at the bend scale. To map bank erosion along two bends of the sand-bedded, 180 m wide Trinity River near Dayton, Texas, USA, we use lidar surveying equipment mounted on an uncrewed aerial vehicle (UAV). Here we will present monthly lidar topography data collected beginning in April 2022 and hourly photos of the channel banks taken with trail cameras. The surveyed bends have been mapped with airborne lidar in 2011, 2015, and 2018 and the river is instrumented with a USGS gage (08067000) 17 km downstream. We processed and differenced all available lidar datasets (airborne and UAV) to examine how the river bank topography has changed over time. From January 2018 to June 2022, we mapped between 0 and 18 m of lateral bank retreat along the two surveyed bends and computed an average erosion rate of 1.75 m/year, which is below the calculated long-term average erosion rate 4 m/year. The two point bars opposite the eroding outer banks of both bends show changes in surface elevation of up to ± 2 m, with both bars generally eroding on their upstream ends and aggrading on their downstream ends. We mapped minimal change in the channel banks between the April to July 2022 surveys, which captured notably dry months. However, we will also present results from continued surveys through fall 2022, which may yield measurable change. Lastly, we compared mapped erosion patterns with a curvature-based model for river bend migration. This high-resolution (in time and space) dataset of river bank evolution will help determine when distinct channel bank erosion processes dominate—e.g., landsliding versus progressive hydraulic abrasion from the river. This project also provides a set of time-lapse data documenting the evolution of channel bank geometry, which can be used to test existing models of alluvial channel bank erosion timing.