Petit Buëch River Dynamics and Bank Erosion

Abstract

This study investigates river morphology dynamics and bank erosion along the floodplain of the Buëch River in the Hautes-Alpes province of south-eastern France using multi-temporal images acquired from Unmanned Airborne Vehicles (UAVs) and LIDAR data. Images were captured in June 2014, 2015, 2022, and 2025, and processed using Structure from Motion algorithms to generate high-resolution OrthoMosaics and Digital Elevation Models (DEMs) with a pixel size of 5 cm. The accuracy of these UAV-derived products was assessed using Real Time Kinematic GPS (RTK-GPS) measurements, demonstrating centimeter-level precision in both positional and vertical dimensions. Analysis of the OrthoMosaics and DEMs revealed changes in river channel, including channel displacements and gravel bank movements, with the Buëch River exhibiting primarily braided properties but also sporadic meandering features. Bank erosion volumes were quantified by comparing DEMs from different years as well as calculating the average height difference between floodplain and river bank to estimate eroded volume, particularly in vegetated areas. Mapping of bank retreat was hindered in some instances by factors such as overhanging vegetation, water reflections, and shadows. The findings highlight the utility of time-series high-resolution UAV imagery for river monitoring, offering a flexible and straightforward approach for acquiring valuable data products suitable for land administration and river management. The high accuracy of UAVderived products in both spatial and vertical dimensions makes them suitable for informing management decisions and designing effective mitigation measures.