Multi-Decadal River Corridor Morphological Change at Villerest, Loire, France: A LiDAR-Based DEM of Difference Analysis

Regulated river corridors downstream of large dams face competing geomorphic pressures: sediment starvation and channel incision (the hungry water effect) and episodic tributary-driven aggradation during floods. Quantifying their net balance over multi-decadal timescales is essential for flood risk assessment and sediment management. This study presents the first LiDAR-based DEM of Difference (DoD) analysis of the 21 km Loire river corridor downstream of the Villerest dam (constructed 1984, France), using co-registered DEMs from 2003 and 2022 (19-year monitoring period). A uniform minimum level of detection (minLoD) of 0.10 m was applied, consistent with airborne LiDAR vertical accuracy (±0.05–0.15 m RMSE). The corridor exhibited dominant aggradation: mean DoD = +0.172 m, net deposition volume = +300,841 m³, and mean annual vertical change rate ≈ 9.1 mm/yr. Despite sediment-starved conditions immediately downstream of the dam, net deposition dominates the corridor budget. Results are consistent with tributary sediment inputs mobilised during four major flood events (2003, 2008, 2016, 2021), though mechanistic attribution requires coupled hydrological–sediment-transport modelling. Localised erosion, restricted to 5.6% of the corridor area, reflects residual hungry water effects along channel margins. These findings provide the first quantitative morphological baseline for this regulated corridor and suggest a progressive reduction in floodplain storage capacity with implications for downstream flood risk in the Roanne agglomeration.