Quantifying Gully Erosion Dynamics in Southern France: A Remote Sensing Approach
Summary
Gully erosion is a major driver of landscape evolution in semi-arid regions, which impacts land use and environmental stability (Vanmaercke et al., 2021). They create deep channels in the landscape and significantly impact soil fertility, water quality, and infrastructure. Driven by factors such as intensive rainfall and poor land management, it accelerates soil loss and increases sediment runoff, adversely affecting ecosystems and communities (Castillo & Gómez, 2016; Mashi et al., 2015; Poesen et al., 2003) Research into gully erosion is vital to predict the impacts of climate change and land use on erosion risks and to develop effective mitigation strategies. This study quantified erosion rates and volume changes in the Agaras gully system, located in the Lodève Basin, southern France.
The literature provided key insights into the successive morphological stages of the Lodève Basin, which served as a basis for estimating erosion rates. During Stage 2, periglacial processes shaped concave footslopes and terraces, while glacial cycles were dominated by mass-wasting and sedimentation (Bonnet et al., 2001). Gully erosion is estimated to begin in the post-glacial phase of the Würm period, approximately 15,075 years before present (calculated from 1950), driven by increased runoff and a shift to wetter climatic conditions. This destabilized the previously stable Stage 2 landscape, triggering significant gully incision. Stage 3 was characterized by intense fluvial erosion, which carved deep valleys and gullies, creating the highly incised badland terrain visible today.
Using high-resolution drone imagery and LiDAR data, a pre-incision landscape was reconstructed through spline interpolation to represent the Stage 2 landscape and compare it with the present-day Stage 3 terrain. This allowed for precise volumetric calculations. French open-source LiDAR data and DEM analyses proved highly reliable for reconstructing historical footslopes and determining erosion rates.
The estimated erosion volume for the Agaras gully system totaled 1.3 × 107 m3, with an average annual erosion rate of 858 m³/year over the past 15.146 years. To put this into perspective, this rate is equivalent to filling an Olympic-sized swimming pool approximately once every three years. These results highlight the scale of sediment displacement and provide valuable insights into the long-term geomorphological processes shaping the region. By comparing these results with neighboring systems, regional erosion trends and driving factors were analyzed. The findings integrate geomorphological, geological, and climatic contexts, providing a comprehensive understanding of gully dynamics and their broader implications for land management and geomorphological processes. This multidisciplinary approach highlights the value of remote sensing and advanced analytical methods in erosion studies.