Twenty-five years of hydromorphological restoration in the high-energy, gravel-bed rivers of southern France: What are the current benefits for bedload dynamics and sediment balance in the left-bank tributaries of the Aude River within the Minervois region?

Abstract

The article synthesizes 25 years of hydromorphological restoration in the high-energy, gravel-bed rivers of southern France. In the Minervois region, the authors highlight the challenges and advancements made in riverbed restoration following the catastrophic flood of November 1999. This event catalyzed research in fluvial geomorphology and led to significant restoration initiatives implemented by the SMMAR. The article pays particular attention to the role of floods and ordinary flow events in the hydromorphological functioning of the channels, specifically focusing on hydraulic geometry, channel pattern, bedload transport, and sediment balance. The methods developed rely on field observations and measurements, as well as image processing. Between 2012 and 2024, the transport distances of cobbles were monitored in the watersheds using RFID technology (passive and active microchips). From 2016 to 2021, sediment balances of the restored river sections were quantified through LiDAR surveys to better understand how rivers respond to the new flow conditions and channel morphology resulting from restoration efforts. The results indicate that the restored sections function as preferential sediment storage areas. Although the restoration has improved sediment transport conditions during floods, several tributaries do not contribute sufficiently to the sediment recharge of the main channels, leading to chronic sediment deficits. The data also emphasize the importance of ordinary flows in sediment transport, which can often result in riverbed incision. To achieve a more balanced sediment supply, the authors advocate for the reactivation of sediment sources at the watershed scale.