Work

Contribution of the Loire River to knowledge about hungry Rivers – Three centuries of a lowland river trajectory

Year: 2026

Type: article

Abstract: Like many rivers, the Loire River (France) has been deeply altered by bed narrowing and incision, to the extent that it can now be considered a “hungry river.” However, understanding its evolution over several centuries is complicated by the complexity of the control factors and the interactions between the various components of the fluvial system. There is also a lack of precise data with which to accurately assess the volumes of erosion and sedimentation. This study aims to analyze the long-term (1755–2023) trajectory of a 72 km section of the Loire River in Burgundy to better understand the respective roles of potential drivers of river degradation, such as embankments, hydrological changes, and sediment mining. Recent developments in high-resolution elevation modelling provide an innovative solution that we have adapted to the Loire River in Burgundy — a stretch that was almost pristine in the 18th century. Our results reveal that the riverbed evolved rapidly due to small dykes (groynes) being built during a period of high hydrology at the end of the 18th century. This induced a rapid readjustment of the riverbed. This initial phase was apparently not accompanied by significant sedimentation, except in artificially abandoned side meanders, emphasizing their role in river equilibrium. The 19th-century embankment with longitudinal levees resulted in increased sediment trapping on the lateral margins of the newly embanked channel. However, the volume of erosion changed little between 1755 and 1953, but increased sharply during the third period (1953–2023). Calculations of the volume of sediment artificially extracted from the riverbed show that this accounts for at least 50–60% of the volume eroded from the channel. Quantification suggests that, in the absence of sand and gravel mining, lateral erosion would have compensated for the sediment deficit during the second half of the 20th century. Consequently, the Loire River in Burgundy may have approached a new dynamic equilibrium within a century of the construction of the embankment. This study highlights the strongly negative impact of excessive mining of sand and gravel conducted over 40 years. The assessment of the sediment budget and the process-based understanding of the river's trajectory also provide solutions for river managers, promoting lateral sediment supply through bank erosion in this river with limited sediment supply.

Source: Geomorphology

DOI: 10.1016/j.geomorph.2026.110415