Interest of geophysical methods to determine the evolution and the spatial distribution of sedimentary deposits upstream of run-of-the-river dams (Upper Rh{\^o}ne, France)

TL;DR

This study demonstrates that combining acoustic and electromagnetic geophysical methods significantly enhances the characterization and understanding of upstream sediment deposits behind dams, aiding better management and safety assessments.

Contribution

The paper introduces the use of combined geophysical techniques to improve sediment deposit analysis upstream of dams, providing detailed internal structures and spatial distribution data.

Findings

Geophysical methods reveal internal sediment structures.

Enhanced spatial mapping of deposits.

Improved volume estimation with limited bathymetric data.

Abstract

Hydraulic structures such as dams have a direct or indirect influence on the hydro-sedimentary functioning of rivers. They can impact the sediment continuity of the river and can create a sediment imbalance with zones of sediment accumulation upstream and a lack of sediment downstream from the dam. Upstream deposits are a major issue for managers as they can impact the operation and/oraffect the safety of the structure and induce extra-flood hazards. Operators therefore seek to determine the physical characteristics of these deposits to determine their remobilization potential.Usually, these sediment deposits are described using bathymetric data, sonar images or samples (dredging, coring). For this study, new measurements from two geophysical methods (acoustic and electromagnetic) were used in addition to these current monitoring methods. The contribution of geophysical techniques is undeniable to improve the characterization of these deposits. These measurements make it possible to: i) define the internal structures of the sediments, ii) determine the spatial distribution of these structures over the entire development, iii) evaluate the volumes deposited when little bathymetric data is available on the reservoir. The coupling of these methods thus makes it possible to reconstruct the evolution and the structuring events of the sedimentary deposits. This approach provides complementary and important elements for managers in terms of exploitation and optimization of sedimentary deposits management scenarios.