Combined usage of geophysical methods in continental water bodies, their benefits and challenging issues: A special focus on sediment deposits in dam reservoirs

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. Sediment deposits upstream dams are a major issue for managers as they can impact the operation and/or affect the safety of the structure and increase the flood risk. 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 sedimentary information (dredging, coring). For this study, new measurements from two geophysical methods (acoustic and electromagnetic) were used in addition to these current monitoring methods. In addition, this method can be essential when historical data is not available. 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 information for stakeholders in terms of dam exploitation and management of sedimentary deposits. •Geophysical methods were reviewed for studying sediment deposits in dam reservoirs.•Sub-Bottom Profiler and Ground Penetrating Radar methods were tested at different dam sites.•The results identified pre-impoundment bottom, sediment characteristics such as thickness, and internal structures.•Geophysical methods can help to identify and quantify sedimentary processes in poorly monitored dam reservoirs.