A multi-technique approach for evaluating sand dynamics in a complex engineered piedmont river system

Area of Science:

• Riverine geomorphology and sediment transport dynamics.

Background:

• Engineered piedmont rivers present unique challenges for understanding sand transport due to modified bedload dynamics and residual sand on gravel substrates.
• Limited research exists on sand dynamics in these altered river systems, necessitating innovative methodological protocols.

Purpose of the Study:

• To propose and apply a multi-technique approach for studying sand dynamics in engineered piedmont rivers.
• To gain insights into sand fluxes at the complex Isère-Rhône confluence, addressing a lack of available sediment flux data.

Main Methods:

• Utilized a combination of bathymetry and turbidity measurements.
• Employed numerical modeling, including sediment rating curves and 2D simulations.
• Conducted sediment budgeting for cross-validation of results.

Main Results:

• Identified that sediment transport capacity was met during a 2015 flushing event, with negligible sand supply when dam gates were closed.
• Observed that suspended sand loads predominated downstream of the final dam but settled rapidly at the confluence.
• Determined that sand deposits were cleared by subsequent minor floods.

Conclusions:

• The developed multi-technique methodology provides valuable insights into sand dynamics in engineered river systems.
• The findings are transferable to other river sites facing similar issues with sand transport and deposition.
• Effective management of sand fluxes is critical for navigation and flood control at river confluences.