A Combined Numerical/Experimental Approach to Understand Stratification and Mixing Processes in the Adour Estuary
Résumé
River plumes play a central role in the input and transport of dissolved and particulate matters that can lead to the dispersion of pollutants into coastal waters. Understanding the dynamics of river plumes is thus essential to evaluate the potential threat to coastal-marine ecosystems, in order to improve management and mitigation policies. The Adour estuary morphology combined with the competition between the tide and the river flow result in a partially stratified estuary. A dual approach, coupling field experiments and numerical modeling, has been carried out to better understand the physical processes that govern the Adour river plume hydrodynamics. A field campaign was performed inside the estuary in September 2017. Velocity profilers and high frequency point current-meters were moored, at two different stations inside the estuary, during one month. Series of salinity profiles were realized at four stations including mooring stations. Meanwhile, a numerical model has been developed based on the open source code TELEMAC-3D to investigate the interaction between light continental waters and heavy salty marine waters, focusing on the salt-wedge intrusion inside the estuary. The resulting density stratification playing a major role in the transfer of water masses and the transport of dissolved and particulate matters, its precise reproduction isone of the cornerstones of our study. Inside the estuary, a competition between density gradient and velocity/bottom shear regulates mixing processes. First comparisons between model and field data show a good agreement between measured and simulated water levels and velocity profiles. The correct representation of density stratification processes by the numerical model remains, as expected, a challenging issue. The choice of the turbulence model, which is of the foremost importance for a good representation of the interaction between water masses, will be discussed within the physical framework provided by field measurements