Tridimensional modeling of nearshore dynamics
Participants: Patrick Marchesiello, Rachid Benshila et Rafael Almar (and colleagues outside LEGOS)
In the past ten years, robust formalisms have emerged to model the three-dimensional effect of waves on the ocean circulation, especially in the nearshore region. Our desire to clarify the different choices and move forward on the convergence of formalisms materialized in 2014 through a French project (LEFE program) bringing together developers of 3D coastal ocean circulation models. The continuation of this project will bring together the scientific community traditionally working separately on shelf and nearshore oceanography, with their different approaches and models: 2D or 3D equations, structured or unstructured grids. Our objectives are also part of longstanding international collaborations with UCLA.
Our work is structured on the basis of two main projects: COMODO-WAVES (LEFE-MANU) and COASTVAR (ANR-ASTRID):
- COMODO-WAVES uses a realistic test case to evaluate the performance of different approaches to modeling. The first task involves the comparison of 2D and 3D models and those with structured and unstructured meshes (accuracy and computational cost) in order to better assess the quality and defects of different approaches. The second task concerns the quantification of intrinsic and forced components of the Very Low Frequency (VLF) variability of coastal current systems (rip currents for that matter). The answer to such questions will also determine the future of coastal models (e.g., promoting phase resolving or averaging models). A last objective is the optimization of the use of coastal video imaging for modeling the coastal flow and morphodynamics, including methods of data assimilation.
- COASTVAR (and side Vietnamese projects presented to MOST) is a an attempt to apply remote sensing and modeling techniques mentioned above for the case of Vietnam and West Africa.
Our project represents a first attempt to coordinate the work of 3D coastal circulation modeling in France and bring together the offshore and nearshore communities. As for the COMODO project, model inter-comparisons alone will provide important outcome that can help decide how to move forward in nearshore and shelf oceanographic disciplines.
The expected methodological contribution of this project lies in the consolidation of the formalisms of wave-current interactions; in optimizing the use of video imagery, which eventually could make in situ measurements less crucial for monitoring; and in benchmarking the models in use today. Toward the end of the project, we will be able to set priorities for the development of shelf and nearshore modeling.
The scientific contribution of the project is expected to establish the role of scale interactions (particularly shelf-surf interactions) and nearshore dynamic processes using a realistic (but sufficiently simple) three-dimensional application. Applications in COASTVAR will identify relevant mechanisms for beach equilibrium dynamics subjected to tropical conditions (tropical cyclones or regular strong swell).