Gravity currents over complex terrain

Gravity currents are key processes that affect atmospheric, ocean and coastal circulations.

Modelling gravity currents mainly rely on classical studies made on uniform slopes with smooth bottom, when most gravity currents in nature occur over complex rough, mobile and/or curved terrain.

While laboratory experiments have successfully revealed some of the global flow characteristics, we still lack detailed measurements of key quantities such as velocities and the overall balance of the turbulent kinetic energy, density fields and local mixing / entrainment of bottom sediments.

Further experiments are therefore needed to correctly parametrise entrainment and turbulent fluxes under more complex bottom conditions.

The project aims at incorporating the effects of rough mobile terrain and curvature in the study of gravity currents thanks to an experimental approach based on two main set ups:

• a “continuously supplied gravity current over a sediment bed” experiment, used to reproduce oceanic gravity currents or katabatic air flows
• a “finite volume with instantaneous release of fluid particles” experiment, to simulate powder snow avalanches and turbidity currents (see photo).

A better understanding of the influence of the bottom roughness and curvature on the dynamics of gravity currents and related mixing phenomena, will deliver some detailed information about turbulent subgrid-scale processes needed for a correct parametrisation of numerical models (both oceanic, atmospheric and coastal).

This work should therefore benefit to a better assessment of risk in mountain areas, of pollutant transport or even of erosion phenomena in coastal regions.