Typical near surface layer current patterns in Lake Geneva’s main basin (Grand Lac)

Abstract:

The Lake Geneva current field is controlled by a variable wind field and thermal stratification. Typical current patterns in the Grand Lac which is oriented roughly in the East-West direction were determined under real time wind conditions and thermal stratifications using the DELFT3D-FLOW hydrodynamic model. The model solves the Reynolds-Averaged Navier-Stokes equations, combined with a k-ε turbulence closure in σ (lakebed-following) coordinates. The model was forced by a space-time dependent wind stress and heat flux over a 2.2 km × 2.2 km horizontal grid (interpolated onto the model grid) provided by the Swiss Meteorological office (COSMO2, MeteoSwiss) in 2012. Modeling results revealed stronger circulation for the large scale gyres in the non-stratified season (winter), compared with the stratified season (summer). A clockwise circulation pattern in the western part and a counter-clockwise current pattern in the central part of the Grand Lac are identified under large scale north-easterly winds (Bise), which occur frequently. For large scale south-westerly winds (Vent), another frequent wind, a long-fetch (up to ~ 30 km) leads to a clockwise circulation pattern in the central part of the main basin while a counter-clockwise recirculating gyre is induced in the eastern part. Strong eastward currents are observed near the Grand Lac north-shore. The simulation results compared well with ADCP data and time series of temperature profiles from the middle of the Grand Lac.