Measurement and modeling of Vidy Bay (Lake Geneva) hydrodynamics

Vidy Bay is located near Lausanne on the northern shore of Lake Geneva in an area where sewage outfalls and drinking water intakes are positioned. Local circulation patterns may control water quality aspects in this part of lake. Currents are mainly influenced by variable wind regimes and the lake's thermal structure. Field experiments and numerical simulations were carried out to quantify the circulation patterns in this part of the lake. A set of Lagrangian drifters was used to capture current patterns and to measure air and water temperature and wind velocity in Vidy Bay. Current measurements were compared with simulations from a 3D hydrodynamic model (Delft3D-FLOW), covering all of Lake Geneva. Higher resolutions of bathymetry and grid mesh size were used for the Vidy Bay. Meteorological data for the model's surface boundary conditions were provided by the high-resolution (2.2 km gridded) MeteoSwiss COSMO-2 model. Modeled currents compared well with the field data. The validated model was used to identify typical current patterns in the bay. Consistent with previous observations of the bay's currents, the modeling results showed that Vidy currents are highly variable both spatially and temporally, although current patterns were found to be follow the forcing by the different wind regimes across the whole lake.