Wind-driven current simulations around the Island Mainau (Lake Constance)

Using three-dimensional numerical modelling for the shallow water equations on the rotating Earth in the Boussinesq approximation, we study the steady barotropic motion around the Island Mainau in Lake ـberlingen, forced by uniformly distributed winds of different directions. The method of substructuring is used to resolve the flow pattern near the Island Mainau with greater accuracy and thus to identify the peculiarities that are induced by the island as an obstruction to the current field within the lake basin. The barotropic response is analysed in detail for 16 different wind directions. It is shown to what extent these winds determine the distribution of the horizontal current and the up- and down-welling zones in the vicinity of the island. Current peculiarities, such as diverging and converging elements, locations of maximum current speeds and, in particular, the flow through the Mainau channel are identified. They provide hints to an optimal design of a flow measuring campaign under homogeneous conditions. It is further demonstrated that the island acts as an obstructing entity that effectively influences the flow within Lake ـberlingen. For wind blowing along Lake ـberlingen the baroclinic motion was also studied. The flow in the upper-layer and the lower-layer-return flow are modified over the lake.