WIT Press

Large Scale Circulations In Shallow Lakes


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G. Curto, J. Józsa, E. Napoli, G. Lipari & T. Kramer


In this paper wind-driven horizontal and vertical large scale circulations in shallow lakes are analysed. As an improved approximation of the external forcing field, the wind speed acceleration due to the abrupt reduction in the surface roughness between the land and the water is quantified along the fetch using a semi-empirical approach which allows the identification of the aerodynamic features and hydrodynamic effects of an Internal Boundary Layer (IBL) growing within the bottom of the atmospheric boundary layer. The consequent fetch-dependence of the wind speed and corresponding wind shear stresses on the lake surface causes the appearance of a wind stress curl, which is responsible, together with changes in bathymetry, for causing strong horizontal circulations. The effects of wind speed changes on the wind-driven flow patterns are analysed both analytically and numerically, showing the need to take these changes into account in order to correctly predict wind-induced water currents in shallow basins. 1 Introduction Shallow lakes have recently been receiving greater attention all over the world. Their unique value and multi-purpose utility have increasingly been recognised which has led to the misuses of a number of them, thus worsening their ecological state even to an alarming extent at places. Furthermore, recent changes in the global climate or, at least, the fact that extreme conditions seem to be more frequent, has also changed the boundary conditions for these vulnerable water bodies. In spite of this, lake studies are still quite moderately financed compared to maritime research,