Currents in Well-Mixed Layers

This article aims at understanding the structure of hydrodynamic currents in the well-mixed layers of lakes and enclosed water bodies, which includes both the upper mixed layer in stratified conditions and the whole depth when stratification is negligible. Currents are typically triggered by wind, which acts on the water surface, and are influenced by the spatial distribution of wind shear stress, lake's bathymetry and Earth rotation. Wind forcing is temporally varying and waves are originated in the water body as a response to its variation. Here, however, we focus on steady-state conditions as a guideline to understand the tendency of the system, in particular for what concerns transport dynamics. The analysis is performed using analytical solutions developed for cases with simplified geometries and boundary conditions. Illustrations from complex numerical simulations and field measurements support the theoretical findings. Simplified steady-state analytical solutions allow for grasping the main factors controlling the hydrodynamics in lakes and reservoirs, and help interpreting the transport patterns that develop also in complex cases.