Internal seiche damping on sloping topography

Abstract Basin‐scale internal waves are a common phenomenon in thermally stratified water bodies, with important implications for aquatic organisms and biogeochemical cycling. While theoretical analyses of internal seiche generation and their properties are mostly based on idealized (rectangular) basin shapes, several studies have highlighted the influence of basin shape and sloping topography. The results, however, tend to be site‐specific and not widely generalized. Here, we investigate how sloping topography affects the generation of internal seiches in reservoir‐shaped water bodies. We simulated the response of 50 hypothetical basins to wind forcing using a three‐dimensional hydrodynamic model, while systematically varying bottom slope (10 −3 to rectangular basin), basin length (1.5–5 km), and forcing conditions (Wedderburn number 2–20). Our results demonstrate that sloping topography plays a critical role in the generation of internal seiches during the relaxation from wind‐induced upwelling. Upslope‐propagating fronts are formed above the sloping bed and interact with the basin‐scale flows that govern seiche formation. This interaction induces enhanced turbulent mixing and bottom boundary layer separation with transport of water from the slope to the lake interior. We found that the effect of these processes on internal seiche damping could be well described by the slope criticality parameter, a parameter relating the direction of internal wave propagation to bottom slope. These findings suggest that the slope criticality parameter can potentially serve as a predictor of dominant basin‐scale circulation and mixing mechanisms, offering valuable insights into the transport of nutrients, sediments, and organisms in lakes and reservoirs.