S<scp>MALL</scp>-S<scp>CALE</scp>H<scp>YDRODYNAMICS IN</scp>L<scp>AKES</scp>

TLDR

Recent small‑scale turbulence observations in lakes, reservoirs, and other enclosed basins reveal distinct mixing regimes: a turbulent surface layer, a quasi‑steady bottom boundary layer, and a comparatively quiet interior. Short‑term current and dissipation profiles vary markedly from steady state, while the bottom boundary layer largely follows a logarithmic law and the interior remains weakly turbulent, indicating that large‑scale motions convert to turbulence mainly at the bottom boundary.

Abstract

▪ Abstract Recent small-scale turbulence observations allow the mixing regimes in lakes, reservoirs, and other enclosed basins to be categorized into the turbulent surface and bottom boundary layers as well as the comparably quiet interior. The surface layer consists of an energetic wave-affected thin zone at the very top and a law-of-the-wall layer right below, where the classical logarithmic-layer characteristic applies on average. Short-term current and dissipation profiles, however, deviate strongly from any steady state. In contrast, the quasi-steady bottom boundary layer behaves almost perfectly as a logarithmic layer, although periodic seiching modifies the structure in the details. The interior stratified turbulence is extremely weak, even though much of the mechanical energy is contained in baroclinic basin-scale seiching and Kelvin waves or inertial currents (large lakes). The transformation of large-scale motions to turbulence occurs mainly in the bottom boundary and not in the interior, where the local shear remains weak and the Richardson numbers are generally large.