Diurnal Dynamics in a Small Shallow Lake under Spatially Nonuniform Wind and Weak Stratification

Diurnal dynamics such as stratification/destratification affects a shallow lake more than a deeper one. Surrounding topographic features such as forests and mountains affect a small lake more than a large one. This paper present a study of a small, shallow, sheltered, and weakly stratified lake in response to meteorological (MET) conditions and indirect effects of surrounding topographic features. Wind measurements at the lake shores indicated that spatial variations of wind speed and direction were substantial in nearshore areas with dense forest stands. Field measurements of velocity profiles and temperature spatial distributions were measured during the summer of 2004. A three-dimensional (3D) ocean model modified by a generic length-scale turbulence model was implemented to address the effects of spatially nonuniform wind caused by trees and weak thermal stratification on lake dynamics. Simulated vertical and horizontal distributions of mean velocities suggested that wind sheltering altered current patterns, particularly in sheltered areas, and weak stratification produced subsurface maximum velocities. Simulated water temperature profiles reproduced an observed diurnal thermal pattern. A modified stratification indicator is shown to yield reliable measure of thermal stratification without internal thermal structure; this indicator had a strong relationship with the 3D model output.