Internal waves and mixing in a stratified reservoir: Insights from three-dimensional modeling

In this study, the three-dimensional (3D) Estuary and Lake COmputer Model (ELCOM) was used to model a mid-sized reservoir (Rappbode Reservoir, Germany) during the period of summer stratification to identify and illustrate the source of internal waves as well as to characterize water exchange between the hypolimnion and epilimnion under different wind speed conditions with a focal point on one episode of high and sustained winds. The modeling revealed that wind stress was the key driver of the observed internal waves while the role of water withdrawal was negligible. Our results also showed that within the range of wind speeds considered, wind-induced upwelling greatly enhanced mixing between the hypolimnion and epilimnion with a rate that varies approximately as the square of the wind speed. This numerical correlation affirmed that processes connected to wind stress, i.e. internal waves or direct upwelling, were responsible for the mixing of the hypolimnetic water into the surface water rather than direct input of turbulent kinetic energy. (C) 2014 Elsevier GmbH. All rights reserved.