Lake Aerator Effect on Temperature Stratification Analyzed by “MINLAKE” Model

ABSTRACT

The paper deals with the prediction of the vertical temperature profiles in a stratified lake during the operation of an air bubble aeration system. The use of such systems is widespread and their effect on water quality very significant. They are installed for a variety of purposes and act as aerators (increasing dissolved oxygen), mixing devices, and often unintentionally as nutrient pumps and local destratification devices. It is not easy to predict the total impact of an air bubble system installed in lake. To gain a better appreciation of its effect, a model can be developed to simulate the flow induced by an air bubble system in a stratified lake. If such a model is incorporated into a dynamic water quality model, the cumulative synoptic interaction between the air bubble system and lake water quality can be simulated. Since lake destratification is not instantaneous, a dynamic model can simulate the interactions of continuous inputs of water, energy, and materials from the watershed and the atmosphere while the air bubble system is in operation. This can assist in the sizing and selection of such systems. This paper sketches the nearfield and farfield computer models available and illustrates the progressive destratification by an air bubble system in a temperature-stratified lake with the aid of the computer simulation. The nearfield computer model called BUBBLES treats the mixing in the vicinity of the air bubble plume. The farfield computer model called MINLAKE is for natural lake temperature stratification. The combined model is applied to Lake Calhoun (Minneapolis, Minnesota) for illustration.