Numerical simulation of circulation and thermal stratification in Torrens Lake, Adelaide, South Australia

Abstract

Thermal stratification in natural and artificial lakes prevents circulation of deeper water to the surface, and vice versa. This can exacerbate the formation of potentially toxic algal blooms in fresh water lakes, and undesirable algal suspended solids in waste stabilisation ponds (WSPs). If these shallow water bodies are used as the source of drinking or reuse water, the presence of these algae may lead to increased costs in water or wastewater treatment. An ever-increasing number of computer codes have been developed recently to examine circulation and thermal stratification in surface water bodies. Some of these codes have been used to simulate the hydrodynamics of WSPs, in an attempt to improve the methodology underlying their design, as well as the efficiency of their operation. In almost all cases, however, these computer codes are limited in their ability to model very shallow water bodies, where the depth-to-width (or length) ratio is extremely small (less than 1%). In addition, they often have difficulty in being able to model free-surface movement resulting from wind stresses—a critical forcing function for inducing circulation, and thereby reducing the persistence of thermal stratification. To overcome the difficulties of existing generalised commercial packages, we have developed a three-dimensional numerical code specialised for shallow water flows. This code has been designed specifically to model free-surface movement in shallow water bodies, with the capability of simulating the thermal distribution therein. Using this model, the circulation patterns and thermal structure