Use of computational fluid dynamics to model reservoir mixing and destratification

Destratification of reservoirs by the use of artificial mixing is a method of improving the impounded water quality. In order to design a destratification device at Stocks Reservoir, NW England, a Computational Fluid Dynamics model was used to trial different types and sizes of mixing device. It was found that a perforated pipe bubble mixing device performed far better than a large banana blade mixer at destratifying Stocks Reservoir. Two important criteria for the effective operation of a mixing device were established. These were a minimum upflow velocity of entrained water through the reservoir, and the need for a reverse flow along the surface of the reservoir away from the abstraction point. These criteria have been incorporated into design equations which can be extended to use at other reservoirs. A bubble mixer was installed at Stocks Reservoir, and has been shown to fully destratify the reservoir and to reduce the levels of dissolved manganese in the water by more than 50%.