The ability to reliably predict the fluid flow through a pond and relate these hydraulic characteristics to pond treatment performance would clearly be a very valuable tool to the design engineer. The application of computational fluid dynamics (CFD) mathematical modelling has the potential to do this.

In recent years there has been rapid advancement of computing power and mathematical modelling software. CFD simulation gives the pond designer the potential to explore the hydraulic performance for a wide range of design configurations and scenarios. This paper reports on the application of the PHOENICS CFD package for this purpose.

To demonstrate the potential application of CFD to pond design, this paper presents a series of simulations of a small community pond. The simulations undertaken were three-dimensional and incorporated the k-e turbulence model. The first of these modelled the existing pond arrangement, after which the effects of adding a baffle is shown as an example of how CFD can be applied for design.

In addition to the fluid velocity field, plots of a simulated tracer slick were produced. This simulated tracer movement is used to produce hydraulic retention time distribution curves of the tracer concentration at the outlet. These are then integrated with a simple, first-order decay model for BOD removal and faecal coliform die-off to calculate treatment efficiency. This allowed direct comparison of the expected treatment efficiencies with and without the baffle modification.

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