Circulation and water quality model for stormwater ponds

A two-dimensional vertically averaged hydrodynamic model has been adapted to compute the circulation and sedimentation patterns in a proposed stormwater detention pond. The model had previously only been used in applications with grid lengths greater than about 50 m and time steps of a minute or more. This application has shown that the model can be used with grid sizes of 5 m or less and a time step of 1 second. The model is an improvement over existing plug flow models based on a series of constantly stirred tank reactors that cannot compute circulation patterns. The model can identify areas in the pond where short-circuiting and dead zones occur. Sedimentation, based on first order decay, was computed and the rates were highest in areas of the pond where water transport speeds were the smallest.