Comparison of CFD with Reservoir Routing Model Predictions for Stormwater Ponds
The hydraulic design of stormwater detention ponds is usually directed towards outflow peak reduction. It is generally calculated with the reservoir routing approach, which is essentially a discrete solution for the continuity equation at such ponds. The reservoir routing approach has been successful in predicting this outflow peak attenuation, and is implemented in various computational models such as SWMM 5 (USEPA, 2009). However, the reservoir routing approach does not provide information on the velocity fields that are expected within the pond. This parameter could be useful in assessing the location and extent of dead zones, as well as regions in which velocities may be outside a desired range. Such velocity fields can be obtained with the use of more complex computational fluid dynamics (CFD) models, but such models usually have steep learning curves and are also computationally intensive applications that may be expensive to perform for simpler reservoir systems. This chapter presents the result of a capstone project in which a comparative study of the flow predictions yielded by the reservoir routing approach and those of a two dimensional CFD model. The CFD model has a very user friendly interface, and is applied to two hypothetical detention ponds, one of them being a simplified version of a pond in Sao Paulo, Brazil. The shape and the peak discharge in the outflow hydro-graphs obtained by the CFD model were compared, and the locations of high and low velocity zones for each simulation condition were also determined with the model. The results indicate that the peak discharges in both methods agreed very well, but there are some discrepancies in the predicted shapes of the hydrographs after the peak flows. Results presented in this chapter show that velocity profiles may be useful in order to avoid configurations that will lead to scour and undesirable sediment deposition.
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