2019 CSCE Annual Conference - Laval (Greater Montreal)

2019 CSCE Annual Conference - Laval (Greater Montreal) Conference

Can a Vortex Improve Flow Conditions in a Stormwater Retention Pond or a Clearwell?

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Mr. Rocky Chowdhury, City of Meadow Lake
Dr. Kerry Mazurek, University of Saskatchewan (Presenter)
Dr. Gordon Putz, University of Saskatchewan
Mr. Cory Albers, Source2Source Inc.

Both stormwater retention ponds and clearwells are large, open storage reservoirs a few meters in depth. Both originally were designed for water storage without much consideration to the flow dynamics through them. In each case, the residence time of the flow in the reservoir is important. For retention ponds, longer residence times provide time in the pond for settling of solids and treatment of pollutants before the stormwater is discharged into receiving streams. Clearwells, used in water treatment plants, need a long contact time for the disinfectant that is injected in the water flow to react before the water enters the distribution system. Both often suffer from poor flow dynamics with short-circuiting and dead space, which reduce treatment times. To improve performance, it is sometimes necessary to modify the flow behavior. These modifications are often done using baffles. This paper investigates whether or not modifying the typical flow path in a reservoir to a large vortex will improve performance. Tests were carried out in scale models of a 50 and 100 m diameter circular cells with each of 2 m depth, where there was a radial inflow and a central outlet. The residence time distribution was evaluated using tracer studies for varied flow rate and time of initiation of flow in the model. Observations showed that although dead space was relatively small (mostly near 2 %), however, the time of first observation of dye was unexpectedly early because of a secondary flow component that was produced in the overall flow, which resulted in a radial inflow near the bed towards the outlet. It appears that if the secondary flow can be prevented, the vortex would provide an excellent option for improving residence times in these types of reservoirs.