Stormwater management ponds (SWMPs) represent one of the early ‘best management practices’, which was initially applied to control runoff peaks from developing areas. Besides reducing the flood risk, the well-designed and operated SWMPs are currently recognized for many benefits, including: stormwater treatment, visual and recreational amenities, subpotable water supply, and, provision of ecological services (e.g., creation of aquatic habitats). On the other hand, SWMPs, and particularly those, which may be obsolete or inadequately maintained, can also cause adverse environmental effects, e.g., by creating ecological traps, or releasing heated effluents or polluted sediments. Thus, there is a continuing interest in assessing the actual environmental performance of existing ponds in the context of the current pond design guidelines.

The assessment process starts with pond performance diagnosis, based on field inspection records and surveys, and comparisons of pond design features and parameters against the current guidelines. The main points of interest include pond layout; storage capacities; inlet and outlet structures; hydraulic efficiency; stormwater treatment (largely sedimentation); pond water and effluent quality; seasonal regimes (summer – concerns about heating, winter – concerns about accumulation of chloride and circulation under ice): and, potential downstream impacts (e.g., stream erosion). The diagnostic findings are matched against the proposed corrective (upgrading) measures, and their feasibility and benefits. Corrective measures focus on influent pretreatment, facility enlargement, modified layout and depths, sediment storage and removal, internal flow berms and baffles, outlet modifications, SW treatment, and effluent polishing. An example of such a process applied to a deficient SWMP in Kingston, Ontario is demonstrated using actual data.

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