Retrofitting Stormwater Ponds for Water Quality Control

During the last 15 years, many stormwater ponds were built in Canada. These ponds were designed to control runoff flows by peak shaving and thereby prevent flooding resulting from urbanization, but they are ineffective in protection of water quality in the receiving waters. Thus, one of the emerging challenges in urban water management is the retrofitting of existing stormwater ponds to meet the current environmental concerns. The retrofitting measures proposed include changes in flow regimes, storage pool volumes and flow velocities, achievable by structural changes in inlet, storage and outlet structures; treatment of runoff by sedimentation or filtration; enhancement of biological processes contributing to pollutant removal through longer detentions and introduction of aquatic plants; and, improvement of aquatic life habitat. A case is made for an ecosystem approach where the pond is one element in the urban stormwater treatment train which controls catchment, pond and receiving waters.