Welcome to the City of Toronto website

Stormwater management retention/detention ponds

In urban areas the carrying capacities of the storm and combined sewer systems vary widely, depending on when they were built. One common factor is that the systems have difficulty handling the runoff from very infrequent and intense storms. As result one may have observed one or more of the following hazards:

• sewer backup into basements (basement flooding)
• flooded properties and roads
• manhole cover blown off and water gushing from manholes, sometimes several metres high, and
• swollen and rapidly flowing stream

The City of Toronto has constructed and is continuing to construct ponds in known problem areas. This reduces flooding by directing as much excess storm runoff as possible away from roads and sewers to properly-designed storage facilities rather than randomly-occurring flood locations. The water is contained in these areas until the sewers are able to handle it.

A retention pond, such as Milliken Park near Steeles Avenue and Markham Road in the Scarborough community, always contains water. It also has the capacity to handle excess rainwater when necessary. In addition, these "wet ponds" are often built to allow for settlement of suspended solids through extended detention time.

A detention pond, such as Scarden Park at Warden Avenue and Cass Avenue, also in the Scarborough community, is a dry area such as a park or an open space with the necessary mechanics to close off access to sewers and direct water into the detention area. These areas are well-signed so that residents are aware that they should leave the area during a storm. Each area is also equipped with an alarm system that activates should water start to flow in. At that point, staff are notified to check the area.

Since conditions vary from site to site, here are a number of safety precautions used:

• alarm systems alert staff to check the area when it is activated (inspection staff carry lifesaving equipment)
• enough signs are erected and maintained to warn residents of possible danger
• each area is made as vandal-proof as practical and avoids, as much as possible, any structure that might trap a child against a grating
• each entrance point for water into a detention area has a rock structure that dissipates fast-flowing waters
• all unfenced areas have a very gradual slope of four feet horizontal for each foot vertical
• fences are built at least one metre back from the high-water level of the pond

All safety practices are reviewed regularly and modified as necessary based on experience.