Designed to be an attractive feature for residents, but with an environmental benefit, storm water management ponds (SWMPs) can be found in many residential and commercial areas throughout London. The ponds are to collect runoff from the local storm sewer system following a rainfall or snowmelt event, or from activities such as watering lawns and washing cars. SWMPs are built to temporarily hold water, provide treatment to remove the pollutants, and then slowly release it back to our waterways.
In a natural landscape, rain water or snowmelt will soak into the soil, be absorbed by trees and other plants, evaporate into the air, or travel over land to receiving streams, lakes, rivers or wetlands. In developed areas where driveways, parking lots, buildings and roads cover the soil, water cannot be absorbed. As it flows over these surfaces, the runoff also collects pollutants such as dirt, fertilizer, oil and debris such as grass-clippings and trash.
SWMPs have two functions. They clean the water and control the flow. Run off water is collected in storm sewers and delivered to the pond. It enters the first half where the contaminants are allowed to settle to the bottom. Clear water then moves to the second half and is allowed to flow into streams and waterways at a controlled rate. Without these ponds, large amounts of dirty water would enter a stream all at once, causing flooding and eroding soil from the stream banks.
SWMPs are an important factor in keeping our waterways clean by allowing pollutants and sediment to settle before it enters the stream or river. In addition, the buffer areas around the SWMP are landscaped with dense natural vegetation and grasses that also help to filter sediment from water entering the pond overland.
Routine maintenance of the pond is required to remove debris in and around the pond and provide general maintenance of the vegetation. This includes removal of invasive vegetation, and maintenance of structures. Weed control including the use of pesticides is not required or recommended. Grass cutting is also not recommended in order to maintain a natural environment. Additionally, a clean-out of the SWMP is required approximately every 5-10 years to remove accumulated sediment. This involves drainage of the pond as well as soil sampling to ensure proper disposal of the sediment removed.
As attractive as they are, ponds are not designed for recreational use. They might seem calm on the surface, but due to the nature of the pond construction, there can be rapid water level fluctuations. Swimming, skating, boating, and fishing are also strictly prohibited. Safety / warning signs are placed around the pond to inform the public of prohibited activities. Parents living in neighbourhoods with storm water management ponds are encouraged to visit the pond with their children to review the warning signs and impress the importance of safety to them.
SWMPs are not typically considered good mosquito breeding sites since the water level is continuously changing and exposure to wind is high. Therefore, SWMP’s do not create any greater threat of west nile virus than would already exist.
To ensure our SWMP’s remain healthy, residents with property near or abutting such ponds, are encouraged to:
- take care in disposing of trash, grass clippings and leaves to avoid accumulation in and around ponds
- minimize the use of fertilizer on their property
- prevent swimming pool discharges or toxic substances from entering the storm sewers that lead to the pond
- not plant trees, shrubs or flowers around the pond and
- avoid disturbing the naturally vegetated areas.
The City of London recently updated their website to include a handy section about how residents can help ensure the ponds continue to provide a great habitat for birds and animals – check - https://www.london.ca/residents/Sewers-Flooding/stormwater/Pages/Living-Near-Stormwater-Management-Ponds.aspx
Peder Madsen is the president of the London Home Builders' Association and Vice President of CCR Building and Remodeling in London.