What are retention ponds?
All retention ponds are designed to handle large fluctuations in water levels. During wet weather events like large rain storms or spring snow melt, or because of a large water main break, the water levels of a retention pond may increase dramatically. Temporarily storing excess runoff in retention ponds helps prevent our sewer system from being overloaded, and helps reduce the occurrence of basement and overland flooding.
There are three types of retention ponds in Winnipeg.
These ponds typically have grass embankments and may have a stone shoreline around the perimeter of the pond.
Naturalized retention ponds are designed to have vegetation, like cattails and native prairie grasses, growing on their shorelines and embankments.
Dry ponds typically have grass embankments and are normally not filled with water.
These ponds may fill up with water temporarily during significant rainfall events or snow melt.
The City of Winnipeg maintains and operates fountains and underground structures found in retention ponds, such as pumps, wells and gates. Maintenance of retention ponds includes:
- Removing debris in surrounding areas
- Controlling grasses and weeds that grow through the stone shoreline
- Managing aquatic vegetation like algae and water weeds
Traditional ponds may be maintained with herbicides or by harvesting aquatic vegetation. These activities are not required for naturalized or dry ponds, because vegetation in these ponds is beneficial and is growing there by design.
The City does not maintain shorelines or landscaping on private property.
Some retention ponds are equipped with water fountains. These fountains are for aesthetic purposes, and were installed by the developer of the subdivision in which these ponds are located. They do not provide aeration for the purpose of controlling or eliminating algae or weeds.
Retention ponds are designed to operate within a range of water levels. The water levels will sometimes fluctuate between their normal water level and what would be considered a high water level.
The water levels will typically rise as a result of a wet weather event, like heavy rain or snow melt. They can even rise as a result of a water main break. Water levels can rise significantly – up to 1.2 meters or more– and can last anywhere from a few hours to several days, before gradually returning to their normal water level. Weirs and pumps help to regulate a pond’s water levels, allowing for excess runoff to be temporarily stored and then gradually released into the land drainage sewer system.
Residents living adjacent to a retention pond should be aware that water levels can increase significantly on a short-term basis, causing temporary flooding around the pond. For this reason, residents should be mindful of this when deciding where to install structures, when landscaping or when storing items on their properties.
Properties adjacent to retention ponds typically have notable grade breaks or slopes leading down to the pond. These slopes, as illustrated above, can help residents determine where the retention pond water may rise to during normal and high-water level events.