Stormwater is water from rain or melted snow that flows over roofs, yards, parking lots, ditches and streets, and eventually enters a city's storm sewer system. The storm sewer system is a network of ditches, culverts and sewers that transports stormwater to nearby creeks, lakes or rivers. Catch basins are the openings you see along curbs in streets and parking lots where rainwater can enter the storm sewer system.

City of Ottawa

Most of the stormwater in the city of Ottawa does not go to the City's sewage treatment plant, so it is important to prevent pollutants from entering the system and damaging the water ecosystem. In most areas of the City of Ottawa, the wastewater collection system and the stormwater collection system are a separate network of pipes. In the oldest part of the City of Ottawa there is only one sewer system for both waste streams - it is called the combined sewer area. The wastewater including the flow from the combined sewer area travels through the wastewater collection pipes to the city's wastewater treatment plant, the Robert O. Pickard Environmental Centre, where is it treated to strict quality standards before it is released into the Ottawa River. 

Overflow events

Overflow events occur in the City of Ottawa when there is heavy rainfall. The combined sanitary and stormwater sewer system that covers older downtown neighbourhoods can reach capacity and regulators must be opened to divert some of the stormwater and sewage into the Ottawa River. While the mixture of stormwater and sewage is diluted it amount of overflow can be in the thousands of cubic metres. The City monitors these events and reports them to the Ontario Ministry of the Environment.

However, some of the regulators are more than 50 years old, and can malfunction allowing sewage to spill unnecessarily into the river. A huge overflow event occurred in 2006, which has prompted the City of Ottawa to invest $25 million into upgrades to the sewer system.

City of Gatineau

In addition to the City of Ottawa, Gatineau also sends sewage into the river when there is a heavy rainfall or the snow melts too quickly for its combined storm and sanitary sewers to handle.
Waste from older neighbourhoods between Aylmer and Buckingham doesn't necessarily go to Gatineau's sewage treatment plant on Notre-Dame and Campeau streets. Much of it flows into the river through 96 storm water outlets. Quebec Ministry of Municipal Affairs records show that Gatineau released sewage into the Ottawa and La Lievre rivers 1,231 times in 2005.

Gatineau's combined storm and sanitary sewers can handle up to three times the normal flow from rainfall, but when there is too much water, the excess water and sewage is directed automatically into the river rather than toward the city's sewage treatment plant. The City of Gatineau is conducting a study to determine which parts of its sewage system should be improved first.

Learn how you can prevent polluted stormwater from flowing into the Ottawa River.

Sourced from the Ottawa Citizen,  Heavy rain or fast melt runs through 96 outlets, - Friday, December 15, 2006, and Sewage overflow fix to cost $25 million, Patrick Dare, Ottawa Citizen
Published: Friday, August 01, 2008