The sewer system (secondary and main networks) on the Island of Montreal includes 170 overflow structures. An overflow structure consists of an underground control chamber that directs wastewater into the collection and interception network under normal operating conditions to the treatment plant. During rain, melt or during an operation associated with maintenance or impairment, the inputs exceed the regulatory capacity and this excess is overflowed by the structure in question in the watercourses. It is under these conditions that part of the water combining rainwater and wastewater flows to the receiving watercourse for a short period of time (via the outfall). Obviously, the receiving watercourse to the south is the St. Lawrence River and that to the north, the Rivière des Prairies.**This third party metadata element was translated using an automated translation tool (Amazon Translate).**