The Salinity of the St. Lawrence River Under Scrutiny: For a Better Understanding of the Anticipated Impacts of its Variability on the Drinking Water Supply of the CMQ

At the interface between the Fluvial Estuary and the Upper Estuary of the St. Lawrence River lies a zone where surface freshwater from the river mixes with deep saltwater from the Gulf of St. Lawrence.

Average sea level rise, combined with a possible long-term reduction in freshwater flowing into the St. Lawrence from the Great Lakes, the Ottawa River and its many tributaries, could cause the salinity front to shift 30 km upstream during periods of severe low flow or storm surges. While it remains imprecise, the current limit of the salinity transition zone is found near the eastern tip of Île d'Orléans.

An upstream shift in the salinity transition zone could compromise the freshwater supply of some municipalities in the Communauté métropolitaine de Québec (CMQ) and have environmental repercussions such as the modification of coastal habitats and the corrosion of water treatment equipment, distribution systems and plumbing in general.

• Analyze the current spatial and temporal variability of water salinity observed near and at drinking water intakes in the St. Lawrence River and identify the causes;

• Model the movement of the salinity front under scenarios of sea level rise and changes in river flow in 25 and 50 years;

• Promote and disseminate the new knowledge to potential end users and beneficiaries.

The approach is based on the production of a current and future picture of salinity variability, by:

• Identifying spikes and sources of salinity and their causes;

• Modelling current salinity propagation using a 2D model near and at drinking water intakes;

• Modelling spikes in salinity at drinking water intakes under different climate change scenarios;

• Modelling the salinity front using a 3D hydrodynamic model under different climate change scenarios;

• Performing a situation assessment;

• Promoting and disseminating new knowledge to potential end users and beneficiaries.

The project will generate five scientific reports, two models and two situation assessments. In addition, meetings with partners and stakeholders will provide opportunities for knowledge transfer.

This project is funded by the Government of Quebec and meets the objectives of the Plan pour une économie verte 2030.