Sea Water Intrusion

Primary reference(s)

NRC, 2011. Saltwater Intrusion and Climate Change: A primer for local and provincial decisionmakers. Natural Resources Canada (NRC). Accessed 13 October 2020.

Additional scientific description

With rising sea levels, saline water intrusion into coastal aquifers, surface waters and soils is expected to become more frequent and advance further inland. Salinisation of groundwater, surface water and soil resources also increases with landbased drought events, and decreasing river discharge in combination with water extraction and sea-level rise (Oppenheimer et al., 2019).

Seawater intrusion is also known as saltwater intrusion, and defined as ‘a process by which saltwater invades freshwater in service water or groundwater bodies’ (WMO, 2012).

Metrics and numeric limits

Surface water salinity is described by units of electrical conductivity (EC). Groundwater salinity is described by units of parts per million (ppm). Scientific reports use decisiemens per metre (dS/m) as the main unit of measure (USGS, 2019).

The concentration is the amount (by weight) of salt in seawater, as expressed in parts per million (ppm) (USGS, 2019). Salinity is the measure of the concentration of dissolved (soluble) salts in water from all sources.

Examples of drivers, outcomes and risk management

Saltwater intrusion refers to the process by which sea water infiltrates coastal groundwater systems, thus mixing with the local freshwater supply. Groundwater is stored in the pores and fractures of rock beneath the surface, and the rock formations containing groundwater are referred to as aquifers (Prince Edward Island Department of Environment, Labour and Justice, 2011).

Aquifers are naturally replenished (or recharged) by way of precipitation (rain, snowmelt) that seeps into the ground and eventually reaches the water table. Because saltwater is denser than freshwater, this saline groundwater may ‘intrude’ beneath fresh groundwater, creating a saltwater ‘wedge’ at the coastline. In addition to the local hydraulic and density gradients, the nature of this saltwater–freshwater interaction is controlled by many factors, including the characteristics of the aquifer (such as permeability and thickness) and the characteristics of any layers of rock underlying or overlying the aquifer (confining layers) (NRC, 2011; Government of Australia, 2015; Chun et al., 2018).

Further natural and anthropogenic drivers of seawater intrusion are discussed by White and Kaplan (2017).

The table provides a summary of strategies, approaches, and tools to mitigate the impacts of saltwater intrusion (Montanari, 2017; White and Kaplan, 2017).

As part of the Regional Adaptation Collaborative (RAC) of Natural Resources Canada, case studies have been developed in each of the Atlantic Canadian provinces in order to better understand saltwater intrusion, as well as the challenges and needs it presents. Case studies are being conducted to investigate existing conditions and the potential impacts of climate change on groundwater resources (NRC, 2011).