Saltwater Intrusion

Primary reference(s)

European Environment Agency, no date. Helpcenter definition: intrusion of saltwater. Intrusion of saltwater — European Environment Agency (Accessed 13 May 2025).

Annotations

Key relevant UN convention / multilateral treaty

Not identified.

Drivers

Many factors contribute to the severity of the seawater inclusion, among others, pumping and recharge events, aquifer geometry (specifically, depth at the seaside), geological and hydrological parameters, boundary conditions, natural freshwater flux from the land side, and land use (Werner et al., 2013).

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

A major factor of seawater inclusion is groundwater abstraction. Further natural and anthropogenic drivers of seawater intrusion are discussed by White and Kaplan (2017).

Impacts

Seawater intrusion can render freshwater drinking water supplies unusable, especially dangerous for people with hypertension who need to reduce their salt intake (Government of British Columbia, no date). 

In low-lying atoll islands, sea-level rise will make seawater intrusion in shallow aquifers more frequent, in fact too frequent for the aquifers to recover between intrusions, resulting in atolls becoming uninhabitable (Storlazzi et al., 2018). 

Seawater intrusion is also a threat to agriculture, both in coastal areas (U.S. Department of Agriculture Northeast Climate Hub, no date) and in regions where water supply and availability are limited, like Saudi Arabia (Benaafi et al., 2023). Saltwater is unsuitable for irrigation because of its elevated salinity, sodium and magnesium, resulting in salinity and alkalinity hazards that decrease with distance from the sea (Benaafi et al., 2023). 

In addition to the elements cited above, seawater intrusion may also contaminate the aquifer with B, Se, F and Zn which were present above the permissible WHO standards. Other heavy metals were measured but at an acceptable level (Alshehri et al., 2021).   

Saltwater can also impact water quality by 'unlocking' nutrients from fertilisers in farm fields. This is due to the unique chemistry of saltwater and how it interacts with soil. Once these nutrients become mobile, they can travel through networks of agricultural ditches into larger coastal water bodies such as tidal creeks and marshes. There, the excess nutrients can cause excess algae growth. When the algae die, they are broken down by bacteria. This process can use up all the oxygen in the water. Depleted oxygen levels can result in fish kills, loss of animal habitat, and other harmful effects on coastal ecosystems and wildlife (U.S. Department of Agriculture Northeast Climate Hub, no date). This is a threat to agriculture and environmental water uses. 

In an urban context, seawater inclusion, making water saltier and more corrosive, damages pipes and other elements of the water supply and water drainage and sewer system. Other infrastructure like roads, bridges and buildings may also be damaged (Coastal City Resilience and Extreme Heat Action Project (CoCHAP), no date). During Hurricane Katrina in New Orleans in 2005, 90% of City Park was submerged in saltwater, leading to damages estimated at over $43 million (Williams, 2010).

Multi-hazard context

The figure below summarises common interactions between seawater intrusion and other hazards. This information should be used with caution and not be solely relied upon in Disaster Risk Management, particularly as some interactions may not have been included. Note that hazardous events occurring together or locally in space or time may not necessarily cause, amplify, or be otherwise related to each other. Specific examples of multi-hazard contexts can be found in the ‘Hazard drivers’ and ‘Impacts’ sections above.

Multi-hazard diagram

Risk Management

Proper management of seawater intrusion issues requires good knowledge of aquifer systems and the ability to predict their future behaviour under different scenarios of naturally forcing and anthropogenic interactions. In this respect, numerical simulation is widely used to examine seawater intrusion in coastal aquifers and to evaluate alternative groundwater-resource-management scenarios (Jeen et al., 2021). 

Management techniques are generally divided into two main types: managing the pumping of water from the groundwater aquifers and putting in place physical barriers to prevent saltwater from intruding into the aquifers (Wu et al., 2020). The table below 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 (Prince Edward Island Department of Environment, Labour and Justice, 2011).

Monitoring

The section and the table below offer an overview of monitoring for seawater intrusion. This information can be used for forecasting within a national early warning system (EWS). Since EWS capacities and processes differ across countries, the most current and specific information regarding EWS should be obtained from the appropriate national or regional agency/authority responsible for disaster management.