Seawater intrusion is the movement of salt water from the ocean into freshwater aquifers. This can occur when the water table near the coast is lower than the sea level, creating a gradient that draws saltwater inland. Seawater intrusion can also occur when there is a change in the land surface, such as when a barrier island is breached, allowing saltwater to flood into the aquifer.

The most significant consequence of seawater intrusion is the contamination of freshwater supplies with salt. This can make the water undrinkable and unusable for irrigation, which can have a devastating impact on coastal communities. Seawater intrusion can also lead to the degradation of ecosystems, as the salt water can kill plants and animals that are not adapted to living in saline conditions.

There are a number of things that can be done to mitigate the effects of seawater intrusion, including:

* Managed Aquifer Recharge (MAR): MAR involves injecting freshwater into an aquifer to raise the water table and create a barrier to saltwater intrusion.

* Desalination: Desalination is the process of removing salt from water, and can be used to provide freshwater for drinking and irrigation in areas affected by seawater intrusion.

* Aquifer Storage and Recovery (ASR): ASR involves storing freshwater in an aquifer during times of low demand and withdrawing it during times of high demand. This can help to maintain the water table and prevent saltwater intrusion.

Seawater intrusion is a serious problem that is expected to worsen as sea levels rise due to climate change. By taking steps to mitigate the effects of seawater intrusion, we can help to protect our freshwater resources and coastal ecosystems.