Seawater

Seawater intrusion is the movement of saline water from the ocean or estuaries into freshwater systems. The seawater that has crept up the Mississippi River in the summer and early fall of 2023 is a reminder that coastal communities teeter in a fragile land-sea balance. Fresh water is essential for drinking, irrigation and healthy ecosystems. When seawater moves inland, the salt it contains can wreak havoc on farmlands, ecosystems, lives and livelihoods. I am a coastal hydrogeologist and have studied water across the land-sea interface for 25 years. I think of seawater intrusion as being like a seesaw: The place where fresh water and salt water meet is the balance point between forces from land and forces from the sea. A push from the land side, such as heavy rainfall or high river flows, moves the balance point seaward. A push from the sea side – whether it’s sea-level rise, storm surge or high tides – moves the balance point landward. Droughts or heavy us...

Coastal urban centers around the world are urgently looking for new, sustainable water sources as their local supplies become less reliable. In the U.S., the issue is especially pressing in California, which is coping with a record-setting, multidecadal drought. California Gov. Gavin Newsom recently released a US$8 billion plan for coping with a shrinking water supply. Along with water conservation, storage and recycling, it includes desalination of more seawater. Ocean desalination, which turns salt water into fresh, clean water, has an intuitive appeal as a water supply strategy for coastal cities. The raw supply of salt water is virtually unlimited and reliable. Ocean desalination is already a major water source in Israel and the United Arab Emirates. Cities in the Middle East, Australia, Mediterranean Europe, the U.S. Southwest and Australia also rely on it. There are more than 20 ocean desalination plants operating in California, plus a few in Florida. Many more plants acr...