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Research & Discovery

A Blog Devoted to UD Innovation, Excellence and Scholarship

Fresh water under the ocean

by | May 24, 2019

UD study examines the dangers of depleting freshwater resources beneath the world’s oceans

The last place most people would expect to find fresh groundwater is tens or hundreds of kilometers offshore in the ocean. Yet not only is that where freshwater can be found, in the ground of the continental shelf beneath the ocean, but simulations have shown that it could be a common occurrence across a range of geologic systems.

These offshore groundwater resources could be exploited for uses such as drinking, agriculture and oil recovery, but new research from the University of Delaware’s Holly Michael and Xuan Yu, who worked as a postdoctoral researcher at UD, suggests that tapping into those resources could lead to adverse onshore impacts.

The research was published in Geophysical Research Letters and is part of Michael’s National Science Foundation CAREER Award.

Through simulations and computer modeling, the research explores how using offshore freshwater resources could threaten onshore aquifer systems, lead to diminished onshore groundwater availability and cause widespread land subsidence.

Coastal communities may consider using these offshore groundwater resources as populations increase and the limited freshwater resources are degraded by overuse and pollution, but a more immediate use of the offshore fresh and brackish groundwater is to enhance oil recovery.

University of Delaware President Dennis Assanis takes a quick “selfie” with Delaware’s U.S. Senators — Chris Coons (center) and Tom Carper (right) during the fifth “UD Day in D.C.” event on Capitol Hill.

ABOVE: Some oil rigs are hundreds of miles offshore. Some are much closer, like these rigs off the Southern California coast.

If that water is pumped out for low-salinity waterflooding, the pressure is changed underground and it can reduce the ability of the aquifer to support the weight of the city.

Subsidence has been seen in megacities with the constant extraction of water below ground, with examples being Venice and Tokyo. Pumping offshore freshwater resources for low-salinity waterflooding could have this same affect.

“This effect can hardly be simulated when a simple geologic structure is assumed,” said Yu, who is now an associate professor in the school of civil engineering at Sun Yat-sen University in China. “Our model results suggested that the magnitude of subsidence in homogenous and layered geology is much smaller than the heterogeneous cases.”

In addition to land subsidence, another possible consequence of oil companies tapping into these offshore freshwater resources is that the freshwater aquifers onshore could experience increased salinization, again through the connection between the offshore freshwater and the freshwater onshore.

The reduction in onshore fresh groundwater from low-salinity waterflooding can also have an impact on coastal population centers, especially in locations where oil reservoirs lie offshore of highly populated cities, such as those in Southeast Asia and the Mediterranean Basin.

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