Water securityMap shows seawater threat to California Central Coast aquifers
More than half the world’s population lives within 37 miles (60 kilometers) of the coast, and three-quarters of all large cities are located in coastal areas. Many coastal communities rely on groundwater to satisfy their drinking and farming water needs. But removing too much of that groundwater can change the fluid pressure of underground aquifers, drawing seawater into coastal aquifers and corrupting water supplies. Saltwater intrusion is often irreversible. Researchers have transformed pulses of electrical current sent 1,000 feet underground into a picture of where seawater has infiltrated freshwater aquifers along the Monterey Bay coastline.
Researchers from Stanford and the University of Calgary have transformed pulses of electrical current sent 1,000 feet underground into a picture of where seawater has infiltrated freshwater aquifers along the Monterey Bay coastline.
The findings, which will be published in an upcoming issue of the Journal of Hydrology Energy help explain factors controlling this phenomenon, called saltwater intrusion, and could help improve the groundwater models that local water managers use to make decisions about pumping groundwater to meet drinking or farming needs.
“The hope is that local water managers can use these findings to better identify regions most impacted by saltwater intrusion where targeted management practices can be most effectively implemented,” said study co-author Meredith Goebel, a Ph.D. candidate at Stanford’s School of Earth, Energy & Environmental Sciences.
Goebel’s graduate advisor, Rosemary Knight, specializes in adapting geophysical imaging tools to monitor and manage freshwater resources. “In the same way that medical imaging has revolutionized the approach to managing human health, I believe that Earth imaging using geophysical methods can revolutionize the approach to managing the health of our groundwater systems,” said Knight, who is the George L. Harrington Professor at Stanford.
Stanford notes that according to the United Nations, more than half the world’s population lives within 37 miles (60 kilometers) of the coast, and three-quarters of all large cities are located in coastal areas. Many coastal communities rely on groundwater to satisfy their drinking and farming water needs. But removing too much of that groundwater can change the fluid pressure of underground aquifers, drawing seawater into coastal aquifers and corrupting water supplies. Saltwater intrusion is often irreversible.
ERT
To determine the extent of saltwater intrusion in the Monterey Bay region, the research team used a geophysical imaging technique called electrical resistivity tomography (ERT) to map the salinity of groundwater along a 28-mile (45-kilometer) stretch of coastline from Aptos to Monterey. ERT measures a property called electrical resistivity. Seawater is electrically conductive due to its high salt content, while freshwater is electrically resistive (View video here). ERT could provide a cheaper and better alternative than the current method used to monitor saltwater intrusion, which involves drilling “sentinel” wells at specific locations. “Unlike wells, which only give you information at one location, ERT gives you a full two-dimensional slice with spatial coverage that is just not possible with wells,” Knight said.
