Freshwater Challenge: Imaging Saltwater Intrusion Along Monterey Bay

A team led by Stanford Earth groundwater expert Rosemary Knight and faculty colleague Adam Pidlisecky from the University of Calgary performed an ambitious experiment to determine the extent of ocean saltwater intrusion into freshwater aquifers in the Monterey Bay region with unprecedented resolution.

Many California communities, including the agriculturally productive Monterey and Santa Cruz coasts, rely on groundwater to meet the freshwater needs of their residents and farmers. In California, 80% of groundwater goes to agriculture. (photo by Stacy Geiken)

Pumping freshwater out of the ground changes the fluid pressure of aquifers, and if the aquifer is located near the coast, saltwater can move in. Saltwater intrusion can dramatically change the salinity of an aquifer, rendering it unusable. (photo by Stacy Geiken)

Saltwater has been intruding farther into the coastal groundwater aquifer in the Monterey Bay region since the 1940s. In the fall of 2014, a team led by Stanford Earth groundwater expert Rosemary Knight and faculty colleague Adam Pidlisecky from the University of Calgary performed an ambitious experiment to determine the extent of ocean saltwater intrusion into freshwater aquifers in the Monterey Bay region with unprecedented resolution. (Source: Monterey County Water Resources Agency)

The researchers embedded hundreds of metal electrodes into the sand along the coast. They then ran a strong electric current through the line connecting the electrodes to image the subsurface in an advanced geophysical method known as electrical resistivity tomography (ERT). (photo by Stacy Geiken)

To successfully image saltwater intrusion along miles of coastline, the research team used dune buggies to deploy their electrode sensors and the cables that connected them. (photo by Stacy Geiken)

Stanford Earth PhD student Meredith Goebel attached the electrodes along the beach to gather data on saltwater intrusion. Acquiring the data took two weeks, followed by several months of analysis and interpretation, yielding valuable information for Monterey groundwater managers. (photo by Stacy Geiken)

Stanford Earth professor Rosemary Knight (left) explained the team’s work to local reporters while on the beach. The news reports gave Monterey Bay area residents much needed information about saltwater intrusion and an introduction to the tremendous value of using geophysical imaging techniques. (photo by Stacy Geiken)

The initial results of the mapping study show how far saltwater has intruded along the Monterey Bay coastline in unprecedented detail (Red colors indicate saltier water, blue colors indicate fresher water). Local groundwater managers can use this information for informed proactive groundwater management.

"The more information we have, the better we understand our groundwater systems and the better we can manage our vital freshwater aquifers." -Rosemary Knight (above)

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Freshwater Challenge: Imaging Saltwater Intrusion Along Monterey Bay

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Freshwater Challenge: Imaging Saltwater Intrusion Along Monterey Bay

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