Case

Managing risk of saltwater intrusion in coastal water-scarce basins

The Soquel Creek Water District (SCWD) in Monterey Bay, CA is experiencing a shortage of freshwater resources. Surrounded by mountains and the Pacific Ocean, saltwater intrusion has become a primary concern.

This has become a widely recognised issue in growing cities along the coast and highlights the importance of aquifer management. For SCWD, understanding the saltwater-freshwater interface in the aquifer is crucial and can be done using the geophysical airborne electromagnetic method (AEM).

To better understand this saltwater-freshwater interface, SCWD used an AEM survey to produce 3D subsurface imagery. Flown by a helicopter towing the sensor as a sling load, an AEM survey measures variation in conductivity in the subsurface, which translates to salinity. Due to safety and possible data disturbance by power lines and other man-made structures, the survey was flown along the coast and 1.5 km offshore.

In certain areas, the results showed freshwater pushing the saline water out into the bay. In other areas, saline water was close to extraction wells. To substantiate the AEM results, SCWD measured salinity in screened intervals at different depths. The correlation of these two data sets ensured SCWD had an accurate snapshot of the saltwater-freshwater interface. The district plans to conduct a second survey after a period of five years to see if changes in recharge or extraction rates have changed the location of the saltwater-freshwater interface.

Contributors: Ramboll, SkyTEM

About author

Ramboll employs more than 16,500 experts globally and has especially strong representation in the Nordics, UK, North America, Continental Europe, Middle East and Asia-Pacific. With 300 offices in 35 countries, Ramboll combines local experience with a global knowledgebase constantly striving to achieve inspiring and exacting solutions that make a genuine difference to our clients, the end-users, and society at large. Ramboll works across the following markets: Buildings, Transport, Planning & Urban Design, Water, Environment & Health, Energy and Management Consulting.

Primary contact
Anders Dyrelund

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