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
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Contributors to this solution
SkyTEM Surveys is a Danish airborne geophysical company with more than 12 years of experience in the mapping water resources. SkyTEM is an innovative and technologically advanced helicopter-borne geophysical system specifically designed to map buried aquifers. This unique technology, capable of mapping the top 500 metres of the Earth in