Airborne Electromagnetic Survey

SLVWD Board President Mahood made an announcement at the November 3, 2022 Board Meeting which she subsequently expanded on in the message below (originally posted to NextDoor):

A literal “heads up” to my SLV neighbors! A geophysical survey to better understand underground geologic structures that control groundwater in the San Lorenzo River watershed will happen Nov. 6-17. This involves a helicopter flying about 300’ above the ground towing an instrumented loop that looks a bit like a gigantic bubble wand about 100’ above the ground. An electrical current flowing through the loop generates a magnetic field that allows us to image—much as happens when you get an MRI—rock layers to a depth of 1000’ underground.

The flights are being undertaken by the California Department of Water Resources to increase our understanding of groundwater-bearing aquifers throughout the state in basins like our local Santa Margarita, Santa Cruz Mid-County, and Pajaro Valley groundwater basins that are in over-draft.  There is no cost to local water districts or groundwater agencies.

In our Santa Margarita groundwater basin the flight lines have been chosen to better understand underground geologic structures in the San Lorenzo Valley watershed for purposes of:

• siting new groundwater production wells to spread out and reduce our local impact on aquifers;

• locating the best places for rainwater infiltration basins to recharge underlying aquifers;

• understanding linkages of creeks, springs, and marshes to groundwater to better protect groundwater-dependent ecosystems and fisheries;

• figuring out the characteristics of rock formations utilized by shallow private well owners (e.g., the Monterey Formation) that contribute to these wells underperforming.

Flight lines further south, along the Monterey Bay coastline are designed to map where seawater has intruded into aquifers as a result of over-pumping.

Flights will happen in daylight hours only, and there will be no flights over concentrations of homes or businesses (e.g., downtown Felton or Scotts Valley). Homeowners located under flight lines have been notified; these include areas near Brookdale, Lompico, Glenwood, Ben Lomond, Quail Hollow, and Olympia, as well as along Bean Creek, Zayante Creek, and Lockhart Gulch.

For further information, I recommend the excellent video available at: https://water.ca.gov/programs/SGMA/AEM

Full disclosure:  I am currently the President of the Board of Directors of the San Lorenzo Valley Water District and the President of the Board of Directors of the Santa Margarita Groundwater Agency, but I am posting this notice to NextDoor as your local neighborhood geologist in anticipation that some of you may wonder what that bizarre contraption is doing flying at low elevations over our valley!