AEM mapping California’s groundwater

Airborne electromagnetic surveys, mapping, and modelling of groundwater sources to help futureproof water access and sustainable water management for communities and farms in California.
We collaborated with SkyTEM and GEI Consultants to conduct airborne electromagnetic (AEM) field surveys for the California Department of Water Resources. A helicopter uses equipment to transmit electromagnetic waves to the earth to paint a digital picture of the terrain below the surface. The goal is to create detailed maps of the state’s high-and mediumpriority groundwater basins.
California is the most populous, most visited, and the third-largest state in the USA by area (2022). Over a third of America’s vegetables and two-thirds of the country's fruits and nuts are grown in California. For both Californian farms and communities to develop sustainable water management systems, ground water is a critical resource.
After a series of droughts, the State of California enacted the Sustainable Groundwater Management Act (SGMA) which requires local groundwater sustainability agencies (GSAs) in high- and medium-priority groundwater basins to develop and implement groundwater sustainability plans.
Mapping California’s underground water by air
To support the SGMA and the GSAs work, Ramboll led the collaborative effort with SkyTEM and GEI Consultants to conduct airborne electromagnetic (AEM) field surveys for the California Department of Water Resources (DWR).
Surveys are completed by a helicopter using equipment to transmit electromagnetic waves to the earth to paint a ‘digital picture’ of the subsoil below the surface. These detailed maps of the state’s high-and medium-priority groundwater basins provides valuable data. Such data is used to help improve understandings of large-scale aquifer structures and support the implementation of the SGMA.
“AEM data gives a better, localised understanding of groundwater basins and provides datasets that support the overall implementation of California’s Sustainable Groundwater Management Act and the development of groundwater sustainability plans,” said Steven Springhorn, technical assistance manager of the Sustainable Groundwater Management Act for the California Department of Water Resources.
Sustainable outcomes and opportunities
Mapping groundwater enables us to find untapped groundwater opportunities that can help communities become less dependent on surface water. With accurate water data, communities can future proof their development by creating water management systems with secure and consistent water supply.
The AEM project provides state and federal agencies, GSAs, stakeholders, and the public with basin-specific and cross-basin geophysical data, tools, and analyses.
Ramboll and SkyTEM have previously collaborated to create similar detailed groundwater resource maps in California and in other countries. To meet specific local needs, we can tailor the design of management systems to be flexible enough to account for system extensions and future conditions.
The project is generating coarse-grid subsurface maps that provide framework information about large-scale aquifer structure. The AEM data hence supports the development or refinement of hydrogeologic conceptual models as well as helps to identify possible areas for recharging groundwater.
Strong alliances to address water challenges
Since 2018, we have collaborated on water-related issues with the State of California due to the Water Technology Alliance (WTA). Established in 2015, the WTA’s purpose is to disseminate knowledge about the Danish water models and support the Danish water industry.
Today, we continue to strengthen our groundwater-related collaborations with California, by applying and adapting proven Danish technologies and approaches.
“I am pleased Danish expertise and technology will be a part of California’s efforts in sustainable groundwater management. International partnerships and knowledge-sharing are essential for climate adaption. We’re excited to strengthen our collaboration with California and take joint steps towards a climate-friendly water sector,” said Lone Dencker Wisborg, Danish ambassador to the US.
Watch the video of the helicopters, AEM, and project team in action solving California’s extraordinary water challenges.
The project is expected to be completed in 2026. For more information about the project, visit DWR’s state-wide AEM surveys project webpage.

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  • Ian Gottschalk

    Ian Gottschalk

    Senior Geophysicist

  • Joakim Hollenbo Westergaard

    Joakim Hollenbo Westergaard

    Senior Geolog

    +45 51 61 11 85