Improving groundwater understanding to reduce overdraft and manage groundwater for long term sustainability

In 2014, the California State Legislature adopted the historic Sustainable Groundwater Management Act (SGMA), which established a statewide framework to help protect groundwater resources. Groundwater Sustainability Agencies (GSA) are responsible for achieving long-term sustainable management of their groundwater basins and to develop and implement groundwater sustainability plans (GSP). 

As different challenges occurred when implementing new legislation for California Department of Water Resources, it was important to provide the GSAs with solid data material by filling lack of data and accurate data needed data for groundwater sustainability plans. 


Assist local water agencies to successfully meet California state mandates for groundwater sustainability under the Sustainable Groundwater Management Act

Ramboll is conducting regional-scale airborne electromagnetic (AEM) surveys to map aquifer systems under contract to the California Department of Water Resources (DWR). Team member SkyTEM developed the AEM method towed by helicopter specifically for groundwater investigations, making it ideal for this application.  

The AEM project provides state and federal agencies, stakeholders, and the public with basin-specific and cross-basin geophysical data, tools, and analyses, and for GSAs. These new data support implementation of the Sustainable Groundwater Management Act (SGMA) to manage groundwater for long term sustainability. The foundation of this statewide AEM program is the Stanford Groundwater Architecture Project (GAP), a three pilot effort using AEM to help demonstrate the viability of the technology for mapping California’s aquifer systems, which was funded by the state of California, the three local water agencies involved in the pilots, and the Kingdom of Denmark. 

During an AEM survey, a helicopter tows electronic equipment that sends signals into the ground which bounces back. The process has been compared to taking an MRI of the ground’s subsurface. The data collected is used to create continuous images that are interpreted for subsurface geology and aquifer system lithologies. The resulting information provides a standardized, statewide dataset that improves the understanding of aquifer system components and geometry that contributes to the development or refinement of hydrogeologic conceptual models (HCMs) and can help identify suitable areas for recharging groundwater. 


Use airborne electromagnetics to map aquifer system lithology and geometry at regional scale quickly and effectively

Ramboll has worked closely with SkyTEM and DWR to test the limits of the AEM equipment for improving near surface resolution to identify potential surface infiltration sites for aquifer recharge, and for mapping deep aquifer system and geological structures. 

In the southeast San Joaquin Valley, along the Upper San Joaquin River below Friant Dam, adjustments were made to the SkyTEM system to increase shallow subsurface data collection, resulting in successfully increasing shallow lithology resolution. On a separate local agency project, a deeper-focused and more powerful SkyTEM system designed for mineral exploration was used to successfully map the bottom of the deep aquitard and top of the deep aquifer, which was integrated with other AEM data in the groundwater basin to update the HCM and groundwater flow model.  

Local agencies have been and are continuing to apply the statewide AEM data in groundwater evaluations and projects. In the Indian Wells Valley Groundwater Basin, the AEM data were used to update the hydrogeologic conceptual model for the basin, which was subsequently integrated with reprocessed legacy seismic data to inform the basin geometry, thickness of sediments, and groundwater storage volume. 

AEM is literally helping us identify the needle in the haystack

Kassy Chauhan, Executive Director, North Kings Groundwater Sustainability Agency

In the San Joaquin Valley, some water managers indicate that the AEM data is fundamentally changing how they decide where to build expensive recharge basins or restrict pumping. Aaron Fukuda, General Manager of the Tulare Irrigation District, said the AEM data revealed that the aquifers on the eastern edge of the Kaweah Subbasin, which covers Visalia and parts of Tulare County, were shallower than originally thought. The data also showed that there was more recharge potential on the western side of the basin. As a result, Fukuda said groundwater pumping is limited or more closely monitored on the east while new recharge projects have been built or planned for the western side. In the neighboring Kings Subbasin, water managers are looking to take advantage of a paleo valley northeast of Fresno discovered in the AEM data. “AEM is literally helping us identify the needle in the haystack (…)”, said Kassy Chauhan, executive director of the North Kings Groundwater Sustainability Agency. Local and state groundwater managers said that AEM data helped this spring in determining the best areas to spread floodwater from the winter storms and Sierra snowmelt (Wester Water, June 2023).

To date, the California statewide AEM project has flown over 22,000 line-kilometers and completed a significant portion of the reporting. Maps and reports are posted on the DWR- AEM website. One additional survey is scheduled for fall 2023 for the statewide regional-scale AEM project, where subsequent data analysis and reporting is scheduled to be completed in the third quarter of 2024. 

Next steps in California include some potential AEM infill areas with regional scale that need refinement for specific objectives, such as increased resolution for recharge feasibility analysis, and further improvement of aquifer system understanding. In addition, a new DWR program is planned which will involve additional groundwater investigations with land-based and floating towed TEM systems. The program will involve a series of pilots to help demonstrate best practices for application of geophysics and other technologies in groundwater investigations and management for sustainability. 



SkyTEM, Sinton Helicopters , and GEI 


Katherine Dlubac
California Department of Water Resources