The effort to improve groundwater management in the state is not a new one, and following the passage of the Sustainable Groundwater Management Act (SGMA), tech has driven the conversation. While online maps have improved understanding, the Department of Water Resources (DWR)’s project using AEM project aims to further these efforts and support long-term sustainability.
California has historically faced drought-related challenges, and this year, drought conditions are impacting farmers in Central Valley, causing farmers to rely on depleted groundwater supplies.
According to the most recent drought update from the state on May 16, January, February and March of this year were the driest on record for over 100 years. All 58 of California’s counties were under a drought emergency proclamation at the time of this report.
As outlined in an April 2022 policy brief from the Public Policy Institute of California, this drought has raised challenges for SGMA implementation. The report underlines that dry conditions will persist in 2022, increasing impacts — both economically and agriculturally.
The SGMA was signed into California state law in 2014, requiring local groundwater sustainability agencies to be formed to ensure groundwater management decisions minimize negative environmental impacts. In 2018, Proposition 68 was passed by voters, authorizing $4 billion for water infrastructure and environmental protection and restoration projects. $12 million of this funding was allocated to conduct the AEM survey and analysis for drought and groundwater investments, building on the efforts of SGMA.
Steven Springhorn, a supervising engineering geologist and manager at DWR, said that the enactment of the SGMA was a pivotal moment for the state’s groundwater management practices. But it was the funding from Proposition 68 that enabled this AEM data collection.
So what does this data collection project actually entail? DWR engineering geologist Katherine Dlubac, project manager for DWR’s statewide AEM surveys, explained that the geophysical method of gathering data involves a helicopter flying at about 200 feet, towing a large hoop about 100 feet beneath.
“So when we fly across the Earth along defined flight paths, we send signals into the subsurface, and we receive them when they bounce back,” she explained. “And we can use that information and interpret it for aquifer properties.”
Layers of aquifers — permeable rock that can contain groundwater — make up a groundwater basin.
The specific properties the agency is interpreting for within these aquifers are the distribution of materials like sand, gravel, silt and clay. Sands and gravels within an aquifer typically allow for water flow, while silts and clays typically inhibit water flow. The AEM data provides DWR with images of an aquifer’s large-scale properties for a depth of about 1,000 feet.
But the data collected is really information about the electromagnetic properties, like the electrical resistivity of different materials. High electrical resistivity typically corresponds to coarse grain materials like sands and gravels, while low electrical resistivity typically corresponds to fine grain materials like silts and clays.
Through those properties, and with the additional information the agency already has available from boreholes, DWR can interpret where different materials are located.
So the short-term goal, Springhorn said, is to get this AEM data into local agencies’ hands so they can use it to inform their local groundwater management decisions — like what locations are best for groundwater recharge projects.
The long-term goal, though, is to support California’s Groundwater (Bulletin 118), a document with a compendium of information about the status, condition and management of groundwater in the state — both from the AEM technology and other information sources. This resource will help inform a comprehensive understanding of the basin's hydrology, which can be used by DWR, local groundwater managers and members of the public.
The compendium is published every five years, and the latest update was finished in 2021.
The surveying started in summer 2021 and takes place for a few months at a time. This spring has involved collecting data throughout the state’s Central Valley, Dlubac said. This is where the majority of groundwater use is occurring. When this area’s data collection is complete, only 15 percent of the data collection will remain.
Some data is already released to the public, but the remaining data will be made available publicly through the year 2023.
The data helps guide decision-making in drought conditions. For example, in planning to better withstand future droughts, the technology helps to understand where the water is, where it can be accessed and where it may be stored for future droughts. Springhorn underlined that during drought conditions, groundwater basins make up about 60 percent of the state’s water supply.
In addition, more surveying enables DWR to further define high-priority areas that are connected to drought. This can help highlight where disadvantaged communities may be at risk of declining groundwater levels, for example.
Over the next year, Springhorn said the focus will shift to supporting local agencies through partnerships and data delivery.
Groundwater sustainability agencies throughout the state are forming groundwater sustainability plans, which define how groundwater will be managed over the next 20 years and beyond, Springhorn said.
The Mid-Kaweah Groundwater Sustainability Agency, which was formed in 2017, was able to access groundwater basin data prior to other local agencies, because the Tulare Irrigation District served as a pilot program for this type of data collection in 2015 in partnership with Stanford University.
According to Aaron Fukuda, general manager of the Tulare Irrigation District and of the Mid-Kaweah Groundwater Sustainability Agency, this data collection has transformed the image water managers have of what their groundwater looks like.
“We’re making multimillion-dollar decisions,” he explained. “We’re potentially making decisions that impact our communities based upon everything underground that you cannot see.”
Fukuda said that prior to this project, the images were essentially two-dimensional “crayon drawings,” but as he explained, having a better image of what is beneath the surface allows for better decision-making.
As he explained it, in order to plan where to go for a trip, one needs to have a map. This data provides that map to help local agencies better chart their course.
