Could the answer to groundwater resources come from above?
Groundwater accounts for 30 to 50 percent of the California water supply, but until recently there were few restrictions on its recovery. Then, in 2014, California became the last western state to require regulation of its groundwater. With deadlines starting this year, for the first time, water managers in the country’s premier agricultural region – the state’s central valley – are tasked with estimating available groundwater. It is a major technological challenge.
Now, a new computer approach developed by scientists at the Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab) offers a simple, high-tech method: it combines high-resolution satellite-derived images with computer modeling advanced to estimate the change in aquifer volume from soil deformation observations. The method could help streamline groundwater monitoring in an area, once several local management agencies start submitting water management plans to comply with the 2014 Law on Sustainable Groundwater Management ( or SGMA, pronounced “sigma).
“Drought has been prevalent throughout California’s history and is inevitable in the future. Traditional methods of measuring groundwater levels have limitations for the type of integrated management required under SGMA, ”said Pierre Nico, Berkeley Lab environmental geochemist and researcher involved in the effort. “Using this technique, it is possible to create a ‘living’ model of the groundwater resources of the central valley that could be updated frequently and used on a very local or very large scale. “
The method applies one of the key strengths of the Berkeley Lab – computer science – to an area that is important to the Lab: water sustainability. Scientists believe this could establish the necessary framework for water managers to represent the groundwater resources of the Central Valley on a small local scale and also on a larger scale that takes into account the aggregate resources of various neighboring jurisdictions. .
What land deformation says about aquifer volume
In this project, scientists used data obtained from Synthetic Aperture Radar (SAR) satellites representing observed surface subsidence, or where the earth is sinking and groundwater storage capacity has declined. . These data provide a much more detailed, macro-level snapshot of aquifer compaction, a process sensitive to groundwater levels in the central valley. They paired satellite observations with a public database of wells drilled in California to estimate the spatial distribution of the volume of the aquifer that is lost each month in the state due to pumping.
Their findings, recently published in the journal Nature Scientific reports, suggest that the volume of the aquifer is influenced by variations in the effective pressure in the soil surrounding the wells documented. For the periods studied, the spatial patterns of changes in the volume of the aquifer vary considerably between the years representing drought (October 2015 to 2016), precipitation (2017) and near-average precipitation (2018), reflecting the differences. pumping of groundwater, which changes depending on the deliveries of surface water to farmers.
The researchers believe their methods might be relatively straightforward for local groundwater sustainability agencies to implement, as spatially explicit estimates of aquifer volume loss are relatively inexpensive to obtain and can be used by practitioners. local agencies to estimate localized areas of intensive pumping and overconsumption of groundwater.
“This technique makes it possible to assess groundwater resources not only at a very local level, but on a larger scale, in order to benefit multiple stakeholders,” said Nico.
The hyperlocal approach risks doubling the available water
For a long time, groundwater was regularly pumped in California to meet water needs when surface water from rivers, lakes, and streams was insufficient – so much so during the many years of persistent drought that over-pumping pushed the state to change the course. SGMA legislation.
SGMA requires water users to end overdraft and bring critically exposed groundwater pools to balanced pumping and recharge levels by 2040. Local groundwater sustainability agencies responsible for Developing sustainable management policies for oversubscribed groundwater basins are now faced with the difficult task of estimating groundwater use and aquifer storage capacity. without sufficient systematic and quantitative monitoring, according to researchers at the Berkeley Lab.
Unfortunately, there is no cost-effective method that has proven to be useful for monitoring aquifer storage with sufficiently high resolution but over necessary spatial expanses, even in highly developed agricultural areas such as the Central Valley of California, according to Don Vasco, principal investigator at the Berkeley Lab and principal author of the article for Scientific Reports.
For example, an approach using observed water levels in borehole monitoring throughout the central valley to indicate aquifer status is largely ineffective, as boreholes are generally shallow and may not accurately represent the state of the aquifer. health of deeper aquifers. The generally dispersed boreholes would also not provide information over sufficient spatial extents to detect localized areas of high water consumption.
“Monitoring is essential to assess the loss of storage capacity in a given aquifer – and to determine the rate of groundwater depletion – at a resolution that matches the needs of agencies responsible for groundwater management, from a few kilometers away. tens of kilometers away, ”says Vasco.
The Public Policy Institute of California recently assessed 36 groundwater sustainability plans submitted to the state for 11 severely deficient basins in the San Joaquin Valley, California’s largest agricultural region. Their review identified the potential pitfalls of hyperlocal management, showing that while estimates of water supply may seem reasonable when plans are considered individually, examining plans as a whole exposes the potential for double counting of water supplies in adopting such a localized approach.
This perspective highlights the need for an integrated monitoring tool that can be applied on a small scale, but also provide integrated insight across large jurisdictions encompassing multiple management areas to prevent any impact from falling through the cracks. .
“If adopted statewide, the computational approach we have developed could allow new local groundwater sustainability agencies (GSAs) established under the SGMA to estimate the spatial variation of the use of groundwater for their own area and the wider region at the same time, ”Nico said. .
The technique could also become a new approach that stakeholders in other U.S. states as well as other nations might consider as part of their water management strategies, the researchers said.
The effort is supported by the Berkeley Lab’s Laboratory-Led Research and Development Program (LDRD), through which the laboratory directs funding to specific areas of research.
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Founded in 1931 on the conviction that the greatest scientific challenges are best met by teams, Lawrence Berkeley National Laboratory and its scientists have been awarded 13 Nobel Prizes. Today, researchers at the Berkeley Lab are developing sustainable energy and environmental solutions, creating useful new materials, pushing the boundaries of computing, and probing the mysteries of life, matter, and the universe. Scientists around the world rely on the laboratory facilities for their own scientific discoveries. Berkeley Lab is a national multi-program laboratory, operated by the University of California for the Office of Science, US Department of Energy.
The DOE’s Office of Science is the largest supporter of basic research in the physical sciences in the United States and works to address some of the most pressing challenges of our time. For more information, please visit energy.gov/science.