A team of Stanford University researchers believe they have identified the best way to replenish the shrinking aquifers beneath California’s Central Valley.
The groundwater beneath the Central Valley has been steadily depleting, particularly as the state’s $50 billion agricultural industry relied on it during a series of droughts. Each year, more water exits the aquifer than goes into it.
The study from Stanford’s School of Earth, Energy and Environmental Sciences, published in the journal Water Resources Research, found that unless action is taken, the ground in that region will sink more than 13 feet over the next 20 years.
“There is a time delay in the system,” said Stanford geophysicist Rosemary Knight, senior author on the study. “The only way we can stop it is to be strategic about what we do with our available recharge water.”
Knight said that the Central Valley is in the midst of “a perfect storm” of conditions — including little rain, rising temperatures and an abundance of clay, which is prone to subsidence, or caving in — that will contribute to ground collapse.
Much of that clay, which compacts as it dries out, is loaded with arsenic that could be pumped into the water supply.
In order to “recharge” aquifers, farmers have taken to strategic flooding of their fields and orchards.
“The key question is where does the water go?” Knight said. “If you’re going to flood a farmer’s field, you should be sure it’s going to work.”
The approach recommended by the study relies on “a marriage of two types of remote sensing data” that analyzes sand and clay layers in the ground. It “could be applied across large agricultural regions at relatively low cost,” according to a statement announcing the report.
As researchers collect more data, they will be able to better predict where the ground is most at risk of sinking. The study authors said this will be vital in the future.
“As groundwater demand grows globally due to climate change, more basins are experiencing land subsidence, making it essential that we can accurately model the impacts of groundwater depletion and design effective management strategies to reduce or avoid subsidence,” they concluded in the study.
Former Gov. Jerry Brown in 2014 signed a law to increase regulation of over-drafted groundwater basins. It takes effect gradually. By 2020, newly formed groundwater management agencies must develop plans to make their aquifers sustainable.
After he signed the law, farmers dug hundreds of new wells. In 2016 alone, Central Valley farmers created 2,500 new wells, according to a Sacramento Bee analysis of state records.