The storm that soaked Southern California two years ago was not sufficient to replenish deep underground aquifers that had been pumped and depleted over the past 20 years, new research found.
Scientists at Stanford University analyzed how the historic 2023 storm affected groundwater levels across Los Angeles and Orange Counties. They found that while shallow aquifers repelled, more than 150 feet of underground aquifers have only recovered about 25% of the water lost to pumping since 2006.
“The rain that is rained by a big explosion, much of it charges shallow aquifers, but it doesn’t necessarily penetrate deeper,” says Stanford, a seismologist and geophysicist. said William Ellsworth, professor of geophysics at Stanford. study. “It’s a reminder for everyone that these long-term drought damages are not being replenished.”
A series of giant storms in 2023 filled reservoirs across California after three years of severe drought. The study, published this week in the journal Science, showed that even this large amount of water only compensates for some of the decline in water levels in recent years.
“We found that there is still a significant depletion in the deep aquifer,” said Shujuan Mao, the study’s lead author who conducted the study at Stanford University and is now an assistant professor at the University of Texas at Austin. It states. “A single epic storm season doesn’t seem to be enough to recover from the depletion of groundwater accumulated in recent droughts. More moisture will be added to the deep aquifers to fully recover. Masu.”
According to Southern California’s Metropolitan Water District, an estimated third of the area’s water supply comes from wells that pump groundwater. Other supplies have been imported into aqueducts and pipelines in Northern California, the Colorado River and East Sierra.
When rain falls, the water naturally penetrates the ground, where it is not decoupled into storm drains or concrete waterways. Local agencies have also invested in projects in recent years that will either spread rainwater into the basin or use purified wastewater to replenish groundwater.
City wells usually attract drinking water from hundreds of feet of underground, utilizing aquifers that are often impermeable clay and under the silt layer, known as aquitals. These layers block downward movement of water at locations and can slow penetration to a deeper level.
Scientists hope that their findings will help local water personnel access additional data, inform decisions regarding water use and conservation, and guide efforts to replenish groundwater He said.
Researchers have developed a new approach to tracking groundwater levels by reusing seismic data from California’s earthquake monitoring network.
Rather than monitoring earthquakes, Mao Zedong and her colleagues used the data to track microscopic vibrations underground. “Background noise” is “background noise” created by movements that blow through and blow through ocean waves, highway passing, trains of driving. .
“All of these produce noise,” Ellsworth said. “These are vibrations that are constantly happening on Earth from all kinds of different sources.”
“Ambient seismic vibrations can be used to analyze seismic wave velocity and sense the aquifer,” he said.
This technique is called seismic interferometry. Ellsworth said it was the first study to use this approach to assess groundwater levels in such detail, up to 2,600 feet underground.
Mao has also developed a new “seismic drought index” to assess water deficits at various depths.
Measurements of groundwater levels in deep aquifers traditionally include drilling deep wells, which is expensive and allows water levels to be recorded only in a single location. A new method using seismic data can measure water levels across groundwater basins and at a significantly lower cost.
“Earthquake infrastructure has already been implemented and data has been continuously captured for decades,” Mao said. “This is one technology for one purchase.”
Ellsworth called this new method an innovative tool for studying aquifers.
Gregory Belosa, co-author and professor of Earth Sciences at Stanford University’s Sustainability School, said the approach is a major leap in groundwater management.
“It drives us to a future where we could potentially measure groundwater charging, just like river gauges for surface water, where it is,” he said.
This study examined trends in several basins and groundwater basins, including three large basins, the San Gabriel Basin, the Los Angeles Central Basin, and the Santa Ana Basin, as well as small basins such as Santa Monica and Hollywood.
It has been found that more groundwater charging occurs in some areas, while less in others. For example, a significant increase in groundwater levels have been seen in parts of the San Gabriel Valley following the 2023 storm, including deep aquifers along the base of the San Gabriel Mountains.
Researchers have not seen long-term aquifer depletion in the Santa Ana Basin in Orange County for the past 20 years. Mao said this indicates that the area’s groundwater benefits from managed charging efforts.
One important factor appears to be the Orange County groundwater refill system. There, purified wastewater is permeated and injected into the aquifer for use.
Roy Herndon, head of hydrology for the Orange County Water District, confirmed the study that local groundwater charging efforts “effectively maintain sustainable amounts of groundwater pumping.” He said.
The study also supported water level data for the district, Herndon said.
He said the method of this study provides a cost-effective way to measure groundwater changes in some California, where there are no extensive wells dedicated to water level monitoring, using existing seismic sensors. Ta.
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