Groundwater basins return to pre-drought level

Study confirms heavy winter rains, water conservation refilled aquifer

Santa Clara County’s groundwater — which provides nearly half the drinking water every year for 2 million Silicon Valley residents — fell by up to 60 feet during the state’s recent historic drought due to heavy pumping.

But now the vast underground basins have filled back up to the levels where they were before the drought started in 2011, a welcome trend that experts say was driven by heavy winter rains and strict water conservation rules during the drought that eased the need for pumping.

Monitoring wells run by the Santa Clara Valley Water District first picked up the recovery. And now a new scientific paper published Monday further verifies it.

“People did an amazing job at conserving water during the drought. The entire aquifer recovered,” said Estelle Chaussard, an assistant professor of geology at the University of Buffalo who led the study.

Chaussard analyzed data from four Italian

“People did an amazing job at conserving water during the drought. The entire aquifer recovered.” — Estelle Chaussard, University of Buffalo

satellites, which measured tiny changes in the surface levels of the ground in Santa Clara County during California’s five-year drought. She found that as groundwater levels plummeted during 2013 and 2014, the ground itself fell as the amount of water underneath it was depleted, a phenomenon known as subsidence. From 2011 to the summer of 2014, for example, an area just north of Happy Hollow Zoo near downtown San Jose saw a 2-inch drop in the ground level, as the ground dried out like a sponge sitting in the sun.

Monitoring wells in the same area showed that the groundwater table fell by at least 60 feet during that time. Similar drops occurred in the Campbell and San Martin areas, and drops of 12 to 19 feet happened in the water table under Sunnyvale and South San Jose’s Coyote Valley.

But when Gov. Jerry Brown and the Santa Clara Valley Water District moved from voluntary to mandatory conservation measures, the district limited yard watering, boosted rebates for water-efficient appliances, and hired “water cops” to leave door hangers and send letters to people watering wastefully during the hot part of the day. And significantly less water was pumped from the aquifers, sand and clay formations saturated with water.

At the same time, the water district continued to recharge the aquifers with some water it had in local reservoirs by moving it into dozens of percolation ponds spread throughout the county. It also used water imported from other places, such as the Semitropic Water District, where it stores groundwater near Bakersfield, to keep recharging the ground like a homeowner putting money back into the bank every month during an economic downturn.

“We were working on all fronts to reduce pumping,” said Vanessa De La Piedra, groundwater management unit manager for the Santa Clara Valley Water District. “We saw the very positive results of that. Groundwater levels started to recover in 2015 even though we were still in the drought.”

The ground level began to slowly rebound in 2015, Chaussard’s research showed, as more water essentially pushed it back into place. In 2015, Santa Clara County residents reduced water use 27 percent overall from 2013 levels.

When El Niño storms finally brought normal rainfall to Northern California in the winter of 201516, Santa Clara County’s aquifers continued to recover. And by 2017, when the wettest winter in 20 years caused downpours and floods, they were back to pre-drought levels, the district’s wells showed.

The study was published in the Journal of Geophysical Research, and also includes researchers from NASA’s Jet Propulsion Laboratory in Pasadena, UC Berkeley and Purdue University.

It helps demonstrate that satellite technology can be a useful tool in enabling communities to track the health of their groundwater basins, said Jay Famiglietti, a senior water scientist at NASA’s Jet Propulsion Laboratory, and a professor of earth system science at the University of California, Irvine.

But the good news in Santa Clara County isn’t being replicated in other parts of the state, he said. Of particular concern is the San Joaquin Valley, where farmers for years have overpumped groundwater with little or no recharging efforts, increasing pumping costs and causing roads and concrete canals to buckle and crack as the ground sinks.

“Most of the groundwater that is being pumped in the southern San Joaquin and Tulare Lake basins is much, much deeper,” Famiglietti said. “Those aquifers would take decades to centuries of extremely strict management to recover significantly.”

Santa Clara County has a long history of groundwater struggles. The water table fell nearly 200 feet from 1915 to 1960 as farmers and residents of growing suburbs increased their water use. Subsidence caused the ground to fall as much as 13 feet around San Jose. But when the water district began to construct local reservoirs, import water from the Delta and impose what’s commonly known as “the pump tax” to fund groundwater recharge programs, the water table began to slowly recover.

It is currently back up to basically the same level it was 100 years ago, despite the fact that the county’s population has grown more than tenfold in the past century from 83,000 in 1910 to 2 million today. Even during the lowest point in the recent drought, the county’s water table was still far higher than it had been in the 1960s and 1970s.

In 2014, in what may be the most important lasting legacy from California’s 2011-2016 drought, state lawmakers passed a sweeping new law aimed at better regulating groundwater in California. Most other Western states, including Texas, were decades ahead of California.

That law requires local government agencies in places where groundwater is most at risk to draw up plans to recover it — which could include local agencies levying fees and taxes on farmers and other users to pay for groundwater recharge projects, and potentially, for limits to be placed on how much groundwater can be removed in any year.