Storing extra surface water boosts groundwater supply during droughts

March 24, 2016
The California Aqueduct (left) and the Delta-Mendota Canal (right) wind through California's Central Valley. Credit: US Department of the Interior

Although years of drought and over-pumping have significantly depleted groundwater in Arizona and California, a new study shows the situation has an upside: It has created underground reservoirs where extra surface water can be stored during wet times so it is available during drought.

The study, published in the journal Environmental Research Letters in March, also found that regions that actively store surface in underground aquifers have increased their supply over time, even as surrounding areas depleted theirs.

The findings are important because they show that techniques used to increase groundwater storage are working. With droughts and floods projected to increase due to climate change, and California investing $2.7 billion to expand water storage, these techniques could help drought-prone regions prepare for extremes, said lead author Bridget Scanlon of The University of Texas at Austin's Bureau of Economic Geology. The bureau is a research unit at The University of Texas Jackson School of Geosciences.

"In many regions now we're dealing with these extremes of drought and then intense floods, and that's a real challenge for water resource managers," Scanlon said. "To try and resolve this disconnect between supply and demand, we can store water in depleted aquifers."

The Agua Fria Water Recharge Facility, a spreading basin in Arizona. Water collected by the facility percolates into the aquifer below it. Credit: Central Arizona Project

The study examined decades' worth of groundwater data from California's Central Valley and active management areas across central Arizona—both regions that collect extra water from surface reservoirs and store it in underground aquifers using a technique called managed aquifer recharge. The method has been used in the Central Valley since the 1960s and in Arizona since the 1990s.

As part of the storage strategy, the regions also managed their water resources through conjunctive use, relying primarily on surface aquifers during wet periods and on groundwater during dry periods.

"When you do that, you stop pumping the groundwater so it can recover," Scanlon said. "But you are also adding recharge from , so you have a double benefit."

The researchers found that groundwater in Arizona's active management areas has been rising an average of 0.3 to 1.6 feet per year since the early 2000s. In contrast, nearby areas saw groundwater declines of 1.5 to 4 feet per year. The Central Arizona Project aqueduct, completed in 1993, allowed aquifer recharge and conjunctive use by delivering water from Lake Mead that replaced groundwater-based irrigation in farms. The water was also transported to spreading basins where it percolated into the aquifer.

Composite groundwater levels in active management areas in Arizona (top) compared to areas without active management (bottom). Credit: Bridget Scanlon

In California, the researchers found that water imported through the Central Valley Project and California State Water Project canals helped reverse long-term declining groundwater levels by reducing groundwater pumping during wet periods and recharging groundwater using spreading basins. For instance, in one managed aquifer recharge site, the study shows that groundwater levels today would be about 300 feet lower if water storage techniques had not been applied. And although declines in were observed during drought, the declines were not as dramatic as those observed outside of the managed aquifer recharge areas.

Thomas Harter, the Robert M. Hagan Endowed Chair in Water Management and Policy at the University of California, Davis, said the research illustrates the value of techniques by blending long-term data with detailed accounts of water management strategies.

"I appreciate Bridget's work to provide a synthesis, not just in California, but also the comparison between California and Arizona, that points toward the larger, global significance of aquifer recharge and conjunctive use," Harter said.

There is plenty of storage space left in aquifers, researchers found. Central Valley aquifers have about 44 cubic kilometers of space, the same amount of space as all of California's surface reservoirs. In Arizona, the space in the aquifers corresponds to about 100 cubic kilometers of space, about three times the capacity of Lake Mead, the largest surface reservoir in the U.S.

Developing additional aquifer recharge projects could help fill the empty space, and enhance water security during climate extremes, Scanlon said.

"These approaches will help in dealing with these current extremes and will help in the future when we have to deal with them even more," Scanlon said.

Explore further: How climate change will affect western groundwater

More information: Bridget R Scanlon et al. Enhancing drought resilience with conjunctive use and managed aquifer recharge in California and Arizona, Environmental Research Letters (2016). DOI: 10.1088/1748-9326/11/3/035013

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EnviroEquipment_Com
5 / 5 (1) Mar 24, 2016
Although it sounds great that efforts to increase groundwater storage are working, this assumes that there will be as many "wet years" in the future as have been in the past, something which is being called into question by scientists who are studying climate change.
retrosurf
5 / 5 (2) Mar 24, 2016
Central Valley aquifers have about 44 cubic kilometers of space, the same amount of space as all of California's surface reservoirs.


One good thing, though: for people that think, a study this can nullify the astroturf about the need to build more damns in California. It's likely to be more cost-effective to hasten aquifer recharge by preserving and enhancing wetlands and regulating groundwater withdrawals in impacted areas. The legal groundwork for groundwater regulation is laid with a statewide law, although the details are going to be in regional committees for years to come.
Shootist
2 / 5 (4) Mar 24, 2016
Storing extra surface water boosts groundwater supply during droughts


True. Better yet pumping desalinized and deionized water back into the aquifers is an even better idea (no loss to evaporation). We just need to build 100 1000 megawatt fission plants to flash sea-water (an effectively endless resource) into fresh.

Fresh water shortages and depleted aquifers solved plus GREEN CARBON FREE energy (I can sense all the little stiffys from all the watermelons). 'Cause if you don't support fission you really don't support lower carbon emissions, you just like confiscatory taxation and the control of other people that comes with that.
dustywells
not rated yet Mar 27, 2016
Maybe we need another research grant to perform a study of the impact of worldwide aquifer depletion on the rise of sea level. It might be surprising to find that it has more effect than deglaciation.

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