How cities are pumping water underground to stop land from sinking

Groundwater has historically been a lifeline in California's Coachella Valley. Water for farming, for your home and community? It came from under your feet, but the extractions didn't go unnoticed. Much like taking air out of balloon, the ground began sinking.

From 1995 to 2010, parts of the valley fell by as much 0.6 meters (2 feet), a process called land subsidence. The ground became destabilized, creating large cracks in the earth. Uneven sinking damaged the foundations of buildings and roads. The Coachella Canal started to sag to the point that water flow was interrupted.

The scenario seemed too familiar, especially in populated, dry places. Another city pumped too much groundwater and began dropping, struggling with water demands and unstable land. But unlike other sinking cities, water managers performed a rare feat: they paused the sinking, even partially reversing it in some areas.

Water managers pushed new water conservation approaches, used the Colorado River and recycled water for non-potable uses (farming, golf courses) and even put water back into the ground. Subsidence rates slowed by 50 to 75 percent in many areas. The northern part of the valley experienced uplift up to 60 millimeters (2.3 inches) over the following years.

"I’ve been working on land subsidence for a long time and we don't really get too many good news stories that we get to tell, but Coachella Valley is one of them," said Michelle Sneed, a hydrologist at the U.S. Geological Survey who has studied subsidence in the region. "The water district there has just been really proactive in water management and land subsidence."

Across the world, excessive groundwater pumping is one of the main culprits causing cities to lose ground. Some communities that only experience a millimeter or so of sinking may not notice drastic changes, but communities subsiding at higher rates face increased flooding along the coast and damages to structures. By 2024, researchers estimate that nearly one-fifth of the world's population may be living on land slowly sinking under their feet because of groundwater extractions.

So far, only a small portion of affected places are tackling how to slow or pause land subsidence.

"Unless you have damage from subsidence, then there is the ‘What problem is there to fix?’ kind of thing," said Sneed. "There hasn't really been the impetus to [address subsidence] … but more are."

Fixing land subsidence doesn't have a simple solution. Well, unless you stop pumping groundwater. But most of the time not using groundwater isn't feasible for communities that need to supply water to a large amount of residents.

Instead, a different approach is to replenish the groundwater. This approach is called a managed aquifer recharge, also known as water banking.

To understand how it works, we must first learn how groundwater is stored and extracted. The ground has several layers of various types of sediments. An aquifer, which can appear near the surface or very deep down, is a body of rock or sediments that has a lot of porous space between the grains. These empty spaces are well-connected, much like a kitchen sponge. Aquifers can accommodate water and also allow water to flow easily through it. To extract water, imagine sticking a straw into the aquifer and sucking water.

A managed recharge system will collect water to put back into the aquifer. The water source can come from precipitation, flooding, treated wastewater or rivers. The water can be withdrawn to supply a community with water. The added liquid can also add volume back into the ground, but only to a certain extent because clay layers compact in the soil.

"If you make this managed aquifer recharge operational when the water is available during, for example, wet seasonal floods, that water can be treated and injected into the ground to be stored there," said Manoochehr Shirzaei, who works in remote sensing engineering and environmental security at Virginia Tech. "You reverse the subsidence … and you save the waters for the next year or year after that."

Several places across the world have employed a managed aquifer recharge system and seen subsidence changes, including in the Coachella Valley, California's Santa Clara and Santa Ana, Spain's El Carracillo district, Israel's Negev desert area, South Carolina's Hilton Head Island, Perth in Australia and Beijing.

Most places, however, install the system to better supply their groundwater needs. Addressing land subsidence is just a nice bonus.

For instance, in Orange County, more than 2.5 million residents get 85 percent of their water supply from the ground through their recharge system, according to the county district's chief hydrogeologist Roy Herndon. As an offshoot from that, Herndon said they see minor ups and downs in the land, but they haven't seen subsidence getting worse on a longer scale — that's a good sign.

In Perth, Australia, researchers found that a managed aquifer recharge system lifted parts of the land by around 20 millimeters over 3.5 years.

Water managers are also experimenting with managed aquifer recharge systems around Norfolk, which is experiencing the most land subsidence on the U.S. East Coast. While some of land subsidence is from natural processes, much of the change is due to groundwater extraction, said Jamie Heisig-Mitchell, the director of water quality for the Hampton Roads Sanitation District.

In a pilot project, the Hampton Roads Sanitation District set up a recharge system that treated wastewater and recharged the aquifer with 1 million gallons a day. Heisig-Mitchell said they originally set up the system to look for a sustainable supply of groundwater for the region because the Potomac River system was being overused. But they found the ground was rising too.

"You can tell that we’re putting water in the ground and that the ground is raising. Very, very, very small amounts, but it is raising," said Heisig-Mitchell. That's only with 1 million gallons of aquifer recharge in a day, she said. In 2026, they will operate their first full-scale facility, which will recharge 34 million gallons per day.

USGS's Sneed said she hasn't seen managed aquifer recharge systems significantly reverse any subsidence trends on its own. Traveling to conferences and studying other systems, she said the most rebound that she's heard was about 3 inches. That doesn't make a substantial dent in places like California's Central Valley, which has subsided several feet over the years. The impact on land subsidence can also be very local.

"The best approach is to stop it from happening in the first place. If it's too late, it's already happening," said Sneed. "You can just move forward and try to alleviate or mitigate it."

Shirzaei, part of the UNESCO Land Subsidence International Initiative, said a goal for managed aquifer systems is to stabilize subsidence rates over longer periods of time, although levels may go up and down between seasons.

But the systems aren't without challenges. From a cost perspective, such a system can be difficult to set up in a place with fewer resources. Orange County's Herndon said they have a large tax base to spread the costs over, but funding a big multimillion dollar recharge project could be challenging for a smaller urban or rural community.

In some places, managed aquifer systems may also be difficult to set up widely. For instance, pilot programs exist in Mexico City, but researchers found local governments and existing regulations make it difficult to provide more of them in the area.

"Managed aquifer recharge won't work everywhere," said Sneed. "It's kind of a local situation and what alternatives what mitigation strategies might be appropriate for any particular area."