We’ve Irreversibly Damaged Our Groundwater Storage. Here’s What We Do Next.
In just three years, California permanently altered its ability to store groundwater. Three years. It took millions of years to form the layers of clay, sand and gravel that cradle the water under California’s Central Valley. We changed the fundamental structure of those layers in slightly more time than it would take me to walk the perimeter of the United States.
To be fair, we’ve been depleting the aquifer for decades, but are only measuring it now. And the ground level sank dramatically while we measured. I’ll get to that in a minute, but let’s talk about what it means.
An aquifer is an underground layer of permeable rock, gravel or sand, that can absorb and hold water. The Central Valley aquifer was formed by runoff from surrounding mountain ranges, lakes, and rivers, and occasional flooding from the Pacific Ocean. That geologic action created a stretch of fertile soil 400 miles long and 50 miles wide in a climate ideal for growing, but where surface water resources are now stretched thin.
To compensate, we have, for more than a century, pumped out what seemed like an endless supply of groundwater that seeped into the aquifer. Except that it isn’t endless, and pumping has serious consequences.
Simply put, when we pump water out of the dense clay layers deep in the aquifer, we deflate California’s largest storage tank. And not for the first time. The U.S. Geological Survey estimates that, in the last century, California has depleted the groundwater reserves in this aquifer by 125 million acre-feet, 20 million of that in the last decade alone. That’s a lot of water lost to pumping, and a lot of storage lost to collapse. Because of the layers compacted, the aquifer was unable to recharge during the rainy years, exacerbating the devastation of the 2012–16 drought, when the ground level sank ½” per month.
During the 2007–2010 drought, the ground level changes were measured, and the numbers are sobering. Using remote sensors, researchers at Stanford University and NASA’s Jet Propulsion Lab (JPL) found that overpumping groundwater caused the ground in the Central Valley to sink almost three feet in those three drought years, permanently reducing the storage capacity of the aquifer by about 600,000 acre-feet. For perspective, the Hetch Hetchy Reservoir stores 360,000 acre-feet of fresh water for the entire San Francisco Bay Area.
We’ve pumped water from aquifers for a long time, but during water shortages we drill deeper, deflating the tank more rapidly. Particularly detrimental is drilling into the layers of clay. Compacted clay is difficult to pump water through; it’s better to use the water closer to the surface in less dense sand and gravel layers, where surface water will replenish stores more quickly. The depth and location of those layers varies, so until recently, the only way to know if a well would be in sand, gravel or clay has been to drill.
We’re facing some hard choices, and no longer have the luxury of time. Overpumping doesn’t just deplete resources, it damages infrastructure. As ground level sinks, aqueducts crack, roads and bridges become less stable, and buildings shift. Agriculture is particularly hard hit: If farmers cut back on production, there is less food and a shrinking regional economy, but making industry-wide upgrades to more efficient irrigation methods is cost prohibitive.
Technology is the answer. Technology, and common sense.
Recently, the JPL discovered a way to image the subsurface from the air to create a map of clay, sand, and gravel — a remarkable step toward making better decisions about where and how much water we can pump and sustain our aquifers.
After the water has been pumped and is in our water infrastructure, onsite reuse within buildings has reduced the use of potable water by up to 95% in some buildings. Growth in the technology that purifies water locally has helped build an industry around the beneficial uses for the nutrients, minerals, trace organics that are filtered out.
Smart home technology has been great tool for making households aware of their water usage habits. Buoy’s device and app categorizes water use in real time, and lets owners shut off water remotely if there’s a leak.
In agriculture, soil tension sensors have seen great success in the last decade, monitoring water use, temperature, weather and humidity to more efficiently use existing irrigation systems. If farmers can’t implement these larger solutions, sensors that detect leaks on water pumps provide valuable information to prevent waste.
It is these advances that give us hope. We have to take control of our water resources, and, fortunately, improvements in technology and a growing commitment to sustainable solutions have made responsible resource management a real possibility. Knowing where to drill, and closely monitoring ground and water levels, gives us better information than ever before. Paying attention to changing drought-flood cycles, adjusting to changes in climate, and monitoring water usage will all help. We know the history, we’re learning how our decisions have led us to where we are. Now, we have to use every tool available to be smart about how we grow, how we use our resources, and how we plan for a prosperous future.