After a few weeks almost constant rain and floodCalifornia is finally drying up, but hopefully not getting too much dry because the state needs all the rain it can get to deal with the historic drought. This is California at its most violent and controversial: climate change is making both dry spells and rainstorms more intense, stressing the state’s water systems between critical deficit and floods extending beyond the canals.
The simultaneous solution to both extremes is right under the feet of Californians: aquifers, which are made up of underground layers of porous rock or sediment such as gravel and sand, that are filled with rainwater seeping through the soil above. This water can come to the surface naturally, forming a spring, or you can dig a well to access it. Nowadays, powerful pumps lift water from depths of hundreds of feet.
California’s Central Valley is filled with such aquifers, capable of storing about 46 trillion gallons of water, three times more than all of the state’s reservoirs. But this part of the state has long been over-exploiting them; a 20,000-square-mile valley rich in agriculture is growing 40 percent national fruits, nuts and other table products. (Agriculture as a whole is 80 percent of all water use in California.) In extreme cases, this has resulted in land deformation, with elevation in some places in California lowered by tens of feet.
This has led to a dramatic imbalance, says UC Davis hydrogeologist Graham Fogg, who studies California aquifers. “Civilizations around the world have been real experts at sucking up groundwater almost uncontrollably, but we’ve been terrible at putting water back into the ground,” he says. “It’s like bank account mismanagement where you’re really good at withdrawing funds but ignoring deposits for decades.”
Worse, California’s mounting water debt now must be repaid. The government’s open-air reservoir system is designed to collect water during the rainy season and then distribute it during the dry Mediterranean summer. But during a drought, the level of these reservoirs drops to a critical level, as before the recent atmospheric rivers that collapsed in late December and early January. On top of that, ever warmer temperatures end up evaporating more of this water.
But Fogg and his colleagues have a plan to balance the state’s water budget: use giant sensors dangling from helicopters and towed behind ATVs to strategically target specific areas to recharge the aquifer. They just need to find places with the right geology.
Fogg and his the team is looking for ancient features called paleo-valleys.
Interestingly, the underground waterways of the Central Valley were created by water flows. higherEarth. The Sierra Nevada, a mountain range that fringes the eastern edge of the valley, was once covered in glaciers. As the ice melted, the resulting rivers cut their channels, spewing out various types of sediment that were deposited in layers. These paleo-valleys are up to a mile wide and 100 feet deep. They are very good at directing water underground.