How Sensor-Dangling Helicopters Can Help Beat the Water Crisis

After weeks With near-constant rain and flooding, California is finally drying up – but hopefully it won’t to dry because the state needs as much rain as it can get to pull itself out of a historic drought. This is California at its most frenetic and contradictory: climate change is exacerbating both dry spells and rainstorms, and is tipping the state’s water systems between critical bottlenecks and channel-toting floods.

A simultaneous solution to both extremes lies right under Californians’ feet: aquifers, which are composed of subterranean strata of porous rock or sediment such as gravel and sand, that fill with rainwater that seeps through the ground above. This water can come to the surface naturally and form a spring, or you can dig a well to tap it. Today, powerful pumps draw water from hundreds of feet below the surface.

California’s Central Valley is full of such aquifers, which can store about 46 trillion gallons of water, three times the amount of all of the state’s reservoirs. But this part of the state has long overfished them; The 20,000-square-mile agricultural valley produces 40 percent of the nation’s fruits, nuts and other foods. (Agriculture generally accounts for 80 percent of all California water use.) In extreme cases, this has wrinkled the land, with elevation dropping dozens of feet in some places in California.

That has created a dramatic imbalance, says UC Davis hydrogeologist Graham Fogg, who studies California’s aquifers. “Civilizations around the world were really experts at sucking up groundwater in a way that was pretty much uncontrolled, but we were terrible at putting water back into the ground,” he says. “It’s kind of like mismanaging a bank account where you get really good at withdrawing money but ignore deposits for decades.”

Worse, California’s mounting water debt is now due. The state’s system of open-air reservoirs is designed to collect water during the rainy season and then redistribute it Mediterranean-style during the dry summer. But during droughts, these reservoirs fall to critical levels, as they did before recent atmospheric flows, which hit in late December and early January. In addition, ever hotter temperatures will cause more of this water to evaporate.

But Fogg and his colleagues have a plan to balance the state’s water balance: They use giant sensors dangling from helicopters and towed behind ATVs to strategically target specific areas for aquifer replenishment. You just have to find the spots with the right geology.

Fogg and his team are looking for ancient features called paleo valleys.

Interestingly, the Central Valley’s underground waterways were created by flowing water AboveFloor. The Sierra Nevada, the mountain range that delimits the eastern rim of the valley, was once covered by glaciers. As the ice melted, the resulting rivers cut channels and spewed out various types of sediment that were deposited in layers. These are the paleo valleys that are up to a mile wide and 100 feet deep. They are very, very good at channeling water underground.