Calif. Central Valley Sank 3 Feet During Historic Drought

PALO ALTO, Calif. (CN) – While this past winter busted California’s five-year drought, a new Stanford University study shows how the dry years did permanent damage to Central Valley aquifers.

A satellite remote-sensing study performed by Stanford researchers shows a portion of the Central Valley sank by as much as three feet due to overpumping of groundwater during the drought, permanently reducing the region’s capacity for water storage.

“California is getting all of this rain, but in the Central Valley, there has been a loss of space to store it,” said study co-author Rosemary Knight, a professor at Stanford’s School of Earth, Energy and Environmental Sciences.

The alteration of the clay layers that comprise the San Joaquin Valley translates into a permanent loss of natural storage capacity of anywhere between 360,000 to 600,000 acre-feet of water, the study says.

As a point of comparison, the Hetch Hetchy Reservoir – which provides water to San Francisco and is roughly the size of the Yosemite Valley – holds about 360,000 acre-feet of water.

While the study focuses on a drought that lasted from 2007 to 2010, the researchers say the results can be extrapolated to the most recent five-year drought that finally ended this year.

“I think it’s safe to say that the latest drought may have caused at least as much, or even more, subsidence and permanent compaction in the region than the last one,” said Ryan Smith, a doctoral candidate who co-authored the study along with Knight.

The water loss has ecological and economic consequences, as the agriculture in the San Joaquin Valley is a $17 billion industry that feeds much of the world.

Farmers have been forced to turn to groundwater as their allotments from the Central Valley Water Project shrank to as little as 5 percent of what they are entitled to last year.

The good news is that the U.S. Bureau of Reclamation recently announced farmers would get 100 percent of their allocation this year, after the Sierra – which supplies a good portion of the state’s water – saw the wettest year on record this winter.

The Northern Sierra’s 8-station index has so far seen a total of 90.2 inches of precipitation, beating the previous record of 88.5 inches set in 1982-83.

Gov. Jerry Brown officially declared an end to the drought emergency on April 7 and

The state’s Department of Water Resources took its critical April 1 snowpack measurement and found that it was 94 inches deep, one of the deepest ever recorded. The snowpack will continue to replenish reservoirs on both sides of the Sierra well into the summer months.

However, the permanent loss of storage in the Central Valley will make inevitable future droughts much harder for the region’s farmers to endure. It also makes it more difficult to extract groundwater in the present, according to the researchers.

“It’s like trying to suck water from a really thin straw,” Knight said. “The pressure that needs to be exerted to pull the water out gets greater and greater as the clay structure collapses.”

The researchers got their data using satellite technology called Interferometric Synthetic Aperture Radar, or InSAR, which is used to measure small-scale changes in elevation.

They say the technology is a good example of how such satellites can provide real-world applications to water supply and agriculture.

While compaction due to water loss in the clay layers is irreversible, the scientists say there are solutions to the problem.

They encourage farmers to stop pumping water from the clay layers and instead draw water from sandy or gravel layers of the earth, which are less susceptible to permanent compaction and are replenished more easily through rainfall.

While identifying sandy and gravel layers was previously possible only by drilling expensive wells, researchers are working on a method to permanently map the sediment layers of the Central Valley using a helicopter and electromagnetic tools.

 

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