Subscribe to our free daily newsletters
. Earth Science News .

Subscribe to our free daily newsletters

Overpumping Reduces California's Groundwater Storage
by Staff Writers
Pasadena CA (JPL) Apr 17, 2017

File image.

Decades of overpumping groundwater have irreversibly altered layers of clay beneath California's Central Valley, permanently reducing the aquifer's ability to store water, finds a new satellite remote sensing study by scientists at Stanford University, Stanford, California; and NASA's Jet Propulsion Laboratory in Pasadena, California.

The study, published online in the journal Water Resources Research, reveals that overpumping caused land in the state's San Joaquin Valley to sink almost 3 feet (85 centimeters) during a recent drought from 2007 to 2010. As a result, the aquifer permanently lost between 336,000 and 606,000 acre-feet of natural water storage capacity. An acre-foot is equal to 326,000 gallons. In comparison, the Hetch Hetchy Reservoir that stores the primary water supply for the San Francisco Bay area has a capacity of about 360,000 acre-feet.

The San Joaquin Valley is one of the largest U.S. agricultural hubs, producing an estimated $17 billion of crops a year. The new findings come just as the state is experiencing its wettest season in years following an extended, record-setting drought.

"California is getting all of this rain, but in the Central Valley, there has been a loss of space to store it," said study coauthor Rosemary Knight, George L. Harrington professor at Stanford's School of Earth, Energy and Environmental Sciences.

Knight and her colleagues used data acquired with a satellite technology called Interferometric Synthetic Aperture Radar (InSAR) collected by the Phased-Array L-band Synthetic Aperture Radar (PALSAR) instrument on the Japan Aerospace Exploration Agency's Advanced Land Observing Satellite to measure centimeter-scale changes in elevation in the San Joaquin Valley between 2007 and 2010. The scientists compared multiple satellite InSAR images of Earth's surface to calculate how much the land subsided (sank).

"Our work is a good example of the use of Earth-observing satellites to answer down-to-Earth questions about the sustainability of water resources," said JPL research scientist and study coauthor Tom Farr.

Subsidence happens when the water pressure in the subsurface dips below a critical level when too much groundwater is removed, causing the sediments to compact. "As you pump groundwater out of an aquifer, the water pressure in the tiny pores of the sediment drops," said study first author Ryan Smith, a doctoral candidate in Knight's lab. "That reduces the ability of the aquifer to hold up the ground above it and causes it to collapse. That collapse is manifested at the surface as subsidence."

If too much water is extracted, particularly from clay layers, the compaction becomes irreversible, and the soil's ability to retain water is permanently diminished. "When too much water is taken out of clay, its structure is rearranged at the microscopic level and it settles into a new configuration that has less storage space," said Knight, who is also affiliated with the Stanford Woods Institute for the Environment.

This not only makes it more difficult to store water in the future, but also makes it harder to draw any existing water out of the ground today. "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 scientists only examined InSAR data collected during the drought period between 2007 and 2010. Since then, California has experienced a more severe drought, from 2012 to 2016. "Although our paper didn't deal with the most recent drought, 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," Smith said.

"This is because the rate of water decline increased during that period, causing the groundwater to drop to historically low levels. Recent InSAR studies by JPL, not included in this study, also demonstrate that subsidence continued at a similar, and in some cases even greater, rate compared with what we saw from 2007 to 2010."

One way farmers in the region could alleviate the problem, Knight said, is to avoid drawing water from clay layers and instead pump groundwater from more shallow sand and gravel layers, which are more easily recharged and are less susceptible to permanent compaction.

Until recently, however, distinguishing clay layers from sand and gravel from the surface required drilling expensive wells. But Knight's group is testing a novel geophysical electromagnetic method that involves flying a helicopter equipped with instruments capable of imaging the subsurface from the air to create a three-dimensional map of clay, sand and gravel deposits.

"With the right geophysical tool," Knight said, "we can not only better understand the composition of the subsurface, but also help guide pumping and groundwater recharge efforts."

Other study coauthors include Howard Zebker, Jessica Reeves and Jingyi Chen from Stanford University and Zhen Liu at JPL. Funding for the study was provided by the S.D. Bechtel Jr. Foundation, NASA's Terrestrial Hydrology Program and the National Science Foundation.

New England's glacial upland soils provide major groundwater storage reservoir
Amherst MA (SPX) Apr 13, 2017
A recent study of natural groundwater storage reservoirs in New England by hydrologist David Boutt at the University of Massachusetts Amherst found that upland aquifer systems dominated by thin deposits of surface till - a jumbled, unsorted material deposited by glaciers - make up about 70 percent of the active and dynamic storage for the region. As Boutt explains, "This is the first time ... read more

Related Links
Water News - Science, Technology and Politics

Thanks for being here;
We need your help. The SpaceDaily news network continues to grow but revenues have never been harder to maintain.

With the rise of Ad Blockers, and Facebook - our traditional revenue sources via quality network advertising continues to decline. And unlike so many other news sites, we don't have a paywall - with those annoying usernames and passwords.

Our news coverage takes time and effort to publish 365 days a year.

If you find our news sites informative and useful then please consider becoming a regular supporter or for now make a one off contribution.

SpaceDaily Contributor
$5 Billed Once

credit card or paypal
SpaceDaily Monthly Supporter
$5 Billed Monthly

paypal only

Comment using your Disqus, Facebook, Google or Twitter login.

Share this article via these popular social media networks DiggDigg RedditReddit GoogleGoogle

Sri Lanka ends search for garbage survivors as toll hits 32

At least 97 migrants missing as boat sinks off Libya

Smoking to kill 200 million in China this century: WHO

Haiti to rebuild National Palace toppled in 2010 quake

New method for 3-D printing extraterrestrial materials

Ultra-thin multilayer film for next-generation data storage and processing

USC Viterbi researchers develop new class of optoelectronic materials

Recent advances and new insights into quantum image processing

New membranes can remove viruses from drinking water

Croatian rivers face hydroelectric peril

Migration from sea-level rise could reshape cities inland

India likely to receive normal monsoon rains this year

Researchers ask public to help them count Weddell seals

How polar bears find their prey

Glacier shape influences susceptibility to melting

Polar glaciers may be home to previously undiscovered carbon cycle

Organic cover crop methods examined for weed control

Can Prosecco help Italy unlock China wine market?

Busy harvest time in China's bamboo forests

Ag scientists using electronics to control plant growth

At least 11 killed in Colombia floods: Red Cross

At least 16 killed in Colombia floods: government

Death toll at 113 in Peru floods, mudslides; while 6.2 quake rumbles

Lessons from Parkfield help predict continued fault movements after earthquakes

DR Congo suspends military cooperation with Belgium

Four dead in army, police clashes in Nigeria: source

Three killed in Mogadishu army camp attack: military

El Nino can warn on cholera outbreaks in Africa: study

Science says: Let a stranger pick your profile picture

Neuroscientists measure 'higher' state of consciousness

Putting social science modeling through its paces

Study reveals 10,000 years of genetic continuity in northwest North America

Memory Foam Mattress Review
Newsletters :: SpaceDaily :: SpaceWar :: TerraDaily :: Energy Daily
XML Feeds :: Space News :: Earth News :: War News :: Solar Energy News

The content herein, unless otherwise known to be public domain, are Copyright 1995-2017 - Space Media Network. All websites are published in Australia and are solely subject to Australian law and governed by Fair Use principals for news reporting and research purposes. AFP, UPI and IANS news wire stories are copyright Agence France-Presse, United Press International and Indo-Asia News Service. ESA news reports are copyright European Space Agency. All NASA sourced material is public domain. Additional copyrights may apply in whole or part to other bona fide parties. All articles labeled "by Staff Writers" include reports supplied to Space Media Network by industry news wires, PR agencies, corporate press officers and the like. Such articles are individually curated and edited by Space Media Network staff on the basis of the report's information value to our industry and professional readership. Advertising does not imply endorsement, agreement or approval of any opinions, statements or information provided by Space Media Network on any Web page published or hosted by Space Media Network. Privacy Statement