Please select your home edition
Edition
T Clewring - Cruising

A new way to see saltwater intrusion into groundwater

by Ker Than on 6 Apr 2014
Map of underground saltwater-freshwater interface along the California coast between Marina and Seaside made using electrical resistivity tomography. Rosemary Knight
A Stanford geophysicist has employed novel surface technology to study intrusion of saltwater into freshwater aquifers along the California coast.

California coastal communities have long been dependent on groundwater to satisfy their drinking and farming water needs. But the amount of pumping is drawing seawater into coastal aquifers and corrupting water supplies. 'Once you have saltwater in your freshwater aquifer, it’s hard to get it back out,' said Rosemary Knight, a leading geophysicist and an expert in developing and using leading edge technologies to generate images enabling the evaluation and management of groundwater resources. Knight is a Stanford Woods Institute senior fellow, by courtesy.

To better understand how serious this problem is in California, Knight and her team are testing a new technique to map where underground pockets of freshwater and saltwater meet along the coast of Monterey Bay. The technique, called electrical resistivity tomography, can map out the salinity of groundwater. It involves sinking electrical rods that are connected by a wire into the ground and running an electrical current through the wire. 'The technology measures a property called electrical resistivity,' said Knight, the George L. Harrington Professor in Stanford Earth Sciences and also a senior fellow at the Stanford Woods Institute for the Environment. 'If you have more salt in the water, it’s electrically conductive. If you have very little salt, it’s electrically resistive.'

Upon request of Monterey area Stanford alumni, Knight recently explained her research and the technique her team developed at an invitation-only event.

In a pilot study conducted along a four-mile (seven-km) stretch of coastline between the cities of Seaside and Marina in 2012, Knight and her team successfully created an electrical resistivity map that reached a depth of nearly 500 feet (150 meters). A larger field experiment, slated for late October, will create a similar map for the entire accessible coastline of Monterey Bay–a distance of about 28 miles (45 kilometers). Knight expects that map will probe to a depth of nearly 1,000 feet (300 meters). This work is being conducted in collaboration with Adam Pidlisecky from the University of Calgary, formerly a graduate student with Knight and an expert in the acquisition and interpretation of electrical resistivity data.

California communities are reliant on groundwater aquifers to meet their water needs. In Santa Cruz County, about 70 percent of the freshwater comes from aquifers; in Monterey County, the figure is nearly 100 percent. Pumping freshwater out of the ground changes the fluid pressure of aquifers, and if an aquifer is located near the coast, it can lead to saltwater intrusion. 'There’s a delicate pressure balance between the groundwater and the saltwater,' Knight said. 'When you pump the groundwater, the saltwater can move in.'

The problem could worsen in coming years if the state’s current drought continues. A drought would not only lead to more groundwater pumping because of increased water demands, it would also mean less water going into aquifers . 'At any time, it’s a balancing act between the amount of water that goes into the aquifer and the amount that comes out,' Knight said. 'During a drought, there is less precipitation, so the natural recharge of the aquifer does not occur.'
If Knight’s team can show that electrical resistivity tomography works at larger scales, it would be a better alternative than the current method used to monitor saltwater intrusion, which involves drilling so-called 'sentinel' wells at specific sites. 'The problem with wells is you’re only getting data at one specific point,' Knight said. Wells are also expensive. Four of the wells used to monitor saltwater intrusion along Monterey Bay had a cost estimate of nearly $1 million to drill. The Stanford team may be able to do a better job for a fraction of the cost.

Knight hopes that the data her team collects can be used to inform groundwater management decisions in California. 'Options could include changing the locations and extent of pumping to reduce the extraction of freshwater from the aquifers. It could also include proactively increasing the freshwater going into the aquifers through the engineered injection or infiltration of freshwater,' Knight said.

'If this problem is not addressed soon, we will need to look elsewhere for a supply of freshwater for the Monterey Bay region.'

Barz Optics - Melanin LensesKilwell - 1Bakewell-White Yacht Design

Related Articles

America's Cup - Arbitration Panel Hearing over Kiwi Qualifier for July
ACEA CEO, Russell Coutts has confirmed that the Arbitration Panel will hold its first Hearing in July. In a yet to be published interview in Sail-World, America’s Cup Events Authority CEO, Russell Coutts has confirmed that the Arbitration Panel will hold its first Hearing in July. This is the first official indication that the three person Arbitration Panel had even been formed, however Sail-World’s sources indicated that it had been empanelled since last January, possibly earlier.
Posted on 27 May
Rio 2016 - The Qualification Games - Part 2
Yachting NZ's refusal to nominate in three classes won in the first round of 2016 Olympic Qualification is unprecedented Yachting New Zealand's refusal to nominate in three classes won in the first round of 2016 Olympic Qualification is without precedent. Subject to Appeal, the Kiwis have signaled that they will reject 30% of the positions gained in the ISAF World Sailing Championships in Santander in 2014.
Posted on 22 May
Gladwell's Line - World Sailing changes tack after IOC windshift
Over the past year, we've given the International Sailing Federation (now re-badged as World Sailing) a bit of stick Over the past year, we've given the International Sailing Federation (now re-badged as World Sailing) a bit of stick. Every blow well earned over issues such as the pollution at Rio, the Israeli exclusion abomination plus a few more. But now World Sailing is getting it right.
Posted on 21 May
Rio 2016 - The Qualification Games - Part 1
Antipodean selection shenanigans aside, the Qualification system for the Rio Olympics appears to be achieving its goals Antipodean selection shenanigans aside, the Qualification system for the Rio Olympics appears to be achieving goals set in the Olympic Commission report of 2010. Around 64 countries are expected to be represented in Rio de Janeiro in August. That is a slight increase on Qingdao and Weymouth, but more importantly a full regional qualification system is now in place
Posted on 19 May
Taming the beast-a conversation with Stuart Meurer of Parker Hannifin
While AC72 cats were fast, they difficult to control, so Oracle partnered with Parker Hannifin to innovate a better way. If you watched videos of the AC72s racing in the 34th America’s Cup (2013), you’re familiar with the mind-boggling speeds that are possible when wingsail-powered catamarans switch from displacement sailing to foiling mode. While foiling is fast, there’s no disguising the platform’s inherent instability. Now, Oracle Team USA has teamed up with Parker Hannifin to innovate a better way.
Posted on 18 May
From foiling Moths to Olympic starting lines-a Q&A with Bora Gulari
Bora Gulari’s is representing the USA at the Rio 2016 Olympics in the Nacra 17 class, along with teammate Louisa Chafee. Bora Gulari (USA) has made a strong name for himself within high-performance sailing circles, with wins at the 2009 and 2013 Moth Worlds. In between, he broke the 30-knort barrier and was the 2009 US SAILING Rolex Yachtsman of the Year. His latest challenge is representing the USA at the Rio 2016 Olympics in the Nacra 17 class as skipper, along with his teammate Louisa Chafee.
Posted on 12 May
Concern for Zika at Rio Olympics is now deadly serious
Alphabet soup is one description that has thus far not been used for either Guanabara Bay, Alphabet soup is one description that has thus far not been used for either Guanabara Bay, or the Rio Olympics. Many others have, and they were apt, but things have changed. So here now we have a situation where one man, Associate Professor Amir Attaran, who does have a more than decent string of letters after his name, is bringing nearly as many facts to bear as references at the article's end
Posted on 12 May
Zhik - The brand born of a notion, not its history
here is probably every reason that ocean rhymes with notion. Zhik’s tagline is officially marketed as Made For Water There is probably every reason that ocean rhymes with notion. Zhik’s tagline has been officially marketed as Made For Water, and this is precisely what the company has done for the last eight years before the succinct and apt strapline came from out of R&D and into mainstream visibility.
Posted on 8 May
Shape of next Volvo Ocean Race revealed at Southern Spars - Part 1
Southern Spars has been confirmed as the supplier of spars for the 2017-18 Volvo Ocean Race. In mid-April, Race Director, Jack Lloyd and Stopover Manager Richard Mason outlined the changes expected for the 40,000nm Race during a tour of Southern Spars 10,000sq metre specialist spar construction facility. A total of up to seven boats is expected to enter, but time is running out for the construction of any new boats.
Posted on 3 May
Sailing in the Olympics beyond 2016 - A double Olympic medalist's view
Bruce Kendall takes a look at what he believes Sailing needs to do to survive beyond the 2016 Olympics. Gold and Bronze medalist and multiple world boardsailing/windsurfer champion, Bruce Kendall takes a look at what he believes Sailing needs to do to survive beyond the 2016 Olympics. A key driver is the signalled intention by the International Olympic Committee to select a basket of events that will be contested.
Posted on 29 Apr