MAPPING WHAT LIES BENEATH Using electrodes dropped into reservoirs or wells to create a magnetic field, Willowstick's AquaTrack technology allows engineers to map subsurface water Image: © WILLOWSTICK TECHNOLOGIES
More In This Article
Sri Lanka's Samanalawewa dam on the country's Walawe River has been leaking since the day it was completed in 1992. In the interim, the country has spent more than $65 million to plug the leaks in its second-largest dam, built to power the 120-million-watt Samanalawewa Hydroelectric Project. A 2005 study found that the reservoir—located near the town of Balangoda about 100 miles (160 kilometers) southeast of the capital Colombo—was leaking continuously at a rate of 475 gallons (1,800 liters) per second. And shotgun-type methods to solve the Samanalawewa dam problem—including the use of 13,640 tons of cement to reinforce the dam and the dumping of 1.8 million cubic feet (50,000 cubic meters) of clay to plug the holes—have failed.
The problem is that geologists and engineers do not know where all of the leaks are. So they turned to U.K. engineering consultant firm Atkins Global. Atkins performed a preliminary inspection of the dam and surrounding area for three weeks in February using AquaTrack technology developed by Draper, Utah–based Willowstick Technologies. The roughly $3-million project calls for Atkins Global to do additional survey work using AquaTrack this summer to pinpoint the sources of the leakage and spend the subsequent wet season planning precisely where to inject grout to plug those holes, work that Andy Hughes, the company's director of dams and reservoirs, anticipates will begin early next year.
Here's how AquaTrack works: Two electrodes—each three feet (one meter) long—are lowered down, one into the reservoir and the other someplace on the opposite side of the dam (typically in a sinkhole or other standing water downstream of the dam). The top of each electrode is connected with a wire. Once they switch on the electricity, "We've basically created a large circuit," says Paul Rollins, Willowstick's vice president of business development. Because groundwater is a conductor, the electrical current follows it between the electrodes, creating a magnetic field that can be detected on the surface using a sensitive magnetic receiver.
View images of how AquaTrack works
Once the magnetic field is generated, Willowstick's scientists walk the ground between the probes in a gridlike pattern with an instrument that collects data about the frequencies it detects underground. (The researchers are most interested specifically in the 380 hertz signals that AquaTrack's electrodes emit). The instrument is contained in a box that is three feet (one meter) tall and six inches (15 centimeters) square and held upright by a tripod and can collect thousands of readings in just five minutes, according to Rollins. (The technology has already been used successfully at a number of dams, including River Reservoir Dam No. 3 on the Little Colorado River in Arizona and Wolf Creek Dam on the Cumberland River in southern Kentucky.)