River monitoring network uncovers Peru’s dwindling water supply

By on February 7, 2012

With the help of restored stream monitoring stations, a group of university researchers has determined that a country depending on melting glaciers for water now faces a shrinking supply of the resource.

Peru depends on water that flows down from the Cordillera Blanca mountains on its way to the Pacific Ocean. The water irrigates expansive agriculture on the country’s coast and drives some of the hydro power stations that supply 80 percent of the country’s electricity.

Peru is the leading exporter of asparagus, and grows sugarcane and other crops that would be impossible to grow without the irrigation water drawn from the Rio Santa, according to Bryan Mark, associate professor of geography at Ohio State University.

“The geography is fascinating in Peru because you have this desert coast and a lot of its water resources are coming from mountains that are glacier covered,” Mark said. “It’s a major population relying on water from these mountains.”

But a warming climate has the mountains’ glaciers in a state of constant retreat. And while an ever-shrinking glacier initially sweats an increasing supply of water into mountain watersheds and streams, that doesn’t last forever. It’s just a short-term pulse into the system, Mark said.

In a recent study of the water supply of Peru’s mountain glaciers, Mark and other researchers determined that the initial increase of meltwater is over. From now until the glaciers melt completely, Peru will have to adapt to a dwindling supply of mountain water.

“Here’s a real change in the landscape that people haven’t seen ever in their cultural history,” Mark said. “These are some real important fundamental human development questions.”

To determine the change in water supply, the researchers used historical data from a network of stream discharge monitoring stations along the Rio Santa. The stream gauges were originally operated by the Peruvian government, but many were shut down when the electrical utilities were privatized in the ’90s. To get recent discharge data to compare with the historical record, the researchers had to get those old monitoring sites back online.

Beginning in 2008, Ohio State University, McGill University, the French Institut de Recherche pour le Developpement, and the Peruvian glaciology unit of the Autoridad Nacional del Agua joined on a project to install water level loggers at 13 sites along the Rio Santa, including five sites that were part of the historical monitoring network.

Before the new stations could start making automated discharge measurements, the equipment had to be calibrated with manual stream flow measurements. The crew used the Sontek RiverSurveyor M9, an acoustic Doppler current profiler that can be towed back and forth across a stream while it sends discharge data to a bankside computer over a wireless Bluetooth connection.

Discharge measurements are often made by measuring water velocity while wading across a stream. That would have been too dangerous in the rushing waters of the steep mountain rivers Mark and his colleagues were studying.

“We can measure discharge in small streams pretty readily, but it’s the big flowing rivers that are a challenge,” Mark said. “That’s where the M9 has been really good.”

The next extension of Mark’s work in the watershed will look at water quality. Mining is a leading industry in Peru’s economy, but it often leaves the country’s rivers vulnerable to pollution from dumped tailings or spillover from leachate ponds.

“If you think about impact, quantity is one part of the equation,” Mark said. “But quality becomes ever more important as you have less of the water.”

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