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Health, Science & Environment

Study: Colorado River Flow Is Half Groundwater

Matt Miller/USGS
A new study quantifies the groundwater that makes up the Colorado River at Lee's Ferry, just south of the Utah border. It offers insights about streamflow and may become a predictive tool

A team of Utah-based scientists with the U.S. Geological Survey has come up with a new way of measuring Colorado River flows. It helps answer a big question for the West: How much water flows down the river as it leaves Utah?

“At the basin scale, just over half the streamflow was estimated to have originated from groundwater,” says Matt Miller, the study’s lead author. “And that really shows -- with numbers -- that there’s this connection between the groundwater resource and the surface water resource.”

The study team also determined that irrigation and evapotranpiration means around 80 percent of that groundwater never reaches Lee’s Ferry above the Grand Canyon. The paper’s authors say it’s crucial to count groundwater -- along with mountain snow and rain -- when projecting streamflow.

The study’s attracting attention because 50 million people in seven states rely on the Colorado for crops, drinking water, power generation and other uses -- and that number’s growing fast. Plus, wildlife and the environment depend on Colorado River water too.

Gary Wockner, director of a conservation group called Save the Colorado, says the new measurements highlight an old problem.

“We’re taking way more water out of the reservoirs,” he says, “we’re taking way more water out of the ground than is coming down from the sky in rain and snow, and there’s what's called a cumulative deficit.”

Wockner welcomes the latest study as another tool for improving our understanding of a complex basin where so much is at stake.

Meanwhile, the USGS scientists are collaborating with the U.S. Bureau of Reclamation on a follow-up study aimed at using the new measuring techniques to predict Colorado River flows.

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