Study finds surprising source of Colorado River water supply

Every spring, snow begins to melt throughout the Rocky Mountains, flowing down from high peaks and into the streams and rivers that form the mighty Colorado River Basin, sustaining entire cities and ecosystems from Wyoming to Arizona. But as spring becomes summer, the melting snow slows to a trickle and, as summer turns to fall, all but stops. Scientists have known for a long time that flow in rivers is sustained by contributions from both snowmelt runoff and groundwater.  The groundwater is composed of rivulets of water hidden below ground —some thousands of years old — that are particularly important for sustaining a river’s flow after the spring snowmelt has subsided. Less clear, however, was exactly how much of the flow in rivers came from groundwater, a critical source of much of the West’s water supply. Now, a new study, released last month by the U.S. Geological Survey (USGS), helps quantify just how much: more than half the flow of rivers in the upper part of the Colorado River Basin is sustained by groundwater. That finding, say experts, highlights the need to better protect a resource threatened by overuse and climate change...more