April 4, 2006
The snow that covers Oregon's highest mountains is only the most visible part of the storage system that supplies water to streams and rivers flowing from the Cascades.
The very rock that makes up the peaks soaks up rain and melting snow into an underground basin the size of Great Salt Lake.
The water from deep under the ground surfaces through springs five, 10, sometimes even 50 years later.
Each basin in Oregon depends on these water supplies to different degrees. About 28 percent of the North Santiam River system comes from this High Cascade region. By comparison, 6 percent of the South Santiam River system is classified as High Cascades, according to research by scientists at the Pacific Northwest Research Station, a part of the U.S. Forest Service.
"The number is significant because our work has demonstrated how the presence of these young volcanic rocks has a lot to do with where the rain goes when it falls and where the snow goes when it melts and the timing on which it re-emerges," said Gordon Grant, a research hydrologist. "And ultimately, it says something about the availability of water late into the summer."
Snowpack is the most obvious storage system for rain, but once the weather warms, that trapped water is released quickly into streams and rivers.
A cover of porous volcanic rock -- basalt, pumice and ash -- means that melted snow can trickle into a large reservoir and be stored yet again before being sent to the ocean.
Scientists estimate that about five to 10 years of water is stored in these ground systems. They can determine the age of the water by testing it for tritium, a radioactive isotope of the element hydrogen.
Areas where a lot of water is stored underground have an advantage: A more steady water flow in streams throughout the summer. It's apparent when someone compares the North Santiam and South Santiam rivers in late August, Grant said.
"The South Santiam, you can wade it with only getting your knees wet," he said.
A steady flow is important for all water users, particularly energy companies.
The Deschutes River basin relies heavily on this underground system -- and the owners of Round Butte Dam, west of Madras, benefit.
"This is the most reliable electrical production unit; we can count on it for that steady flow," said Mark Fryburg of Portland General Electric, which owns the dam with the Confederated Tribes of Warm Springs. "While everyone was concerned about drought in the last five years, Round Butte kept chugging along."
Rare fish like the stored water because it tends to bubble from springs much colder than if it had just melted from snowpack.
"It allows bull trout to have really good habitat," said Don Ratliff, a fish biologist for PGE.
Although a vast groundwater system gives water users and conservationists more leeway in dry years, Grant warned that rain and snowpack still are vital.
"If it stopped raining or snowing, we would start to see diminished flow," Grant said. "If we didn't have a snowpack in any given year, we wouldn't have the new water coming into the 'tank' to drive the old water out."
Liz Redon, a coordinator for the North Santiam Watershed Council, said it was good news that some of this basin relies on groundwater reserves because so many people rely on the North Santiam River, including all of the residents of Salem, farmers and recreationists who use Detroit Lake.
However, increasing needs for water will put even more pressure on the system, she said.
"It's good news to know that we aren't totally reliant on snowpack (in any given year)," Redon said. "But the reality is that water is a limited resource. So, we still have to take care of it and practice water conservation and take care of water quality."
bcasper@StatesmanJournal.com or (503) 589-6994