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Cooling Off the Columbia: Can Dams Do More? by Cassandra Profita Ecotrope, September 6, 2011

The lake behind Grand Coulee Dam can hold water for months at a time to help control flooding on the Columbia River. But with spring and summer water temperatures rising to levels past the point of what's safe for salmon and steelhead, some argue the U.S. Army Corps of Engineers should be spilling more water throughout the basin to keep the river cooler. Would that work?

I talked with Dave Ponganis of the U.S. Army Corps of Engineers about how dams on the Columbia River affect water temperature and what his agency does to keep the water at cool enough for threatened and endangered salmon and steelhead.

As I wrote last week (The Columbian covered the issue too), much of the Columbia's water has been warmer than the legal limit set by the Clean Water Act for at least 11 years. It's warmer than what's healthy for salmon and steelhead and in some places it's actually reaching temperatures that can be lethal to fish (though they can swim to cooler waters, which still exist in the Columbia). But who's at fault for the warm water and how to bring the temperature down are two questions that don't have easy answers.

Environmentalists with Columbia Riverkeeper and clean water regulators say the federal dams on the river drive temperatures up by slowing down the water flow - particularly at reservoirs, which provide important water storage for flood control, hydropower, and irrigation. Some say increasing summertime water spills over the dams would help cool things down.

Ponganis said the Corps has many considerations to take into account when managing dams, including fish survival. But there are a variety of unique factors that affect water temperature at each dam, such a the depth of the reservoir and what it's used for, which tributaries feed into it and what's downstream from the dam. Moreover, he said, it's hard to say what the river would be like without the dams. It would probably be even warmer.

"You wouldn't see the flows you have right now," he said, "and the temperatures would far exceed what they are now."

Spilling water over the dams wouldn't necessarily help, he said, because the spill water comes from the top of the reservoirs, where water is the warmest. The cooler water is at the bottom, and that's where the Corps pulls water for hydroelectric turbines.

Each dam has its own unique constraints, he explained. Some, like Grand Coulee, are used primarily to store water for flood management. So water can spend months there whereas other dams only store water for a few days. The temperature of tributaries above each reservoir can affect water temperature, too. And in some cases, such as Libby Dam in Montana or Dworshak Dam in Idaho, the water being released is actually supposed to be warmer for sturgeon or hatchery fish below.

"It's a complex system," Ponganis said. "Each project is different. We do take water temperature seriously. There are a lot of competing demands when you talk about how we manage for temperature, and a lot of competing interests we have to consider."

The Corps follows rules set out in the Biological Opinion for the hydropower system (which is still hung up in Judge James Redden's federal court). And the agency takes temperature measurements in three places at each dam.

Clean Water Act regulators understand the constraints on the hydro system, Ponganis said, and the National Marine Fisheries Service has determined that the current plan for dam management is not likely to jeopardize salmon and steelhead survival. As part of the latest plan, the Corps and other federal agencies will be looking cold water refuge areas in the Columbia and trying to understand how they work.

"Water temperature is based on a lot of factors, including sunshine and thermal inputs and how much water is in the river," Ponganis said. "We did consider all that. NOAA's finding, their overall conclusion, is our operations - including operations for temperature - are appropriate. We can't do everything, but we're doing what we can."