The University Record, September 5, 2000

Heat, dams, fires threaten Pacific Northwest salmon

By Rebecca A. Doyle

The treacherous journey through man-made dams like the Lower Granite Dam (above) on the Snake River poses threats to the Salmon 'smolts'' existence. Natural predators and environmental hazards such as water temperature and habitat loss due to fire also threaten the smolts. Photo courtesy Army Corps of Engineers
Steelhead, chinook, sockeye and chum—names that conjure up visions of fast-moving freshwater streams and National Geographic photographs of riverbank-to-riverbank fish—are among the endangered or threatened anadromous species that contribute so much both to the character and the economy of the Pacific Northwest.

Anadromous fish are those that begin life in fresh water, travel miles to the oceans to mature and return to their freshwater origins to spawn. Their travels take them up and down the Columbia, Snake, Kootenai and Clearwater rivers in the Pacific Northwest, a trip that many of them will not survive even under optimal conditions.

Temperature is a vital factor in the lives of these species, says Steven J. Wright, professor of civil and environmental engineering. Wright spent a sabbatical leave last winter term exploring options for control of the temperature in salmon streams and rivers with the National Marine Fisheries Service, the Bonneville Power Administration, and the Fish and Wildlife Service through the Boise Center of the University of Idaho.

Habitat decline and hydroelectric dams that provide power to states in the Columbia River Basin (Idaho, Montana, Oregon and Washington) have contributed to the diminishing number of salmon and steelhead. Now, recovery of the fish and other aquatic species in the area is threatened by one more factor—fire.

Salmon 'smolts' released from hatcheries travel down Idaho's rivers to the Pacific Ocean, only to return four years later to spawn at their birth site. Photo courtesy Army Corps of Engineers
More than 706,000 acres in Idaho—1.3 percent of the state’s total area—and 658,000 acres in Montana have succumbed to wildfires this year, including 32,500 acres in Idaho’s Frank Church-River of No Return Wilderness. The Frank Church Wilderness Area drains a portion of both the Snake River and Clearwater River systems, Wright says. According to the National Interagency Fire Center in Boise, Idaho, more than five million acres in the United States have burned this year, almost twice the 10-year average. Decades of conservative wildfire control have contributed to a dense buildup of combustible undergrowth that make a hotter fire and one more difficult to control.

Wright, who teaches courses in hydraulics and hydrology at both the undergraduate and graduate levels, looked at the consequences of managing the flow of cooler waters from the Clearwater River in order to improve survival rates in the summer when temperatures in the Snake River rise. Salmon, steelhead and other cold-water species die when water temperatures exceed 20 degrees Celsius (68 degrees Fahrenheit).

His computer models of temperature changes and the difference the cooler flow from the Clearwater River would make to the temperature of the rivers are the basis for an ongoing study that considers removing four dams on the Snake River, introducing the colder Clearwater River water, increasing the number of salmon released from hatcheries and controlling the salmon harvest.

“There are lots of factors to consider in this commitment to preventing extinction of these salmon,” Wright says. “And every factor has a consequence.” Breaching the Snake River dams would affect the power production in the region. Releasing colder water over the Dworshak Dam on the Clearwater River would lower the water temperature when temperatures in the Snake River rise above the danger level. But it also would further threaten the bull trout, already listed as a threatened species, which lives in the waters above the dam.

In addition, sudden onrushes of water have their own consequences, Wright says.

“Fish that are beneath the dam when there is a release can die from an overdose of nitrogen.” Water cascading over the spillway incorporates air bubbles and becomes supersaturated with nitrogen. The extra nitrogen remains in the water for some time, affecting fish as much as 100 miles downstream.

“In effect,” Wright says, “they get the bends just like divers do when they surface too quickly.”

Before modifications at dams on the Snake River, fewer than 15 percent of the smolts (young salmon and steelhead) survived the run. In 1977, Wright says, a dry summer combined with nitrogen gas bubble disease and fish caught in the dam’s turbines resulted in fewer than 1 percent survival of the smolts.

Breaching the four dams on the Snake River would return much of the river basin to its natural state, Wright says, but it also would release mud, silt and debris that has been trapped behind the dam, which also would kill fish as it made its way downstream.

“However, dams have had the most negative effect on the biology of these areas,” Wright notes. “Migration of the young salmon to the mouth of the Columbia River used to be about 10 days. Now, it takes them about two months to make that same trip.” Removing the dams also would increase the spawning area by about 70 percent for fall-run chinook salmon, but positive results would be tempered by the fact that the dams generate about 5 percent of the power in Oregon and Idaho. Locks on the Snake River, much the same as the Soo Locks in Michigan, allow transportation of goods such as wheat on the river.

Fires in the surrounding park and wilderness areas would probably have only a minimal short-term warming effect on the rivers, Wright says. But after the fires, when the rains come, he says “there is more runoff and more erosion. After the fire, if the stream bank vegetation is destroyed, there would be more direct solar heating of the water. A lack of riparian vegetation is known to cause an increase in stream temperatures.”

Wright based his studies on existing temperature data for the Snake River and graphed the water temperatures in warm and cool years, calculating the difference that adding cooler waters from the Clearwater River would produce.