How One Dam Increased Fish Survival By Managing Its Water
RICHLAND, Wash. -- For better salmon survival: be sure to keep salmon eggs and newly hatched fish under the water. Those are the key findings of a new study that says large numbers of fish survived when a Central Washington dam carefully controlled its water releases.
The study looked at an area of the Columbia River known as Hanford Reach, a 50-mile stretch in Central Washington along the Hanford site. It's one of the longest free-flowing areas of the river.
Several times during the 1970s water was drained too quickly out of the Hanford Reach area, killing large numbers of juvenile fall chinook salmon and redds. The two main problems that happen in those situations are:
Fish can basically suffocate in a process known as "dewatering," which is when water levels drop and fish or eggs do not stay underwater.
Fish can become stuck in small pools of water that are disconnected from the river, when water levels drop too quickly. The pools can dry up and kill the fish or become too warm for the fish to survive.
The dewatering problems in the 1970s led to two agreements to better manage water releases at Priest Rapids Dam.
Researchers at Pacific Northwest National Laboratory studied a 30-year time period that took place before and after those agreements. The study is published in the Canadian Journal of Fisheries and Aquatic Sciences.
Ryan Harnish, the study’s lead author, said after the agreements 40 percent of juvenile salmon survive at Hanford Reach, compared to 10 percent of chinook populations throughout the Northwest.
“Forty percent is off the charts and is pretty high for any chinook salmon population in the Pacific Northwest,” Harnish said.
Harnish said that makes the Hanford Reach fall chinook population is one of the most productive populations in the Northwest.
To achieve these results the Grant County Public Utility District said dam operations have been greatly altered to protect salmon.
During periods when fall chinook salmon are spawning, dam operators have reversed the normal hours when they generate energy. Usually more water is released during the day. Under the agreements, dam operators release more water at night, said Russell Langshaw, fisheries scientist at Grant PUD and co-author of the study, which the PUD funded.
Most people think of dams causing juvenile salmon mortality as they make their way out to the ocean. Langshaw said, but in this case, the dams help salmon survive. He said the way the Priest Rapids Dam releases water helps protect salmon from droughts or floods that they might experience if they were spawning in an undammed river. Langshaw said Priest Rapids Dam helps provide a consistency so that juvenile salmon and redds are always underwater.
Harnish said the Priest Rapids Dam is the only dam on the mainstem Columbia where dams can be managed like this, although there are other smaller dams, like on the Skagit River, that operate this way and have found similar success.