Analysis: Breaching Two Snake River Dams
by K.C. Mehaffey
"Anything less than that four-dam breach scenario
doesn't have a lot of chance of success."
-- Tucker Jones, Oregon Department of Fish & Wildlife
The Fish Passage Center analyzed breaching two Snake River dams instead of four and concluded "a 2-dam breach will not be adequate to avoid continuing salmon and steelhead population decline particularly under climate change conditions occurring now and predicted for the future."
Scientists used Comparative Survival Study modeling -- also used in the 2020 Columbia River System Operations Environmental Impact Statement -- to compare average smolt-to-adult return rates from Lower Granite Dam to Bonneville Dam if any two of the four dams were breached with SARs from other EIS alternatives. Comparisons in the Sept. 16 memo also include results of a prior FPC analysis of breaching the four dams and spilling to 125-percent total dissolved gas levels at the four lower Columbia River dams.
The comparisons included average SARs for yearling Chinook salmon and steelhead. The analysis also predicted probabilities that returns of those species would be less than 1 percent, or greater than 2 percent, based on an 80-year water record. Achieving SARs of between 2 and 6 percent is a goal adopted by the Northwest Power and Conservation Council. SARs below 1 percent are associated with continued population declines.
Results of the analysis showed that breaching two dams would be similar to the high-spill scenario analyzed in the EIS. According to the memo, generational declines -- or SARs less than 1 percent -- would occur once every three or four years if two dams are breached, but only once every six to 13 years if four dams are breached and the four lower Columbia River dams spill to 125-percent TDG levels.
The analysis was done by request for the Oregon Department of Fish and Wildlife and the Yakama Nation after NOAA Fisheries released a draft report in July on rebuilding Columbia Basin fish stocks. Officials said during a press conference that breaching one or more of the dams would be necessary to achieve healthy and harvestable returns of salmon and steelhead. When releasing the final report, the agency clarified that all four dams should be breached to achieve the salmon recovery goals beyond preventing extinction, but that adaptive management is needed when implementing any large-scale restoration efforts.
Darryll Olsen, board representative for the Columbia-Snake River Irrigators Association, has also been asking for this kind of analysis after suggesting deep drawdowns at two dams -- Lower Granite and Little Goose -- as a compromise in the dam-removal debate.
To him, the analysis indicates that there's not a great difference between the probabilities of reaching at least 2-percent SARs under the two- or four-dam breaching scenarios. According to the analysis, salmon would have a 45-percent probability of reaching 2-percent SARs under a two-dam breaching scenario, compared to a roughly 60-percent probability if four dams are breached.
He told NW Fishletter that he considers the difference marginal, but the difference for irrigators or for power generation between breaching two dams compared to four is significant. Costs would also be far less. "Given all the uncertainty, do you really want to fight for that delta between the two and four dams?" Olsen asked.
Another striking factor about the memo, he said, is that even with four dams removed, goals for smolt-to-adult return rates would not be met 40 percent of the time. "If I take the Fish Passage Center memo at face value, there's no guarantee that the four-dam breach is going to get you to recovery," he said.
But Tucker Jones, Columbia River and ocean salmon program manager for ODFW, told NW Fishletter it's more than just a matter of meeting or not meeting 2-percent SARs.
"My takeaway, and what the memo said, is really that anything less than that four-dam breach scenario doesn't have a lot of chance of success," he said. He said just looking at how often the 2-percent threshold is achieved loses the importance of achieving SARs between 2 and 6 percent, with 4 percent as an average. Those years can act as a buffer for the years when SARs drop below 1 percent, he added.
Jones also said the analysis uses the prior 80-year water record, and that climate change is likely to produce worse water conditions for salmon in the next 80 years. "Some of those populations are at quasi-extinction right now, so they don't have the luxury of going much lower for very much longer," he said. And although 2022 brought good returns for some stocks, steelhead counts at Bonneville Dam were 63rd out of 84 recorded years. "It's hard to call that great. Summer steelhead are in real trouble," he said. He said it was hardly a banner year for spring or fall Chinook, even though returns were better than predicted.
Jones added that while Oregon is committed to rebuilding Columbia Basin fish populations, it is also committed to making sure the benefits of the dams are replaced if breaching occurs. "It can't all be on the backs of the ratepayers or irrigators," he said.
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