The state Department of Ecology is proposing to increase the maximum amount of water that can be spilled over the lower Columbia and Snake River dams with the goal of improving juvenile salmon survival rates. However, some stakeholders are urging caution, as previous studies conducted by Ecology have warned of detrimental effects when water levels are too high.
In April 2018, additional spill over the dams was carried out by the U.S. Army Corps of Engineers (USACE) as the result of a 2017 U.S. District court order. Spill limits are determined by the total dissolved gases (TDG) in the rivers. Those limits are intended to protect salmon from injury or death as a result of high levels of dissolved oxygen blocking blood flow and interfering with the respiratory system.
In December, a Flexible Spill Agreement was reached among state, federal and tribal partners that will be in effect through 2021. As part of the agreement, the TDG limit was raised from 115 percent to 120 percent for 2019, with plans to gradually increase it up to 125 percent by 2021. At the same time, the Bonneville Power Administration (BPA) would be able to suspend the spill for eight hours a day to recoup some of the lost energy.
In its draft Environmental Impact Statement (EIS) to the Environmental Protection Agency (EPA), Ecology proposes amending the surface water quality standards under the federal Clean Water Act to make the 125 percent TDG limit permanent; that limit would be allowed during the spring season on either river.
The proposal was also among the recommendations made in the Southern Resident Orca Task Force’s 2018 report (page 48). The state agency has already conducted two public hearings this month on the draft EIS.
Citing previous studies, Ecology’s EIS argues that juvenile salmon leaving the river systems have higher survival rates when they move through the dams by spillways compared to turbines or bypass systems.
However, some stakeholders such as Northwest River Partners Executive Director Kurt Miller say Ecology should wait until the impact of the recent spills can be studied. Miller’s nonprofit emphasizes the value of the region’s hydropower system, with membership consisting of public utilities, businesses, farmers and ports.
“The real proof won’t come back for another three years at least,” Miller said. “We won’t know how those salmon ended up (until then). We see these as important tests.”
Ecology’s proposal is in part based on a Comparative Survival Study (CSS) juvenile fish passage survival model that predicts salmon survival and population would increase if the TDG level was raised to 125 percent. The CSS is a joint project run by federal, tribal and Pacific Northwest state agencies. A 2017 CSS report concluded based on modeling “that increasing spill for fish passage within the safe limits of 125 percent total dissolved gas has a high probability of improving smolt to adult return rates.”
Others, such as the Columbia River Intertribal Fish Commission, argue that the TDG levels don’t harm salmon until they reach 130 percent or higher. They cite a 2014 update to the Spirit of the Salmon: The Columbia River Anadromous Fish Restoration Plan, which states “data collected from 1995 to the present still supports the original 1995 risk assessment that levels of TDG up to 125 percent pose little risk to aquatic species.”
However, Miller points to the conclusions of a 2009 Ecology study conducted with the state of Oregon. It found that there “would be a potential for a small benefit to salmon related to fish spill” if the 115 percent TDG limit were removed, “but there would also be the potential for a small increase in harm from increased gas bubble trauma.”
The study further noted that TDG levels above 110 percent “can cause” trauma in fish, and “the weight of all the evidence from available scientific studies clearly points to detrimental effects on aquatic life near the surface when TDG approaches 120 percent. Ecology strongly encourages implementing actions that increase salmonid survival without further increasing total dissolved gas.”
In a public comment on the scope of the proposed rule in May, NOAA Fisheries Assistant Regional Administrator Michael Tehan recommended that the 125 percent TDG be limited to April 3 to June 20, which is the juvenile spring migration period for the fish, and for no more than 16 hours per day.
Miller told Lens that while his organization supports the Flexible Spill Agreement “we want to make sure before it (Ecology’s proposed rule) becomes permanent…that it’s validated by science, by actual results.”
Public comments for the draft EIS is due Sept. 26.