Chief Joseph Dam

Water being spilled at Chief Joseph Dam.

The Washington State Department of Ecology says it plans to adopt a final rule in December after reviewing comments on its proposal to permanently increase total dissolved gas limits in the Snake and Columbia rivers to 125 percent during spring spill season, from April 3 to June 20. The comment period ended Sept. 26.

Meanwhile, the Oregon Department of Environmental Quality expects to release on Oct. 4 a draft proposal for increasing TDG, and will accept comments for 30 days before seeking action from its Environmental Quality Commission at its January meeting.

The Washington proposal to increase TDG limits during the spring spill season would apply at the eight lower Snake and Columbia river dams, and at five mid-Columbia dams, Bryson Finch, Ecology’s water quality and hydropower lead scientist, told participants in a Sept. 19 webinar. Before going into effect, the new standards for dissolved gas must be approved by the U.S. Environmental Protection Agency.

Finch said the proposed change is driven by the Comparative Survival Study, an ongoing modeling study by the Fish Passage Center indicating that higher percentages of salmonid smolts will return as adults if dams spill up to 125 percent TDG. According to Ecology’s draft EIS on the proposal, the Comparative Survival Study predicts a two- to two-and-one-half-fold increase in Snake River spring Chinook abundance if spill is increased to 125 percent for 24 hours a day, along with a significant increase in steelhead.

Michael Garrity, Columbia River water policy manager for the Washington Department of Fish and Wildlife, said fish managers hope to see about two-thirds of the improved smolt-to-adult ratios under the Flexible Spill Agreement, designed to operate dams at higher spill for 16 hours and at performance levels for eight hours each day.

Finch said the agreement involving federal agencies, states and tribes, which balances fish needs with hydropower generation, is another reason for the proposal.

The “final motivating factor,” he said, was a recommendation by the Southern Resident Orca Task Force to increase spill criteria to 125 percent and align the state's standards with Oregon’s.

But adding dissolved gas to the river can also harm fish, so Washington’s proposal to increase TDG limits also requires continued monitoring of salmon and steelhead, and at least five years of monitoring nonsalmonids for gas bubble trauma, Finch said.

In order to implement the higher TDG levels, dam operators would be required to examine at least 50 salmonids and 50 nonsalmonid fish each week, when possible, Finch said. The nonsalmonid fish should include at least three native species, and at least 10 of each species. Those fish can be caught in fish bypass systems, or in the river within 1 mile downstream of a project.

Monitoring will not have to occur at every dam, but would be required within three zones, which include the four Snake River dams, the four lower Columbia River dams, and the five mid-Columbia River dams. Finch said if biological thresholds for gas bubble trauma are exceeded, the dams can no longer spill to 125 percent until gas bubble trauma subsides to acceptable levels.

Finch said no additional monitoring took place during the 2019 spring spill, but monitoring will begin next year if TDG limits are increased, and will focus on native fish, depending on which species are going through the fish bypass system. “There are invasives that also move through; in the end of the day they may have to be counted just to meet the sample sizes,” he said. “So 2020 will be sort of a pilot year.”

According to the draft EIS, Ecology would approve the monitoring plans, and hydropower operators on the Snake and Columbia rivers that do not submit a biological monitoring plan must meet standards prior to the Flexible Spill Agreement. That includes 115 percent TDG forebays and 120 percent TDG tailrace criterion, and the 125 percent maximum TDG level.

Gas bubble trauma, or GBT, occurs when fish are exposed to high levels of total dissolved gas. It’s the biggest risk identified in increasing TDG in Ecology’s draft EIS. “Spilling to higher TDG levels than the current standards over long periods would be a concern for chronic effects of TDG on aquatic life, given that data suggests that GBT is more prevalent at lower TDG levels when an exposure is prolonged. Literature suggests that fluctuating TDG levels over multi-day periods may provide some relief from TDG symptoms,” the EIS says.

The EIS also says that, despite multiple studies, several uncertainties remain about the impacts of TDG in aquatic life. “While several studies have collected and examined resident fish (i.e. non-salmonids) for GBT or studied various fish indigenous to the Snake and Columbia rivers in laboratories, several data gaps exist on their life history traits. Knowledge on spawning, early life stage development and movement, coping mechanisms for high TDG conditions, foraging needs, and water column preferences for several resident fish are unknown,” it says.

However, the EIS says, uncertainties can be compensated for by incorporating a margin of safety.

The document notes an ongoing smolt monitoring program to collect data on juvenile fish condition and gas bubble trauma since 1995, and a reduction in spill is required when more than 15 percent of fish show signs of gas bubble trauma, or more than 5 percent of fish sampled show severe signs of GBT. Severe signs occur when 26 percent or more of a fin area is occluded with bubbles. The criteria incorporates a margin of safety, since studies have shown significant mortality does not occur until about 60 percent of the population shows signs of GBT.

Finch said if an exceedance occurs, dam operators can no longer spill to 125 percent until the gas bubble trauma goes below these biological thresholds over the next seven-day averaging period. After that, the 125 percent TDG spill can resume.

Finch said the nonsalmonid monitoring would focus on native species, but could include invasive species since they are often present in the bypass systems and can indicate how resident fish are doing. He said biologists do not expect impacts to white sturgeon, in particular, because they are bottom dwellers, and water has more capacity to dissolve gases at greater depths.

In scoping comments, the three action agencies—U.S. Army Corps of Engineers, BPA and Bureau of Reclamation—asked Ecology to limit the increased TDG standards to 16 hours a day during spring spill season, as outlined in the flexible spill agreement (CU No. 1882 [9]). The agencies also said Washington should limit the increase to the duration of the flexible spill agreement, which expires in 2021, or when a record of decision is signed for a new EIS for Columbia River System Operations.

The agencies argued that it’s premature to permanently change TDG limits before varying levels of spill are analyzed and a long-term strategy for CRSO is identified. In addition, they wrote, lessons learned from implementing higher spill levels could be incorporated into a permanent rule change, if warranted. “This factor is particularly important given the potential adverse effects of high TDG levels on aquatic species,” their letter states. The action agencies also expressed concern that EPA may not act in time for the 2020 spring spill season if a permanent rule change is sought.

Ecology’s proposal, however, is to permanently change TDG limits in the Snake and Columbia rivers during the spring spill season, and to allow the 125 percent TDG for 24 hours a day throughout the spring spill season. The draft EIS notes that the flexible spill agreement, which ends after the 2021 spring spill season, leaves uncertainty about future spill regimes. “A permanent Washington rule that includes rule language adopted directly from the Spill Agreement would need to be amended in 2021 and therefore is less desirable than a rule that provides flexibility on implementation of different spill configurations,” it states. “Furthermore, a rule that directly follows Flexible Spill operations provides little flexibility to hydropower operators under unforeseen circumstances.”

Last year, Ecology removed the 115 percent TDG requirement in a short-term modification of the rule to align with the flexible spill agreement, for up to three years. Chief Joseph and Grand Coulee dams are not included in the criteria, since there is no fish passage at those projects.

© Copyright 2021 NewsData, LLC, 5625 NE Elam Young Pkwy, Ste 100 Hillsboro, OR | Terms of Use | Privacy Policy Powered by BLOX Content Management System from

K.C. Mehaffey covers fish issues for Clearing Up, and is editor of the NW Fishletter. She joined the NewsData writing team in February 2018. From lawsuits to scientific studies, she is enjoying the deep dive into the Columbia Basin's many fish topics.