Rulemaking could boost survival of salmon in Snake and Columbia riversThere are many efforts happening to help support orca and salmon recovery in Washington. Governor Inslee has directed Ecology to take the necessary steps to allow increased water to spill over the Snake and Columbia River dams during the spring season, with the end goal of helping more juvenile salmon reach the ocean. This work is also reflected in the Southern Resident Orca Task Force recommendations to the Governor.
|McNary Dam on the Columbia River |
(U.S. Army Corps of Engineers)
The rule change would apply to the ‘spring spill season’ – generally from early April through June, when large amounts of runoff from melting snowpack typically lead to high water flows in the Columbia and Snake River systems. The spring spill season is also when juvenile salmon are migrating out to the ocean and when adult Spring Chinook and sockeye are migrating up river to spawn.
At this time, we are in the rule development phase to change the allowable TDG level. We are opening a comment period on the scope of the Environmental Impact statement (EIS) until May 29. The EIS will review the potential for aquatic life impacts of more TDG from increased spill.
This might sound familiarIn March 2019, we issued a short-term modification to allow increased TDG during the spring spill season at the eight federal dams on the lower Snake and Columbia rivers. We wrote a blog post when we were working on the short-term modification. Without a rule change, the short-term modification will expire after the 2021 spill season.
What is Total Dissolved Gas?Increasing the water spilling over a dam can push air into the water and increase TDG. TDG is mostly made up of nitrogen and oxygen gases that are trapped in the water and produce pressure (see figure below). This pressure in the water column is measured relative to atmospheric gases which means more gases in the water than in the air is considered supersaturated. TDG is recorded as a percentage - 100% is normal or “in equilibrium” with the atmosphere. Water above 100% TDG is considered “supersaturated”. For example, 110% TDG is creating 10% more pressure in the water column than normal.
|As water plunges over a dam it can trap more gas and can become super saturated. |
Graphic used with permission from University of Iowa IIHR Hydroscience and Engineering
Why do we limit Total Dissolved Gas?
Why increase spill at dams?
What happens next?This is the development phase of the rule. Right now, you can comment on the scope of the EIS, until May 29. At this time, we expect comments on alternatives, mitigation measures, adverse impacts, and any other considerations we should include in the EIS. In the coming months, we expect to have a proposed rule available for public comment.
Unrelated to changes to the TDG criteria for the Columbia and Snake rivers, we are also considering revisions to the surface water quality standards to address several additional changes, including those needed to meet legal obligations, align shellfish criteria with Department of Health requirements, and clarify descriptions for marine aquatic life uses. You’ll see these mentioned in the CR-101 and the scoping notice for the Draft EIS. There will be an opportunity to comment on the proposed changes in the coming months.
Visit the rulemaking webpage for additional information and instructions on how to comment.
Learn more about Ecology’s role in the Orca Task Force.