Friday, June 18th 2018
NOAA Fisheries last month delivered its first report on court-ordered spring spill for juvenile salmon and steelhead passage to the U.S. District Court in Oregon.
The report describes spill operations by the U.S. Army Corps of Engineers at four lower Snake River and four lower Columbia River dams during April. Additional spring spill up to the maximum total dissolved gas levels allowed by state water quality rules, called gas caps, was ordered by the court one year ago. However, its implementation was delayed a year by the court to allow time for federal agencies to develop a spill plan.
Total dissolved gas limits are intended to protect young fish from gas bubble trauma in the dams’ tailraces during spill.
The additional spill began April 3 on the Snake River and April 10 on the Columbia River.
The request for injunctive relief for more spill was enjoined with an earlier case argued in District Court. The initial case, heard by Judge Michael H. Simon, resulted in a May 2016 remand of the federal Columbia River power system biological opinion for salmon and steelhead listed under the Endangered Species Act.
The spill plea was brought to Simon in January 2017 by plaintiffs in the original case, the National Wildlife Federation and the State of Oregon, among others, asking the court to begin ordering spill to maximum total dissolved gas levels as set by Oregon and Washington beginning April 3, 2017 and to continue for each year of the BiOp remand.
Simon agreed that more spring spill would benefit ESA-listed fish, but delayed the action until 2018 while federal agencies completed a spill plan for the dams. The plan is for additional spill only during the spring of 2018 to the total dissolved gas caps set by Oregon and Washington, as well as for earlier PIT-tag monitoring of juvenile salmon.
NOAA Fisheries, Northwest RiverPartners, the Kootenai Tribe of Idaho, the states of Idaho and Montana, and the Inland Ports and Navigation Group appealed Simon’s spill injunction in early June 2017 to the Ninth Circuit Court of Appeals. However a three-judge panel of the appeals court ruled April 2 in favor of Simon’s spill ruling.
According to the spill report, April 2018 was characterized by above average flows for the lower Snake and lower Columbia Rivers along with average to slightly above average air temperatures and above average precipitation across most of the Columbia River Basin.
The Northwest River Forecast Center observed the April adjusted runoff for the lower Snake River at Lower Granite Dam at 131 percent of the 30-year average (1981-2010) with a volume of 5.97 million acre feet. The April adjusted runoff for the lower Columbia River at The Dalles was 119 percent of the 30-year average with a volume of 16.5 MAF. The April observed precipitation was 104 percent of average on the lower Snake River above Ice Harbor Dam and 118 percent of average on the lower Columbia River above The Dalles Dam.
During the April 2018 reporting period, the planned 2018 Spring Fish Operations Plan spill operations began April 3 at lower Snake River dams – Lower Granite, Little Goose, Lower Monumental and Ice Harbor dams – with spill caps that achieve a 120 percent TDG in the tailwater of each dam and 115 percent in the forebay of each dam directly downstream.
FOP spill operations at lower Columbia River dams began April 10, with the same gas caps as Snake River dams.
Operating to gas caps is “a more complex operation to implement than the past years’ operations,” the report says.
The Corps had to evaluate conditions every day to establish spill targets that would meet gas caps. The evaluation considered environmental conditions (e.g., river flow, wind, water temperature, barometric pressure, incoming TDG from upstream, and water travel time) and project operations (e.g., spill level, spill pattern, tailwater elevation, proportion of flow through the turbines, and project configuration), according to the report.
In April, "Low flow" operations at the dams are triggered when inflow is insufficient to provide both minimum generation and the target spill levels.
“In these situations, the projects operate at minimum generation and pass the remainder of project inflow as spill and through other routes, such as fish ladders, sluiceways, and navigation locks,” the report says. “As flows transition from higher flows to low flows, there may be situations when flows recede at a higher rate than forecasted. In addition, inflows provided by nonfederal projects upstream are variable and uncertain.”
A combination of factors can result in times when unanticipated changes to inflow result in forebay elevations dropping to the low end of the Minimum Operating Pool, according to the report. Since these projects have limited operating flexibility, maintaining minimum generation, MOP elevation and the target spill may not be possible throughout every hour and actual spill can vary up to 2,000 cubic feet per second within an hour.
In addition, a number of factors influence actual spill and resulting TDG, including hydraulic efficiency, exact gate opening calibration, spillway gate hoist cable stretch due to temperature changes, and forebay elevation (e.g. a higher forebay results in a greater level of spill since more water can pass under the spill gate).
During April TDG in the Lower Granite Dam forebay (the upper of four lower Snake River dams) was under 106 percent, whereas its tailwater varied between 115 and the 120 percent gas cap, but not exceeding the gas cap.
The Little Goose forebay – the next dam downstream of Lower Granite – exceeded the gas cap of 115 percent 16 times during April, on one occasion (April 27) reaching 120 percent. The Little Goose tailwater varied, but never exceeded 120 percent.
TDG in the Lower Monumental forebay exceeded the 115 percent gas cap 21 of 30 days, reaching 120 percent on one day (April 7) . TDG in the dam’s tailwater did not exceed the 120 percent TDG gas cap during the month.
The Ice Harbor Dam forebay TDG exceeded state limits 16 times in April, reaching 119 percent once (April 27). The dam’s tailwater reached 121 percent on four occasions in April.
In the lower Columbia River, the McNary Dam forebay TDG didn’t exceed state limits of 115 percent until late in April when it exceeded the limit three times. McNary tailwater remained at or below the 120 percent TDG cap during the entire month.
John Day Dam forebay TDG exceeded state limits seven times, all in the latter part of the month, reaching 121 percent on April 26 and 27. John Day tailwater remained within the 120 percent TDG cap over the entire month.
The Dalles Dam forebay TDG exceeded the 115 percent gas cap 14 times during the month, reaching as high as 119 percent. The Dalles tailwater remained within gas cap limits.
The Bonneville Dam forebay exceeded TDG limits 17 days in April, reaching 120 percent twice. Tailwater at Bonneville Dam exceeded the 120 percent gas cap seven times in April, reaching 123 percent on the month’s last day.