Friday, June 08, 2018
As the snow melt-off progresses and nears an end in some areas, river flows in the Snake and Columbia rivers are declining and so is involuntary spill at eight dams on the rivers that in May forced total dissolved gas levels higher than Washington and Oregon clean water standards allow.
Lower flow at most dams is allowing the U.S. Army Corps of Engineers to begin to return to court-ordered spring spill up to state mandated total dissolved gas levels, known as gas caps – 120 percent TDG in tailraces and 115 percent TDG in the downstream dam’s forebay.
Higher than normal flows, spill and TDG that impacted the spill cap operations in May are returning to lower levels, according to Dan Turner of the Corps’ River Control Center, speaking at the interagency Technical Management Team meeting Wednesday, June 6.
Even with falling stream flows (flow at Lower Granite Dam on the Lower Snake River is 110,000 cubic feet, 10 percent below the 30-year forecast), the water supply outlook through early summer is looking good with forecasts at all major dams higher than the 30-year average.
A three-judge panel of the Ninth Circuit Court of Appeals ruled April 2 in favor of an April 2017 U.S. District Court injunction allowing more spring spill at four lower Snake and four lower Columbia river dams. With the decision, spill to the gas cap began April 3 at lower Snake River dams and at lower Columbia River dams April 10. The additional spill through June 15 is designed to aid migrating juvenile salmon and steelhead.
With lower stream flows at Snake River dams, the Corps is again managing to spill targets. It has now hit that target at Lower Granite Dam (31,000 cubic feet per second) since June 3 and has kept TDG levels at or slightly under gas cap levels since June 1. TDG in Lower Granite’s tailwater reached 126 percent May 26 and 27. The Little Goose Forebay hit 120 percent May 28 and 29.
Flow on June 3 at Lower Granite was 110 kcfs, but had been over 200 kcfs at one point in May. It is forecasted to drop precipitously by July 1 to under 60 kcfs, according to Turner.
The Little Goose spill target is 26 kcfs, which the Corps nearly hit June 5 and 6 when TDG levels fell within gas-cap levels. TDG in the tailwater hit 127 percent May 27 when the river was spilling 81 kcfs. The downstream forebay at Lower Monumental Dam hit 127 percent the next day.
“LoMo is in transition,” Turner said, noting that the Lower Monumental Dam spill target has yet to be hit, but TDG levels were within the gas cap June 6. Tailwater TDG a LoMo hit 128 percent May 23 and the downstream forebay at Ice Harbor Dam hit 123 percent May 28 and 29.
Ice Harbor Dam, the lower dam on the Snake River, has for the most part met its spill target of 80 kcfs since June 3, but the forebay at the next downstream dam, McNary, on the Columbia River continues to exceed the 115 percent TDG cap. TDG at Ice Harbor’s tailwater hit 130 percent May 27 and the forebay at McNary hit 125 percent May 23 and 24.
Flow at The Dalles Dam on June 3 was about 350 kcfs. At one point in May, flow exceeded 500 kcfs. The forecast is for a flow level of about 225 kcfs by July 1.
Although flows are also dropping in the Columbia River, involuntary spill is continuing and TDG at all four lower Columbia River dams – McNary, John Day, The Dalles and Bonneville dams – continue to exceed water quality standards set by the states.
Water supply forecasts remain high with an April – August forecast at The Dalles Dam of 105,908,000 acre feet, which is 121 percent of the 30-year average (1981 – 2010).