Sean C. Morgan
Green Peter Reservoir is nearly at the bottom of its “conservation pool,” but it is not expected to dip any lower than that barring a lack of rain in the next month.
On Friday, Green Peter was at 927.29 feet with an inflow of 50 cubic feet per second and an outflow of 330 cubic feet. Its minimum conservation pool is 922 feet.
Foster Lake was at 600 feet with an inflow of 360 cubic feet per second and an outflow of 550 cubic feet at the beginning of its draw down cycle.
As of Sept. 21, Green Peter was 72.2 percent below its rule curve. The rule curve is an established upper limit for the reservoir for any given date. The lake cannot exceed the limit, maintaining the ability to control floods.
Under the rule curve, Green Peter must be at minimum by Dec. 30 to handle winter rain, Matt Rea, U.S. Army Corps of Engineers Willamette Basin coordinator, said. “In a good water year, that’s how we’ll operate. This has, of course, not been a good water year.”
Green Peter was used to meet water flow requirements downstream. With Green Peter reaching the bottom of its conservation pool, the Corps will tap Foster to meet downstream flow requirements. Foster is normally drawn down beginning on Oct. 1.
Whether Foster will provide enough depends on long-term weather, Rea said. Right now, the long-term forecast is for rain.
If, by early November, there has not been significant rain, “then we may have to look at serious alternatives.”
That means dipping into power pools at Green Peter and elsewhere, Rea said. “There’s still quite a bit of storage left.”
That storage is maintained to make sure water is available for winter emergencies, such as cold snaps, requiring more power, Rea said. The Corps is not allowed to dip into the power pools except in “very serious” low-water years.
“That is not something normally we do or want to do,” Rea said.
Right now, the Corps is pretty much planning on rain, so it does not expect to touch the power pools.
The lakes are refilled beginning in February, Rea said. It takes two to three months depending on water conditions.
Foster is a special operation and is drawn down to minimum in April to promote the passage of steelhead. The reservoir is kept empty until just before Memorial Day when it is refilled quickly with flow from Green Peter.
“We’re just hoping it starts raining again, as per usual,” Rea said. “We just hope for a good water year. This has been a dicey year.”