Green Peter will reach “empty” by mid-October at the rates it is receiving and releasing water.
That means the reservoir will reach the minimum “conservation pool,” which is still above the amount necessary to produce some power.
“July was one of the driest inflow months ever recorded,” U.S. Army Corps of Engineers Hydrologist Karl Kanbergs of the Northwest Division Office in Portland said. The lake was used in the spring to bolster river levels in the Willamette for fish needs.
Since then, dry weather has kept lake levels dropping.
The reservoir has had an average inflow of 100 to 120 cubic feet per second (cfs). To maintain flows, Green Peter and Foster dams have been releasing 550 cfs. This maintains the Foster pool level and draws down Green Peter’s.
Normally, this time of year, Green Peter-Foster releases 650 cfs, Kanbergs said. Flows from the dams are measured together.
As of Thursday at midnight, Green Peter was 24 percent above minimum pool, 948 feet, Kanbergs said. It reaches full pool at 1,010 feet. It is considered at minimum conservation pool at 922 feet.
The Corps estimates it will reach that point in mid-October if conditions remain dry.
At that point, Green Peter dam can still do minimal power generation, Kanbergs said, but the lake is out of usable water for other uses.
By that time, the Corps normally begins drawing down Foster Lake.
Inflows have been as low as 80 cfs by that point in the past, Kanbergs said. The Corps is releasing 100 cfs less than normal “mainly to conserve water at this point, so we don’t run out.”
There are also endangered species issues in the fall that require water in the lake, Kanbergs said.
Green Peter was one of two projects, also including Lookout Point, used to keep flows up in the spring.
Cougar Reservoir was unavailable to help this year because the Corps is building a water temperature control tower. The lake is empty and will remain so through 2004 during the project.
Cougar holds 9 percent of the Willamette’s storage capacity, Kanbergs said. It would have been used during the spring to meet flow targets at Salem.
Green Peter represents 16 percent and Lookout Point 19 percent of the Willamette’s storage capacity.
Detroit Reservoir, with 18 percent of the capacity is not usable for the Albany’s spring flow targets, Kanbergs said. It will be drawn down later this month to help maintain target flows at Salem.
The main reason Green Peter is empty is because the weather “got hot, and the rains just stopped,” Kanbergs said.