With the reservoir behind the Wynoochee Dam nearly full, the U.S. Army Corps of Engineers now must bring the level down to create storage space in case another big storm hits.
By midnight last night, the reservoir was two feet below the "full" level, higher than it's ever been during a time of the year when flooding was possible, said Larry Merkle, chief hydrologist for the Corps' Seattle District.
But by this morning, river flows in the Wynoochee had dropped dramatically enough that dam operators could release more water from the dam and still not cause more damage downstream, Merkle said.
At 10 a.m. Wednesday the Wynoochee was flowing about 24,000 cubic feet per second at the measuring station near the mouth of Black Creek. By this morning it was at 14,000, Merkle said.
The Corps thinks of 18,000 cfs measured at that station as a "zero damage" level, so a measurement of 14,000 allowed them to speed release of water at the dam so they could get storage space back faster, Merkle said. Releases at the dam held at 4,500 cfs through the day and night Wednesday, but by this morning the Corps had increased it to 6,500. Before the storm hit last weekend, the release from the dam was about 500 cfs.
The dam is owned by the City of Aberdeen and operated by Tacoma City Light, which receives the hydroelectric power it generates.
The Corps steps in and directs the operation during a flood. Merkle said the Corps will try to balance flows to provide adequate storage in the reservoir and make maximum use of the water for hydropower.
The Corps can "spill" water quickly if there is a threat of more flooding and spilling it won't do damage downstream. Or, if it doesn't expect weather that will bring more flooding, it can release the water more slowly so Tacoma City Light can take maximum advantage of the hydropower.
The risk is that another bad storm would hit before the reservoir has enough storage capacity to hold it.
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