Seattle City Light is completing a year-long maintenance project at Boundary Dam on the Pend Oreille River in northeast Washington that will require lowering the reservoir behind the dam twice this month.
“Boundary Dam is a vital resource for Seattle City Light, providing about half of the electricity we produce for our customers, and a significant contributor to the economy of Pend Oreille County,” Superintendent Jorge Carrasco said. “Completing this maintenance work is an important part of ensuring its operation for years to come.”
Crews are finishing rehabilitation work on a sluice maintenance gate for the dam. The 312-ton gate sits underwater and is used to seal off one of the dam’s seven sluices so that regular maintenance can be performed on the gates that are opened or closed to control the amount of water in the reservoir. You can watch a video of workers removing the sluice maintenance gate last year here.
To put the maintenance gate back in place, City Light will lower the reservoir and back a trailer carrying the gate into the reservoir, then raise the water level to float the gate and move it near the dam. A second lowering of the reservoir will allow crews to mount the gate back on the dam.
Each time the water level drops, the Metaline Falls, located up river from the dam will be exposed for a short time. The falls were uncovered last September during an earlier draw down to take the gate off the dam.
Low water conditions will prevent access at all boat launch facilities on the Boundary reservoir, including the Boundary Forebay, Metaline Park, and Campbell Park immediately below Box Canyon Dam from Sept. 15 through 21. The Forebay Recreation Area remains closed. It is scheduled to reopen Sept. 30.
“We recognize this needed maintenance work has disrupted some recreational uses at the reservoir,” Carrasco said. “We apologize for any inconvenience and appreciate their patience while we complete this work and return to normal operations.”
The current reservoir level is 1990 feet of elevation above sea level. From Sept. 15 through 17, the reservoir level will be 20 feet or more lower in order to prepare for the 312 ton gate’s movement from land to the river.
The reservoir will be raised to 1990 feet in elevation by 9 a.m. Sept. 19 to float the gate for transfer back to the dam.
The reservoir will again be lowered, reaching approximately elevation 1960 feet by 9 a.m. Sept. 20. The elevation will remain at that level for about 5 hours while the gate is reattached to the dam. By the end of the day, the lake will be returned to normal operation at 1990 ft.
During the very short time the water level is at the lowest elevation of 1960 ft above sea level, the falls will be exposed.
It’s been 28 years since the sluice maintenance gate was last removed and rehabilitated.
Seattle City Light is the 10th largest public electric utility in the United States. It has some of the lowest cost customer rates of any urban utility, providing reliable, renewable and environmentally responsible power to nearly 1 million Seattle area residents. City Light has been greenhouse gas neutral since 2005, the first electric utility in the nation to achieve that distinction.