Dix Corp., a Spokane heavy-construction contractor, is expected to start work this month on a project to replace a 1.7 million-pound navigation lock gate at Lower Monumental Dam. The project is one of two such jobs it has won worth a combined total of $25.5 million.

Lower Monumental is on the Snake River about 100 miles southwest of Spokane. The U.S. Army Corps of Engineers late last year awarded Dix a $12 million contract to replace the gate, then earlier this year awarded it a $13.5 million contract to replace the downstream navigation lock gate at The Dalles Dam with a 2 million-pound gate structure. The Dalles Dam is on the Columbia River, about 90 miles upstream from Portland.

Meanwhile, Max J. Kuney Co., also of Spokane, has been awarded a $1.1 million contract to remove and replace aging concrete at Lower Monumental Dam.

The gates at both dams will be replaced during a planned outage of the navigation lock system on the two rivers from Dec. 10 to March 18, during which shippers along the river system will need to arrange overland transportation alternatives, the Army Corps says. It's having maintenance work done on the locks at other dams on both rivers in that period.

During the outage, Kuney will remove and replace 8,400 cubic feet of concrete from the north wall inside the Lower Monumental navigation lock, coordinating that work with Dix, says Gina Baltrusch, an Army Corps spokeswoman in Walla Walla. That concrete, which is more than 40 years old, has cracked, and chunks of it have fallen off in recent years, she says. The concrete work also is scheduled to begin this month and is expected to be completed by mid-February, Baltrusch says.

The Army Corps designed the upgrade projects. The Corps' Walla Walla District will oversee the Lower Monumental work, and its Portland District will oversee The Dalles project, Baltrusch says.

Thompson Metal Fab Inc., of Vancouver, Wash., made the Lower Monumental gate in three 570,000-pound pieces, which Dix will weld into a 110-foot-tall, 86-foot-wide structure, she says.

The Lower Monumental gate pieces were being barged from Vancouver and were scheduled to arrive at that dam in late November.

Thompson also is fabricating the gate for The Dalles Dam in two 1 million-pound pieces, says Scott Clemans, a Corps spokesman in Portland.

The gate at The Dalles consists of two horizontally swinging leaves that will overlap. Because the new gate will be fabricated with complete 106-foot-tall, 54-foot-wide leaves, it will take less time to install than the Lower Monumental gate, which will require more assembly onsite, Clemans says.

The Dalles gate leaves are scheduled to be delivered on Feb. 8 and installed Feb. 11 through March 11, he says.

A massive crane that will hoist the gate pieces into place at Lower Monumental Dam is being erected, and site preparations are under way to erect another such crane at The Dalles, Clemans says.

Also during the lock outage, the lower gate at the navigation lock at John Day Dam will be replaced. Advanced American Construction, of Portland, is the contractor on that project.

The gates will be replaced to keep the facilities safe to use for decades, the Corps says in a notice posted on its Web site.

"The alternative to this planned, coordinated outage is an unplanned emergency outage that might shut down the navigation locks for a year or more," the notice says.

The Corps operates navigation locks at eight dams serving a 465-mile shipping route that reaches from the Pacific Ocean to Lewiston, Idaho.

Last year, traffic through the navigation locks at Lower Monumental Dam, which is the sixth farthest upstream dam in the system, included shipments totaling 2.3 million tons of grain, petroleum products, fertilizer, wood products, and other cargo, the Corps says.