UMATILLA, Ore. — Access to Columbia River dams has been under tight wraps since the 9/11 terrorist attacks.
But on Saturday, McNary Dam will hold an open house from 9 a.m. to 3 p.m. that will give parents a chance to show their youngsters how a hydroelectric dam works. Curious adults also may want to take advantage of the rare opportunity.
McNary held its first open house two years ago and it drew more than 800 people. This year that number is expected to grow to more than 1,000.
"There was such an overwhelming turnout in 2008 that we decided to do it again this year," said Pasqualie Anolfo, a park ranger for the Army Corps of Engineers.
Visitors will be able to visit the power house, the fish viewing room and navigation locks on the Washington side of the dam.
"It's a rare opportunity these days to see the navigation lock because the public can't get into the dam area on the Washington side anymore," Anolfo said.
They also will be able to take a extraordinary peek inside the quarter-mile-long power house, where they'll be able to see workers replacing the copper wiring in one of two generator units being overhauled this year.
Anolfo said being able to see the wiring coils being replaced is "a real behind the scenes kind of experience."
McNary has 14 massive hydroelectric generators turned by the power of falling water to produce electricity for thousands of homes and businesses in the Mid-Columbia. The generators together can produce up to 980 megawatts of hydropower, or enough for 686,000 homes.
In 2009, the dam produced 5.1 billion kilowatt-hours of electricity, according to engineer Dave Coleman, McNary's operations manager.
Visitors will be able to see inside the core of one generator, where they'll see a ring of rotating magnets that is about 35 feet in diameter and part of the generator's rotor assembly. As the magnets rotate, their magnetic field induces electrical current in the copper wiring surrounding the 1,200-ton rotor turbine assembly.
Wiring in the turbines is about 50 years old and the insulation around it is starting to degrade, which reduces the turbines' productivity, Coleman said. Each generator has 45,000 pounds of copper wiring, which is recycled after removal.
Four of the dam's generators have failed since the first one went online in 1953, and those were overhauled in 1999 and 2006. The other 10 turbines are being overhauled as part of a five-year, $64 million project funded by the Bonneville Power Administration.
Coleman said it takes five to six months to disassemble, overhaul and reassemble each generator. Permanent cranes inside the powerhouse are used to lift the massive pieces in and out of place.
During the last open house, the most popular viewing areas were the navigation locks and fish ladder on the Washington side of the Columbia River. The locks allow tugs, barges and boats to travel up and down the river.
The north shore also is where the original fish ladders are located and where fish are counted as they pass through the dam.
"That fish ladder seems to be the best memory many people have of the dam," Anolfo said. "The water flow is restricted (narrower) there, so every fish can be seen passing through."
Those planning to attend Saturday's open house can access McNary's visitor centers on both sides of the river. Visitors over the age of 18 should expect to show their driver's license at the security gates. No cameras or cell phones that can take photos will be allowed.
From the Oregon side, a park ranger will be on hand to give tours. Those who would rather not drive to both sides of the river can hop on a shuttle provided by the Corps of Engineers.