A temporary steel bridge once used to access forestland isolated by the Mount St. Helens eruption in 1980 is now creating access to forestland near Applegate Lake.

A 220-foot structure known as a Bailey Bridge, invented for Allied armies during the invasion of Germany in World War II, has replaced, for now, the old Middle Fork Applegate Bridge on Forest Service Road 1040.

The 140-foot timber bridge that crossed the Middle Fork of the Applegate River was closed April 26 after inspectors discovered rotten and damaged understructure, according to the Rogue River-Siskiyou National Forest.

The 180,000-pound temporary bridge, which was put together in pieces and slowly pushed on rollers over the Middle Fork with an excavator, now rests atop the old bridge but is anchored on both sides.

The temporary bridge is strong enough to carry all commercial vehicles, including wildland firefighting equipment, says David Scovell, the forest's bridge engineer.

That is considered crucial because it is the only vehicle access into remote forestland along the Oregon-California border considered at high risk for catastrophic fire, Scovell says.

"It can carry almost anything," Scovell says. "It can carry an M-1 tank. It's pretty stout."

The Bailey bridge system was invented for quick and effective construction over obstacles such as rivers for traveling armies, according to the Forest Service.

Many of these same types of bridges were built after the Mount St. Helens eruption, and various Forest Service regions have collected enough pieces to rebuild them when needed for occasions like this, Scovell says.

The bridge had to be 220 feet long so there would be enough counter-balance weight to keep it from falling into the river as it inched across the span, Scovell says.

The forest spent about $17,000 to transport the bridge, which came in more than 3,000 pieces from a Forest Service storage facility in Auburn, Wash., Scovell says. The forest then paid $66,000 for a Bureau of Land Management crew and equipment to install the bridge, he says. 

Scovell says he already has designed a concrete replacement but it will cost as much as $1 million to build, and there is currently no funding for it.

"Usually we try to get these (temporary bridges) out after a couple years," Scovell says. "Sometimes it's tough to get funding for these (permanent bridges)."

Reach Mail Tribune reporter Mark Freeman at 541-776-4470 or mfreeman@mailtribune.com. Follow him on Twitter at www.twitter.com/MTwriterFreeman.