PORT ANGELES — When two 100-foot-plus dams that block the Elwha River start coming down Sept. 15, errant, water-borne logs could cause traffic delays on the U.S. Highway 101 bridge that spans the river.

The bridge on the transcontinental backbone of the Pacific coast will be exposed to an open, uncontrolled river for the first time once the dams are dismantled.

Chris Keegan, operations engineer for the state Department of Transportation’s Olympic region, said Monday that logs and other debris could build up beneath the two-lane bridge as the Glines Canyon dam is dismantled and the 415-acre Lake Mills reservoir created by the dam is drawn down.

Transportation is concerned that when both the Elwha and Glines Canyon dams start being dismantled later this year, logs long held in watery stasis could, once propelled downriver, “scour,” or wear away, the earthen banks under both sides of the arched bridge and possibly knock out Highway 101, Keegan said.

So, the state highway agency wants the debris to course through the center arch, not around it, Keegan said.

The bridge is too high above the river to wash out, and workers “dug down to hard rock to put the piers in,” he said.

“We can control whatever comes down there,” Keegan said.

“We want to make sure that when the dam is removed, we are really careful about what’s going on, that we keep logs from building up.”

Once — or if — that buildup occurs, an excavator would pluck logs and other debris from the river and drop it back in free-flowing water to make its way farther downstream.

The bridge could be reduced to one lane while the excavator does its work, Keegan said.

The 450-foot-long U.S. Highway 101 bridge lies at the bottom of a steep, winding hill road four miles west of the state Highway 112 intersection, at the southern end of Lake Aldwell and north of Lake Mills.

“All the large, woody debris that comes down once the dams are removed — anything that comes down that river — is going to have to go under the Highway 101 bridge,” Clallam County Engineer Ross Tyler said.

Olympic National Park spokeswoman Barb Maynes said in an interview that the effects of dam removal were fully explored in environmental studies on the project but could not recall any specific information on the Highway 101 bridge.

Two other bridges also cross the Elwha, but neither is of concern to state and local officials, they said Monday.

One span on state Highway 112 nine-tenths of a mile west of the Highway 101 junction is an arch “anchored high up on the gorge,” Keegan said.

“The water is way down below.”

A third bridge that crosses the Elwha is also the newest — a 589-foot, double-deck span that stretches more than eight stories above the river on Elwha River Road.

The west side of the bridge is anchored into natural rock bluff, Tyler said.

The east-side wall is glacial till protected by riprap.

Shafts that support the bridge are drilled 60 feet to 80 feet into the riverbed.

Lake Mills still has about seven acres of logs waiting to be pushed through the dam’s spillway.

It’s part of a log-removal project that began more than two weeks ago after a delta was cleared of alder for sediment control last September.

Those logs are pressing against a log boom at the dam’s spillway meant to keep obstructions away from the dam.

The lake, too frozen to run logs out of the spillway, probably won’t warm up enough to resume the project until March, Kevin Yancy, Elwha Dam power plant supervisor, said Monday.

“I would say probably we’ll have most of them out of there” when workers from Barnard Construction Inc. of Bozeman, Mont., start dismantling the dams Sept. 15, Yancy said.

But after nearly 100 years of blocked Elwha River, there’s no telling how many logs are nestled on the bottom of Lakes Mills and Aldwell, Yancy said.

“We may find all kinds of stuff,” he quipped.

The $26.9 million tear-down of the 108-foot Elwha Dam and 210-foot Glines Canyon Dam is scheduled to take three years.

It’s part of the federal government’s $351.4 million Elwha River Restoration Project, the goal of which is to restore a salmon run that dwindled from 400,000 fish before the dams were built to 3,000.

The highway bridge was built in 1925 — when the road was known simply as Olympic Highway.

The U.S. 101 designation was applied in 1926, when the U.S. highway numbering system was introduced nationwide.

The Olympic Highway loop, including the U.S. 101 portions, was signed as Primary State Highway 9 from 1937 to 1964.

The Elwha Dam was completed in 1913 and the Glines Canyon Dam was built in 1927.

________

Senior Staff Writer Paul Gottlieb can be reached at 360-417-3536 or at paul.gottlieb@peninsuladailynews.com.