OLYMPIC NATIONAL PARK — The tale of two dams has reached a milestone.

Last week, the Elwha River became a single, unhindered torrent rushing through a broad channel where the Elwha Dam once stood.

On the left side of the Elwha Dam site facing downstream, a man-made, dam-related channel was fully blocked by a berm Thursday and will be completely filled in by the end of July, project superintendent Aaron Jenkins said Friday.

As Barnard Construction workers start to wrap up work at the Elwha Dam site, they are focusing more attention on its imposing sister edifice 9 miles upstream, Glines Canyon Dam.

Workers began Friday to dismantle the upper dam’s powerhouse, Jenkins said.

Workers began tearing down the Glines Canyon and Elwha dams the same week in mid-September.

Elwha Dam, completed in 1913, blocked the river just 5 miles from where the waterway pours into the Strait of Juan de Fuca at the Lower Elwha Klallam reservation.

Its demise after a century of damming the river opens the door for the return of several species of salmon, enabling them to swim upstream on their storied migration beginning — project managers hope — by the time the $325 million river restoration project is completed in September 2014.

Workers will continue excavating the entrance of the canyon, where a diversionary cofferdam still stands, for up to about five more weeks.

The river is finally coursing on its natural route, but fish won’t swim fully upstream to Glines until the end of April when Lake Aldwell, created when Elwha Dam was completed, should be fully drained, Olympic National Park spokeswoman Barb Maynes said Saturday.

That can’t happen until contractors remove about 30 feet left from a check dam that contractors built in the native channel to slow the flow of water to the channel that was blocked by a berm Thursday, she said.

The check dam must be removed gradually because the reservoir can be lowered only 11/2 to 2 feet a day to control the flow of sediment.

In about 10 days, work on removing the check dam will stop during a 14-day “hold” so the river can move back and forth across the reservoir, erode and build up more sediment, Maynes said Saturday.

“While the river is staying at the same level, it’s just sort of meandering back and forth across the plane left behind,” she said.

“It’s all centered around sediment transport and managing that, and where they get to certain levels of the reservoir.”

When the check dam is gone, “there will be no more reservoir,” Maynes said.

“[The river] will be restored to the type of flow it had before, and salmon will be able to return upstream like they did before.”

This slow, measured effort will open up 70 miles of river and tributaries and is intended to return the waterway to its former storied, salmon-rich glory.

Like Lake Aldwell, Lake Mills, created by Glines Canyon Dam, is being lowered no more than 11/2 to 2 feet a day.

It’s where Barnard’s approximately 30 workers and subcontractors will soon be turning their full attention.

At 210 feet tall, it was nearly twice the height of the 108-foot Elwha Dam and the tallest dam to be dismantled in U.S. history, but it’s slowly being cut down.

Barnard wants to demolish Glines Canyon Dam, completed in 1927, by 2013, Jenkins said.

Workers have removed 70 feet, lowering Lake Mills by 60 feet; 10 feet of the dam was above water.

They expect to remove another 30 feet by May 1, cutting the dam down to about half its original size, Jenkins said.

That’s when they must stop lowering the dam for a two-month “fish window” to protect salmon, Jenkins said.

Jenkins said there are 51/2 months of fish windows remaining this year: May 1-June 30, Aug. 1-mid-September and Nov. 1-Dec. 31.

That leaves 10 weeks of dam-removal work after June 30: July, the last half of September and October.

The fish windows are required to protect migrating fish from the 21 million to 28 million cubic yards of sediment piled mostly behind Glines Canyon Dam.

“There’s a lot of fish windows here on out for the rest of the year,” Jenkins said, adding that it’s caused the project to take longer than it otherwise might have.

Again, it’s all about the movement of sediment.

About half of the sediment is coarse, which is good for salmon habitat, and half is fine, which is not so good, said Brian Winter, river restoration project manager for Olympic National Park.

The park is overseeing the project through the National Park Service because Glines Canyon Dam and almost all of the Elwha River lies within the park’s boundaries, though Elwha Dam doesn’t.

During May and June, the outmigration of smolt going downstream would be affected by the fine sediment, which compromises their ability to take oxygen out of water, Winter said last week.

“You want clean water and natural water conditions for them to go downstream,” Winter said last week, adding that each fish window has a specific protective purpose, depending on what fish species is in what stage of migration.

The 1980 explosion of Mount St. Helens provided a blueprint for establishing the fish windows that are slowing down the demolition of Glines Canyon Dam, Winter said.

The eruption triggered a flow of vast quantities of sediment into the Toutle River.

“Fish that would have normally returned to the Toutle River bypassed it because the sediment loads were so high,” Winter said.

During the fish windows, workers will continue dismantling Glines Canyon Dam’s powerhouse, Jenkins said.

They also will work on removing the penstock, surge tower and gatehouse — until they can return the dam itself to the limelight Aug. 1.

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