OLYMPIC NATIONAL PARK — Barnard Construction crews will start rock blasting this week near Glines Canyon to clear a passage for salmon migrating along the Elwha River.

The blasting will not take down any of the remaining 50 feet of the once-210-foot dam and will have little effect on sediment released into the river, according to National Park spokeswoman Barb Maynes.

The short series of blasts will decrease the size of several boulders likely left over from a rockfall and possibly related to the dam’s original construction in the river just downstream of the remnants of Glines Canyon Dam, Maynes said.

“We know that the pre-dam river channel through Glines Canyon was clear and free of large obstructions,” Olympic National Park Superintendent Sarah Creachbaum said in a statement.

“Removing the rockfall debris will restore the pre-dam channel conditions and provide clear passage for returning fish once dam removal is completed next year.”

Not yet scheduled

Brian Krohmer, construction project manager for Barnard Construction, based in Bozeman, Mont., said the day blasting will begin hasn’t been scheduled.

“We’re not sure exactly what day it’s going to be,” he said.

He also could not say how long blasting might take, as crews will assess the results of each blast to see if more is needed.

All areas west and downhill of the Whiskey Bend Road are closed to public entry, with the exception of the Upper Lake Mills Trail and upper Lake Mills delta.

Krohmer said Whiskey Bend Road will be closed temporarily immediately before and after each blast, likely for between 20 and 30 minutes.

Removal of the remaining part of Glines Canyon Dam, part of the overall $325 million Elwha River dam-removal and restoration project, is expected to begin later this fall, according to the Park Service.

Demolition has been on hiatus because of repairs needed to Olympic National Park’s water-treatment plant, which became clogged with sediment after dam removal began, and because of a “fish window” for migrating salmon.

The removal of Elwha Dam, downstream from Glines Canyon Dam, was finished in March 2011.

Park officials say the Glines Canyon Dam demolition is expected to be finished in 2014.

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Reporter Jeremy Schwartz can be reached at 360-452-2345, ext. 5074, or at jschwartz@peninsuladailynews.com.