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PALMER — A state emergency project to protect the Old Glenn Highway from the Matanuska River shifted to attack mode as the river threatened its banks — for the second time in about a week.
An emergency declaration from Gov. Bill Walker at the request of the Matanuska-Susitna Borough last week triggered the start of a $2 million, 1,100-foot trench filled with rock.
But work on the trench paused Thursday afternoon after the unpredictable glacial river began undercutting the bank between Maud and Smith roads, authorities said. Crews began dropping huge boulders into the river to shore up the bank so they could resume work on the trench.
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The actual river level is dropping, but its main channel is directed at property along its banks, threatening the highway but also more than a dozen homes.
The river "shifted significantly" in the last 24 to 36 hours, according to an Alaska Department of Transportation and Public Facilities update issued at noon Friday.
Last Friday, as the rain-swollen river chewed at a narrow strip of bank, crews shifted into defensive mode and began dropping rocks into the river to redirect the water.
Then, with 735-feet of trench constructed as of Thursday, parts of the bank again began calving into the river. Crews dropped huge rocks up to 3,000 pounds each into the river to stabilize the bank, according to an update from the Matanuska-Susitna Borough.
The state-contracted crew pulled from about 500 tons of rock staged for that purpose at the south end of the project, according to the borough spokesperson Patty Sullivan. A blog with updates is located on the borough's website.
The Matanuska is proving changeable, as usual. The original place where the river threatened the trench site now has a gravel bar in front of it instead of water, according to DOT. The most erosive forces are now downstream.
Crews are building about 120 feet of trench a day when they can focus on the emergency project instead of shoring up the bank with rock, officials say.