Armouring against Matanuska River

PALMER — The rock armour is staged. The big cottonwood trees are felled. Thursday, excavation begins on the 1,100-foot trenchline between the river and powerlines. The angular riprap will be keyed into place in the trench, ten to 20 feet deep, in an effort to deflect the future force of the Matanuska River with an immoveable granite-mixed wall.

Some 17 homes in the community of Butte are the closest downhill from a quickly eroding riverbank. It’s not floodwaters causing trouble. The river is low. The river is pounding into soft riverbank. It used to run parallel to the bank. Three days ago the Matanuska-Susitna Borough declared disaster, followed a few hours later, by a disaster declaration of Alaska Gov. Bill Walker.

As the shoreline collapses by feet nearly each day, the Old Glenn Highway and the powerlines are getting closer to it. Today the highway is 120 feet from the river in its narrowest spot, the powerlines are 60 feet from the river near mile 15 of the Old Glenn Highway. The trench will run on the river side between the roads of Leeside Circle and Graham Circle. Gov. Walker is allowed up to $1 million in disaster mitigation costs without requiring legislative approval.

Alaska Dept. of Transportation and Public Facilities Maintanence crewmen drove trucks all Tuesday to deposit up to 5,000 cubic yards of the big rock in its staging location along a paved bike path, according to Justin Scott, Engineering Technician with DOT’s Construction crew. Wednesday, the decision was made to extend the trench. To the north the new trench will tie into an existing buried rock wall and to the south it will extend past the north end of the old quarry pond.

The construction work is expected to take two to three weeks.