Matanuska-Susitna Borough

Building a 1,100-foot Rock Trench

Mat-Su | Patty Sullivan | Wednesday, August 24, 2016

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.

SHELTER SITE  

If flooding occurrs and residents need to evacuate they may go to the  7th Day Adventist Campgrounds at 16970 E. Maud Road. The site has Cabins, RV sites, tent sites, and a gym.

Reach it by driving the Old Glenn Highway, turn east onto Maud Road, drive 1 mile, and the site is on your right. It is not yet open to the public.

Watch the video of riprap being unloaded and an overview of the events since Monday at this link:

 

For more information email Stefan Hinman atThis email address is being protected from spambots. You need JavaScript enabled to view it.

For DOT project information call Shannon McCarthy at 907 269-0448 or This email address is being protected from spambots. You need JavaScript enabled to view it.

Video produced by Stefan Hinman, Mat-Su Borough Public Affairs.

Photos by Patty Sullivan, Mat-Su Borough Public Affairs.

See earlier press release with evacuation checklist. https://www.matsugov.us/news/borough-and-governor-declare-disaster

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Photos

Dump truck hauling rock armour The 525 foot wall will extend to 1,100 feet The soft riverbank Dot crew at work Staging of the rock armour off bike path water rolling over log