Letter to governor concerning Matanuska River threat

Dear Governor Walker,

We have a growing problem on the lower Matanuska River that poses a serious threat to life and property from erosion and/or flooding. This is an advisory alert in advance of a possible emergency declaration and the need to mobilize state resources now to help protect people and the Old Glenn Highway.

The Matanuska main current has again shifted to the Butte side, chewing sections of unprotected bank very quickly at times. Roughly 2/3rds of the 1980’s flood dike washed away years ago. The remaining section of dike was hit briefly two weeks ago above Ye Old River Road demonstrating that the dike is also susceptible to a breach by the main force of the river as is the long section of unprotected bank.

If the main current breaches into low lying areas between the Old Glenn and the current bank there’s not much to stop water running along the highway or washing out the highway. Once the Maud Road extension is either washed out or partially dug up, (as it was in 2012), inundation of people and property would follow causing much more damage than the relatively small amount of river water that breached a low bank near MPlS in 2012. The dike that has kept water out, downriver from Maud Road extension, would switch to holding water in low lying areas next to the highway.

In places, only 40' to 100' of gravel and silt currently holds the river back from the low lying areas of concern.

Nearly a week ago I took GPS waypoints along the new bank. They are shown as the red dots overlaid on the attached photos. One is 2011aerial imagery. The gray photo is a LIDAR image showing historic water channels under the earth that could facilitate water flow if the bank is breached to them.

After I posted the annotated images,I received a drone image (courtesy of Arcticzone Drone, Deb Winkelman, and Chris Coyle) from July 26. It is also attached and looks down river to the south in the same area as the other images. The long narrow “pond” near the center of the photo is an old gravel pit in a low lying area that is now closer to the river than the highway.

The 2012 Hydrology and Hydraulics for the Knik-Matanuska Floodplain Study Supplement to the FEMA Floodplain Information Report Draft (p.S) states:

“In 1971, a break-out flood from an unnamed lake on Granite Creek (approximately 30 miles northeast of the Butte) breached the embankment of the Old Glenn Highway, causing widespread flood damages to the area. The floodwater entered Bodenburg Creek and flowed into the Knik River.”

The report also states this particular event is unlikely to recur, however the embankment along the Old Glenn was many hundreds of feet further away from the highway than it is now, and erosion likely poses a similar kind of inundation threat.

In August and September 2012, flood waters entered lands near MP 15 and flowed along the highway. Maud road was dug up, at the intersection with the Old Glenn Highway, to release the water pressure that subsequently caused flooding and property damage between the old dike and the Old Glenn Highway for a couple of miles.

Borough officials notified AK DOT that the highway could face serious risks. An emergency was declared well in advance of incursion of the right-of-way by river water. Riprap revetment was put in place to protect the road,but not properties between the road and the river.

Flooding also occurred in 2015 in the Sutton area at MP 64,where DOT put in 350' of revetment there as well. Somehow preventive work needs to be accomplished outside the road right-of-way in order to better protect both people and the road at less cost.

DOT could acquire properties for right-of-way protection and give DEC the ability to buy properties for removal of homes and contaminants before they end up in the river.

As the river continues to erode closer to the highway, we are looking for modeling and other information to get a realistic grip on the various risks and what can be done to prevent a disaster.

If we wait until a disaster is actually occurring, there will be no time to take action that will help anybody. A further advance emergency declaration is being looked at. Borough Emergency Services, the Borough Manager, and area legislators are being kept up to date. Mapping is being done to figure out areas of greatest risk.

FEMA buyout grant applications are pending for about a dozen houses below Maud Road, and about a half dozen in Sutton. Whether the grants are successful or not, the risk remains for many people downstream who may not realize the potential risks that seem to be growing.

At the current time the situation is somewhat stable, but erosion continues. No one knows if it will be days, weeks or years, but big water isn’t far away from causing a disaster.

If an engineering solution cannot be found, such as emergency dredging or something else, then we need to help people be aware they may need to leave to avoid being washed out.

Please use your ability to help find resources to deal with this situation and maintain close watch on the situation with the Borough Manager and the Department of Emergency Services. Thank you.

—Jim Sykes

Assembly Member, District 1