After the major flooding in 2012, the Mat-Su Borough recognized the changing river patterns around Talkeetna. While flooding was the initial issue, Borough Floodplain Administrator Taunnie Boothby says the community was more concerned about erosion.
The 2023 flood that destroyed the existing revetment brought into sharp focus the importance of understanding the river flow shifts and increased erosion. The Borough already had begun a study through the Army Corps of Engineers with Planning Assistance to States, or PAS, when the flood wiped out the revetment. The program provides technical assistance to quantify the issue and support future funding requests.
The PAS erosion report is now complete and shows an increase in erosion rates, though Boothby says that is not a surprise. However, she says the erosion rates farther south were interesting and a reminder that the problem goes beyond the Main Street area.
Boothby says unlike a flood study, where the topography doesn’t change much and different precipitation patterns can be used to predict outcomes, erosion is unpredictable. She says
“All we can do is look at what has happened and understand what is going on now.”
She explains that any repairs need to be able to slow and collect sediment and be able to withstand the high velocity from the Susitna and Chulitna Rivers. The two rivers have changed course. They once flowed to the west side toward Trapper Creek, but now they are aiming directly at Main Street.
The PAS report provided several options for armoring the bank, however, only one is viable given the velocity and turbidity of the rivers. The Army Corps of Engineers suggests a rock revetment with toe protection to armor the bank and prevent the river from undermining the system. The Corps suggests about 3,400 feet of revetment that ties in with existing erosion control structures.
This PAS study will help the Borough support funding requests for construction. Boothby says the project is larger than what the Borough can do on its own. Though federal funding has been requested, new projects can only move forward when a budget is approved. Congress is currently operating under a continuing resolution.
Boothby and a representative from the Army Corps of Engineers will be on hand to present findings and answer questions at the Talkeetna Community Council meeting on February 5.
