North Twin Bridge needs reinforcement
Fifteen years after the south Twin Bridge collapsed in Madison County, the tables have turned and now the north bridge is showing signs of trouble.
The Army Corps of Engineers is working to stabilize the bridge and they’re asking for the community to help by weighing in on what to do.
The river has actually shifted course.
It’s flowing much more heavily through the north fork than it did just a few years ago.
Madison public works director Dave Walrath described the changing nature of the south fork of the Snake River by saying the stream has shifted.
Both flows used to go down the south channel and under the south Twin Bridge, which is no longer the case.
“Those flows have reversed and now the bulk of the flows are coming into the north channel. This replacement bridge was not designed for those types of flows,” said Walrath.
A good amount of water is rushing into the bank and then traveling under the bridge. That’s because the north bridge needs to be twice the length it is right now.
Last year, crews took rocks and fortified the embankment, but with the continual shift in the river, it’s still not enough.
It’s slowly eroding.
Walrath said the corps has devised a plan to save the bridge without rebuilding, which includes adding more rocks or rip-rap rivetment and steel reinforcement.
“We’re going to make sure that at least in the interim the water is not able to circle around the bridge to the south,” said Walrath.
He and the corps recognize this may not be a permanent solution.
“I think everyone who’s been involved with this project realizes that at some point we’re going to need a longer bridge,” said Walrath.
The Twin Bridges were rebuilt back in 1998 following a severe flood that caused the south twin bridge to collapse and damaged the north bridge beyond repair.
The corps is taking public feedback until Sept. 3.
If you would like to offer a comment on the reinforcement project, send an email to TwinBridgesEA@usace.army.mil or mail a letter to U.S. Army Corps of Engineers, Environmental Compliance Section, RE: Twin Bridges EA, 201 North 3rd Ave., Walla Walla, WA 99362.
