REED POINT — The bridge over the Yellowstone River on Twin Bridges Road near Reed Point is under threat of collapse due to heavy scouring of the riverbed on a bridge pier in the river channel, said Stephanie Brandenberger, bridge engineer for Montana Department of Transportation, Wednesday.
"Over the years, the river has actually moved the material around that pier to the very bottom of the foundation, and in fact it is going underneath the foundation in some locations. There’s not a good foundation under that support for the bridge," Brandenberger said.
The bridge has been in service since 1931. MDT identified the problem in December 2020 and crews have since been moving quickly to demolish the bridge.
On Tuesday, Montana Fish, Wildlife and Parks closed 100 feet of the Yellowstone River on either side of the bridge. MDT has also closed the bridge to the public.
“We do want to protect public safety. If anything were to happen to that structure, we want to make sure that there’s nobody in the vicinity and that nobody gets hurt," Brandenberger said.
The bridge serves as an unofficial fishing access and boat ramp for anglers and boaters. Locals call it Twin Bridges because the road bridge is directly next to a railroad bridge.
Nowadays, the bridge serves to connect one home on the north side of the river to Interstate 90. Brandenberger said the bridge was to be demolished within the next five years due to its light traffic, but the scouring tightened the time line for removal.
“We do want to try to get at least the portion of the bridge out that’s in the active channel of the river before high water. That’s when the most damage is going to continue to occur on that footing," Brandenberger said.
The bridge has five piers. Pier four, in the main river channel, has the most damage. Divers measured a three-foot-deep hole under the footing recently. Two other piers in the river channel are showing less severe scaling damage, Brandenberger said.
The goal is to at least remove pier four before the spring runoff, Brandenberger said. If the bridge collapses before then, it will make a tougher job for the demolition crew.
“An uncontrolled situation like that is never good. There are many contractors who are skilled at bridge demolition. They have a process. They have the tools, but if this were to start to collapse, it makes their job a lot harder and a lot more dangerous," Brandenberger said.
The residents of the home served by the bridge lease the land from MDT. Brandenberger said the state agency has helped find those people a new place to live.
“They have found another place, we’ve helped them to find another location to live, but they were leasing the land from MDT," Brandenberger said.
In the meantime, MDT bridge inspectors are at the bridge daily, ensuring it is safe to cross.
"We do have our bridge inspectors out there looking at the bridge, taking measurements, taking survey before those residents can use the bridge for the day. We want to make sure that it is still sound, that it is not exhibiting any kind of settlement or damage before they use it. We really are trying to limit the use of that bridge by those folks, but we can’t abandon them over there and they are getting their personal effects out in the next few weeks," Brandenberger said.
Whether the bridge collapses, Brandenberger said there would be no long-term environmental impact from its removal. The demolition crew will remove all traces of the bridge, including the piers from the river.
MDT is hoping to fill a contract to demolish the bridge in early March, with work expected to start later that month.
There are other bridges over the Yellowstone River that were built during the same era as Twin Bridges Road bridge. Brandenberger said MDT conducts underwater dive inspections of "scour-critical" bridges every five years. All bridges in the state get a top-to-bottom inspection for safety and maintenance every two years.