MISSOULA — The bridge on Rock Creek Road crossing the Clark Fork River was recently found to be “scour critical,” and Missoula County is working to pursue countermeasures to keep the bridge intact and open to traffic.
Erik Dickson, the county's assistant director of public works, said the Montana Department of Transportation placed the bridge under scour critical status due to the structure's shallow footings and active channel erosion.
“The abutments on the bridge are either shallow or unknown foundations, and with the changes in the river channel over the years, it has started to cause some erosion in the channel,” Dickson said Tuesday.
He added that the county is required to have a plan of action, including a detour route to Interstate 90 if the bridge were to fail or need closing for repairs. Given the area's terrain, a detour involves a lengthy drive.
“It's not a convenient route to go through Phillipsburg to get back to the interstate, but that's the available detour route,” Dickson said.
The county also must pursue a mitigation plan in order to remain illegible for federal or state assistance to address any needed repairs. On Tuesday, county commissioners approved a $32,000 contract with the WGM Group to design a scour mitigation plan.
The funding will come from the county's bridge fund.
“If we don't have a plan of action, or if we're not actively seeking scour counter-measures, then if this bridge had an issue even this spring, where erosion leads to potential damage or even requires closure of the bridge, we would not be eligible for assistance,” Dickson said.
He added that the most basic fix would likely involve rip-rap to stabilize the bridge piers in the river. However, it's estimated that the mitigation plan could take several months to complete. The county would then need to secure the necessary permits.
