St. Regis River Culvert Analysis

The St. Regis River has its headwaters at St Regis Lakes, Mineral County, approximately 3 miles Southwest of Lookout Pass on Interstate 90.  The watershed encompasses more than 233,000 acres of land in western Montana.  91% of this land is managed by the Lolo National Forest.  The St. Regis River is an important westslope cutthroat trout (WCT) production area and supports reproducing bull trout. 

Culvert data was collected from the Lolo National Forest’s most recent culvert inventory and analyzed to establish a comprehensive list of the priority fish passage barriers within the St. Regis River watershed.  With this information, stakeholder groups should be able to more effectively plan projects to improve aquatic stream conditions and water quality within the watershed.  There are 131 inventoried culverts in the St. Regis River Watershed.  83 culverts have been identified as partial or total fish passage barriers. 

Problem culverts were analyzed for removal or replacement based on a number of factors, including miles of upstream fish habitat, potential sediment load at complete pipe failure, fish assemblage, and road type. High priority was given to culverts where quality habitat could be opened to native fish populations or where tributaries could be connected to the main St. Regis River.  Culverts on streams with a bankfull width less than six feet were not included in the assessment.

Stream connectivity was calculated as a ratio of miles of historically connected stream to the miles of currently connected stream.  The connectivity in the St. Regis River watershed is 20%, a low figure compared to similar size streams in the Middle Clark Fork River.  Fish data was taken from a previous assessment by Trout Unlimited which incorporated both Montana Fish, Wildlife and Parks and Lolo National Forest fish population surveys.

Randolph Creek

 Culvert replacement is typically a requirement when the road is the main travel route or required for access. Roads already identified for decommissioning are most often targeted for culvert removal and naturalization of the streambed.  Culvert removal and crossing protection is typically much less expensive than upgrading a crossing structure and typically provides a long-term maintenance-free solution to barrier concerns.  In either case, crossing restoration will increase the stream habitat available to migratory native fish and improve the connection of tributary streams to the main stem St. Regis River.