W Catron Creek Culvert Extension FWP-DN-Fisheries-R3-25-017

May 9, 2025 12:50 PM

The project extends North 27th Avenue in Bozeman between Baxter Lane and Cattail Street. This work requires installation of stormwater inlets with stabilized outfalls and extension of an existing culvert within W Catron Creek. In total, 0.07 acres of wetlands and 150 linear feet of W Catron Creek will be permanently impacted. The culvert extension design maintains aquatic habitat and fish passage. Morrison-Maierle engineers and environmental scientists consulted with MT FWP during project planning. Stormwater inlets, with stabilized outfalls, will drain stormwater from the newly constructed road to the creek, which is classified as an “urban waterway” by the City of Bozeman. A roundabout will be installed at the intersection of Cattail Creek and North 27th Ave, and the existing culvert beneath Cattail Street within W Catron Creek will be extended 110 feet for a total length of approximately 180 feet. To reduce disturbance, the project will retain an existing 70–90-foot culvert and tie into it rather than replacing the entire structure, which limits in-channel work and reduces costs. The proposed culvert extension will be a 48-inch diameter pipe, set one foot below the existing streambed to allow for a natural substrate and maintain a roughly 3- foot bank flow width, consistent with current conditions. A manhole set halfway through the culvert will allow for fish resting space.

The project site follows Thomas Drive north from Baxter Lane towards Cattail Street, encountering W Catron Creek and its wetland fringe approximately halfway through the project area. At the north end of the project site, W Catron Creek flows northwards to its confluence with the East Gallatin River approximately 1.4 miles downstream. Approximately 1,104 linear feet of W Catron Creek flow through the project area, bordered by 1.41 acres of PEM1Ax/SS wetland. This section of W Catron Creek was rerouted between October 2003 and July 2005. The weedy vegetation within the wetland fringe also evidences this disturbance. The wetland/upland boundary follows the abrupt change in topography from the surrounding upland hay field to W Catron Creek. The upper stream terrace slopes steeply to the creek below and is vegetated with weeds, grasses, and intermittent shrubs and trees. Dominant plant species include smooth brome, Canada thistle, reed canarygrass, and prickly lettuce.