Culvert Replacement with Fish Passage
Northstar worked with Dirigo Engineering to provide hydrologic and hydraulic engineering at the stream crossing of Front Street in Brownville Junction, Maine.
The Town of Brownville proposes to replace the Front Street culvert, removing the existing undersized, perched structure with a larger hydraulically sufficient culvert that would also restore aquatic passage at the site. The existing culvert is described as two old tank cars butted end to end with the middle seam pulling apart and failing. The culvert has overtopped downstream end of the culvert is perched above an existing scour hole and is experiencing erosion due to overtopping. The community is concerned about total failure of the culvert which, according to information provided by the town, could result in loss of emergency services, water, sewer and fire protection to many homes.
With the restoration of the Atlantic Salmon in the Penobscot River watershed, the Pleasant River and therefore this stream are identified by USFW as potential habitat/spawning grounds for both salmon and alewives. A January 2016 Restoration Plan Summary from U.S. Fish and Wildlife Service Gulf of Maine Coastal Program provided recommendations that would improve fish passage and flood passage functionality. The new culvert will restore connectivity to 1.97 miles of potential Atlantic salmon habitat.
Northstar Hydro, Inc. (NHI), was retained by Dirigo Engineering to provide hydrologic, hydraulic and scour evaluations for existing and proposed culverts in association with final design. NHI identified the following additional goals as part of the culvert selection process:
- Analyze peak flows to allow for passage of 100-year peak flow with headwater/diameter ratio (HW/D) less than or equal to 1 or passage of 50-year peak flow with 2’ of clearance as a minimum for high flows. Flow requirements depend on type of structure, with the 2’ clearance guideline directed at bridge structures and the HW/D ratio directed at culvert type of structures.
- Analyze impact of flows from stream watershed and potential backwater from the Pleasant River.
- Fish Passage: Size the culvert to allow passage of fish such that the width is at least 1.2 times BFW of 12’ and velocity and depth during lower flows are within recommended flow velocity targets and depths.
- Foundation protection against scour: foundation type and potential scour will be discussed and evaluated as part of the project.