Performance Assessment of Oversized Culverts to Accommodate Fish Passage

In Minnesota there is not a standard culvert design used at road crossings to improve aquatic organism or fish passage. The design process for fish passage in Minnesota is currently based on the knowledge and experience of local county, state and DNR personnel. The design methodology attempts to maintain the natural stream dimensions, pattern and profile through the culvert crossing. If designed properly aquatic organisms and fish that can make it upstream to the culvert should be able to pass through the culvert. This research was conducted to better understand the hydraulic conditions related to the practice of recessing culverts and other fish passage design elements over a range of landscapes in Minnesota. The design elements analyzed included bankfull width, slope, channel materials, side barrels and recessed culverts. Nineteen culvert sites were survey around the state. The main criterion used to evaluate performance of the culverts was the presence or absence of adequate sediment in the recessed culvert barrel. Six of the fourteen sites with recessed barrels had no sediment accumulation. A likely reason that these culverts lack sediment was increased velocities due to improper sizing relative to bankfull channel width and the accumulation of sediment in the side barrels. Wider Rosgen "C" type channels also correlated with performance issues related to culvert design.