Performance Assessment of Oversized Culvert to Accommodate Fish Passage

Project summary:

Since 1991, the Minnesota Department of Transportation has been installing recessed culverts at road crossings to allow for the passage of fish and to correct issues related to steeper slopes. This methodology attempts to maintain the natural stream dimensions, pattern and profile through the culvert crossing. It is believed that recessed culverts, if designed and installed correctly, can help reduce maintenance costs, improve fish passage, and improve overall stream health (physical and biological).

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 surveyed 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.