Assessing Culverts in Minnesota: Fish Passage and Storm Vulnerability

Principal Investigator(s):

Jessica Kozarek, Research Associate, SAFHL - Hydraulic Lab


Project summary:

When roads cross small streams and rivers, structures allowing for the passage of water underneath roadways are critical for unimpeded and safe roadway travel. However, when viewed from a fish's perspective, road crossings, and culverts in particular, can create barriers to movement within a stream network that can have dramatic consequences for fish populations. In recent decades, concern over stream fragmentation (the inability of fish or other aquatic organisms to move past a barrier) has led to interest in designing culverts to minimize aquatic organism passage impedance at road crossings. Culverts can become barriers when conditions exceed fish or aquatic organism abilities through: excessive drop at outlet, insufficient depth, excess flow velocity, excessive turbulence, or behavioral barriers. Often, in Minnesota, fish passage concerns are addressed by considering maximum flow velocities, recessing or embedding culverts, or, less commonly, by adding culvert retrofits to slow flow through a culvert barrel. Culvert sizing thus becomes important to maintain passable flow velocities, depths, and sediment transport through the culvert. Ultimately, culvert design (including sizing) is a critical factor in maintaining safe and efficient road/stream crossings. Larger culverts, while more expensive, are more resilient to extreme events by providing greater hydraulic capacity. Larger culverts, however, may also create insufficient depths during key movement times of the year or excess sedimentation within culvert barrels. This project is investigating the parameters of culvert design through a modeling study that integrates fish swimming ability for Minnesota fish species (depth and velocity requirements), with current and future hydrologic scenarios.

Project details:

  • Project number: 2019013
  • Start date: 07/2018
  • Project status: Active
  • Research area: Environment and Energy
  • Topics: Environment, Storm water