Culvert Design and Fish Passage: A DOT Perspective

The Michigan Department of Transportation (MDOT) is responsible for the management of 9,669 miles of state highway, comprised of all M, I, and US routes.   Within this network, thousands of stream culverts occur, all of which MDOT is responsible for maintaining or replacing as condition and public safety necessitates.  The design and maintenance of culverts is a complex endeavor that is often a multi-disciplinary exercise.   Primary factors involved in culvert design include hydraulics, funding, federal, state, and local regulations and mandates, constructability, public safety, and schedule.  Fish and aquatic organism passage is primarily driven by the NEPA (National Environmental Policy Act) process or environmental permitting process.  A recent culvert inventory associated with a 20-mile reconstruction of I-75 in Southern Michigan illustrates the challenges and problems associated with existing culverts.  Misalignment, inadequate culvert size, excessive length, and malfunctioning flap gates were some of the issues identified that may limit fish passage.  A collaborative approach with NGOs and government agencies was taken through a SHRP2 grant to mitigate some of the threats to migratory fishes on I-75.  This collaboration and early coordination during project development can pay dividends for both road agencies and the natural environment.