Aquatic Organism Passage Webinar

Barriers to aquatic organism passage (AOP) largely include dams, culverts and utilities, which have extensive effects on entire ecosystems by blocking a river’s free-flowing natural systems. The legacy of infrastructure development has left thousands of barriers throughout our American landscape, and without proper considerations, more are designed and built every day.

This webinar highlighted the different types of barriers, how to mitigate for those in place, and how to avoid creating new ones. Elements for transportation and hydraulic engineers vital to designing with AOP considerations were discussed. Participants learned:

• Types of barriers to aquatic organism passage
• Types of fish passage structures for dams
• Things to consider for culvert/small bridge design
• How AOP designed culverts are superior to traditional culvert design for flood resiliency

Aquatic organisms are defined as all animals that must be in water during a stage of their life. Although mostly focused on fish, aquatic organism passage considers a range of species including mollusks, crustaceans, insects, and amphibians.

Mitigation options for barriers to aquatic organism passage include removal as well as both engineered and nature-like passage structures. Blockage removal and engineered solutions pose significant cost, design and construction challenges, and the latter does not always perform as anticipated. Nature-like installations, including rock ramps, flow constrictor/step-pools, stream simulation and bypass channels, offer a host of benefits by either burying, avoiding or replacing an existing barrier.

Culverts pose a significant challenge due to standard rigid design practices. With the frequency and severity of storms continuing to increase, thousands of road failures are occurring annually. At stream crossings, typical failure mechanisms include woody debris flow, sediment slugs, overtopping, skewed alignments, and abrupt transitions. To build resiliency and AOP into culvert design, design teams need an expert in geomorphology. Bankfull cross-section shape and dimensions, channel slope, channel structure and natural scour conditions are critical components for consideration in a stream-simulation methodology. In addition, shape and size of the culvert is critical, with channel openings as wide or slightly wider than bankfull width. The design must be flexible to account for long-term changes in bed elevation and flood discharges.

For more information, feel free to reach out to our presenter: