Abstract: Session D 3:30 pm (Back to Session D)
Who Gives a Dam? Removing Barriers to Aquatic Organism Passage One Step at a Time
Greg Jennings, PhD, PE
Jennings Environmental PLLC
Connectivity is a fundamental requirement for optimal stream function. Barriers to aquatic organism passage (AOP) are often associated with impoundments, road crossings, and utility crossings. Ecological impacts of these structures include habitat loss in the channel and floodplain, excessive erosion and sedimentation due to hydraulic adjustments, and changes to the natural fluvial sediment transport regime. Remediation measures may include complete structure removal and restoration of the natural ecosystem or a combination of engineering practices to improve stream conditions while maintaining infrastructure functions. This presentation reviews several case study projects that successfully implemented natural stream enhancement techniques to address AOP barriers. Some projects include replacement of undersized and perched culverts with natural bottom crossing structures, while others removed unnecessary dams and culverts entirely. Most of the projects include natural stream bed structures consisting of rocks and logs to transition bed slope from upstream to downstream while facilitating aquatic organism passage. These step structures are critical elements of AOP projects that may be designed as step-pools, cascades, or riffles depending on site conditions and organism requirements. Specific design parameters include step height, flow depth, velocity, shear stress, and hydraulic convergence/divergence length. Design teams must include hydraulic engineers, geomorphologists, and ecologists to ensure that all stakeholder objectives are achieved. Construction teams must be experienced and qualified to install sustainable natural stream restoration measures. Lessons learned from AOP enhancement projects should be integrated into watershed planning to restore stream functions and to avoid future impacts of development infrastructure.