Wetland, Stream Bank, and Shoreline Restoration
Stream Restoration Case Studies Focused on Habitat Enhancement
Stream restoration is the process of enhancing the physical, biological, and chemical conditions of a stream ecosystem to set the stream on a trajectory toward improved ecological functions. Stream restoration projects may have many complementary objectives, including erosion reduction, infrastructure protection, stormwater management, community amenities, and ecological habitat enhancements. This presentation describes several stream restoration case studies focused on habitat enhancements associated with improving connectivity longitudinally, laterally, and vertically to support various aquatic organisms. Aquatic species of concern include fish, mussels, invertebrates, and salamanders, often limited in habitat by disconnections in their environment. Longitudinal connectivity may be limited due to barriers to aquatic organism passage (AOP) such as impoundments, road crossings, and utility crossings. Ecological impacts of these anthropogenic structures include habitat loss in the stream 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 ecological engineering practices to improve stream conditions while maintaining infrastructure functions. Project case studies include replacement of undersized and perched culverts with natural bottom crossing structures and removal of dams and road crossing structures. 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. Vertical and lateral connectivity associated with floodplain functions may be impaired by channel incision and/or artificial levees that force flood flows to remain in the channel. Project case studies exemplify various approaches for reestablishing floodplain connections to manage hydraulic energy during flood flows and to enhance floodplain habitats. Specific design parameters include entrenchment ratio, bank heigh ratio, bankfull flow depth, velocity, shear stress, and stream power. Further enhancements in alluvial stream functions can be achieved by adding sinuosity to a straightened stream, thereby reducing velocity and promoting in-channel riffle-pool bedforms and hyporheic connectivity. Research on streams restored in this manner has documented improved habitats and nutrient retention. Successful stream restoration design teams include engineers, geomorphologists, and ecologists to ensure that all objectives are optimized. Lessons learned from habitat enhancement projects should be integrated into watershed planning to restore stream functions and to avoid future impacts of development infrastructure.