Managing Stream Corridor Evolution in the Sierra Foothills

Year: 2020
Presenter/s: Damion Ciotti
Symposium Session: 2020 - 04 Observe Stage 0
Topics covered: beavers, floodplain, hydraulics, lessons learned, outside PNW, riparian, sediment transport, and stream


Developments in our understanding of stream channel evolution and application of ecological design have changed not only the restoration approach in degraded valley bottoms but also the vision and measure of success. Disconnected alluvial streams are unable to rework floodplain surfaces and have lost their ability to maintain a shifting mosaic of aquatic and terrestrial habitat heterogeneity. In Sierra foothill streams of California this has significant negative consequences for anadromous fish, migratory birds and other ecosystem services such as water and carbon storage. Most valley bottoms in the Sierra foothills have been desiccated for over a century due to mining activities, agricultural and urban development. Common restoration practices aim to stabilize channel banks or construct habitat features in streams that remain isolated from their floodplains. The cumulative effect is a stream corridor that is dominated by oak savanna and blackberry with limited ability to evolve to higher ecosystem value. The U.S. Fish and Wildlife Service is now in its fourth year of applying ecological design principles to the restoration of streams in agricultural and suburban communities of the Sierra foothills. We believe societal and individual landowner needs and goals are compatible with a more functional and dynamic stream corridor. Design attention has moved from the single stream channel focus to modifying the human components of the stream corridor so it may evolve. This involves assessing the constraints to fluvial dynamics including flood risks, transportation and water infrastructure, livestock management, and mitigation projects. Important design components of this shift in approach include; design at the valley scale; assessing natural and artificial geomorphic controls; assisting valley bottom communities and landowners accommodate a more dynamic river; and designing a minimum dosage approach that relies on the ecosystems capacity to recover. Metrics of success focus on the amount of fluvial space and connectivity attained and biogeomorphic processes restored. This approach is not suited for programs or practitioners aiming to immediately construct a specific stream habitat type. By instead working to evolve stream corridors towards higher levels of complexity the practitioner is able to build a more resilient project at a larger spatial scale. A completed demonstration project along with others under various stages of development will be presented.