A process‐based approach to restoring depositional river valleys to Stage 0, an anastomosing channel network

Abstract

Stream restoration approaches most often quantify habitat degradation, and therefore recovery objectives, on aquatic habitat metrics based on a narrow range of species needs (e.g., salmon and trout), as well as channel evolution models and channel design tools biased toward single‐threaded, and “sediment‐balanced” channel patterns. Although this strategy enhances perceived habitat needs, it often fails to properly identify the underlying geomorphological and ecological processes limiting species recovery and ecosystem restoration. In this paper, a unique process‐based approach to restoration that strives to restore degraded stream, river, or meadow systems to the premanipulated condition is presented. The proposed relatively simple Geomorphic Grade Line (GGL) design method is based on Geographic Information System (GIS) and field‐based analyses and the development of design maps using relative elevation models that expose the relic predisturbance valley surface. Several case studies are presented to both describe the development of the GGL method and to illustrate how the GGL method of evaluating valley surfaces has been applied to Stage 0 restoration design. The paper also summarizes the wide applicability of the GGL method, the advantages and limitations of the method, and key considerations for future designers of Stage 0 systems anywhere in the world. By presenting this ongoing Stage 0 restoration work, the authors hope to inspire other practitioners to embrace the restoration of dynamism and diversity through restoring the processes that create multifaceted river systems that provide long‐term resiliency, meta‐stability, larger and more complex and diverse habitats, and optimal ecosystem benefits.

Modeling riparian species occurrence from historical surveys to guide restoration planning in northwestern USA

“…Hence, riparian restoration with native species is limited to narrow inset floodplains where plants can access the water table. However, physical restoration of incised channels can raise the water table so that a greater area of floodplain and terraces can be colonized or replanted with appropriate riparian species (Pollock et al 2014, Powers et al 2019). Similarly, isolation of floodplains by levees reduces width of the riparian area and constrains channel dynamics that created diverse species and age structure on floodplains (Fullerton et al 2006, Hall et al 2007).…”

“…floodplain and terraces can be colonized or replanted with appropriate riparian species (Pollock et al 2014, Powers et al 2019. Similarly, isolation of floodplains by levees reduces width of the riparian area and constrains channel dynamics that created diverse species and age structure on floodplains (Fullerton et al 2006, Hall et al 2007.…”

Management of vegetation encroachment by natural and induced channel avulsions: A physical model

“…Further, the ability to accelerate channel widening and material generation could benefit process‐based restoration aimed at reestablishing rates of erosion and deposition, channel migration, and the growth and succession of riparian vegetation (Beechie et al, ). Coupling induced avulsions with low‐technology hand‐built wood and beaver structures (Wheaton, Bennett, Bouwes, Maestas, & Shahverdian, ) may provide an affordable solution towards depositional multithread rivers (e.g., Stage 0 restoration and Geomorphic Grade Line; Powers, Helstab, & Niezgoda, ).…”

Dam busy: beavers and their influence on the structure and function of river corridor hydrology, geomorphology, biogeochemistry and ecosystems

“…pre-human disturbance) ecological functioning. In the context of unconfined, depositional valleys this specifically includes promoting multi-threaded channel systems with frequent floodplain inundation (Cluer and Thorne, 2014;Powers et al, 2019;Walter and Merritts, 2008), a goal which clearly dovetails with beaver driven impacts (see section 7), and acknowledges the considerable legacy of beaver ecosystem engineering on river corridors prior to their widespread eradication. Combining beavers and the geomorphic basis of stage restoration efforts is particularly well suited to address the broader problem of historical channel incision, as the multithread channel system can reduce reach scale stream power and promote deposition (Pollock et al, 2014).…”