Spawning habitat rehabilitation - I: conceptual approach and methods

Altered sediment and flow regimes in regulated rivers limit available spawning habitat for many fishes, especially salmonids. Mitigation efforts include spawning habitat rehabilitation and dam-removal, but often neglect conceptual or predictive models of hydrogeomorphic and ecological processes. Complete restoration of processes necessary for maintaining spawning habitat is often unrealistic in regulated rivers. However, we present a framework for spawning habitat rehabilitation based on the premise that certain ecologic functions and geomorphic processes can be restored in a manner that facilitates testing of underlying scientific theories. SHIRA (Spawning Habitat Integrated RehabilitationApproach) provides a science-based, systematic framework for reach-scale rehabilitation of salmonid spawning habitat in regulated rivers. This approach is driven by a mix of field data, conceptual models and numerical models to provide predictive and explanatory insight into the rehabilitation process. Conceptual models are advocated for developing multiple design scenarios and explicit hypotheses about hydrogeomorphic processes and ecologic functions provided by said designs. Hydrodynamic, habitat suitability and sediment entrainment models that test the potential validity of design hypotheses prior to construction are reviewed. It is presumed that the added insight would improve the outcome of rehabilitation projects and test underlying scientific theories against the rigors of real-world uncertainties.