Use of hydraulic modelling to assess passage flow connectivity for salmon in streams

TitleUse of hydraulic modelling to assess passage flow connectivity for salmon in streams
Publication TypeJournal Article
Year of Publication2011
AuthorsGrantham, T. E.
JournalRiver Research and Applications
IssueEarly View
Type of ArticleResearch
AbstractThe maintenance of hydrologic connectivity in river networks has become an important principle for guiding management and conservation planning for threatened salmon populations, yet our understanding of how fish movement is impaired by spatial and temporal variation in connectivity remains limited. In this study, a two-dimensional hydraulic modeling approach is presented to evaluate flow connectivity in relation to passage requirements of adult steelhead trout (Oncorhynchus mykiss) in coastal California streams. High-resolution topographic data of stream reaches with distinct channel morphology were collected by terrestrial LiDAR surveys and linked with water surface measurements to calibrate hydraulic model simulations. Quantitative metrics of longitudinal flow connectivity were developed to assess fish passage suitability in relation to stream discharge. Measured flow data from the 2008-09 winter season and simulated long-term records indicated that suitable passage flows occur with relatively low frequency and duration at all sites, suggesting that instream flow protections for fish passage are warranted. Results from the hydraulic modeling simulations were then compared to two alternative methods for assessing passage flows. A regional formula used by the State of California to identify minimum instream flow needs provided conservative estimates of passage flow requirements, while an approach based on riffle crest water depths underestimated flow needs. The hydraulic modeling approach appears well-suited for simulating flows for fish passage studies, and may be particularly useful for testing alternative environmental flow assessment methods and evaluating habitat-flow relationships in stream reaches of importance, such as critical habitat for threatened fish species.