Fish passage at intertidal obstructions: approaches in Washington State

Washington State has an active fish passage barrier correction program, with millions of dollars spent annually on fish passage barrier remediation. Tidal water crossing structures, including culverts, bridges, tidegates and control structures pose a unique problem for assessment and design for fish passage and estuarine habitat connectivity. Current fish passage criteria was developed primarily to allow adult salmon access to upstream spawning habitat and is based on adult fish swimming capabilities during the flow range expected during the period of migration. The hydrology of freshwater systems includes flooding periods that are infrequent and unpredictable. Tidal hydrology, on the other hand, is very predictable, frequent and persistent. Except during periods of peak flooding, the magnitude of the bi-directional flow created by tidal hydrology at intertidal crossing structures often dominates the freshwater contribution. Although tidal events may naturally prohibit migration at some periods of the tide, obstructions can further reduce migration periods, particularly for juvenile salmon, due to increased velocities from undersized culverts or water crossing structures. Little is known about to what extent fish behavioral ecology is modified or how to assess the duration and extent of negative effects to fish migration during the tidal cycles. In an effort to begin the process of developing barrier assessment and fish passage design guidelines, Washington State has partnered with NOAA to perform a literature review of documents relevant to fish behavior and use of intertidal areas and the impacts of intertidal obstructions This presentation will provide an overview of the current procedures being utilized at the Washington State Department of Fish and Wildlife as well as issues relating to the assessment of intertidal culverts for fish passage. Data collected at numerous intertidal obstruction sites throughout Washington State and potential impacts to fish passage and habitat will be presented