Tide Gate Effects on Salmonid Passage and Utilization

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Lyons & Ramsey 2013 provides a synthesis of a tide gate investigation completed by Greene et al 2012, and offers the following conclusions:

• Tide gates limit fish passage and provide less ecological benefits than natural systems
• The effectiveness of self-regulating tide gates varies by species and life history groups
  • For estuarine-dependent species including juvenile Chinook salmon, natural sites in this study supported densities an order of magnitude greater than the systems with tide gates
  • Non-estuarine dependent species and adult salmonids were less negatively affected by tide gates
• Self-regulating tide gates (SRTs) can provide greater ecological benefits than traditional flap gates
  • Beamer 2014 describes findings at the Fisher Slough Restoration that indicate that fish access is most strongly affected by door opening during non-ebb tides.
• Tide gates, including SRTs, vary considerably in type and amount of benefits provided
  • The driving factors related to the effectiveness of tide gates in providing ecological benefits are not well documented
  • Although a good first step, the study was not able to evaluate variability in tide gate operations or design variability among SRTs. More information is needed to understand the potential for significantly improving the benefits of SRTs through informed design and operation
• Continued studies are needed to better understand how tide gate design and operation affect physical process and how these changes affect habitat use by estuarine species, especially in the case of SRTs. Until these issues are better understood it will be difficult to evaluate whether SRTs provide significant enough benefits over traditional flap gates to be considered a useful restoration element. We also need to understand the type and amount of habitat potentially made available upstream of any replacement tide gate in order to gauge the value of the installation.

• Products from the Greene et al 2012 work study can be found in its PRISM contract record, including documents

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