Capturing tidal fluctuations with turbines, tidal barrages, or tidal lagoons.

Tidal Turbines

Land constrictions such as straits or inlets can create high velocities at specific sites, which can be captured with the use of turbines. These turbines can be horizontal, vertical, open, or ducted and are typically placed near the bottom of the water column.

The main environmental concern with tidal energy is associated with blade strike and entanglement of marine organisms as high speed water increases the risk of organisms being pushed near or through these devices. As with all offshore renewable energies, there is also a concern about how the creation of EMF and acoustic outputs may affect marine organisms. It should be noted that because these devices are in the water, the acoustic output can be greater than those created with offshore wind energy. Depending on the frequency and amplitude of sound generated by the tidal energy devices, this acoustic output can have varying effects on marine mammals (particularly those who echolocate to communicate and navigate in the marine environment such as dolphins and whales). Tidal energy removal can also cause environmental concerns such as degrading farfield water quality and disrupting sediment processes. Depending on the size of the project, these effects can range from small traces of sediment build up near the tidal device to severely affecting nearshore ecosystems and processes.

Tidal Barrage

Tidal barrages are dams built across the entrance to a bay or estuary that captures potential tidal energy with turbines similar to a conventional hydrokinetic dam. Energy is collected while the height difference on either side of the dam is greatest, at low or high tide. A minimum height fluctuation of 5 meters is required to justify the construction, so only 40 locations worldwide have been identified as feasible.

Installing a barrage may change the shoreline within the bay or estuary, affecting a large ecosystem that depends on tidal flats. Inhibiting the flow of water in and out of the bay, there may also be less flushing of the bay or estuary, causing additional turbidity (suspended solids) and less saltwater, which may result in the death of fish that act as a vital food source to birds and mammals. Migrating fish may also be unable to access breeding streams, and may attempt to pass through the turbines. The same acoustic concerns apply to tidal barrages. Decreasing shipping accessibility can become a socio-economic issue, though locks can be added to allow slow passage. However, the barrage may improve the local economy by increasing land access as a bridge. Calmer waters may also allow better recreation in the bay or estuary.

Tidal Lagoon

A newer tidal energy design option is to construct circular retaining walls embedded with turbines that can capture the potential energy of tides. The created reservoirs are similar to those of tidal barrages, except that the location is artificial and does not contain a preexisting ecosystem.

Environmentally, the main concerns are blade strike on fish attempting to enter the lagoon, acoustic output from turbines, and changes in sedimentation processes. However, all these effects are localized and do not affect the entire estuary or bay.

Title Author Date Type of Content Technology Type Stressor Receptor
Maine Tidal Power Initiative: Environmental Impact Protocols for Title Power Peterson, M. February 2014 Report Tidal
First Interim Report of the Working Group on Marine Renewable Energy (WGMRE) ICES April 2014 Report Wave, Tidal Ecosystem
Flow Variability in Cook Strait Stevens C. January 2009 Research Study Annex IV Tidal Energy Removal Nearfield Habitat
Tidal Stream Energy Extraction in a Large Deep Strait: The Karori Rip, Cook Strait Stevens, C., Smith, M., Grant, B., Stewart, C., Divett, T. February 2012 Journal Article Tidal
Flow Structure Determination in French Pass NZ Stevens C. January 2006 Research Study Annex IV Tidal Nearfield Habitat
Tidal Flows in Te Aumiti (French Pass), South Island, New Zealand Stevens, C., Sutton, P., Smith, M., Dickson, R. November 2008 Journal Article Tidal
Flow modification in Tory Channel Plew D., Stevens C. January 2010 Research Study Annex IV Tidal Energy Removal, Static Device Farfield Environment
Numerical Modelling of the Effect of Turbines on Currents in a Tidal Channel - Tory Channel, New Zealand Plew, D., Stevens, C. September 2013 Journal Article Tidal Energy Removal Farfield Environment
Impact of Tidal-Stream Arrays in Relation to the Natural Variability of Sedimentary Processes Robins, P., Neill, S., Lewis, M. December 2014 Journal Article Tidal Energy Removal Nearfield Habitat
Assessing the Influence of Inflow Turbulence on Noise and Performance of a Tidal Turbine using Large Eddy Simulations Lloyd, T., Turnock, S., Humphrey, V. November 2014 Journal Article Tidal Noise
Animals Interacting with Wave and Tidal Devices Wave, Tidal
In-Situ Ecological Interactions with a Deployed Tidal Energy Device; An Observational Pilot Study Broadhurst, M., Barr, S., Orme, D. April 2014 Journal Article Tidal Dynamic Device Fish
Array Optimization for Tidal Energy Extraction in a Tidal Channel – A Numerical Modeling Analysis Yang, Z., Wang, T., Copping, A. April 2014 Conference Paper MHK, Tidal Energy Removal Ecosystem
Will Ocean Energy Harm Marine Ecosystems? Hammar L. January 2013 Research Study Annex IV Wave, Ocean Current, Tidal Dynamic Device, EMF, Energy Removal, Noise, Static Device Birds, Farfield Environment, Fish, Invertebrates, Marine Mammals, Nearfield Habitat, Sea Turtles
Power from the Brave New Ocean - Marine Renewable Energy and Ecological Risks Hammar L. February 2009 Research Study Annex IV Wave, Ocean Current, Tidal Dynamic Device, EMF, Energy Removal, Noise, Static Device Birds, Farfield Environment, Fish, Invertebrates, Marine Mammals, Nearfield Habitat, Sea Turtles
Sound of Islay Demonstration Tidal Array, Cable Route Environmental Information ScottishPower Renewables UK Ltd May 2013 Report Tidal Static Device Invertebrates, Nearfield Habitat
Floating Vs. Bottom-Fixed Turbines for Tidal Stream Energy: A Comparative Impact Assessment Sanchez, M., Carballo, R., Ramos, V., Iglesias, G. June 2014 Journal Article Tidal
Admiralty Inlet Final Environmental Assessment Snohomish County Public Utility District No. 1 August 2013 Report Tidal Fish, Marine Mammals, Socio-economics
Marine Renewable Energy Technology and Environmental Interactions Shields, M., Payne, A. January 2014 Book Wave, Tidal, Offshore Wind EMF, Energy Removal, Noise, Static Device Birds, Invertebrates, Marine Mammals, Sea Turtles
Simulating Blade-Strike on Fish Passing Through Marine Hydrokinetic Turbines Romero-Gomez, P., Richmond, M. November 2014 Journal Article In-Stream, Tidal Dynamic Device Fish
Irish Maritime and Energy Resource Cluster (IMERC) University College Cork, Cork Institute of Technology, Irish Naval Service March 2010 Website Wave, Tidal
Influence of Site Bathymetry on Tidal Resource Assessment Perez-Ortiz, A., Borthwick, A., Pescatore, J., Smith, H., Vigars, P., Xiao, Q. August 2014 Conference Paper Tidal Noise
Underwater Active Acoustic Monitoring Network For Marine And Hydrokinetic Energy Projects Stein, P., Edson, P. December 2013 Report Wave, Tidal Dynamic Device, Noise, Static Device Fish, Marine Mammals
Interactions of Marine and Avian Animals Around Marine Energy Devices in Scotland Wave, Tidal
Environmental Risk Evaluation System An Approach to Ranking Risk of Ocean Energy Development on Coastal and Estuarine Environments Copping, A., Hanna, L., Van Cleve, B., Blake, K., Anderson, R. April 2014 Journal Article Wave, Tidal, Offshore Wind Chemical Leaching, Dynamic Device, Energy Removal Birds, Fish, Marine Mammals
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