What Are the Disadvantages of Tidal Fences?

Tidal power is a high-potential alternative energy source.
Tidal power is a high-potential alternative energy source. (Image: Comstock/Comstock/Getty Images)

Tidal fences are a type of tidal energy technology that could be used to harness hydroelectric power. Though the technology for tidal fences is still in its infancy, it has high potential as an alternative energy source. Tides are a more reliable source of energy than wind or sunlight, as the tides change twice daily. Though tidal fences are less disruptive environmentally than dams or tidal barrages, both of which more fully block water channels, the fences do have some disadvantages.

How Tidal Fences Work

A tidal fence is a series of turbines mounted in a row across channels or straits in coastal waters. Each turbine is affixed to a vertical shaft, and these shafts are mounted in the fence. The tidal currents in coastal waters spin the turbines, which turn the attached generator shaft and produce electricity. The turbine and shaft are the only elements of the fence under the water; the generator and transformers of these turbines are above water. According to the U.S. Department of Energy, there are currently no tidal power plants in the U.S., but the Pacific Northwest and the Atlantic Northeast are potentially good sites for tidal power generation.

Changes in Estuary Ecosystems

Construction of tidal plants affects the flow of salt water, which in turn changes salinity, hydrology, and other intrinsic features of the site. Such changes can substantially impact the local ecosystem and its marine wildlife. Estuaries are often nurseries for many forms of marine life and are delicate environments that serve as habitats for a wide variety of organisms. Sudden, major changes in these environments can negatively impact a wide range of plants, animals, and other organisms. Construction of tidal plants can also close off the estuaries from the sea for prolonged periods of time. During the construction of the tidal plant at La Rance, France, for instance, the estuary was closed off from the ocean for two to three years, and it took a significant period of time for the ecosystem to stabilize again.

Effects on Marine Life

Tidal fences can also block channels, which interferes with the movement and migration of fish and wildlife. Spinning turbines also kill fish and hurt or kill larger marine mammals. If not enough consideration is given to the spacing of the turbines, large marine mammals may not be able to pass between spinning turbines. While tidal fences may have fewer disadvantages than other hydroelectric power sources, such as dams or tidal barrages, the fences can still negatively impact their surroundings.

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