May 22 2010

Tidal Barrage

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What are they?

Tidal barrages are built similarly to hydroelectric dams, but they are located in an estuary or tidal bay, as depicted above, with large tidal ranges. They are able to generate energy as the tide comes in and goes out. Below is the largest tidal barrage in the world, which is located on the La Rance estuary in France. The plant supplies 90% of the energy for the region, the equivalent of 30,000 homes. Because they completely block off the estuary where they are placed, tidal barrages have wide ranging effects on the entire system. During construction, 75 hectares of land were dried up with temporary cofferdams to lay down the actual barrage.

 

What are the Impacts?

Tidal barrages have severe impacts on the area they are located during construction, operation, and decommissioning. These are described in the diagram below. They cause a significant change in tidal flow, which will cause the sediment regime to change, shrinking or eliminating tidal flats (1). Many animals, especially migratory birds, rely on these tidal flats and would not be able to utilize any other habitat in their place.

Estuaries are delicate systems that rely on the steady flow of water that tides provide, and the influx of sediment, circulation of water, and movement of nutrients that tidal currents provide. Tidal barrages have a very negative effect on the estuarine systems because they lengthen the periods of high and low tide, shorten the tidal range (difference of maximum and minimum water level) and shorten and intensify the periods of ebb and flow.

Normal estuarine circulation is prevented because the tide is ebbing (falling) and flowing (rising) at a much higher rate than normal due to the damming of the estuary. In an estuary, less dense freshwater flows over, and in the opposite direction of, more dense seawater. The two waters circulate; creating the brackish water that defines an estuary. When a tidal barrage releases water, the water flows too quickly and turbulently to allow for proper circulation. The turbulence of the water flow can also increase the turbidity of the water, creating other biological issues.

The combination of a lack of circulation and increased turbulence of water disrupts nutrient cycles, changing or even destroying the previous ecosystem. (2) Some parts of the estuary may become almost entirely fresh water, destroying the saltwater marsh, while other areas may become too saline to support estuarine life adapted to survival in brackish water. (1)

There are other, secondary effects of a tidal barrage such as possible electromagnetic interference with wildlife, as expected with any project operating electrical equipment in the water (3). Turbines will have a continuing effect of increasing turbidity throughout the estuary(4). Fish and other animals passing through turbines suffer a 15% mortality rate, and since every animal wishing to move between the river and the sea must pass through the turbines this is a relatively significant rate of loss (4).

The extensive and extensively documented mal-effects that tidal barrages have on local ecosystems preclude the creation of new tidal barrages, despite being a large, dependable source of energy for coasts with large tidal ranges.

 

1. Clark, Nigel. “Tidal Barrages and Birds.” Ibis no. 148 (2006): 152–157

2. Friends of the Earth, Cymru. A Severn barrage or tidal lagoons? (Jan. 2004).

3. Gill, Andrew. “Offshore renewable energy: ecological implications of generating electricity in the coastal zone.” Journal of Applied Ecology no. 42 (2005): 605–615.

4. Rourke, Fergal, Fergal Boyle, and Anthony Reynolds. “Tidal energy update 2009.” Applied Energy 87, no. 2 (February 2010): 398-409. Academic Search Premier, EBSCOhost (accessed May 17, 2010).

5. Woollcombe-Adams, Charlie “Severn Barrage tidal power project: implications for carbon emissions.” Water and environment journal : WEJ 23, no. 1 (2009): 63.

 

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104 responses so far




104 Responses to “Tidal Barrage”

  1.   mollymacon 04 Jun 2010 at 1:28 am

    I’m surprised that there is so much information about the negative environmental impacts of this energy source, yet it is being used in so many locations around the world. I hope that anyone considering future installations would find this same information – or refer to your research – and realize that tidal barrages are a bad idea! Estuaries are immeasurably important for spawning and development of juvenile marine species.

    No wetlands, no seafood!

  2.   actuckeron 04 Jun 2010 at 7:45 am

    I definitely have to agree with you, Molly. I just can’t believe that a government would pay billions of dollars for an energy technology that is intermittent and environmentally detrimental. Not only are estuaries important to marine species, but they also provide a filtering system for terrestrial organisms as well. Altering these systems could have vast effects on the environment adjacent to the estuaries as well.

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