May 27 2010
Tidal Lagoons
What are they?
An alternative to Tidal Barrages, Tidal Lagoons utilize a circular (or more organically shaped) retaining wall to hold high or low tides in a central pool, before releasing them to drive turbines (2).
There are two main types of tidal lagoons. Offshore lagoons are built away from the coast, and the pool is surrounded by retaining walls on all sides. In coastal lagoons, part of the coastline is used as a retaining wall.
What are the impacts?
The main impacts of this type of tidal range power generation occur during construction. Building of retaining walls will disturb sediments, resulting in increased turbidity and possibly decrease primary productivity (3). The walls themselves will also likely bury any sedentary creatures in the area (4). Some noise pollution will occur, but because there is no drilling or pile-driving this will be minimal (2). Most importantly, these impacts will all be very localized to the area around the lagoon, rather than affecting the entire estuary (2).
During operation, modified tidal action inside the lagoon will have limited impacts on fish and other free swimming creatures (2). Fish and other creatures passing through the turbines will suffer approximately 15% mortality, though this could be mitigated or prevented by placing screens across the turbine intakes (4). Any changes in sedimentation will be localized and in the case of offshore lagoons this will likely have negligible effects (1). Coastal lagoons will significantly change the sedimentation pattern of areas of coastline within the lagoon (2). In addition to these impacts, electromagnetic interference with wildlife could result from cables running from offshore lagoons to the shore (3).
Decommissioning of tidal lagoons involves removal of the turbines, but not the retaining walls (1). The main effects of this process would be disturbance of sediments, plants, and sedentary animals.
Tidal Lagoons, while still posing a threat to the surrounding environment, do not restrict an entire estuary; because construction of a lagoon can be done wherever there is a significant change tidal range, and not only in the mouths of estuaries they may be a viable alternative to tidal barrages.
1. Clark, Nigel. “Tidal Barrages and Birds.” Ibis no. 148 (2006): 152–157
3. Gill, Andrew. “Offshore renewable energy: ecological implications of generating electricity in the coastal zone.” Journal of Applied Ecology no. 42 (2005): 605–615.
29 Responses to “Tidal Lagoons”
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Tidal Barrage and Tidal Lagoon technology surprised me the most during the presentations. These systems can create energy on a massive scale, but the locations are more or less rare. This is just another example of taking advantage of the resources around you. In looking at the map of Wales and proposed lagoon sites, I was wondering if fish and other life will be permanently trapped in the large enclosures. Many fish hide and rest in the shallows and hunt in deeper waters (and vice versa), so being trapped could lead to some disruption of the ecosystem. I think lagoons should have “fish doors” so they can pass through, as well as screens to prevent mortality from the turbines.
See, there’s kind of a problem with “fish doors” because the whole point of these systems is to trap water, and if you’re letting fish through, then you’re letting water through. Even a small trickle of water going through would eventually drain the reservoir, like a straw out of an aquarium, or at least lower the level, thereby making the whole system much less efficient. I think screens would definitely be the better option, but I’m not sure if they use them. One possible problem I could see with that too is that all that water flowing out of the reservoir will have a bunch of icky stuff floating around too, like blehh, and all that will all get trapped against the screen, so I would imagine that they would have to clean the screens pretty regularly.
But you’re right about massive scale: the biggest project proposed in Wales could generate 15 GW. Chyeahhhh
I was curious if there were any tidal lagoon projects proposed for the United States? I freely admit that I don’t understand this technology very well, but if the environmental impacts associated with tidal lagoons are minimal, do they have exhibit any potential to be used in combination with other coastal energy technologies? For instance, is there anything preventing the combined development of a tidal lagoon and an underwater turbine off of the North Carolina coast to work in conjunction with the wind turbines in the Pamlico Sound? This might be a question outside our scope, but I think it would be interesting to see an environmental impact assessment conducted over a combination of different ORED.
As far as combining tidal lagoons with other technologies, I would imagine that their holding walls would serve as excellent bases for wind turbines. I have seen several proposals to cover the middle of lagoons with solar panels.
As far as the project in pamlico sound goes, I am certain that, for better or worse, tidal range power generation will not be viable for North Carolina’s coast. This is because our largest tidal range is something like 15 centimeters, compared to the 7 meter or larger range needed for an economically viable lagoon (or barrage).
The thing is, environmental impacts associated with lagoons are minimal compared to barrages. There are still huge impacts from installation/decommissioning and some from operation as well. Lagoons already have underwater turbines, so they don’t need to be combined. Some projects actually have propsed putting solar panels on top of the lagoons, so that could be a nice combination. Maybe you could also put wind turbines on that?
As far as viability for North Carolina, as we said before, this kind of power requires a tidal range of at least 7 m to be economically viable, and nowhere in NC has anywhere near that large of a tidal range.
There aren’t any proposed projects in the US for the same reason mostly. Here is a tidal range map. You have to be in the really red areas for this to be possible, and they are somewhat rare and have really crazy tidal ranges, like that episode of Blue Planet we watched.
http://www.pacificstormsclimatology.org/images/glossary/tides.png
Note that there are three places in Alaska where this is possible. http://www.co-ops.nos.noaa.gov/faq2.html#26 (7 metres = 22 feet, as a scale for looking at these tidal ranges)
I understand that blocking an entire estuary with a tidal barrage has extensive consequences on the ecosystem, but what is a little unclear to me is why tidal lagoons seem to not have as severe of an impact when they are essentially the same technology just smaller. Is the difference in impact caused primarily because of the size? How big are these lagoons? Do the lagoons’ ecosystems change as drastically? Does the salinity change within the lagoon?
Je me connecte assez fréquemment sur ce blog, c’est a chaque fois un réel plaisir de vous découvrir.