Tidal (marine)

• Tidal energy relies on the gravitational pull of the Moon, which causes the change in water levels that we call tides. It has been estimated that Britain could provide around 20% of its energy from tidal power

  
• The most common form of tidal power is the tidal barrage. A tidal barrage is a long dam that is built across the mouth of a river where it meets the sea. These are known as 'estuary barrages'

  
• Estuary barrages can be constructed so that the incoming tide passes through turbines generating electricity. The water can then be held in the high tide state upstream of the barrier, until it is needed. It's then released at low tide, flows out through the turbines, again turning them and generating electricity

  
• Disadvantages are that the river would never completely empty, flooding mudflats, which provide a habitat for thousands of birds. There may also be problems of waste disposal as many towns discharge sewage into rivers