Tides

• What are tides? How are they caused?

  • Are the periodic rise and fall in the level of the sea 
  • They are caused by the gravitational pull of the Sun and Moon, although the Moon has much the greatest influence because it is nearer.
  • The Moon pulls water towards it, creating a high tide, and there is a compensatory bulge on the opposite side of the Earth. In areas of the world between the bulges, the tide is at its lowest
• Spring Tide

  Twice in a lunar month when the Sun and Moon are in a straight line the tide-raising force is the strongest. This produces the highest monthly tidal range called a spring tide.
• Neap Tide

  Twice a month when the Sun and Moon are positioned at 90oC to each other in relation to the Earth. This alignment gives the lowest monthly tidal range called neap tides.

  At these times the high and low tides are between 10 to 30 percent lower than average.
• What are tides altered by?

  • They are significantly modified in individual locations by the morphology of the seabed, the proximity of land masses and the impact of the spinning forces of the Earth (coriolis force).
• How does the tidal range affect the coastline?

  Tidal ranges also impact the development of the coastline determining the upper and lower limits of the erosion and deposition and the amount of time each day that the littoral zone is exposed and prone to sub-aerial weathering.
• What are Tidal Storm Surges?

  They are occasions when meteorological conditions give rise to strong winds which can produce much higher water levels than those at high tide.
• How do Tidal storm surges affect the coastline?

  • Depressions (intense low pressure weather systems) over the North Sea produce low pressure conditions that have the effect of rising sea levels. The sea level rises by about 1 centimetre for every one millibar drop in pressure. Strong winds drive waves ahead of the storm, pushing the sea water towards the coastline. This has the effect of piling up water against the coast.
• How do Tidal storm surges in the North Sea affect the coastline?

  The shape of the North Sea means that often water is increasingly concentrated into a space that is decreasing in size (funneling). High tides intensify the effect. E.g. The North Sea was affected by a storm surge in December 2013.