Coastal Environments

Tides are the rising and falling of the ocean due to the gravitational pull of the moon and sun.

The moon has the greatest influence as it is closest to the earth. The sun has the weakest influence as it is furthest from the earth.

The tide cycle is about 12 h 25 minutes long so there are two high and two low tides per day.

When the pull of the moon and the sun combine there are spring tides, this is when tides are the highest and the lowest they could be (largest tidal range). When the moon and sun create a right angle there are neap tides, this is when the high tides are the lowest they could be and the low tides the highest (smallest tidal range).

Local factors can increase or decrease tide height.

EXAMPLES: the North Sea and Irish sea can be 6m higher than in the open ocean. The Severn Estaruy has a range of 13m . Whereas the Mediterranean sea has a tidal range of 0.01m due to the Straits of Gibraltar being too narrow and shallow for significant exchanges of water between the sea and the ocean.

The world's highest tides occur at Canada's Bay of Fundy between Nova Scotia and New Brunswick. Depending on the time of year, the difference between high tide and low tide can be 16m 31cm.