The Cost of Coastal Protection
Sea walls are cast in concrete and supported by steel piles fixed into the rock beneath the sand layer. They are designed to resist wave attack and are usually installed at the foot of vulnerable cliffs or at the top of a beach. They can be flat- faced or curved and up to 5m in height. Curved walls are designed to dissipate energy from incoming waves. They tend to last only 20-30 years as a result of their foundations being undermined by wave action.
Offshore breakwaters, running parallel to the shore, may be installed to stop wave action from reaching the beach. In this respect, however, they are effectively seawalls and their foundations are subject to being undermined by the same forces that affect seawalls themselves.
Groynes are designed to interrupt longshore drift and catch sediment as it moves along the coastline, thus making the beach wider. They usually project out from the beach perpendicular to the shoreline and are made from timber, concrete or rock armour.
Beach replenishment is a method where additional sand and shingle is added to a beach to make it higher and wider. Material is brought inshore by barge, and spread by diggers and bulldozers. Although the typical cost of replenishment is of order £1 million/km, it must be repeated regularly if there is nothing to keep the sand in place. The processes eroding the original sand remain in force to sweep the new sand away.
Shoreform stable bays are formed by installing a line of circular islands, spaced far enough apart for bays to form between them. Sediment for the bays is provided either by natural littoral drift or placing sand offshore of the islands.
This ensures redistribution of the sediment into a stable form between the islands and the shore. Storms will remove some sediment temporarily to an offshore bar at the mouth of each bay but this will be returned to the shore by persistent swell. In this way Shoreform stable bays work with rather than against the sea.
The use of circular artificial islands as sediment accretion devices is protected
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