Coastal protection offshore breakwaters

Various coastal structures, as already discussed, can be applied to solve, or at least, to reduce erosion problems. They can provide direct protection (seawalls, dikes, revetments) or indirect protection (groins and offshore breakwaters of various designs), thus reducing the hydraulic load on the coast (Fig. 20.4). Rock and concrete are usually the construction materials. 

Offshore breakwaters and reefs can be permanently submerged, permanently exposed or inter-tidal. In each case, the depth of the structure, its size, and its position relative to the shoreline determine the coastal protection level provided by the structure. To reduce the cost some alternative solutions using geosystems can be considered. The actual understanding of the functional design of these structures needs further improvement but may be just adequate for these structures to be considered as serious alternatives for coastal protection. 

These advances, together with numerous advantages of GSCs as soft rock, have contributed to extend the use of GSCs to permanent coastal defenses, including a wide range of types of structures such as seawalls, revetments, groins, artificial reefs, offshore breakwaters, perched beaches, dune reinforcement, core of rubble mound structures, scour protection, etc. (Fig. 21.1). 

A seaside town was at risk of coastal erosion and flooding. A set of detailed studies were undertaken to assess the best solution for protecting the town, which was technically achievable, environmentally acceptable and provided maximum cost benefit. These studies identified that an offshore reef breakwater would provide the best solution. This was particularly attractive to those involved as it was a relatively innovative solution and was accepted by the town s population. The designer was then asked to proceed with the detailed design of the scheme. 

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