Breakwater (structure)

A breakwater is a permanent structure constructed at a coastal area to protect against tides, currents, waves, and storm surges.

Breakwaters have been built since antiquity to protect anchorages, helping isolate vessels from marine hazards such as wind-driven waves.

[1] A breakwater, also known in some contexts as a jetty or a mole, may be connected to land or freestanding, and may contain a walkway or road for vehicle access.

Breakwaters may also be small structures designed to protect a gently sloping beach to reduce coastal erosion; they are placed 100–300 feet (30–90 m) offshore in relatively shallow water.

An anchorage is only safe if ships anchored there are protected from the force of powerful waves by some large structure which they can shelter behind.

A breakwater structure is designed to absorb the energy of the waves that hit it, either by using mass (e.g. with caissons), or by using a revetment slope (e.g. with rock or concrete armour units).

They are relatively expensive to construct in shallow water, but in deeper sites they can offer a significant saving over revetment breakwaters.

Wave attenuators consist of concrete elements placed horizontally one foot under the free surface, positioned along a line parallel to the coast.

can be provided in up to approximately 40 tonnes (e.g. Jorf Lasfar, Morocco), before they become vulnerable to damage under self weight, wave impact and thermal cracking of the complex shapes during casting/curing.

Preliminary design of armour unit size is often undertaken using the Hudson's equation, Van der Meer and more recently Van Gent et al.; these methods are all described in CIRIA 683 "The Rock Manual" and the United States Army Corps of Engineers Coastal engineering manual (available for free online) and elsewhere.

For detailed design the use of scaled physical hydraulic models remains the most reliable method for predicting real-life behavior of these complex structures.

However, this can lead to excessive salient build up, resulting in tombolo formation, which reduces longshore drift shoreward of the breakwaters.

Breakwaters may be either fixed or floating, and impermeable or permeable to allow sediment transfer shoreward of the structures, the choice depending on tidal range and water depth.