Floating breakwaters

Floating breakwaters

Floating breakwaters represent an alternative solution to protect an area from wave attack, compared to conventional fixed breakwaters and can be effective in coastal areas with mild wave environment conditions. Therefore, they have been increasingly used aiming at protecting small craft harbours or marinas or, less frequently, the shoreline, aiming at erosion control.

Some of the conditions that favour floating breakwaters are:

1. Poor foundation: Floating breakwaters might be a proper solution where poor foundations possibilities prohibit the application of bottom supported breakwaters.
2. Deep water: In water depths in excess of 6 m, bottom connected breakwaters are often more expensive than floating breakwaters.
3. Water quality: Floating breakwaters present a minimum interference with water circulation and fish migration.
4. Ice problems: Floating breakwaters can be removed and towed to protected areas if ice formation is a problem. They may be suitable for areas where summer anchorage or moorage is required.
5. Visual impact: Floating breakwaters have a low profile and present a minimum intrusion on the horizon, particularly for areas with high tide ranges.
6. Breakwater layout: Floating breakwaters can usually be rearranged into a new layout with minimum effort.

Floating breakwaters are very effective when their width is of order of half the wavelength and/or when their natural period of oscillation is much longer compared to the wave period.

The first requirement is seldom verified, and in this case the performance is uncertain. The performance of a floating breakwater depends on the strongly non-linear interaction of the incident wave (that may partially overtop the module and is in general short-crested and oblique) with the structure dynamics. The interaction becomes complicated by the forces induced by the mooring system and the connections between the modules. Accurate design is necessarily based on the combination of numerical and physical models.

Floating breakwaters are commonly divided into four general categories: #box, #pontoon, #mat and #tethered float. For each category, some types of floating breakwaters are shown in Figure 1. The first three types have been much widely investigated, by means of physical model and prototype experience, than the others.