Breakwaters are marine structures that reduce water forces offshore before they reach land thus preventing erosion. Breakwaters reduce the wave energy by partial reflection as well as by breaking on the structure. Consequently, the water conditions on the protected side of the breakwater remain relatively calm. Breakwaters may be attached to, or detached from, the shoreline. Detached breakwaters are sometimes designed to permanents submerged and may be designed to retain a perched or artificial beach behind.

In dissipating wave energy considerable turbulence can occur at the toe and across the base of breakwaters. If the breakwater is founded on sand, this can result in severe sand erosion and consequent breakwater instability. To prevent this, a Mirafi® FM woven geotextile is installed across the top of the sand foundation prior to the construction of the breakwater to act as a filter in preventing the erosion of the sand foundation through the breakwater. To facilitate easy installation of this filter, Mirafi® FM is fabricated into a fascine mattress which can be floated out to sea and sunk into place. This fascine mattress can then be ballasted into position on the seabed by dropping rocks onto the floating fascine mattress as it sinks.

A better alternative to rock is the Geotube® and Geocontainer® systems which are effective methods of replacing the rock-fill core of breakwaters. This becomes an attractive proposition where rock is expensive and difficult to obtain and where the water forces are not extreme.

TenCate Geosynthetics Asia
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