Gabions
What are gabion?
Gabions are wire mesh baskets filled with cobbles or crushed rock. They are filled insitu, often with locally available material and therefore have a relatively low capital cost. Because they are flexible and porous they can absorb some wave and wind energy, thereby reducing the scour problems associated with impermeable sea defences such as concrete seawalls. The latter are intended for bank or cliff stabilisation and are not normally suitable for use in shoreline situations.
Functions of gabions
The purpose of a gabion revetment is to provide short term (5-10 years) protection from backshore erosion by absorbing wave energy along the dune face. Their application is restricted to the upper part of sandy beaches, since they are not sufficiently durable to withstand regular direct wave action. They should not be installed on shingle beaches because wear and tear will rapidly cause damage to the baskets. As they are porous structures they will tend to trap wind blown sand and allow the growth of vegetation under favourable conditions. This only applies to sloping structures: steep walls of cubic baskets will not attract sand or allow dune vegetation regrowth. Gabions provide a short term alternative to rock armour structures in areas where large rocks are not available at an acceptable cost, or where long term protection is not appropriate.
Advantages
Ease of handling and transportation
Speed of construction
Flexibility (Gabions tolerate movement)
Permeability to water (Good drainage)
Gabions offer an easy-to-use method for decreasing water velocity and
Protect slopes to be eroded
Disadvantages
Gabions are sometimes criticized as being unsightly. They can be made more attractive by use of attractive facing stone toward the front of the wall and by establishing vegetation in the spaces between the rocks.
Low habitat value.
Gabions are more expensive than either vegetated slopes or riprap.
The wire baskets used for gabions may be subject to heavy wear and tear due to wire abrasion by bedload movement in streams with high velocity flow.
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