When dealing with erosion protection in water courses or coastal works, it is important to understand the causes of the problem.
Typically the need for protection results from erosion of the water course bed or erosion of the banks of the water course. It is a similar situation for coastal protection works where it may be beach erosion or erosion of the protection bunds.
The specification of the type of gabion depends upon the corrosion protection required. Where the gabions are subjected to saline conditions or where the water quality may be detrimental to zinc coatings, PVC coated gabions should be specified.
In neutral environments where the soil/water acidity is in the stable zone for zinc (PH7 to10) then galvanised or galfan coated gabions can be specified.
Gabion protection generally takes on two forms, either as a sloping bank protection using a mattress laid on the slope with a geotextile membrane underneath or as a retaining structure to form a steeper face with a geotextile membrane behind and beneath the structure.
In both cases consideration must be given to the possibility of erosion at the toe, therefore a mattress toe protection or an embedded gabion must be provided to prevent underscour.