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. Difficult to install, requiring large equipment. Planning Considerations For easy handling and shipping, gabions are supplied folded into a flat position and bundled together.
Gabions are readily assembled by unfolding and binding together all vertical edges with lengths of connecting wire stitched around the vertical edges. The empty gabions are placed in position and wired to adjoining gabions.
They are then filled with cobblestone-size rock cm in diameter to one-third their depth. Connecting wires, placed in each direction, brace opposing gabion walls together. The wires prevent the gabion baskets from "bulging" as they are filled. This operation is repeated until the gabion is filled. After filling, the top is folded shut and wired to the ends, sides, and diaphragms. Gabions are aesthetically pleasing and blend in with the coastal environment, which is enhanced when vegetation growth is encouraged.
Gabions provide an excellent habitat for all marine and fresh water species. Spaces between the rocks quickly become filled with silt, which encourages vegetation growth. These spaces can also provide protective habitats for small aquatic creatures to live and lay their eggs etc. We have also installed Gabions in many river locations. Visit our website for more information.
November How can Gabions help protect our coastal areas? Regular basket maintenance is required to maximise the life of gabions.
Severely damaged baskets should be refilled and closed with new mesh panels. Replacement mesh should be laid over the entire structure if abrasion or corrosion is widespread.
Under exposed conditions a maximum life of 10 years should be anticipated, after which time a replacement structure may be required. Schemes are best implemented in the spring and early summer when work windows are least restricted and the shoreline has the greatest chance to stabilise before winter storms start to erode the upper beach.
Costs for gabion schemes depend on required dimensions, labour, availability of fill material, transport methods and the amount of minor works required to enhance the dune system. Economic analysis should anticipate no more than a 10 year life expectancy. Gabions become unsightly and dangerous if they are damaged and not properly repaired. Exposed gabions tend to trap strand line debris. As with all fixed dune defences the gabions will interfere with the natural dynamic interchange of material between beach and dune.
They will also influence the longshore transfer of sand, modify dune habitats, disrupt the natural landform and potentially result in localised dune face scour at their terminal ends.
Vertical gabion walls are more prone to structural failure and outflanking, more intrusive on the landscape and are much less likely to become buried by new foredunes relative to sloping gabion revetments. Sloping gabions can provide good erosion protection for periods up to 10 years longer if normally buried. They are often more acceptable and less costly than rock armour. When carefully built and placed they can blend into the dune landscape, and are only exposed during eroding storms.
They are best used in areas where episodic erosion takes place and where natural burial by new foredunes is possible under favourable conditions.
Their applicability in areas subject to persistent erosion is limited to temporary protection. Removal of temporary structures is more difficult with gabions than with sand bag, rock or timber structures.
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