Definition:
Gabions are rectangular galvanized wire baskets filled with stones used as pervious, semiflexible building blocks for slope and channel stabilization. Live rooting branches may be placed between the rock-filled baskets.

Purpose:
Gabions protect slopes and streambanks from the erosive forces of moving water. Rockfilled gabion baskets or mattresses can be used as retaining walls for slopes, to armor the bed and/or banks of channels, or to divert flow away from eroding channel sections. Rock-filled or vegetated rock gabions are used on streambank sections subject to excessive erosion due to increased flows or disturbance during construction. Gabions can be specified where flow velocities exceed 6 ft/sec and where vegetative streambank protection alone is not sufficient. Gabions can be used to construct deflectors or groins intended to divert flow away from eroding streambank sections. Gabions are also used to construct retaining walls and grade control structures. Gabion walls are appropriate where:

The vertical integrity of a soil bank needs a higher tensile strength to reduce sloughing of the streambank.

There is moderate to excessive sub-surface water movements that may be creating erosion and damaging other types of non permeable structures.

An excessively steep stream bank must be stabilized and vegetative or extreme mechanical means of stabilization (i.e., pulling back bank) are not feasible due to site conditions.

Where slope must be modified while heavy machinery is unavailable to the site.

Fill must be disposed of along an eroding streambank (fill can be placed behind gabion to modify slope).

A retaining or toe wall is needed to stabilize the slope.

Rock riprap is an appropriate practice but the available or desired rock size (smaller) is not sufficient alone to resist the expected shear stress exerted on the revetment. Gabions allow the use of a smaller size rock than would be possible without the wire baskets because the rock is bound by the wire mesh, creating a more monolithic structure.