Gabions

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"Gabions are rectangular-shaped baskets or mattresses fabricated from wire mesh, filled with rock, and assembled to form structures such as gravity retaining walls, lined channels, overflow weirs, hydraulic drops, and other erosion control structures. Gabions are also used for spillways and as overtopping protection for small embankment dams as discussed in this chapter. Gabion baskets are generally stacked in a stair-stepped fashion, while mattresses are generally placed parallel to a slope."

"Gabions have advantages over loose riprap because of their modularity and rock confinement properties, thus providing erosion protection with generally less rock volume, within a smaller footprint, and with smaller rock sizes than loose riprap. Reducing the required rock volume and rock size for gabions to provide a similar level of erosion protection—as loose riprap can provide a significant reduction in construction cost. Gabions also have advantages over more rigid structures as they can:

• Conform to ground movement
• Be easily constructed and repaired
• Dissipate energy from flowing water
• Be designed to drain freely

"However, permeability may reduce over time as the voids in the rockfill become progressively filled with silt, promoting vegetation growth."

"Some disadvantages of gabions include appearance, since the wire is exposed (although the use of attractive stone, colored wire coating, and vegetation may alleviate this concern) and durability, since the wire mesh may be subject to abrasion and corrosion damage (although special resistant coatings and materials are available to increase the design life). Gabions are also more susceptible to damage from debris and from vandalism compared to other types of dam overtopping protection, such as RCC or ACBs, requiring more frequent maintenance and repair. As for other types of overtopping protection, gabions can make detection of changed seepage conditions within the embankment and abutment more difficult."

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