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Title:	Gabions for streambank erosion control
Authors:	Freeman, Gary E. Fischenich, J. Craig, 1962-
Keywords:	Riparian areas Erosion Slopes (Soil mechanics)--Stability
Publisher:	Engineer Research and Development Center (U.S.)
Series/Report no.:	Technical Note (Ecosystem Management and Restoration Research Program (U.S.)) ; no. ERDC TN-EMRRP SR-22
Abstract:	Gabions are cylinders that are filled with earth or stones, which are used in building structures such as dams or dikes. Gabions have been used for several millennia in Egypt and China. Prior to 1879, gabions were constructed with plant materials, which severely limited their useful life. In about 1879 a firm in Italy is thought to have first used wire mesh in the construction of gabion baskets. This is possibly the first use of the modern wire mesh baskets as used today. Gabions are now used throughout the world for bed protection, bank stabilization, retaining walls, and numerous other purposes. Gabions come in three basic forms, the gabion basket, gabion mattress, and sack gabion. All three types consist of wire mesh baskets filled with cobble or small boulder material. The fill normally consists of rock material but other materials such as bricks have been used to fill the baskets. The baskets are used to maintain stability and to protect streambanks and beds. The difference between a gabion basket and a gabion mattress is the thickness and the aerial extent of the basket. A sack gabion is, as the name implies, a mesh sack that is filled with rock material. The benefit of gabions is that they can be filled with rocks that would individually be too small to withstand the erosive forces of the stream. The gabion mattress is shallower (0.5 to 1.5 ft) than the basket and is designed to protect the bed or banks of a stream against erosion. Gabion baskets are normally much thicker (about 1.5 to 3 ft) and cover a much smaller area. They are used to protect banks where mattresses are not adequate or are used to stabilize slopes (Figure 1), construct drop structures, pipe outlet structures, or nearly any other application where soil must be protected from the erosive forces of water. References to gabions in this article refer generally to both mattresses and baskets. Sack gabions are rarely used in the United States and are not within the scope of this technical note. Gabion baskets can be made from either welded or woven wire mesh. The wire is normally galvanized to reduce corrosion but may be coated with plastic or other material to prevent corrosion and/or damage to the wire mesh containing the rock fill. New materials such as Tensar, a heavy-duty polymer plastic material, have been used in some applications in place of the wire mesh. If the wire baskets break, either through corrosion, vandalism, or damage from debris or bed load, the rock fill in the basket can be lost and the protective value of the method endangered. Gabions are often used where available rock size is too small to withstand the erosive and tractive forces present at a project site. The available stone size may be too small due to the cost of transporting larger stone from remote sites, or the desire to have a project with a smoother appearance than obtained from riprap or other methods. Gabions also require about one third the thickness of material when compared to riprap designs. Riprap is often preferred, however, due to the low labor requirements for its placement. The science behind gabions is fairly well established, with numerous manufacturers providing design methodology and guidance for their gabion products. Dr. Stephen T. Maynord of the U.S. Army Engineer Research and Development Center in Vicksburg, Mississippi, has also conducted research to develop design guidance for the installation of gabions. Two general methods are typically used to determine the stability of gabion baskets in stream channels, the critical shear stress calculation and the critical velocity calculation. A software package known as CHANLPRO has been developed by Dr. Maynord (Maynord et al. 1998). Manufacturers have generated extensive debate regarding the use and durability of welded wire baskets versus woven wire baskets in project design and construction. Project results seem to indicate that performance is satisfactory for both types of mesh. The rocks contained within the gabions provide substrates for a wide variety of aquatic organisms. Organisms that have adapted to living on and within the rocks have an excellent home, but vegetation may be difficult to establish unless the voids in the rocks contained within the baskets are filled with soil. If large woody vegetation is allowed to grow in the gabions, there is a risk that the baskets will break when the large woody vegetation is uprooted or as the root and trunk systems grow. Thus, it is normally not acceptable to allow large woody vegetation to grow in the baskets. The possibility of damage must be weighed against the desirability of vegetation on the area protected by gabions and the stability of the large woody vegetation. If large woody vegetation is kept out of the baskets, grasses and other desirable vegetation types may be established and provide a more aesthetic and ecologically desirable project than gabions alone.
Description:	Technical Note
Gov't Doc #:	ERDC TN-EMRRP SR-22
Rights:	Approved for public release; distribution is unlimited
URI:	http://hdl.handle.net/11681/3949
Size:	9 pages/1.14 MBs
Types of Materials:	PDF/A
Appears in Collections:	Technical Note