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Potential NYdroloRic Strucntru to MitimiZe /nWaar and MitinR Mtthadr <br />BANK PROTECTION <br />Bank protection may be required during operations, following reclamation, or both. Typically, <br />armoring is performed to reduce bank erosion, but may be used to protect an operation's facilities <br />or materials. Armoring of the mid~hannel baz was identified in split channel mining on Figure <br />D-8. <br />Bank Armoring <br />Armoring of a bank is generally installed through a zone that is likely to experience lateral <br />migration, typically, the outside bank of a curve. Bank protection is a form of channelization and <br />should be undertaken only when absolutely necessary. Frequently the impacts from such <br />stabilization will create scour and erosion at other points in the river system. <br />The design of dikes or revetments should take into consideration the design flood event for which <br />protection is needed, end protection of the dike, tce protection of the dike, and the material <br />available for construction. Conservative engineered designs are important to provide site-specific <br />information, but the armoring is only as good as its installation. The failure to follow the design <br />or the use of inappropriate or undersized materials will result in only temporary bank protection. <br />Operators can install armoring with rip-rap, a combination of vegetation and rip-rap, soil cement, <br />or wired gabion baskets. Rip-rap is a layer of angulaz, durable rock for which the median <br />diameter and a size gradation have been specified. The median diameter of rip-rap is its I~, and <br />50 percent of the rip-rap is larger and 50 percent is smaller. Rip-rap ranges in size from 0.2 x D~ <br />to 2 x Dso . The thickness of the installation ranges from 1.5 x D~ to 1.75 x Dom. Rip-rap <br />requires placement on a graded earthen material filter blanket or geotextile to prevent the loss of <br />fine-grained bank material. Side slopes should be no steeper than 2.5:1 (H:~. <br />General specifications can be reviewed on Figures D-5 and D-6. End protection can be achieved <br />by extending the armoring into a non~rosive area within the floodplam or by doubling the <br />thickness of the armoring at each end (Figure D-'n. Similarly, tce protection can be achieved by <br />burial of the tce of the rip-rap at least five feet, or through the extension of thicker rip-rap into the <br />channel bed (Figure D-8.) <br />Jetties <br />Jetties consist of dike-type structures which may be used for bank protection (Figure D-9). <br />jetties project from the toe of a graded 4:1(H:~ channel bank 15-25 feet. Jetties are installed <br />either perpendicular to a stream's centerline or with a 45 degree orientation downstream. Jetty <br />spacing should be placed at a ratio of centerline spacing to jetty projection less than or equal to <br />three. Thus, if the jetty extends 25 feet from the tce of the baak, jetty installation should occur <br />R1.6561kbn,vY Z6, Isve D-5 <br />