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<br />Aporndix D ~ Porenriaf H~~droloRic Struaurer ro Minim~~r lmaaat and Minnie Mcrhods <br />BANK PROTECTION <br />Bank protection may be required during operations, followine 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-channel bar was identified in split channel mining on Figure <br />8. <br />Bank Armoring <br />Armoring of a banl: is generally installed through a zone that is likely to experience lateral <br />migration, typically, the outside banl: 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 revetemenu should take into consideration the desiert flood event for which <br />protection is needed, end protection of the dike, toe protection of the dike, and the material <br />available for construction. Engineered designs are based on site-specific information, but the <br />armoring is only as ;god as its installation. The failure to follow the design or the use of <br />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 angular, durable rock for which the median <br />diameter and a size eradation have been specified. The median diameter of rip-rap is its D;o, 50 <br />percent of the rip-rap is larger and 50 percent is smaller. Rip-rap ranges in size from 0.2 x Igo to <br />2 x Dso. Standard rip-rap classification types are described in Table D-1. The thickness of the <br />installation ranges from 1.5 z Dso to 1.75 x Dso. Rip-rap requires placement on a graded earthen <br />material filter blanket or geotextile to prevent the loss of fine-grained bank material. Side slopes <br />for rip-rapped banks, should be no steeper than 2.5:1 (H: V). <br />General specifications can be reviewed on Figures D-5 and D-6. End protection can be achieved <br />by extending the armoring into anon-erosive area within the floodplain or by doubling the <br />thiclztess of the armoring at each end (Figure D-7). Similarly, toe protection can be achieved by <br />burial of the toe of the rip-rap at least five feet, or through the extension of thicker rip-rap into the <br />channel bed (Figure D-8.) Photographic examples of bank armoring are shown in Figure D-9. <br />Several of the photographs are from non-mining applications. <br />Biorevetements <br />~A Geotextiles in fluvial settings provide temporary protection prior to the establishment of <br />vegetation. Geotextiles are woven or non-woven fabrics that promote bank stabilization through <br />a mulching capacity or as a strengthener. These synthetic fabrics may be a coarse netted fabric <br />sandwichins a straw, coconut huff, or synthetic btanke[ that are used as mulches. Synthetic, non- <br />woven or finely woven fabrics can be employed as replacements for graded gravel filter blankets <br />below rip-rap. The use of oeotex[iles is considered a biorevetemen[ when seeding is incorporated <br />,~.me~~.e~.~ ~ wse D-~ <br />