Riverbank erosion has both natural and man-made causes. Natural causes include intense rainfall, flooding, wave action and river migration. Man-made causes include land clearing near rivers and creeks, rural and urban development and waves that powerboats make. The two main types of riverbank erosion are bank scour, characterised as removing bank material by flowing water, and mass failure, characterised as sections of the bank sliding into the river.
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Introducing vegetation to eroding riverbanks is the single most effective control solution to riverbank erosion. Plants establish dense root systems, which hold onto the soil that otherwise gets eroded by flowing water. Planting wetland species such as willow by planting willow cuttings is one path. Weaving live willow rods between live willow stakes set into the eroding bank provides a relatively inexpensive solution, because the live willow rods and stakes will soon set roots and continue to grow. When you plant wetland species such as rushes, sedges and willows, the first few months while the plants get established and set roots are crucial. If successful, the plants' roots will hold the soil and keep the bank from eroding.
Geotextiles are permeable fabrics. When you use them with soil, geotextiles can separate, reinforce, filter, protect or drain. A geotextile used for riverbank erosion must be able to allow water to flow through the fabrics and it must be able to retain fine soil particles under the fabric. Geotextiles and other erosion-control fabrics, when mixed with soil and preplanted with wetlands vegetation, have proven to be effective for riverbank erosion problems. A coir net, a net made of natural coconut fibre material, also serves as a base for soils and preplanted wetland plants. The coir net protects and stabilises the plants while they set roots into the riverbank soil.
Applying a thick layer of straw mulch to riverbank topsoil allows the soil to slowly soak up water, protects against falling rain and works to restore pH levels in the soil. Mulching can help hold the soil and will protect seeds as they sprout and set roots. Mulching can also control weeds while wetland plants are getting established. The Western Shasta Resource Conservation District recommends applying netting and straw mulch on a riverbank's steep slopes after seeding with grass or other native plant seeds.
While the rest of the solutions are "soft" solutions, building a retaining wall is a "hard" solution for riverbank erosion. You can build a retaining wall around an eroding area to prevent water runoff. Water runoff leads to further erosion and must be prevented. When used in combination with other methods of erosion control such as semirigid geogrids, geotextiles and native vegetation, retaining walls have proved effective.
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