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Natural levees commonly form around lowland rivers and creeks without human intervention. They are elongated ridges of mud and/or silt that form on the river floodplains immediately adjacent to the cut banks. Like artificial levees, they act to reduce the likelihood of floodplain inundation.
In parts of Britain, particularly Scotland and Northern England, a dyke may be a field wall, generally made with dry stone.
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Dolfman, Michael L., Soldielle Fortier Wasser and Bruce Bergman. "The effects of Hurricane Katrina on the New Orleans economy." Monthly Labor Review. June 2007. (Aug. 1, 2008)http://www.bls.gov/opub/mlr/2007/06/art1full.pdf
The final step in preparing a levee foundation is to remove and replace soft or organic spots with compacted material. Unless foundation surfaces are adversely affected by remolding, the foundation surfaces should be broken up to a death of at least 6 inches before the placement of the first lift of fill. This will ensure a good bond between the foundation and fill, and to eliminate a plane of weakness at the interface. During this process, the foundation should be drained.Safety compromised by bureaucracy: No central agency was in charge of maintaining the levees. This task instead fell to several different private firms and government agencies, leading to communication problems and the breakdown of various upgrade projects. Levees are common in any river with a high suspended sediment fraction and thus are intimately associated with meandering channels, which also are more likely to occur where a river carries large fractions of suspended sediment. For similar reasons, they are also common in tidal creeks, where tides bring in large amounts of coastal silts and muds. High spring tides will cause flooding, and result in the building up of levees.
Matt Rosenberg. "Dikes of the Netherlands— Geography". Geography.about.com. Archived from the original on 1 February 2009 . Retrieved 6 December 2014. A Look at Preventing Levee Erosion". Federal Emergency Management Agency. 11 February 2021 . Retrieved 28 June 2023. Based on the field investigation and the nature of the levee project, the location and spacing of borings should be determined by an engineer. Generally, initial borings are spaced from between 200 to 1,000 feet (60 to 300m) along the alignment. In expected problem areas, the borings should be spaced more closely together. The spacing should not be uniform, but should be based on geologic information. The borings can either be laid out along the levee centerline, or staggered along the alignment to cover more area and provide information on borrow materials. In Phase 2, the locations of borings should be based on Phase 1 results. Undisturbed sample borings should be located where data on soil shear strength is most needed. The most effective method is to group the foundation profiles, which have been developed on the basis of geological studies and exploration in similar conditions, and then locate undisturbed sample borings to define soil properties in critical reaches.New textiles: The Dutch also developed tough, synthetic textiles to better anchor earthen levees. These prevent soil movement and water penetration. The New Orleans levee system began using this technology following Hurricane Katrina. The method of construction must also be considered when designing a levee. A levee may be built using no compaction to carefully controlled compaction, with steep slopes or relatively flat slopes. Levee maintenance is also a factor that must be weighed as part of the long-term viability of the project. Some of the earliest levees were constructed by the Indus Valley civilization (in Pakistan and North India from circa 2600 BCE) on which the agrarian life of the Harappan peoples depended. [12] Levees were also constructed over 3,000 years ago in ancient Egypt, where a system of levees was built along the left bank of the River Nile for more than 1,000 kilometers (600 miles), stretching from modern Aswan to the Nile Delta on the shores of the Mediterranean. The Mesopotamian civilizations and ancient China also built large levee systems. [13] Because a levee is only as strong as its weakest point, the height and standards of construction have to be consistent along its length. Some authorities have argued that this requires a strong governing authority to guide the work and may have been a catalyst for the development of systems of governance in early civilizations. However, others point to evidence of large-scale water-control earthen works such as canals and/or levees dating from before King Scorpion in Predynastic Egypt, during which governance was far less centralized. Levees can be permanent earthworks or emergency constructions (often of sandbags) built hastily in a flood emergency.
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