Levee
A levee (/ˈlɛvi/),[1][2] dike (American English), dyke (Commonwealth English), embankment, floodbank, or stop bank is a structure used to keep the course of rivers from changing and to protect against flooding of the area adjoining the river or coast. It is usually earthen and often runs parallel to the course of a river in its floodplain or along low-lying coastlines.[3]
Levees can be naturally occurring ridge structures that form next to the bank of a river or be an artificially constructed
Ancient civilizations in the
Etymology
Speakers of American English use the word levee, from the French word levée (from the feminine past participle of the French verb lever, 'to raise'). It originated in New Orleans a few years after the city's founding in 1718 and was later adopted by English speakers.[8] The name derives from the trait of the levee's ridges being raised higher than both the channel and the surrounding floodplains.
The modern word dike or dyke most likely derives from the Dutch word dijk, with the construction of dikes well attested as early as the 11th century. The 126-kilometer-long (78 mi) Westfriese Omringdijk, completed by 1250, was formed by connecting existing older dikes. The Roman chronicler Tacitus mentions that the rebellious Batavi pierced dikes to flood their land and to protect their retreat (70 CE).[9] The word dijk originally indicated both the trench and the bank. It closely parallels the English verb to dig.[10]
In
In parts of Britain, particularly Scotland and Northern England, a dyke may be a field wall, generally made with dry stone.
Uses
The main purpose of artificial levees is to prevent flooding of the adjoining
Levees can be permanent earthworks or emergency constructions (often of sandbags) built hastily in a flood emergency.
Some of the earliest levees were constructed by the
Another example of a historical levee that protected the growing city-state of Mēxihco-Tenōchtitlan and the neighboring city of Tlatelōlco, was constructed during the early 1400s, under the supervision of the tlahtoani of the altepetl Texcoco, Nezahualcoyotl. Its function was to separate the brackish waters of Lake Texcoco (ideal for the agricultural technique Chināmitls) from the fresh potable water supplied to the settlements. However, after the Europeans destroyed Tenochtitlan, the levee was also destroyed and flooding became a major problem, which resulted in the majority of The Lake being drained in the 17th century.
Levees are usually built by piling earth on a cleared, level surface. Broad at the base, they taper to a level top, where temporary embankments or sandbags can be placed. Because flood discharge intensity increases in levees on both river banks, and because silt deposits raise the level of riverbeds, planning and auxiliary measures are vital. Sections are often set back from the river to form a wider channel, and flood valley basins are divided by multiple levees to prevent a single breach from flooding a large area. A levee made from stones laid in horizontal rows with a bed of thin turf between each of them is known as a spetchel.
Artificial levees require substantial engineering. Their surface must be protected from erosion, so they are planted with vegetation such as
River flood prevention
Prominent levee systems have been built along the
.The Mississippi levee system represents one of the largest such systems found anywhere in the world. It comprises over 5,600 km (3,500 mi) of levees extending some 1,000 km (620 mi) along the Mississippi, stretching from Cape Girardeau, Missouri, to the Mississippi delta. They were begun by French settlers in Louisiana in the 18th century to protect the city of New Orleans.[14] The first Louisiana levees were about 90 cm (3 ft) high and covered a distance of about 80 km (50 mi) along the riverside.[14] The U.S. Army Corps of Engineers, in conjunction with the Mississippi River Commission, extended the levee system beginning in 1882 to cover the riverbanks from Cairo, Illinois to the mouth of the Mississippi delta in Louisiana.[14] By the mid-1980s, they had reached their present extent and averaged 7.3 m (24 ft) in height; some Mississippi levees are as high as 15 m (50 ft). The Mississippi levees also include some of the longest continuous individual levees in the world. One such levee extends southwards from Pine Bluff, Arkansas, for a distance of some 610 km (380 mi). The scope and scale of the Mississippi levees has often been compared to the Great Wall of China.[15]
The United States Army Corps of Engineers (USACE) recommends and supports cellular confinement technology (geocells) as a best management practice.[16] Particular attention is given to the matter of surface erosion, overtopping prevention and protection of levee crest and downstream slope. Reinforcement with geocells provides tensile force to the soil to better resist instability.
Artificial levees can lead to an elevation of the natural riverbed over time; whether this happens or not and how fast, depends on different factors, one of them being the amount and type of the bed load of a river. Alluvial rivers with intense accumulations of sediment tend to this behavior. Examples of rivers where artificial levees led to an elevation of the riverbed, even up to a point where the riverbed is higher than the adjacent ground surface behind the levees, are found for the Yellow River in China and the Mississippi in the United States.
Coastal flood prevention
Levees are very common on the marshlands bordering the Bay of Fundy in New Brunswick and Nova Scotia, Canada. The Acadians who settled the area can be credited with the original construction of many of the levees in the area, created for the purpose of farming the fertile tidal marshlands. These levees are referred to as dykes. They are constructed with hinged sluice gates that open on the falling tide to drain freshwater from the agricultural marshlands and close on the rising tide to prevent seawater from entering behind the dyke. These sluice gates are called "aboiteaux". In the Lower Mainland around the city of Vancouver, British Columbia, there are levees (known locally as dikes, and also referred to as "the sea wall") to protect low-lying land in the Fraser River delta, particularly the city of Richmond on Lulu Island. There are also dikes to protect other locations which have flooded in the past, such as the Pitt Polder, land adjacent to the Pitt River, and other tributary rivers.
Coastal flood prevention levees are also common along the inland coastline behind the Wadden Sea, an area devastated by many historic floods.[17] Thus the peoples and governments have erected increasingly large and complex flood protection levee systems to stop the sea even during storm floods. The biggest of these are the huge levees in the Netherlands, which have gone beyond just defending against floods, as they have aggressively taken back land that is below mean sea level.[18]
Spur dykes or groynes
These typically man-made hydraulic structures are situated to protect against erosion. They are typically placed in alluvial rivers perpendicular, or at an angle, to the bank of the channel or the revetment,[19] and are used widely along coastlines. There are two common types of spur dyke, permeable and impermeable, depending on the materials used to construct them.
Natural examples
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.
Deposition of levees is a natural consequence of the flooding of meandering rivers which carry high proportions of
If aggradation continues to occur in the main channel, this will make levee overtopping more likely again, and the levees can continue to build up. In some cases, this can result in the channel bed eventually rising above the surrounding floodplains, penned in only by the levees around it; an example is the Yellow River in China near the sea, where oceangoing ships appear to sail high above the plain on the elevated river.[21]
Levees are common in any river with a high suspended sediment fraction and thus are intimately associated with
Failures and breaches
Both natural and man-made levees can fail in a number of ways. Factors that cause levee failure include overtopping, erosion, structural failures, and levee saturation. The most frequent (and dangerous) is a levee breach. Here, a part of the levee actually breaks or is eroded away, leaving a large opening for water to flood land otherwise protected by the levee. A breach can be a sudden or gradual failure, caused either by surface erosion or by subsurface weakness in the levee. A breach can leave a fan-shaped deposit of sediment radiating away from the breach, described as a crevasse splay. In natural levees, once a breach has occurred, the gap in the levee will remain until it is again filled in by levee building processes. This increases the chances of future breaches occurring in the same location. Breaches can be the location of meander cutoffs if the river flow direction is permanently diverted through the gap.
Sometimes levees are said to fail when water overtops the crest of the levee. This will cause flooding on the floodplains, but because it does not damage the levee, it has fewer consequences for future flooding.
Among various failure mechanisms that cause levee breaches,
Osouli et al. (2014) and Karimpour et al. (2015) conducted lab scale physical modeling of levees to evaluate score characterization of different levees due to floodwall overtopping.[24][25]
Another approach applied to prevent levee failures is electrical resistivity tomography (ERT). This non-destructive geophysical method can detect in advance critical saturation areas in embankments. ERT can thus be used in monitoring of seepage phenomena in earth structures and act as an early warning system, e.g., in critical parts of levees or embankments.[26]
See also
- Bridge scour – Erosion of sediment near bridge foundations by water
- Bunding – Retaining wall around pollution source
- Coupure – Structural feature
- Dam – Barrier that stops or restricts the flow of surface or underground streams
- Earth structure – Building or other structure made largely from soil
- Embankment (earthworks) – Wall or bank to carry a road or rail over low ground or water's edge
- Flood control – Methods used to reduce or prevent the detrimental effects of flood waters
- Flood control in the Netherlands – Manmade control of flooding in the Netherlands
- Lava channel
- Nullah – Steep, narrow valley
- Seawall – Form of coastal defence
- Sleeper dike – Dike that backs up a front-line dike
- Subsidence – Downward vertical movement of the Earth's surface
- Trench – Excavated channel in ground
Notes
- ^ "levee – meaning of levee in Longman Dictionary of Contemporary English". Ldoceonline.com.
- ^ "levee Meaning in the Cambridge English Dictionary". Dictionary.cambridge.org.
- .
- ^ "Levee". education.nationalgeographic.org. National Geographic Society. Retrieved 27 March 2023.
- ^ "Levee". National Geographic. Retrieved 28 June 2023.
- ^ "Flood risk reduction with multiple benefits: more space for the river". www.preventionweb.net. 6 May 2022. Retrieved 22 January 2023.
- ^ "A Look at Preventing Levee Erosion". Federal Emergency Management Agency. 11 February 2021. Retrieved 28 June 2023.
- ISBN 0833747223. 1770: "The town [New Orleans] is secured from the inundations of the river by a raised bank, generally called the Levée." Philip Pittman, The Present State of the European Settlements on the Mississippi; with a geographical description of that river. London
- ^ Tacitus Histories V 19
- ^ "Etymologisch woordenboek van het Nederlands, deel 1: A t/m E – Amsterdam University Press". Aup.nl. Archived from the original on 26 March 2017. Retrieved 12 February 2015.
- ^ "Weavers' Way footpath closure – Decoy Road (Hickling) to Potter Heigham 7 January 2011 – 6 April 2012". Countrysideaccess.norfolk.gov.uk. Retrieved 17 May 2013.
- ^ "Indus River Valley Civilizations". History-world.org. Archived from the original on 10 June 2012. Retrieved 12 September 2008.
{{cite web}}
: CS1 maint: unfit URL (link) - ^ Needham, Joseph. (1971). Science and Civilisation in China: Volume 4, Physics and Physical Technology, Part 3, Civil Engineering and Nautics. Cambridge: Cambridge University Press; Brian Lander. "State Management of River Dikes in Early China: New Sources on the Environmental History of the Central Yangzi Region." T’oung Pao 100.4–5 (2014): 325–62.
- ^ a b c Kemp, Katherine. The Mississippi Levee System and the Old River Control StructureThe Louisiana Environment. Tulane.edu
- ISBN 0-374-12890-1.
- ^ Edward B. Perry (September 1998). "levee rehabilitation in USACE Technical Report REMR-GT-26, Innovative Methods for Levee Rehabilitation" (PDF). Dtic.mil. Archived from the original on 8 April 2013. Retrieved 3 April 2019.
- ^ "Trilateral Working Group on Coastal Protection and Sea Level Rise (CPSL), Wadden Sea Ecosystem No. 25 by Jacobus Hofstede, Common Wadden Sea Secretariat (CWSS), Wilhelmshaven, Germany, 2009" (PDF). Waddensea-secretariat.org. Archived (PDF) from the original on 9 October 2022. Retrieved 3 April 2019.
- ^ Matt Rosenberg. "Dikes of the Netherlands — Geography". Geography.about.com. Archived from the original on 1 February 2009. Retrieved 6 December 2014.
- ^ "Hao Zhang, Hajime Nakagawa, 2008, Scour around Spur Dyke: Recent Advances and Future Researches" (PDF). Dpri.kyoto-u.ac.jp. Archived (PDF) from the original on 9 October 2022. Retrieved 17 May 2013.
- ISBN 9781405177832.
- ^ Leeder 2011, pp. 269–271.
- ^ Briaud, J., Chen, H., Govindasamy, A., Storesund, R. (2008). Levee erosion by overtopping in New Orleans during the Katrina Hurricane. Journal of Geotechnical and Geoenvironmental Engineering. 134 (5): 618–632.
- ^ Hughes, S.A., Nadal, N.C. (2009). Laboratory study of combined wave overtopping and storm surge overflow of a levee. Coastal Engineering.56: 244–259
- ISBN 9780784479087.
- ^ "Levee Erosion and Scour Potential Due to Floodwall Overtopping (PDF Download Available)". ResearchGate.
- ISSN 2391-5447.
External links
- "Well Diggers Trick", June 1951, Popular Science article on how flood control engineers were using an old method to protect flood levees along rivers from seepage undermining the levee
- "Design and Construction of Levees" US Army Engineer Manual EM-1110-2-1913
- The International Levee Handbook