Levee

A levee (/ˈlɛvi/),[1][2] dike, dyke, embankment, floodbank or stopbank is an elongated naturally occurring ridge or artificially constructed fill or wall, which regulates water levels. It is usually earthen and often parallel to the course of a river in its floodplain or along low-lying coastlines.[3]

River Levee Cross Section Figure
Components of a levee:
  1. Design high water level (HWL)
  2. Low water channel
  3. Flood channel
  4. Riverside slope
  5. Riverside banquette
  6. Levee crown
  7. Landside slope
  8. Landside banquette
  9. Berm
  10. Low water revetment
  11. Riverside land
  12. Levee
  13. Protected lowland
  14. River zone
Sacramento River Levee
The side of a levee in Sacramento, California

Etymology

Speakers of American English (notably in the Midwest and Deep South), 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.[4] 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 in Frisia (now part of the Netherlands and Germany) well attested as early as the 11th century. The 126 kilometres (78 mi) long Westfriese Omringdijk, completed by 1250, 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 (AD 70).[5] The word dijk originally indicated both the trench and the bank. It closely parallels the English verb to dig.[6]

In Anglo-Saxon, the word dic already existed and was pronounced as dick in northern England and as ditch in the south. Similar to Dutch, the English origins of the word lie in digging a trench and forming the upcast soil into a bank alongside it. This practice has meant that the name may be given to either the excavation or to the bank. Thus Offa's Dyke is a combined structure and Car Dyke is a trench - though it once had raised banks as well. In the midlands and north of England, and in the United States, a dike is what a ditch is in the south, a property-boundary marker or small drainage-channel. Where it carries a stream, it may be called a running dike as in Rippingale Running Dike, which leads water from the catchwater drain, Car Dyke, to the South Forty Foot Drain in Lincolnshire (TF1427). The Weir Dike is a soak dike in Bourne North Fen, near Twenty and alongside the River Glen, Lincolnshire. In the Norfolk and Suffolk Broads, a dyke may be a drainage ditch or a narrow artificial channel off a river or broad for access or mooring, some longer dykes being named, e.g. Candle Dyke.[7]

In parts of Britain, particularly Scotland, a dyke may be a field wall, generally made with dry stone.

Uses

Versterkt talud. Locatie. Haven van Laaxum 002
A reinforced embankment

The main purpose of artificial levees is to prevent flooding of the adjoining countryside and to slow natural course changes in a waterway to provide reliable shipping lanes for maritime commerce over time; they also confine the flow of the river, resulting in higher and faster water flow. Levees can be mainly found along the sea, where dunes are not strong enough, along rivers for protection against high-floods, along lakes or along polders. Furthermore, levees have been built for the purpose of empoldering, or as a boundary for an inundation area. The latter can be a controlled inundation by the military or a measure to prevent inundation of a larger area surrounded by levees. Levees have also been built as field boundaries and as military defences. More on this type of levee can be found in the article on dry-stone walls.

Levees can be permanent earthworks or emergency constructions (often of sandbags) built hastily in a flood emergency. When such an emergency bank is added on top of an existing levee it is known as a cradge.

Some of the earliest levees were constructed by the Indus Valley Civilization (in Pakistan and North India from circa 2600 BC) on which the agrarian life of the Harappan peoples depended.[8] 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 600 miles (970 km), 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.[9] 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.

Another example of a historical levee that protected the growing city-state of Mēxihco-Tenōchtitlan and the neighbouring 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 to be 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 Bermuda grass in order to bind the earth together. On the land side of high levees, a low terrace of earth known as a banquette is usually added as another anti-erosion measure. On the river side, erosion from strong waves or currents presents an even greater threat to the integrity of the levee. The effects of erosion are countered by planting suitable vegetation or installing stones, boulders, weighted matting or concrete revetments. Separate ditches or drainage tiles are constructed to ensure that the foundation does not become waterlogged.

River flood prevention

Sacramento River broken levee
Broken levee on the Sacramento River
GretnaLevee
A levee keeps high water on the Mississippi River from flooding Gretna, Louisiana, in March 2005.

Prominent levee systems have been built along the Mississippi River and Sacramento River in the United States, and the Po, Rhine, Meuse River, Rhône, Loire, Vistula, the delta formed by the Rhine, Maas/Meuse and Scheldt in the Netherlands and the Danube in Europe. During the Chinese Warring States period, the Dujiangyan irrigation system was built by the Qin as a water conservation and flood control project. The system's infrastructure is located on the Minjiang (Chinese: 岷江; pinyin: Mínjiāng), which is the longest tributary of the Chang Jiang, in Sichuan, China.

The Mississippi levee system represents one of the largest such systems found anywhere in the world. It comprises over 3,500 miles (5,600 km) of levees extending some 1,000 kilometres (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.[10] The first Louisiana levees were about 3 feet (0.91 m) high and covered a distance of about 50 miles (80 km) along the riverside.[10] 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.[10] By the mid-1980s, they had reached their present extent and averaged 24 feet (7.3 m) in height; some Mississippi levees are as high as 50 feet (15 m). 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 380 miles (610 km).

The United States Army Corps of Engineers (USACE) recommends and supports Cellular Confinement technology (geocells) as a best management practice.[11] 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 river bed 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 river bed, even up to a point where the river bed is higher than the adjacent ground surface behind the levees, are found for the Yellow River in China and the Mississippi in the USA.

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.[12] 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 of course 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.[13]

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,[14] 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.

Super levee

Important cities in Japan (Tokyo and Osaka) developed a new flood protection known as Super levee. Super levees are thicker levees that will not fail even in the most extreme events[15].

Natural examples

Natural levees commonly form around lowland rivers and creeks without human intervention. They are elongate 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 suspended sediment in the form of fine sands, silts, and muds. Because the carrying capacity of a river depends in part on its depth, the sediment in the water which is over the flooded banks of the channel is no longer capable of keeping the same amount of fine sediments in suspension as the main thalweg. The extra fine sediments thus settle out quickly on the parts of the floodplain nearest to the channel. Over a significant number of floods, this will eventually result in the building up of ridges in these positions, and reducing the likelihood of further floods and episodes of levee building.

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.

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.

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, soil erosion is found to be one of the most important factors. Predicting soil erosion and scour generation when overtopping happens is important in order to design stable levee and floodwalls. There have been numerous studies to investigate the erodibility of soils. Briaud et al. (2008) [16] used Erosion Function Apparatus (EFA) test to measure the erodibility of the soils and afterwards by using Chen 3D software, numerical simulations were performed on the levee to find out the velocity vectors in the overtopping water and the generated scour when the overtopping water impinges the levee. By analyzing the results from EFA test, an erosion chart to categorize erodibility of the soils was developed. Hughes and Nadal in 2009 [17] studied the effect of combination of wave overtopping and storm surge overflow on the erosion and scour generation in levees. The study included hydraulic parameters and flow characteristics such as flow thickness, wave intervals, surge level above levee crown in analyzing scour development. According to the laboratory tests, empirical correlations related to average overtopping discharge were derived to analyze the resistance of levee against erosion. These equations could only fit to the situation similar to the experimental tests while they can give a reasonable estimation if applied to other conditions.

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.[18][19]

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.[20]

See also

Notes

  1. ^ "levee - meaning of levee in Longman Dictionary of Contemporary English". Ldoceonline.com.
  2. ^ "levee Meaning in the Cambridge English Dictionary". Dictionary.cambridge.org.
  3. ^ Henry Petroski (2006). "Levees and Other Raised Ground". 94 (1). American Scientist: 7–11.
  4. ^ "levee". Oxford English Dictionary (3rd ed.). Oxford University Press. September 2005. (Subscription or UK public library membership required.)
  5. ^ Tacitus Histories V 19
  6. ^ "Etymologisch woordenboek van het Nederlands, deel 1: A t/m E — Amsterdam University Press". Aup.nl.
  7. ^ "Weavers' Way footpath closure — Decoy Road (Hickling) to Potter Heigham 7 January 2011 – 6 April 2012". Countrysideaccess.norfolk.gov.uk. Retrieved 17 May 2013.
  8. ^ "Indus River Valley Civilizations". History-world.org. Retrieved 12 September 2008.
  9. ^ 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.
  10. ^ a b c Kemp, Katherine. The Mississippi Levee System and the Old River Control StructureThe Louisiana Environment. Tulane.edu
  11. ^ Edward B. Perry (September 1998). "levee rehabilitation in USACE Technical Report REMR-GT-26, Innovative Methods for Levee Rehabilitation". Dtic.mil. Retrieved 3 April 2019.
  12. ^ "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. Retrieved 3 April 2019.
  13. ^ Matt Rosenberg. "Dikes of the Netherlands — Geography". Geography.about.com.
  14. ^ "Hao Zhang, Hajime Nakagawa, 2008, ''Scour around Spur Dyke: Recent Advances and Future Researches''" (PDF). Dpri.kyoto-u.ac.jp. Retrieved 17 May 2013.
  15. ^ "Levee and Super Levee". Retrieved 5 May 2018.
  16. ^ 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.
  17. ^ 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
  18. ^ Karimpour Mazdak; Heinzl Kyle; Stendback Emaline; Galle Kevin; Zamiran Siavash; Osouli Abdolreza. "Scour Characteristics of Saturated Levees Due to Floodwall Overtopping". IFCEE 2015. doi:10.1061/9780784479087.117.
  19. ^ "Levee Erosion and Scour Potential Due to Floodwall Overtopping (PDF Download Available)". ResearchGate.
  20. ^ Arosio, Diego; Munda, Stefano; Tresoldi, Greta; Papini, Monica; Longoni, Laura; Zanzi, Luigi (13 October 2017). "A customized resistivity system for monitoring saturation and seepage in earthen levees: installation and validation". Open Geosciences. 9 (1): 457–467. Bibcode:2017OGeo....9...35A. doi:10.1515/geo-2017-0035. ISSN 2391-5447.

References

External links

2005 levee failures in Greater New Orleans

On August 29, 2005, there were over 50 failures of the levees and flood walls protecting New Orleans, Louisiana, and its suburbs following passage of Hurricane Katrina and landfall in Mississippi. The levee and flood wall failures caused flooding in 80% of New Orleans and all of St. Bernard Parish. Tens of billions of gallons of water spilled into vast areas of New Orleans, flooding over 100,000 homes and businesses. Responsibility for the design and construction of the levee system belongs to the United States Army Corps of Engineers; the responsibility of maintenance belongs to the local levee boards. The Corps hands components of the system over to the local levee boards upon completion. When Katrina struck on August 29, 2005, the project was between 60–90% complete. Four major investigations were conducted by civil engineers and other experts in an attempt to identify the underlying reasons for the failure of the federal flood protection system. All concur that the primary cause of the flooding was inadequate design and construction by the Corps of Engineers.

There were six major breaches in Orleans Parish:

Three major breaches occurred on the Industrial Canal: one on the northeast side near the junction with Gulf Intracoastal Waterway and two on the southeast side along the Lower Ninth Ward, between Florida Avenue and Claiborne Avenue.

On the west side of New Orleans, the 17th Street Canal levee breached 4 feet (1.2 m) below design specs on the New Orleans side near the Old Hammond Highway Bridge

The London Avenue Canal in the Gentilly neighborhood breached on both sides – on the west side near Robert E. Lee Boulevard and on the east near the Mirabeau Avenue BridgeStorm surge caused breaches in 20 places on the Mississippi River-Gulf Outlet Canal ("MR-GO") in Saint Bernard Parish, flooding the entire parish and the East Bank of Plaquemines Parish.

Aera Energy

Aera Energy LLC (Aera) is a natural gas, oil exploration and production company jointly owned by Shell Oil Company and ExxonMobil headquartered in Bakersfield, California. In addition, Aera Energy LLC is a California limited liability company, and one of California’s largest oil and natural gas producers, with an approximate 2015 revenues of over $2 billion. Aera is operated as a stand-alone company through its board of managers.1

Backswamp

In geology a backswamp is a type of depositional environment commonly found in a floodplain. It is where deposits of fine silts and clays settle after a flood. Backswamps usually lie behind a stream's natural levees. During a flood, water levels will rise over the height of the levee, filling the floodplain with water and sediments. Once the flooding stops there is no place for the water to drain out, so the sediments it carried remain and settle. A backswamp usually lies where a bow river once flowed. A backswamp lies lower than the rest of the river valley.

Chautauqua National Wildlife Refuge

The Chautauqua National Wildlife Refuge is located on the Illinois River in Mason County northeast of Havana, Illinois. It is managed by the U.S. Fish and Wildlife Service as one of the four Illinois River National Wildlife and Fish Refuges.

The refuge consists of 4,388 acres (17.8 km²) of Illinois River bottomland, nearly all of it wetland. The parcel is the former Chautauqua Drainage and Levee District, a failed riverine polder. In the 1920s, workers with steam shovels surrounded the levee district with a large dike in an attempt to create a large new parcel of agricultural farmland. The levee district proved to be financially unable to maintain the dike, however, and the Illinois River reclaimed the polder. The complex alluvial topography that had existed before this intervention was replaced by the broad shallow pool of Chautauqua Lake.

In 1936, the federal government acquired the 4,388-acre (17.8 km2) Chautauqua Drainage and Levee District parcel, including the dikes that enclosed the pool, and began to manage it for wildlife-refuge and flood control purposes. The flood-control aspects of this management have grown more challenging in the years since, as continued agricultural runoff and siltation of the Illinois River has made much of Chautauqua Lake shallower. On some shoreline strips of the lake, the silt has built up to the level of the lake surface, and an alluvial topography of sloughs and floodplain woodlands may be slowly re-establishing itself. However, many of the plant and animal species inhabiting the current Chautauqua Lake and Wildlife Refuge and adjacent Illinois River are nonnative and invasive species such as the Asian carp.

As of 2005, of the 4,388 acres (17.8 km²) of the Chautauqua National Wildlife Refuge, 3,200 acres (12.9 km²) were classified as an open pool, 800 acres (3.2 km²) were classified as "water and timbered bottomland", and the remaining 388 acres (1.6 km²) were classified as upland forest. The closest numbered highway is U.S. Highway 136 in Mason County.

A nesting pair of bald eagles was observed in the Chautauqua National Wildlife Refuge in the winter of 2005-06.The Cameron/Billsbach Unit is a detached section of the refuge located further north, in Marshall County, near Henry, Illinois. It covers an additional 1,079 acres (4.37 km²).

City of Parks

City of Parks is a municipal project to create a continuous paved pedestrian and biking trail around the city of Louisville, Kentucky while also adding a large amount of park land. The project was announced on February 22, 2005. Current plans call for making approximately 4,000 acres (1,600 ha) of the Floyds Fork floodplain in eastern Jefferson County into park space, expanding area in the Jefferson Memorial Forest, and adding riverfront land and wharfs along the Riverwalk Trail and Levee Trail. There are also plans to connect the 100-mile (160 km) Louisville trail to a planned seven mile (11 km) trail connecting the Southern Indiana cities of New Albany, Clarksville and Jeffersonville.

Coupure

For the prehistoric biological event, see Grande CoupureA coupure is a means of closing an opening in a wall, floodwall or levee (dike). The word comes from the French verb couper which means to cut.

In historic times a coupure was a location where a breach in the city walls or the walls of a fortress was closed. In more modern times a coupure is a way of allowing traffic to pass a flood protection structure.

Effects of Hurricane Katrina in New Orleans

As the center of Hurricane Katrina passed southeast of New Orleans on August 29, 2005, winds downtown were in the Category 1 range with frequent intense gusts and tidal surge. Hurricane-force winds were experienced throughout the city, although the most severe portion of Katrina missed the city, hitting nearby St. Bernard and Plaquemines parishes. Hurricane Katrina made its final landfall in eastern St. Tammany Parish. The western eye wall passed directly over St. Tammany Parish, Louisiana as a Category 3 hurricane at about 9:45 am Central Time, August 29, 2005. The communities of Slidell, Avery Estates, Lakeshore Estates, Oak Harbor, Eden Isles and Northshore Beach were inundated by the storm surge that extended over six miles inland. The storm surge affected all 57 miles (92 km) of St. Tammany Parish's coastline, including Lacombe, Mandeville and Madisonville. The storm surge in the area of the Rigolets Pass was estimated to be 16 feet, not including wave action, declining to 7 feet (2.1 m) at Madisonville. The surge had a second peak in eastern St. Tammany as the westerly winds from the southern eye wall pushed the surge to the east, backing up at the bottleneck of the Rigolets Pass.

In the City of New Orleans, the storm surge caused approximately 23 breaches in the drainage canal and navigational canal levees and floodwalls. As mandated in the Flood Control Act of 1965, responsibility for the design and construction of the city's levees belongs to the United States Army Corps of Engineers and responsibility for their maintenance belongs to the Orleans Levee Board. The failures of levees and floodwalls during Katrina are considered by experts to be the worst engineering disaster in the history of the United States. By August 31, 2005, 80% of New Orleans was flooded, with some parts under 15 feet (4.6 m) of water. The famous French Quarter and Garden District escaped flooding because those areas are above sea level. The major breaches included the 17th Street Canal levee, the Industrial Canal levee, and the London Avenue Canal floodwall. These breaches caused the majority of the flooding, according to a June 2007 report by the American Society of Civil Engineers. The flood disaster halted oil production and refining which increased oil prices worldwide.

Between 80 and 90 percent of the residents of New Orleans were evacuated before the hurricane struck, testifying to some of the success of the evacuation measures. Despite this, many remained in the city, mainly those who did not have access to personal vehicles or who were isolated from the dissemination of news from the local governments. The Louisiana Superdome was used to house and support some of those who were unable to evacuate. Television shots frequently focused on the Superdome as a symbol of the flooding occurring in New Orleans.

The disaster had major implications for a large segment of the population, economy, and politics of the entire United States. It has prompted a Congressional review of the Army Corps of Engineers and the failure of portions of the federally built flood protection system which experts agree should have protected the city's inhabitants from Katrina's surge. Katrina has also stimulated significant research in the academic community into urban planning, real estate finance, and economic issues in the wake of a natural disaster.

Floodgate

Floodgates, also called stop gates, are adjustable gates used to control water flow in flood barriers, reservoir, river, stream, or levee systems. They may be designed to set spillway crest heights in dams, to adjust flow rates in sluices and canals, or they may be designed to stop water flow entirely as part of a levee or storm surge system. Since most of these devices operate by controlling the water surface elevation being stored or routed, they are also known as crest gates. In the case of flood bypass systems, floodgates sometimes are also used to lower the water levels in a main river or canal channels by allowing more water to flow into a flood bypass or detention basin when the main river or canal is approaching a flood stage.

Levee, California

Levee is a former settlement in Kern County, California. It was located on the Sunset Railroad 1.5 miles (2.4 km) north of Levee Spur, at an elevation of 289 feet (88 m). Levee still appeared on maps as of 1933.

Levee (ceremony)

The levee (from the French word lever, meaning "getting up" or "rising") was traditionally a daily moment of intimacy and accessibility to a monarch or leader. It started out as a royal custom, but, in America, it later came to refer to a reception by the king’s representatives and, even later, by the president.

Levee Spur, California

Levee Spur is a former settlement in Kern County, California. It was located on the Sunset Railroad 3 miles (4.8 km) northwest of Millux.

Levee Township, Pike County, Illinois

Levee Township is located in Pike County, Illinois. As of the 2010 census, its population was 47 and it contained 39 housing units. Levee formed as Douglas Township from Pike Township in November 1875. Douglas changed its name to Levee in April, 1876.

Levee breach

A levee breach or levee failure (the word dike or dyke can also be used instead of levee) is a situation where a levee fails or is intentionally breached, causing the previously contained water to flood the land behind the levee.

Levée en masse

Levée en masse (French pronunciation: ​[ləve ɑ̃ mɑs] or, in English, "mass levy") is a French term used for a policy of mass national conscription, often in the face of invasion.

The concept originated during the French Revolutionary Wars, particularly for the period following 16 August 1793, when able-bodied men aged 18 to 25 were conscripted. It formed an integral part of the creation of national identity, making it distinct from forms of conscription which had existed before this date.

The term is also applied to other historical examples of mass conscription.

Pierre-Levée

Pierre-Levée is a commune in the Seine-et-Marne department in the Île-de-France region in north-central France.

Revetment

In stream restoration, river engineering or coastal engineering, revetments are sloping structures placed on banks or cliffs in such a way as to absorb the energy of incoming water. In military engineering they are structures, again sloped, formed to secure an area from artillery, bombing, or stored explosives. River or coastal revetments are usually built to preserve the existing uses of the shoreline and to protect the slope, as defense against erosion.

Sacramento–San Joaquin River Delta

The Sacramento–San Joaquin River Delta, or California Delta, is an expansive inland river delta and estuary in Northern California. The Delta is formed at the western edge of the Central Valley by the confluence of the Sacramento and San Joaquin rivers and lies just east of where the rivers enter Suisun Bay. The Delta is recognized for protection by the California Bays and Estuaries Policy. Sacramento–San Joaquin Delta was designated a National Heritage Area on March 12, 2019. The city of Stockton is located on the San Joaquin River on the eastern edge of the delta. The total area of the Delta, including both land and water, is about 1,100 square miles (2,800 km2).

The Delta was formed by the raising of sea level following glaciation, leading to the accumulation of Sacramento and San Joaquin River sediments behind the Carquinez Strait, the sole outlet from the Central Valley to San Pablo and San Francisco Bays and the Pacific Ocean. The narrowness of the Carquinez Strait coupled with tidal action has caused the sediment to pile up, forming expansive islands. Geologically, the Delta has existed for about 10,000 years, since the end of the last Ice Age. In its natural state, the Delta was a large freshwater marsh, consisting of many shallow channels and sloughs surrounding low islands of peat and tule.

Since the mid-19th century, most of the region has been gradually claimed for agriculture. Wind erosion and oxidation have led to widespread subsidence on the Central Delta islands; much of the Delta region today sits below sea level, behind levees earning it the nickname "California's Holland". Much of the water supply for central and southern California is also derived from here via pumps located at the southern end of the Delta, which deliver water for irrigation in the San Joaquin Valley and municipal water supply for southern California.

The Levee, Chicago

The Levee District was the red-light district of Chicago, Illinois, from the 1880s until 1912, when police raids shut it down. The district, like many frontier town red-light districts, got its name from its proximity to wharves in the city. The Levee district encompassed 4 blocks in Chicago's South Loop area, between 18th and 22nd street. It was home to many brothels, saloons, dance halls, and the famed Everleigh Club. Prostitution boomed in the Levee District, and it was not until the Chicago Vice Commission submitted a report on the city's vice districts that it was shut down.

When the Levee Breaks

"When the Levee Breaks" is a country blues song written and first recorded by Kansas Joe McCoy and Memphis Minnie in 1929. The lyrics reflect experiences during the upheaval caused by the Great Mississippi Flood of 1927.

"When the Levee Breaks" was re-worked by English rock group Led Zeppelin as the last song on their untitled fourth album. Singer Robert Plant used many of the original lyrics and the songwriting is credited to Memphis Minnie and the individual members of Led Zeppelin. Many other artists have performed and recorded versions of the song.

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Mountainous
Continental plain
Fluvial
Glacial
Oceanic and
coastal landforms
Volcanic
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