Components of a levee: The side of a levee in Sacramento, California A levee (), dike (

American English American English (AmE, AE, AmEng, USEng, en-US), sometimes called United States English or U.S. English, is the set of variety (linguistics), varieties of the English language native to the United States. Currently, American English is the m ...

), dyke (

Commonwealth English The use of the English language English is a of the , originally spoken by the inhabitants of . It is named after the , one of the ancient that migrated from , a peninsula on the (not to be confused with ), to the area of later nam ...

), embankment, floodbank, or stop bank is a structure that is usually

earthen

and that often runs

parallel Parallel may refer to: Computing * Parallel algorithm In computer science Computer science deals with the theoretical foundations of information, algorithms and the architectures of its computation as well as practical techniques for their a ...

to the course of a

river A river is a natural flowing watercourse, usually freshwater, flowing towards an ocean, sea, lake or another river. In some cases, a river flows into the ground and becomes dry at the end of its course without reaching another body of wate ...

river

in its

floodplain A floodplain or flood plain or bottomlands is an area of land adjacent to a river A river is a natural flowing watercourse, usually freshwater, flowing towards an ocean, sea, lake or another river. In some cases, a river flows int ...

or along low-lying coastlines. The purpose of a levee is to keep the course of rivers from changing and to protect against flooding of the area adjoining the river or coast. Levees can be naturally occurring ridge structures that form next to the bank of a river, or be an artificially constructed fill or wall that regulates water levels. Ancient civilizations in the

Indus Valley The Indus ( ) is a transboundary river A transboundary river is a river that crosses at least one political border, either a border within a nation or an international boundary. Bangladesh has the highest number of these rivers, including tw ...

, ancient Egypt, Mesopotamia and China all built levees. Today, levees can be found around the world, and failures of levees due to erosion or other causes can be major disasters.

Etymology

Speakers of

(notably in the

Midwest The Midwestern United States, also referred to as the Midwest or the American Midwest, is one of four Census Bureau Region, census regions of the United States Census Bureau (also known as "Region 2"). It occupies the northern central part of ...

and

Deep South The Deep South is a cultural and geographic subregion A subregion is a part of a larger region In geography Geography (from Greek: , ''geographia'', literally "earth description") is a field of science devoted to the study of the la ...

) use the word ''levee'', from the French word (from the feminine past participle of the

French verb French verb A verb () is a word In linguistics, a word of a spoken language can be defined as the smallest sequence of phonemes that can be uttered in isolation with semantic, objective or pragmatics, practical meaning (linguistics), meani ...

, 'to raise'). It originated in

New Orleans New Orleans (,New Orleans

a few years after the city's founding in 1718 and was later adopted by English speakers. 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 Dutch commonly refers to: * Something of, from, or related to the Netherlands * Dutch people () * Dutch language () *Dutch language , spoken in Belgium (also referred as ''flemish'') Dutch may also refer to:" Castle * Dutch Castle Places * ...

word , with the construction of dikes in

Frisia Frisia (, ; ) is a cross-border cultural region 's map of native American cultural areas within the territory of the United States (1948) as defined by Melville J. Herskovits influence , homelands of the Celtic languages The Celtic ...

Frisia

(now part of the

Netherlands ) , national_anthem = ( en, "William of Nassau") , image_map = EU-Netherlands.svg , map_caption = , image_map2 = BES islands location map.svg , map_caption2 = , image_map3 ...

and

Germany ) , image_map = , map_caption = , map_width = 250px , capital = Berlin Berlin (; ) is the Capital city, capital and List of cities in Germany by population, largest city of Germany by both area and population. Its 3,769,495 inh ...

Germany

) well attested as early as the 11th century. The

Westfriese Omringdijk The Westfriese Omringdijk (West-Frisian Circular Dyke) is a dyke system that protected the region of Westflinge, part of the historical region of West Friesland (historical region) , West-Frisia. Westflinge is now commonly referred to as West Fries ...

, completed by 1250, was formed by connecting existing older dikes. The Roman chronicler

Tacitus Publius Cornelius Tacitus ( , ; – ) was a Roman historian and politician. Tacitus is widely regarded as one of the greatest Roman historians by modern scholars. He lived in what has been called the Silver Age of Latin literature Classi ...

Tacitus

mentions that the rebellious Batavi pierced dikes to flood their land and to protect their retreat (70 CE). The word originally indicated both the

trench A trench is a type of or depression in the ground that is generally deeper than it is wide (as opposed to a wider , or ), and narrow compared with its length (as opposed to a simple hole or pit). In , trenches result from by rivers or by geol ...

and the

bank A bank is a financial institution Financial institutions, otherwise known as banking institutions, are corporation A corporation is an organization—usually a group of people or a company—authorized by the State (polity), stat ...

. It closely parallels the English verb ''to dig''. In

Anglo-Saxon The Anglo-Saxons were a cultural group Cultural identity is a part of a person's identity Identity may refer to: Social sciences * Identity (social science), personhood or group affiliation in psychology and sociology Group expression ...

, the word 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 Offa's Dyke ( cy, Clawdd Offa) is a large linear Earthworks (Archaeology), earthwork that roughly follows the England–Wales border, border between England and Wales. The structure is named after Offa of Mercia, Offa, the Anglo-Saxon England, ...

is a combined structure and

Car Dyke The Car Dyke was, and to a large extent still is, an long ditch which runs along the western edge of the Fens The Fens, also known as the , is a coastal plain in eastern England. This naturally marshy region supports a rich ecology and numer ...

is a trench – though it once had raised banks as well. In the English

Midlands The Midlands is the central part of England and a cultural area that broadly corresponds to the early medieval Mercia, Kingdom of Mercia. The Midlands region is bordered by Northern England and Southern England. The Midlands were important in th ...

and

East Anglia East Anglia is a geographical area in the East of England The East of England is one of the nine official regions of England. This region was created in 1994 and was adopted for statistics purposes from 1999. It includes the ceremonial ...

, and in the United States, a dike is what a

ditch 150px, Waterplants growing in a ditch in the Netherlands, showing ''Sagittaria sagittifolia'' to the right. A ditch is a small to moderate divot created to channel water. A ditch can be used for drainage, to drain water from low-lying areas, alo ...

ditch

is in the south of England, a property-boundary marker or 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 A catchwater drain is a land drain, a ditch cut across the fall of the land, typically just above the level of low-lying, level ground such as The Fens The Fens, also known as the , is a coastal plain in eastern England. This naturally marshy r ...

, Car Dyke, to the South Forty Foot Drain in

Lincolnshire Lincolnshire (abbreviated Lincs.) is a Counties of England, county in the East Midlands of England, with a long coastline on the North Sea to the east. It borders Norfolk to the south-east, Cambridgeshire to the south, Rutland to the south-w ...

(TF1427). The Weir Dike is a

soak dike The term Soak dike is used in The Fens The Fens, also known as the , is a coastal plain in eastern England. This naturally marshy region supports a rich ecology and numerous species, and helps absorb storms. Most of the fens were drained centuri ...

in Bourne North Fen, near

Twenty

and alongside the River Glen,

. In the

Norfolk Norfolk () is a rural and non-metropolitan county A county is a geographical region of a country used for administrative or other purposesChambers Dictionary The ''Chambers Dictionary'' (''TCD'') was first published by William Chambe ...

Norfolk

and

Suffolk Suffolk () is a ceremonial county A county is a geographical region of a country used for administrative or other purposesChambers Dictionary The ''Chambers Dictionary'' (''TCD'') was first published by William Chambers (publisher), W ...

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. In parts of

Britain Britain usually refers to: * United Kingdom The United Kingdom of Great Britain and Northern Ireland, commonly known as the United Kingdom (UK) or Britain,Usage is mixed. The Guardian' and Telegraph' use Britain as a synonym for the United ...

Britain

, particularly

Scotland Scotland ( sco, Scotland, gd, Alba Alba (Scottish Gaelic Scottish Gaelic ( gd, Gàidhlig or Scots Gaelic, sometimes referred to simply as Gaelic) is a Goidelic language (in the Celtic languages, Celtic branch of the Indo-European ...

and

Northern England Northern England, also known as the North of England or simply the North, is the most northern area of England England is a that is part of the . It shares land borders with to its west and to its north. The lies northwest of England ...

, a dyke may be a field wall, generally made with

dry stone Dry stone, sometimes called drystack or, in Scotland, drystane, is a building method by which structures are constructed from stones In geology Geology (from the Ancient Greek γῆ, ''gē'' ("earth") and -λoγία, ''-logia'', (" ...

Uses

The main purpose of artificial levees is to prevent flooding of the adjoining

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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

polder A polder () is a low-lying tract of land that forms an artificial hydrological Hydrology (from Greek: ὕδωρ, "hýdōr" meaning "water" and λόγος, "lógos" meaning "study") is the scientific study of the movement, distribution, and ...

polder

s. 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 wall Dry stone, sometimes called drystack or, in Scotland, drystane, is a building method by which structures are constructed from Rock (geology), stones without any Mortar (masonry), mortar to bind them together. Dry stone structures are stable be ...

s. Levees can be permanent

earthworks Earthworks may refer to: Construction *Earthworks (archaeology), human-made constructions that modify the land contour *Earthworks (engineering), civil engineering works created by moving or processing quantities of soil *Earthworks (military), mil ...

or emergency constructions (often of

sandbag A sandbag or dirtbag is a bag or sack made of hessian (burlap), polypropylene or other sturdy materials that is filled with sand or soil and used for such purposes as flood control, military fortification A fortification is a militar ...

sandbag

s) built hastily in a flood emergency. Some of the earliest levees were constructed by the

Indus Valley Civilization The Indus Valley Civilisation (IVC), also known as the Indus Civilisation, was a Bronze Age The Bronze Age is a prehistoric that was characterized by the use of , in some areas , and other early features of urban . The Bronze Age is ...

(in

Pakistan Pakistan, . Pronounced variably in English as , , , and . officially the Islamic Republic of Pakistan, is a country in South Asia. It is the world's List of countries and dependencies by population, fifth-most populous country, with a popul ...

and

North India North India is a loosely defined region consisting of the northern part of India India, officially the Republic of India (Hindi: ), is a country in South Asia. It is the List of countries and dependencies by area, seventh-largest count ...

from circa 2600 BC) on which the agrarian life of the Harappan peoples depended. Levees were also constructed over 3,000 years ago in

ancient Egypt Ancient Egypt was a civilization A civilization (or civilisation) is a that is characterized by , , a form of government, and systems of communication (such as ). Civilizations are intimately associated with additional char ...

, where a system of levees was built along the left bank of the

River Nile The Nile, , Bohairic , lg, Kiira , Nobiin Nobiin, or Mahas, is a Northern Nubian languages, Nubian language of the Nilo-Saharan languages, Nilo-Saharan language family. "Nobiin" is the genitive case, genitive form of ''Nòòbíí'' ("Nubi ...

for more than , stretching from modern

Aswan Aswan (, also ; ar, أسوان, ʾAswān ; cop, Ⲥⲟⲩⲁⲛ, Souan ) is a city in the south of Egypt Egypt ( ; ar, مِصر ), officially the Arab Republic of Egypt, is a transcontinental country spanning the North Africa, northeast ...

Aswan

to the

Nile Delta The Nile Delta ( ar, دلتا النيل, or simply , ) is the delta Delta commonly refers to: * Delta (letter) (Δ or δ), a letter of the Greek alphabet * River delta, a landform at the mouth of a river * D (NATO phonetic alphabet: "Delta"), ...

on the shores of the

Mediterranean The Mediterranean Sea is a sea connected to the Atlantic Ocean, surrounded by the Mediterranean Basin and almost completely enclosed by land: on the north by Western Europe, Western and Southern Europe and Anatolia, on the south by North Africa ...

. The

Mesopotamia Mesopotamia ( grc, Μεσοποταμία ''Mesopotamíā''; ar, بِلَاد ٱلرَّافِدَيْن ; syc, ܐܪܡ ܢܗܪ̈ܝܢ, or , ) is a historical region of Western Asia situated within the Tigris–Euphrates river system, in th ...

n civilizations and

ancient China The earliest known written records of the history of China date from as early as 1250 BC, from the Shang dynasty The Shang dynasty (), also historically known as the Yin dynasty (), was a Chinese dynasty Dynasties in Chinese h ...

also built large levee systems. 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 The prehistory of Egypt spans the period from the earliest human settlement to the beginning of the Early Dynastic Period around 3100 BC, starting with the first Pharaoh Pharaoh ( , ; cop, , Pǝrro) is the vernacular, common title now us ...

, 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 bank A man-made lake in Keukenhof with grass banks In geography Geography (from Greek: , ''geographia'', literally "earth description") is a field of science devoted to the study of the lands, features, inhabitants, and phenomena of the ...

s, and because

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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 ''Cynodon dactylon'', known as Bermuda grass, ''Dhoob'', ''dūrvā'' grass, ''ethana grass'', ''dubo'', dog's tooth grass, Bahama grass, devil's grass, couch grass, Indian ''doab'', ''arugampul'', ''grama'', wiregrass and scutch grass, is a gras ...

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

revetment Revetments in stream restoration Stream restoration or river restoration, also sometimes referred to as river reclamation, is work conducted to improve the environmental health of a river A river is a natural flowing watercourse, usually ...

s. Separate ditches or drainage tiles are constructed to ensure that the foundation does not become waterlogged.

River flood prevention

Prominent levee systems have been built along the

Mississippi River The Mississippi River is the second-longest river and chief river A river is a natural flowing watercourse, usually freshwater, flowing towards an ocean, sea, lake or another river. In some cases, a river flows into the ground and b ...

and

Sacramento River The Sacramento River ( es, Río Sacramento) is the principal river of Northern California Northern California (colloquially known as NorCal) is a geographic and cultural region that generally comprises the northern portion of the U.S. state ...

in the

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, and the Po,

Rhine ), Surselva Surselva Region is one of the eleven administrative districts Administrative division, administrative unitArticle 3(1). , country subdivision, administrative region, subnational entity, first-level subdivision, as well as many s ...

Rhine

Meuse River The Meuse ( , , , ; wa, Moûze ) or Maas ( , ; li, Maos or ) is a major European river, rising in France and flowing through Belgium and the Netherlands before draining into the North Sea The North Sea is a sea The sea, connected ...

Rhône The Rhône ( , ; german: Rhone ; wae, Rotten ; it, Rodano ; frp, Rôno ; oc, Ròse ) is one of the major rivers of Europe and has twice the average discharge of the Loire The Loire (, also ; ; oc, Léger; la, Liger) is the longest r ...

Rhône

Loire The Loire (, also ; ; oc, Léger, ; la, Liger) is the longest river in France and the 171st longest in the world. With a length of , it drains , more than a fifth of France's land while its average discharge is only half that of the Rhône ...

Loire

Vistula The Vistula (; pl, Wisła, , german: Weichsel) is the longest river in Poland Poland, officially the Republic of Poland, is a country located in Central Europe. It is divided into 16 Voivodeships of Poland, administrative provinc ...

Vistula

, the delta formed by the Rhine, Maas/Meuse and

Scheldt The Scheldt ( ; french: Escaut ; wa, Escô; nl, Schelde ) is a river that flows through northern France France (), officially the French Republic (french: link=no, République française), is a country primarily located in Western Eur ...

Scheldt

in the

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and the

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Danube

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Europe

. During the Chinese

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, the

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was built by the

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as a water conservation and flood control project. The system's infrastructure is located on the Minjiang (), which is the longest tributary of the Chang Jiang, in

Sichuan Sichuan (; , ; alternatively romanized as Szechuan or Szechwan) is a landlocked province A province is almost always an administrative division Administrative division, administrative unitArticle 3(1). , country subdivision, admini ...

Sichuan

China China (), officially the People's Republic of China (PRC; ), is a country in East Asia East Asia is the eastern region of Asia Asia () is Earth's largest and most populous continent, located primarily in the Eastern Hemisphere ...

China

. The Mississippi levee system represents one of the largest such systems found anywhere in the world. It comprises over of levees extending some along the Mississippi, stretching from

Cape Girardeau Cape Girardeau (, french: Cap-Girardeau ; colloquially referred to as "Cape") is a city in Cape Girardeau County and Scott County in the U.S. state of Missouri Missouri is a U.S. state, state in the Midwestern United States, Midwestern re ...

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, to the

Mississippi delta The Mississippi Delta, also known as the Yazoo–Mississippi Delta, or simply the Delta, is the distinctive northwest section of the U.S. state In the United States The United States of America (USA), commonly known as the United ...

. They were begun by French settlers in

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in the 18th century to protect the city of

New Orleans New Orleans (,New Orleans

.Kemp, Katherine
''The Mississippi Levee System and the Old River Control Structure''The Louisiana Environment.
Tulane.edu The first Louisiana levees were about high and covered a distance of about along the riverside. 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

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to the mouth of the

in Louisiana. By the mid-1980s, they had reached their present extent and averaged in height; some Mississippi levees are as high as . The Mississippi levees also include some of the longest continuous individual levees in the world. One such levee extends southwards from Pine Bluff,

Arkansas Arkansas () is a U.S. state, state in the South Central United States, South Central region of the United States, home to more than three million people as of 2018. Its name is from the Osage language, a Dhegihan languages, Dhegiha Siouan la ...

, for a distance of some . The United States Army Corps of Engineers (USACE) recommends and supports

cellular confinement Cellular confinement systems (CCS)—also known as geocells—are widely used in construction for erosion control Erosion control is the practice of preventing or controlling wind or water erosion In earth science, erosion is the action of ...

technology (geocells) as a best management practice. 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

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of a river.

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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

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in China and the

Mississippi Mississippi () is a U.S. state, state in the Southeastern United States, Southeastern region of the United States, bordered to the north by Tennessee; to the east by Alabama; to the south by the Gulf of Mexico; to the southwest by Louisiana; a ...

in the USA.

Coastal flood prevention

Levees are very common on the marshlands bordering the

Bay of Fundy The Bay of Fundy (french: Baie de Fundy) is a bay between the Canadian provinces of New Brunswick and Nova Scotia, with a small portion touching the US state of Maine. It has an extremely high tidal range. The name is likely a corruption of the F ...

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and

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Canada

. The

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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, British Columbia, 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. 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 ) , national_anthem = ( en, "William of Nassau") , image_map = EU-Netherlands.svg , map_caption = , image_map2 = BES islands location map.svg , map_caption2 = , image_map3 ...

, which have gone beyond just defending against floods, as they have aggressively taken back land that is below mean sea level.

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

, 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 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

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 tide#Range variation: springs and neaps, 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) 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 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. 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.

Notes

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
{{Authority control Dikes, Flood control Fluvial landforms Riparian zone

Etymology

Uses

River flood prevention

Coastal flood prevention

Spur dykes or groynes

Natural examples

Failures and breaches

See also

Notes

External links