Levee

Levee

Overview

A levee, levée, dike embankment, floodbank or stopbank is an elongated naturally occurring ridge or artificially constructed fill
Fill dirt
Fill dirt is earthy material which is used to fill in a depression or hole in the ground or create mounds or otherwise artificially change the grade or elevation of real property....

 or wall, which regulates water levels. It is usually earthen
Soil
Soil is a natural body consisting of layers of mineral constituents of variable thicknesses, which differ from the parent materials in their morphological, physical, chemical, and mineralogical characteristics...

 and often parallel
Parallel (geometry)
Parallelism is a term in geometry and in everyday life that refers to a property in Euclidean space of two or more lines or planes, or a combination of these. The assumed existence and properties of parallel lines are the basis of Euclid's parallel postulate. Two lines in a plane that do not...

 to the course of a river
River
A river is a natural watercourse, usually freshwater, flowing towards an ocean, a lake, a sea, or another river. In a few cases, a river simply flows into the ground or dries up completely before reaching another body of water. Small rivers may also be called by several other names, including...

 in its floodplain
Floodplain
A floodplain, or flood plain, is a flat or nearly flat land adjacent a stream or river that stretches from the banks of its channel to the base of the enclosing valley walls and experiences flooding during periods of high discharge...

 or along low-lying coastlines.

The word levee, from the French word levée (from the feminine past participle of the French verb lever, "to raise"), is used in American English
American English
American English is a set of dialects of the English language used mostly in the United States. Approximately two-thirds of the world's native speakers of English live in the United States....

 (notably in the Midwest and Deep South
Deep South
The Deep South is a descriptive category of the cultural and geographic subregions in the American South. Historically, it is differentiated from the "Upper South" as being the states which were most dependent on plantation type agriculture during the pre-Civil War period...

).
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Encyclopedia

A levee, levée, dike embankment, floodbank or stopbank is an elongated naturally occurring ridge or artificially constructed fill
Fill dirt
Fill dirt is earthy material which is used to fill in a depression or hole in the ground or create mounds or otherwise artificially change the grade or elevation of real property....

 or wall, which regulates water levels. It is usually earthen
Soil
Soil is a natural body consisting of layers of mineral constituents of variable thicknesses, which differ from the parent materials in their morphological, physical, chemical, and mineralogical characteristics...

 and often parallel
Parallel (geometry)
Parallelism is a term in geometry and in everyday life that refers to a property in Euclidean space of two or more lines or planes, or a combination of these. The assumed existence and properties of parallel lines are the basis of Euclid's parallel postulate. Two lines in a plane that do not...

 to the course of a river
River
A river is a natural watercourse, usually freshwater, flowing towards an ocean, a lake, a sea, or another river. In a few cases, a river simply flows into the ground or dries up completely before reaching another body of water. Small rivers may also be called by several other names, including...

 in its floodplain
Floodplain
A floodplain, or flood plain, is a flat or nearly flat land adjacent a stream or river that stretches from the banks of its channel to the base of the enclosing valley walls and experiences flooding during periods of high discharge...

 or along low-lying coastlines.

Levee


The word levee, from the French word levée (from the feminine past participle of the French verb lever, "to raise"), is used in American English
American English
American English is a set of dialects of the English language used mostly in the United States. Approximately two-thirds of the world's native speakers of English live in the United States....

 (notably in the Midwest and Deep South
Deep South
The Deep South is a descriptive category of the cultural and geographic subregions in the American South. Historically, it is differentiated from the "Upper South" as being the states which were most dependent on plantation type agriculture during the pre-Civil War period...

). It originated in New Orleans a few years after the city's founding in 1718 and was later adopted by English speakers.
The French pronunciation is ləˈve, English ˈlɛviː.

Dike


The modern word dike most likely derives from the Dutch
Dutch language
Dutch is a West Germanic language and the native language of the majority of the population of the Netherlands, Belgium, and Suriname, the three member states of the Dutch Language Union. Most speakers live in the European Union, where it is a first language for about 23 million and a second...

 word "dijk", with the construction of dikes in the Netherlands
Netherlands
The Netherlands is a constituent country of the Kingdom of the Netherlands, located mainly in North-West Europe and with several islands in the Caribbean. Mainland Netherlands borders the North Sea to the north and west, Belgium to the south, and Germany to the east, and shares maritime borders...

 well attested as early as the 12th century. The 126 kilometres (78.3 mi) long Westfriese Omringdijk
Westfriese Omringdijk
The Westfriese Omringdijk is a dyke system that protected the region of Westflinge, part of the historical region of West-Frisia...

 was completed by 1250, and was formed by connecting existing older dikes. The Roman chronicler Tacitus
Tacitus
Publius Cornelius Tacitus was a senator and a historian of the Roman Empire. The surviving portions of his two major works—the Annals and the Histories—examine the reigns of the Roman Emperors Tiberius, Claudius, Nero and those who reigned in the Year of the Four Emperors...

 even mentions that the rebellious Batavi
Batavians
The Batavi were an ancient Germanic tribe, originally part of the Chatti, reported by Tacitus to have lived around the Rhine delta, in the area that is currently the Netherlands, "an uninhabited district on the extremity of the coast of Gaul, and also of a neighbouring island, surrounded by the...

 pierced dikes to flood their land and to protect their retreat (AD 70). The word dijk originally indicated both the trench
Trench
A trench is a type of excavation or depression in the ground. Trenches are generally defined by being deeper than they are wide , and by being narrow compared to their length ....

 and the bank
Bank (geography)
A geographic bank has four definitions and applications:# Limnology: The shoreline of a pond, swamp, estuary, reservoir, or lake. The grade can vary from vertical to a shallow slope....

. It is closely related to the English verb to dig (EWN).

According to the 1911 Encyclopedia Britannica:
In Anglo-Saxon
Old English language
Old English or Anglo-Saxon is an early form of the English language that was spoken and written by the Anglo-Saxons and their descendants in parts of what are now England and southeastern Scotland between at least the mid-5th century and the mid-12th century...

, the word dic already existed and was pronounced with a hard c 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 the bank. Thus Offa's Dyke
Offa's Dyke
Offa's Dyke is a massive linear earthwork, roughly followed by some of the current border between England and Wales. In places, it is up to wide and high. In the 8th century it formed some kind of delineation between the Anglian kingdom of Mercia and the Welsh kingdom of Powys...

 is a combined structure and Car Dyke
Car Dyke
The Car Dyke was, and to large extent still is, an eighty-five mile long ditch which runs along the western edge of the Fens in eastern England. It is generally accepted as being of Roman age and, for many centuries, to have been taken as marking the western edge of the Fens...

 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
Ditch
A ditch is usually defined as a small to moderate depression created to channel water.In Anglo-Saxon, the word dïc already existed and was pronounced 'deek' in northern England and 'deetch' in the south. The origins of the word lie in digging a trench and forming the upcast soil into a bank...

 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
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 of eastern England, where some land, tens of kilometres from the sea is at about sea level...

, Car Dyke, to the South Forty Foot Drain in Lincolnshire
Lincolnshire
Lincolnshire is a county in the east of England. It borders Norfolk to the south east, Cambridgeshire to the south, Rutland to the south west, Leicestershire and Nottinghamshire to the west, South Yorkshire to the north west, and the East Riding of Yorkshire to the north. It also borders...

 (TF1427). The Weir Dike is a soak dike
Soak dike
The term Soak dike is used in The Fens of eastern England to mean a ditch or drain running parallel with an embankment, for the purpose of taking any water that soaks through from the river or drain beyond the bank...

 in Bourne North Fen
Bourne, Lincolnshire
Bourne is a market town and civil parish on the western edge of the Fens, in the District of South Kesteven in southern Lincolnshire, England.-The town:...

, near Twenty
Twenty, Lincolnshire
Twenty is a small, somewhat remote hamlet, east of the market town of Bourne, in Lincolnshire, England. Agriculture is the major industry.-Location:...

 and alongside the River Glen
River Glen, Lincolnshire
The River Glen is a river in Lincolnshire, England with a short stretch passing through Rutland near Essendine.The river's name appears to derive from a Brythonic Celtic language but there is a strong early English connection.-Naming:...

, Lincolnshire
Lincolnshire
Lincolnshire is a county in the east of England. It borders Norfolk to the south east, Cambridgeshire to the south, Rutland to the south west, Leicestershire and Nottinghamshire to the west, South Yorkshire to the north west, and the East Riding of Yorkshire to the north. It also borders...

. In the Norfolk
Norfolk
Norfolk is a low-lying county in the East of England. It has borders with Lincolnshire to the west, Cambridgeshire to the west and southwest and Suffolk to the south. Its northern and eastern boundaries are the North Sea coast and to the north-west the county is bordered by The Wash. The county...

 and Suffolk
Suffolk
Suffolk is a non-metropolitan county of historic origin in East Anglia, England. It has borders with Norfolk to the north, Cambridgeshire to the west and Essex to the south. The North Sea lies to the east...

 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.

Artificial levees


The main purpose of an artificial levee is to prevent flooding of the adjoining countryside; however, they also confine the flow of the river, resulting in higher and faster water
Water
Water is a chemical substance with the chemical formula H2O. A water molecule contains one oxygen and two hydrogen atoms connected by covalent bonds. Water is a liquid at ambient conditions, but it often co-exists on Earth with its solid state, ice, and gaseous state . Water also exists in a...

 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
Polder
A polder is a low-lying tract of land enclosed by embankments known as dikes, that forms an artificial hydrological entity, meaning it has no connection with outside water other than through manually-operated devices...

, 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
Fortification
Fortifications are military constructions and buildings designed for defence in warfare and military bases. Humans have constructed defensive works for many thousands of years, in a variety of increasingly complex designs...

. More on this type of levee can be found in the article on dry-stone walls.

Levees can be permanent earthworks
Earthworks (engineering)
Earthworks are engineering works created through the moving or processing of quantities of soil or unformed rock.- Civil engineering use :Typical earthworks include roads, railway beds, causeways, dams, levees, canals, and berms...

 or emergency constructions (often of sandbag
Sandbag
A sandbag is a sack made of hessian/burlap, polypropylene or other materials that is filled with sand or soil and used for such purposes as flood control, military fortification, shielding glass windows in war zones and ballast....

s) 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
Indus Valley Civilization
The Indus Valley Civilization was a Bronze Age civilization that was located in the northwestern region of the Indian subcontinent, consisting of what is now mainly modern-day Pakistan and northwest India...

 (in Pakistan
Pakistan
Pakistan , officially the Islamic Republic of Pakistan is a sovereign state in South Asia. It has a coastline along the Arabian Sea and the Gulf of Oman in the south and is bordered by Afghanistan and Iran in the west, India in the east and China in the far northeast. In the north, Tajikistan...

 and North India
North India
North India, known natively as Uttar Bhārat or Shumālī Hindustān , is a loosely defined region in the northern part of India. The exact meaning of the term varies by usage...

 from circa 2600 BC) on which the agrarian life of the Harappan
Harappan
Harappan can refer to:* Aspects related to Harappa an archaeological site and city in northeast Pakistan* The Indus Valley Civilization that thrived along Indus River...

 peoples depended. Also levees were constructed over 3,000 years ago in ancient Egypt
Ancient Egypt
Ancient Egypt was an ancient civilization of Northeastern Africa, concentrated along the lower reaches of the Nile River in what is now the modern country of Egypt. Egyptian civilization coalesced around 3150 BC with the political unification of Upper and Lower Egypt under the first pharaoh...

, where a system of levees was built along the left bank of the River Nile for more than 600 miles (965.6 km), stretching from modern Aswan
Aswan
Aswan , formerly spelled Assuan, is a city in the south of Egypt, the capital of the Aswan Governorate.It stands on the east bank of the Nile at the first cataract and is a busy market and tourist centre...

 to the Nile Delta
Nile Delta
The Nile Delta is the delta formed in Northern Egypt where the Nile River spreads out and drains into the Mediterranean Sea. It is one of the world's largest river deltas—from Alexandria in the west to Port Said in the east, it covers some 240 km of Mediterranean coastline—and is a rich...

 on the shores of the Mediterranean. The Mesopotamia
Mesopotamia
Mesopotamia is a toponym for the area of the Tigris–Euphrates river system, largely corresponding to modern-day Iraq, northeastern Syria, southeastern Turkey and southwestern Iran.Widely considered to be the cradle of civilization, Bronze Age Mesopotamia included Sumer and the...

n civilizations and ancient China 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
King Scorpion
Scorpion, or Selk, also King Scorpion or Scorpion II refers to the second of two kings so-named of Upper Egypt during the Protodynastic Period. Their names may refer to the scorpion goddess Serket...

 in Predynastic Egypt
Predynastic Egypt
The Prehistory of Egypt spans the period of earliest human settlement to the beginning of the Early Dynastic Period of Egypt in ca. 3100 BC, starting with King Menes/Narmer....

 during which governance was far less centralized.

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 sandbag
Sandbag
A sandbag is a sack made of hessian/burlap, polypropylene or other materials that is filled with sand or soil and used for such purposes as flood control, military fortification, shielding glass windows in war zones and ballast....

s can be placed. Because flood discharge intensity increases in levees on both river banks, and because silt
Silt
Silt is granular material of a size somewhere between sand and clay whose mineral origin is quartz and feldspar. Silt may occur as a soil or as suspended sediment in a surface water body...

 deposits raise the level of riverbed
Riverbed
Riverbed may refer to:*Stream bed, the channel bottom of a stream or river or creek*Wadi, a dry riverbed that contains water only during times of heavy rain*Riverbed Technology, an American technology company...

s, 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 with willow
Willow
Willows, sallows, and osiers form the genus Salix, around 400 species of deciduous trees and shrubs, found primarily on moist soils in cold and temperate regions of the Northern Hemisphere...

s, weighted matting or concrete revetment
Revetment
Revetments, or revêtements , have a variety of meanings in architecture, engineering and art history. In stream restoration, river engineering or coastal management, they are sloping structures placed on banks or cliffs in such a way as to absorb the energy of incoming water...

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
Mississippi River
The Mississippi River is the largest river system in North America. Flowing entirely in the United States, this river rises in western Minnesota and meanders slowly southwards for to the Mississippi River Delta at the Gulf of Mexico. With its many tributaries, the Mississippi's watershed drains...

 and Sacramento River
Sacramento River
The Sacramento River is an important watercourse of Northern and Central California in the United States. The largest river in California, it rises on the eastern slopes of the Klamath Mountains, and after a journey south of over , empties into Suisun Bay, an arm of the San Francisco Bay, and...

 in the United States
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...

, and the Po
Po River
The Po |Ligurian]]: Bodincus or Bodencus) is a river that flows either or – considering the length of the Maira, a right bank tributary – eastward across northern Italy, from a spring seeping from a stony hillside at Pian del Re, a flat place at the head of the Val Po under the northwest face...

, Rhine, Meuse River
Meuse River
The Maas or Meuse is a major European river, rising in France and flowing through Belgium and the Netherlands before draining into the North Sea...

, Loire
Loire
Loire is an administrative department in the east-central part of France occupying the River Loire's upper reaches.-History:Loire was created in 1793 when after just 3½ years the young Rhône-et-Loire department was split into two. This was a response to counter-Revolutionary activities in Lyon...

, Vistula
Vistula
The Vistula is the longest and the most important river in Poland, at 1,047 km in length. The watershed area of the Vistula is , of which lies within Poland ....

, the delta formed by the Rhine, Maas/Meuse and Scheldt
Scheldt
The Scheldt is a 350 km long river in northern France, western Belgium and the southwestern part of the Netherlands...

 in the Netherlands
Netherlands
The Netherlands is a constituent country of the Kingdom of the Netherlands, located mainly in North-West Europe and with several islands in the Caribbean. Mainland Netherlands borders the North Sea to the north and west, Belgium to the south, and Germany to the east, and shares maritime borders...

 and the Danube
Danube
The Danube is a river in the Central Europe and the Europe's second longest river after the Volga. It is classified as an international waterway....

 in Europe
Europe
Europe is, by convention, one of the world's seven continents. Comprising the westernmost peninsula of Eurasia, Europe is generally 'divided' from Asia to its east by the watershed divides of the Ural and Caucasus Mountains, the Ural River, the Caspian and Black Seas, and the waterways connecting...

.

The Mississippi levee system represents one of the largest such systems found anywhere in the world. It comprises over 3500 miles (5,632.7 km) of levees extending some 1000 kilometres (621.4 mi) along the Mississippi, stretching from Cape Girardeau
Cape Girardeau, Missouri
Cape Girardeau is a city located in Cape Girardeau and Scott counties in Southeast Missouri in the United States. It is located approximately southeast of St. Louis and north of Memphis. As of the 2010 census, the city's population was 37,941. A college town, it is the home of Southeast Missouri...

, Missouri
Missouri
Missouri is a US state located in the Midwestern United States, bordered by Iowa, Illinois, Kentucky, Tennessee, Arkansas, Oklahoma, Kansas and Nebraska. With a 2010 population of 5,988,927, Missouri is the 18th most populous state in the nation and the fifth most populous in the Midwest. It...

 to the Mississippi Delta
Mississippi Delta
The Mississippi Delta is the distinctive northwest section of the U.S. state of Mississippi that lies between the Mississippi and Yazoo Rivers. The region has been called "The Most Southern Place on Earth" because of its unique racial, cultural, and economic history...

. They were begun by French settlers in Louisiana
Louisiana
Louisiana is a state located in the southern region of the United States of America. Its capital is Baton Rouge and largest city is New Orleans. Louisiana is the only state in the U.S. with political subdivisions termed parishes, which are local governments equivalent to counties...

 in the 18th century to protect the city of New Orleans. The first Louisiana levees were about 3 foot (0.9144 m) high and covered a distance of about 50 miles (80.5 km) along the riverside. The US 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
Cairo, Illinois
Cairo is the southernmost city in the U.S. state of Illinois. It is the county seat of Alexander County. Cairo is located at the confluence of the Mississippi and Ohio rivers. The rivers converge at Fort Defiance State Park, an American Civil War fort that was commanded by General Ulysses S. Grant...

 to the mouth of the Mississippi delta
Mississippi Delta
The Mississippi Delta is the distinctive northwest section of the U.S. state of Mississippi that lies between the Mississippi and Yazoo Rivers. The region has been called "The Most Southern Place on Earth" because of its unique racial, cultural, and economic history...

 in Louisiana. By the mid-1980s, they had reached their present extent and averaged 24 feet (7.3 m) in height; some Mississippi levees are as much as 50 feet (15.2 m) high. The Mississippi levees also include some of the longest continuous individual levees in the world. One such levee extends southwards from Pine Bluff
Pine Bluff, Arkansas
Pine Bluff is the largest city and county seat of Jefferson County, Arkansas, United States. It is also the principal city of the Pine Bluff Metropolitan Statistical Area and part of the Little Rock-North Little Rock-Pine Bluff, Arkansas Combined Statistical Area...

, Arkansas
Arkansas
Arkansas is a state located in the southern region of the United States. Its name is an Algonquian name of the Quapaw Indians. Arkansas shares borders with six states , and its eastern border is largely defined by the Mississippi River...

 for a distance of some 380 miles (611.5 km).

Coastal flood prevention


Levees are very common on the flatlands bordering the Bay of Fundy
Bay of Fundy
The Bay of Fundy is a bay on the Atlantic coast of North America, on the northeast end of the Gulf of Maine between the Canadian provinces of New Brunswick and Nova Scotia, with a small portion touching the U.S. state of Maine...

 in New Brunswick
New Brunswick
New Brunswick is one of Canada's three Maritime provinces and is the only province in the federation that is constitutionally bilingual . The provincial capital is Fredericton and Saint John is the most populous city. Greater Moncton is the largest Census Metropolitan Area...

 and Nova Scotia
Nova Scotia
Nova Scotia is one of Canada's three Maritime provinces and is the most populous province in Atlantic Canada. The name of the province is Latin for "New Scotland," but "Nova Scotia" is the recognized, English-language name of the province. The provincial capital is Halifax. Nova Scotia is the...

 Canada
Canada
Canada is a North American country consisting of ten provinces and three territories. Located in the northern part of the continent, it extends from the Atlantic Ocean in the east to the Pacific Ocean in the west, and northward into the Arctic Ocean...

. The Acadians who settled the area can be credited with construction of most of the levees in the area, created for the purpose of farming the fertile tidal flatlands. These levees are referred to as "aboiteau". In the Lower Mainland
Lower Mainland
The Lower Mainland is a name commonly applied to the region surrounding and including Vancouver, British Columbia, Canada. As of 2007, 2,524,113 people live in the region; sixteen of the province's thirty most populous municipalities are located there.While the term Lower Mainland has been...

 around the city of Vancouver
Vancouver
Vancouver is a coastal seaport city on the mainland of British Columbia, Canada. It is the hub of Greater Vancouver, which, with over 2.3 million residents, is the third most populous metropolitan area in the country,...

, British Columbia
British Columbia
British Columbia is the westernmost of Canada's provinces and is known for its natural beauty, as reflected in its Latin motto, Splendor sine occasu . Its name was chosen by Queen Victoria in 1858...

, there are levees to protect low-lying land in the Fraser River
Fraser River
The Fraser River is the longest river within British Columbia, Canada, rising at Fraser Pass near Mount Robson in the Rocky Mountains and flowing for , into the Strait of Georgia at the city of Vancouver. It is the tenth longest river in Canada...

 delta, particularly the city of Richmond
Richmond, British Columbia
Richmond is a coastal city, incorporated in the Canadian province of British Columbia. Part of Metro Vancouver, its neighbouring communities are Vancouver and Burnaby to the north, New Westminster to the east, and Delta to the south, while the Strait of Georgia forms its western border...

 on Lulu Island
Lulu Island
Lulu Island is the name of the largest island in the estuary of the Fraser River. The island makes up most of the City of Richmond, a major suburb of Vancouver, British Columbia...

. There are also levees to protect other locations which have flooded in the past, such as land adjacent to the Pitt River
Pitt River
The Pitt River in British Columbia, Canada is a large tributary of the Fraser River, entering it a few miles upstream from New Westminster and about 25 km ESE of Downtown Vancouver. The river, which begins in the Garibaldi Ranges of the Coast Mountains, is in two sections above and below Pitt...

 and other tributary rivers.

Spur dykes



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
Revetment
Revetments, or revêtements , have a variety of meanings in architecture, engineering and art history. In stream restoration, river engineering or coastal management, they are sloping structures placed on banks or cliffs in such a way as to absorb the energy of incoming water...

, and are used widely along coastlines. Spur dykes are generally divided into two types: permeable and impermeable, depending on the materials used.

Natural levees


Levees are commonly thought of as man-made, but they can also be natural. The ability of a river to carry sediments varies very strongly with its speed. When a river floods over its banks, the water spreads out, slows down, and deposits its load of sediment. Over time, the river's banks are built up above the level of the rest of the floodplain
Floodplain
A floodplain, or flood plain, is a flat or nearly flat land adjacent a stream or river that stretches from the banks of its channel to the base of the enclosing valley walls and experiences flooding during periods of high discharge...

. The resulting ridges are called natural levees.

When the river is not in flood state it may deposit material within its channel, raising its level. The combination can raise not just the surface, but even the bottom of the river above the surrounding country. Natural levees are especially noted on the Yellow River in China
China
Chinese civilization may refer to:* China for more general discussion of the country.* Chinese culture* Greater China, the transnational community of ethnic Chinese.* History of China* Sinosphere, the area historically affected by Chinese culture...

 near the sea where oceangoing ships appear to sail high above the plain on the elevated river. Natural levees are a common feature of all meandering rivers in the world.

Levees in tidal waters


Natural levees may be formed along creek banks that are subject to periodic flooding due to oceanic tides. Levee formation occurs as the incoming tide carries suspended sediment of all grades upstream to the limit imposed by the energy of the tidal flow. As the tidal waters overflow the creek banks, the water flow spreads out to cover a wider area than it did when confined to the stream's main channel. As the water spreads into the flood zone, its flow rate at the brink rapidly slows and much of the sediment that had been carried upstream by the tidal current is deposited along the bank. Over time, during the course of repeated tidal flooding, this sedimentation process forms a levee.

At the height of the tide, the water flow in flooded salt-marsh or flats is the most still and the finer particles slowly settle, forming clay. In the early ebb, the water level in the creek falls leaving the broad expanse of water standing on the marsh at a higher level. In an active system, the levee is always higher than the marsh. That is how it came to be called "une rive levée", or raised shore.

Levee failures and breaches



Man-made levees can fail in a number of ways. The most frequent (and dangerous) form of levee failure is a levee breach
Levee breach
A levee breach or levee failure is a situation where a levee fails or is intentionally breached, causing the previously contained water to flood the land behind the levee.-Causes of failure:...

. A levee breach is when part of the levee actually breaks away, leaving a large opening for water to flood the land protected by the levee. A breach can be a sudden or gradual failure that is caused either by surface erosion or by a subsurface failure of the levee. Sometimes levees are said to fail when water overtops the crest of the levee.

See also

  • Breakwater (structure)
    Breakwater (structure)
    Breakwaters are structures constructed on coasts as part of coastal defence or to protect an anchorage from the effects of weather and longshore drift.-Purposes of breakwaters:...

  • Bridge scour
    Bridge scour
    Bridge scour is the removal of sediment such as sand and rocks from around bridge abutments or piers. Scour, caused by swiftly moving water, can scoop out scour holes, compromising the integrity of a structure....

  • Bunding
    Bunding
    Bunding, also called a bund wall, is the area within a structure designed to prevent inundation or breaches of various types.-Liquid containment:...

  • Dam
    Dam
    A dam is a barrier that impounds water or underground streams. Dams generally serve the primary purpose of retaining water, while other structures such as floodgates or levees are used to manage or prevent water flow into specific land regions. Hydropower and pumped-storage hydroelectricity are...

  • Floodway
  • Jetty
    Jetty
    A jetty is any of a variety of structures used in river, dock, and maritime works that are generally carried out in pairs from river banks, or in continuation of river channels at their outlets into deep water; or out into docks, and outside their entrances; or for forming basins along the...

  • Sleeper dike
    Sleeper dike
    A sleeper dike is a dike which does not normally face water, but serves as a backup if a "front-line" dike in front of it breaks....

  • Subsidence
    Subsidence
    Subsidence is the motion of a surface as it shifts downward relative to a datum such as sea-level. The opposite of subsidence is uplift, which results in an increase in elevation...

  • Trench
    Trench
    A trench is a type of excavation or depression in the ground. Trenches are generally defined by being deeper than they are wide , and by being narrow compared to their length ....


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