What is a levee and how does it work?
A levee is a natural or artificial wall that blocks water from going where we don’t want it to go. The banks form levees made of sediment, silt, and other materials pushed aside by the flowing water. Levees are usually parallel to the way the river flows, so levees can help direct the flow of the river.
What are the disadvantages to levees?
- Length of levees that different US streams from their floodplains: >40,000 km
- Percent of floodplain lost in the Danube bowl: 92
- Percent lost in the Elbe, Rhine and Tiza bowls: >80
- Zone of Louisiana’s coastal wetlands that have vanished since 1930s: >4,900 sq. ...
What is the meaning of 'levees'?
So people build levees. A levee is a natural or artificial wall that blocks water from going where we don’t want it to go. Levees may be used to increase available land for habitation or divert a body of water so the fertile soil of a river or sea bed may be used for agriculture.
What is the function of levees?
Levees are used to hold back flooding from waterways during heavy rains, are the most cost effective method of lake construction. Levees distribute water over vast distances to crops and cities hundreds of miles away where they are often lined with concrete. Levees are a big part of our lives even though we seldom notice them.
What are levees short answer?
What are levees GCSE geography?
What is the purpose of a levee?
What is ocean levee?
How are levees formed Geography AQA?
How are levees formed GCSE answer?
What is the difference between a dam and a levee?
What's the difference between a dyke and a levee?
What is a levee structure?
What is a natural levee quizlet?
How do levees make things worse?
What is the levee system in New Orleans?
What is a levee made of?
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.
Why are levees important?
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 .
How many miles are there in the Mississippi levee system?
The Mississippi levee system represents one of the largest such systems found anywhere in the world. It comprises over 5,600 km (3,500 mi) of levees extending some 1,000 km (620 mi) along the Mississippi, stretching from Cape Girardeau, Missouri, to the Mississippi delta.
What causes a levee to fail?
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.
How tall are Mississippi levees?
By the mid-1980s, they had reached their present extent and averaged 7.3 m (24 ft) in height; some Mississippi levees are as high as 15 m (50 ft). The Mississippi levees also include some of the longest continuous individual levees in the world.
What are the sluice gates called?
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.
What is a breach in a 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.
How tall are levees?
Levees along the Mississippi River may range from 10 to 20 feet (3 to 7 meters) tall. In Holland, they can top 30 feet (10 meters).
What is a levee in New Orleans?
A levee is simply a man-made embankment built to keep a river from overflowing its banks or to prevent ocean waves from washing into undesired areas. Advertisement. In New Orleans, the levees attempt to perform dual duties: On one side of the city, levees protect against floods from the Mississippi River, and on the other side, ...
What is the Dutch levee system?
Much of the Dutch levee system relies on the understanding that levees require regular maintenance, constant monitoring and a long-term appreciation for how rivers, oceans and storms behave. When these are in place, communities can thrive safely alongside the beauty and convenience of coastal and riverside areas.
How do dikes help the land?
In parts of the Netherlands, dikes stop ocean waters from reclaiming thousands of miles of land, much of which is either at or below sea level. The famous windmills of Holland pump water from behind the dikes and back out to sea to keep the land dry.
How tall are levees in Mississippi?
Levees along the Mississippi River may range from 10 to 20 feet (3 to 7 meters) tall. In Holland, they can top 30 feet (10 meters). But there's no set height for levees. Their measurements vary according to the storms the area receives, even if those storms occur only once every hundred or thousand years.
Why did the New Orleans levee system fail?
Engineers built the levee system with the goal of creating a system that could stand up to the worst storm possible in 200 years.
Why were the levees shorter in New Orleans?
As a result, New Orleans' levees were shorter and weaker. Safety compromised by bureaucracy: No central agency was in charge of maintaining the levees. This task instead fell to several different private firms and government agencies, leading to communication problems and the breakdown of various upgrade projects.
Why are levees important?
Levees are designed to reduce flood risk from flooding events; however, they do not eliminate the risk entirely. It is always possible that a flood will exceed the capacity of a levee, no matter how well the structure is built. Levees are designed to manage a certain amount of floodwater and can be Figure 2. Levee Components
What is a levee in flood insurance?
The National Flood Insurance Program (NFIP) defines a levee in Title 44, Chapter 1, Section 59.1 of the Code of Federal Regulations (44 CFR 59.1) as “a man-made structure, usually an earthen embankment, designed and constructed in accordance with sound engineering practices to contain, control, or divert the flow of water so as to reduce risk from temporary flooding.” The NFIP regulations define a levee system as “a flood protection system which consists of a levee, or levees, and associated structures, such as closure and drainage devices, which are constructed and operated in accordance with sound engineering practices.” For the purposes of this document, levees and levee systems are referred to as “levees.”
What is a levee?
Definition of levee (Entry 2 of 3) 1 a : an embankment for preventing flooding. b : a river landing place : pier. 2 : a continuous dike or ridge (as of earth) for confining the irrigation areas of land to be flooded.
What does "levee" mean in French?
History and Etymology for levee. Noun (1) French lever, from Middle French, act of arising, from ( se) lever to rise. Noun (2) French levée, from Old French, act of raising, from lever to raise — more at lever. Keep scrolling for more.
How are levees formed?
Levees are formed by the repeated flooding of the river. When the river floods, the biggest, most coarse material will be dumped close to the river banks. This will continue to build up the levee over time.
What are the different types of landforms in a river?
River landforms can be divided into upper, middle and lower course features. As the river moves from the upper course to the lower course, the features in the river will change.
Why are floodplains important?
This makes floodplains a good place for agriculture. Every time that a river floods its banks, it will deposit more silt or alluvium on the flood plain. A build-up of alluvium on the banks of a river can create levees, which raise the river bank.
What is a floodplain?
Floodplains. The river will now have a wide floodplain. A floodplain is the area around a river that is covered in times of flood. It is a very fertile area due to the rich alluvium deposited by floodwaters. This makes floodplains a good place for agriculture.
What happens when a river reaches the end of its journey?
The river channel is now deep and wide and the landscape around it is flat. However, as a river reaches the end of its journey, energy levels are low and deposition takes place .
A famous flood solution, levees will not work for all communities
Contrary to the mixed reputation levees have garnered, they can serve as a valuable addition to flood protection infrastructure. Despite famously breaking during Hurricane Katrina and allowing New Orleans to flood in 2005, communities benefit from levees with the right safety measures, good design, and proactive maintenance.
The Takeaway
High-density communities prone to frequent, small floods can benefit from adding levees to their flood mitigation strategy, but particular care is needed to prevent increased flooding downstream.
Formation
- Levees are usually made of earth. The natural movement of a body of water pushes sediment to the side, creating a natural levee. The banks of a river are often slightly elevated from the river bed. The banks form levees made of sediment, silt, and other materials pushed aside by the flo…
Construction
- Levees can also be artificially created or reinforced. Artificial levees are usually built by piling soil, sand, or rocks on a cleared, level surface. In places where the flow of a river is strong, levees may also be made of blocks of wood, plastic, or metal. Where the area beside a river or other body of water is in particular danger, levees may even be reinforced by concrete.
History
- People have been building and reinforcing levees since the beginning of civilization. As early as 2500 BCE, the Indus Valley Civilization, with urban centers in what is today Mohenjo Daro and Harappa, Pakistan, used levees to protect land near the Indus River. Farmers were able to grow crops like cotton and rice.
Prevention
- In addition to creating living space and cropland, levees can also provide a measure of protection from invaders. Levees can make a river like a moat, preventing people from easily invading territory on the other side. Destroying levees can also stop invading forces. In 1938, Chinese leaders intentionally broke levees on the Yellow River to prevent the Japanese military from adv…
Conservation
- Artificial levees need to be protected. They have to stand up to erosion, or wearing away, by the nearby water. Sometimes, trees and plants like Bermuda grass are planted near levees to anchor the soil. Engineers need to maintain levees with structural work to reinforce the boundaries.
Treatment
- In emergencies, temporary levees can be made of sandbags. These soak up the water and usually prevent excess water from seeping past the sand.
Purpose
- Artificial levees prevent flooding. But they also create a new problem: levees squeeze the flow of the river. All the rivers power is flowing through a smaller space. Water levels are higher and water flows faster. This puts more pressure on levees downstream and makes the water more difficult to control. If levees break, it also makes containing the flood more difficult.
Background
- Since the 18th century, levees have protected Louisiana and other nearby states from flooding by the Mississippi River. When Hurricane Katrina struck New Orleans in 2005, the levees could not withstand the storm surge. The levees broke, and water flooded 80 percent of the city.
Geology
- The Bay of Fundy, which borders the provinces of New Brunswick and Nova Scotia, Canada, has one of the highest tidal ranges in the world. The tidal range reaches more than 17 meters (55 feet) in some places. To make the most use of land that would otherwise be underwater during high tide, Canada has constructed levees along parts of the Bay of Fundy.
Overview
A levee , dike (American English), dyke (Commonwealth English), embankment, floodbank, or stop bank is a structure that is usually earthen and that often runs parallel to the course of a river in its floodplain 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 cons…
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. The name derives from the trait of the levee's ridges being raised higher than both the channel and the surrounding floodplains.
Uses
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 a…
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 br…
See also
• Bridge scour – Removal of sediment from around bridge abutments or piers by the movement of water
• Bunding – Retaining wall around pollution source
• Coupure – Structural feature
• Dam – Barrier that stops or restricts the flow of surface or underground streams
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". American Scientist. 94 (1): 7–11. doi:10.1511/2006.57.7.
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