Levees

What are Levees?

Living close to water is a great thing—aside from when there is a flood. So, individuals fabricate levees. A levee is a characteristic or fake divider that squares water from going where we do not need it to go. Levees might be utilized to increment accessible land for residence or redirect a waterway, so the fertile soil of a stream or ocean bed might be utilized for agribusiness. They keep waterways from flooding urban communities during a storm. Be that as it may, if a levee breaks, the results can be disastrous. 

Illustration describing levees

Levees are generally made of earth. The standard development of a waterway pushes residue to the side, making it a natural levee. The banks of a waterway are regularly somewhat raised from the stream bed. The bank’s structure levees are made of residue, sediment, and different materials pushed aside by the streaming water. Levees usually are corresponding to how the waterway streams, so levees can help direct the progression of the stream. 

Levees can likewise be artificially made or fortified. Artificial levees are generally made by heaping soil, sand, or rocks on a cleared, level surface. In places where the progression of a waterway is solid, levees may likewise be made of squares of wood, plastic, or metal. Where the territory adjacent to a waterway or other waterway is specifically perilous, levees may even be fortified by concrete. 

Individuals have been assembling and fortifying levees since the start of human progress. As far back as 2,500 BCE, the Indus Valley Civilization, with urban settlements in what is today Mohenjo Daro and Harappa, Pakistan, utilized levees to protect land close to the Indus River. Ranchers had the option to develop crops like cotton and rice. 

Notwithstanding providing living space and cropland, levees can likewise give a proportion of security from intruders. Levees can make a waterway like a canal, keeping individuals from effectively attacking the territory on the opposite side. Destroying levees can likewise prevent attacking powers. In 1938, Chinese pioneers deliberately broke levees on the Yellow River to keep the Japanese military from progressing. Over 500,000 individuals, Japanese and Chinese, died in the subsequent flood. 

Artificial levees should be secured. They need to confront erosion or eroding by the nearby water. Some of the time, trees and plants like Bermuda grass are planted close to levees to hold back the soil. Architects need to keep up levees with auxiliary work to strengthen the limits. 

In crises, brief levees can be made of sandbags. These absorb the water and typically keep overabundant water from leaking past the sand. 

Artificial levees forestall flooding. Moreover, they additionally present another issue: levees press the progression of the waterway. All the waterway’s capacity is coursing through a small space. Water levels are higher, and water streams are quicker. This pressurises levees downstream and makes the water progressively harder to control. On the off chance that levees break, it likewise makes containing the flood progressively more troublesome. 

Since the 18th century, levees have shielded Louisiana and other close by states from flooding by the Mississippi River. At the point when Hurricane Katrina struck New Orleans in 2005, the levees could not withstand the force of the flood. The levees broke and water flooded 80% of the city. 

Levees on the Sea 

Albeit most levees exist to control streams, they can likewise exist on the coast. The Netherlands has a detailed arrangement of embankments, levees, and dams to keep back the North Sea. Land for homesteads, industry, and private use has been made from land that was at one time, under the sea. 

The Bay of Fundy, which outskirts the areas of New Brunswick and Nova Scotia, Canada, has one of the most noteworthy tidal ranges in the world. The tidal range rises to more than 17 meters (55 feet) in certain spots. To utilize land that would in some way or another be underwater during high tide, Canada has built levees along with parts of the Bay of Fundy. 

Advantages and Disadvantages of Levees and Floodwalls 

Advantages 

  • Levees and floodwalls can safeguard a structure and the encompassing territory from immersion without considerable changes to the structure of the plan flood level is not surpassed. 
  • There is no weight from floodwater to do essential harm to the structure. 
  • These hindrances usually are more affordable than lifting or moving the structure. 
  • Tenants do not need to leave the structure during development. 

Disadvantages 

  • These methods cannot be accustomed to bringing a seriously harmed or improved structure into alignment with floodplain advancement principles. 
  • May disregard floodplain improvement models, especially in floodway areas, by causing hindered streams or in expanded flood potency. 
  • Failure or overtopping of a levee or floodwall results in as much harm as though there was no assurance (or more). 
  • May limit access to the structure. If human mediation is required for terminations, there must be adequate admonition time. 
  • It may be costly. 
  • For structures with cellars, hydrostatic weight from groundwater may even now cause harm. 
  • Neighbourhood waste can be influenced, perhaps causing water issues for other people. 
  • Inside, waste must be given. 
  • Levees require impressive land territory. 
  • Require periodic upkeep. 
  • No decrease in flood protection premiums. 
  • Try not to wipe out the need to empty during floods. 

Summary

Levees can either be conventional or human-made. Human-made levees are endeavours that are intended to keep water in. They are built next to waterways to shield them from flooding their banks. They are produced using less impermeable soils, for example, earth, and are limited at the top yet more extensive at the base. They can expand in stature because there is no set tallness on how high they can be. 

There are numerous factors in favour of levees. They permit individuals to live by streams or seas without the dread of flooding, except if the levee breaks. They additionally give assurance. In the Netherlands, the preferred function of utilizing a levee is that it has halted the sea waters from streaming onto the land. This has permitted the land to be inhabited by individuals. Levees additionally keep lakes under control and waterways from flooding their banks. 

Levees also have a few disadvantages. While giving assurance from flooding in one spot, levees can redirect the water somewhere else, causing flooding in another place. Crops can suffocate and be devastated by floods impacting ranchers. Levees can likewise fall short. They can fail by overtopping, undercurrent, drooping, or erosion. Overtopping is the point at which the water transcends the levee. Undercurrent is when water pervades the sand stores underneath the levee and water ascends on the opposite side. At the point when the heaviness of the water is unreasonably substantial for the levee, it can push over the sides. This is called overtopping. Erosion is the point at which the sides and top of the levee gradually begin to wear out because of the rushes of water. 

Intriguing Facts about Floods 

A Flood of Damages 

  • Number of individuals the UN assessments will live in the way of a potential harming flood by 2050: $2 billion 
  • Increment over the present figures: 100% 
  • A yearly number of “significant floods” worldwide: 
  • 1950s to 1970s: 7-9 
  • 1980s: 20 
  • 1990s: 34 
  • Number of harmful floods in Europe from 1989-2002: 100 
  • Surmised number of individuals uprooted: 500,000 
  • Cost of harm: $30 billion 
  • The sum spent by the US government on flood-control plans (chiefly dams and levees), 1960-85: $38 billion 
  • The normal swelling balanced expense of flood harm each year from 1964 to 1993: $4.6 billion 
  • Increment in cost of flood damage during that time over past 30-year term: Approximately 66% 
  • Increment long of dikes in the Indian province of Bihar from 1952-98: 22 occasions 
  • Percentage expansion in the flood-inclined zone in Bihar at that time: approx. 300 
  • Percentage expansion in flood harms in Bihar between the 1950s and 1970s: practically 400 
  • Number of individuals in Bihar living inside banks: $2 million 

Controlled Rivers 

  • Length of levees that different US streams from their floodplains: >40,000 km 
  • Percentage of floodplain lost in the Danube bowl: 92 
  • Percentage lost in the Elbe, Rhine and Tiza bowls: >80 
  • Zone of Louisiana’s coastal wetlands that have vanished since the 1930s: >4,900 sq. Km. 
  • Tallness, in places, of the bed of China’s Yellow River over the encompassing flood plain: 20 meters 
  • Levees and Dams: Technical Difficulties 
  • Number of levee failures during the “Incredible Flood” of 1993 in the Mississippi Basin: 1,575 
  • Percentage of all the levees in the flood zone: 68 
  • Regions immersed by supplies worldwide: >260,000 sq. Km. 
  • Percentage of China’s 85,000 dams needing critical fixes: >33 
  • Yearly property-harm cost of dam disappointments in the US in the mid-2000s: $100 million 
  • Number of US dams currently declared “hazardous”: >3,500 
  • Absolute venture expected to bring them into security consistence: >$30 billion 

A Better Way 

  • Percentage of India’s storm run-off that could be caught and put away as groundwater: 25 
  • Percentage of stored water that could be recovered later for water systems: 75 
  • Cost of moving 5,100 homes and organizations in Illinois and Missouri after the Great Flood: $66 million 
  • Protection instalments used to fix and modify those structures in past floods: $191 million

    Read more about River Discharge

References

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  • To Levee or Not to Levee? . (n.d.). Retrieved from Anacostia Watershed Society: https://www.anacostiaws.org/blog/levee-or-not-levee.html
  • What are the advantages and disadvantages of raised levees? (n.d.). Retrieved from Quora: https://www.quora.com/What-are-the-advantages-and-disadvantages-of-raised-levees

Cite/Link to This Article

  • "Levees". Geography Revision. Accessed on August 19, 2022. https://geography-revision.co.uk/a-level/physical/levees/.

  • "Levees". Geography Revision, https://geography-revision.co.uk/a-level/physical/levees/. Accessed 19 August, 2022.

  • Levees. Geography Revision. Retrieved from https://geography-revision.co.uk/a-level/physical/levees/.