Levee

Generally speaking, “levees are structures built near rivers and sometimes lakes to protect certain areas from flooding,” and the U.S. Federal Emergency Management Agency (FEMA) defines them as “a man-made structure, usually an earthen embankment, designed and constructed in accordance with sound engineering” to “provide protection from temporary flooding” [1]. Levees are often built “along a river or canal path” and can also be created naturally, “when a river floods over the bank and deposits sediment,” and the earthen core of a levee may be “reinforced by rocks or concrete to prevent erosion” [5].

However, where “the flow of a river is strong, levees may also be made of blocks of wood, plastic, or metal” and receive “reinforcement by concrete” if “the area beside a river or other body of water is in particular danger." Another form of a levee is with sandbags, which can form a “temporary levee” to “soak up the water and usually prevent excess water from seeping past the sand” [6].

The embankment component of the levee is simply the “mound of earth raised to retain or divert water,” and levees are designed to “include a series of culverts, canals, ditches, storm sewers, and pump stations” to transfer water that would “normally drain from the land side to the river” back “over to the water side." Another term for “levee” is “dike," and similar structures include “a floodwall” (or floodbank) which is a “vertical wall” that is “typically made of concrete or steel” and “erected in urban locations where there is not enough room for a levee” [1].

As the features of embankments and floodbanks are not easily distinguishable from those of levees, are subsets or components of levees, or are frequently covered by concrete or other cover in levees, all three terms within the Atlantis dataset are referred to as 'levee,' or the overarching label. To talk more about embankments, specifically, they may be “artificial mounds” which are then “compacted, to support (structures)” such as “roadways or railways” [7]. This elevates the grade of the area “above the level of the existing surrounding ground surface,” and it should be mentioned that embankments may also consist of “aggregate, rock, or crushed paving material” [8].

Another visually identifiable aspect of embankments is that embankments should not have “overly steep slopes,” because if these are used, “shallow embankment slides on the downstream slope” may occur [4]. Embankment dams will also “include a vegetative cover (grass) and riprap (rock). Grass cover is usually applied to most embankment surfaces, while riprap is often used on the shoreline of the upstream slope” and alternative protective covers can include “cement, concrete, asphalt, and articulated concrete blocks” [4].

Levees, or embankments, are not perfect flood defenses, though, as “embankments on the outside of bends and overlying old river courses are highly vulnerable to failure” and “embankments bordering tributary systems are also vulnerable to failure as a result of being perpendicular to the direction of flow across the floodplain during inundation” [3]. Levees are “designed to protect against floods up to a certain size” but in the case of a large flood, “floodwaters will flow over the levee” and may also “damage levees” leading to “openings, or breaches” [1].

Physically, “there’s no set height for levees,” and “their measurements vary according to the storms the area receives, even if those storms occur only once every hundred or thousand years” [2].

References

[1] ASCE Inter-Institute Levee Committee. (2009). So, You Live Behind a Levee! American Society of Civil Engineers (ASCE). Retrieved (2021, July 16), from https://mrcc.illinois.edu/1913Flood/awareness/materials/SoYouLiveBehindLevee.pdf

[2] Brain, M., & Lamb, R. (n.d.). What is a levee? HowStuffWorks. Retrieved (2021, July 16), from https://science.howstuffworks.com/engineering/structural/levee.htm

[3] Gilvear, D.J., Davies, J. R., & Winterbottom, S. J. (1994, November 1). Mechanisms of floodbank failure during large flood events on the rivers Tay and Earn, Scotland. Quarterly Journal of Engineering Geology and Hydrogeology, 27(4), 319–332. Retrieved (2021, July 17), from https://pubs.geoscienceworld.org/qjegh/article-abstract/27/4/319/325457/Mechanisms-of-floodbank-failure-during-large-flood?redirectedFrom=PDF

[4] Government of India Central Water Commission Central Dam Safety Organization. (2017, June). Guidelines for Safety Inspections of Dams. Retrieved (2021, August 2), from https://www.researchgate.net/publication/321288327_Guidelines_for_Safety_Inspection_of_Dams

[5] Rogers, C. (n.d.). What is a Levee? (with pictures). AllThingsNature. Retrieved (2021, July 17), from https://www.allthingsnature.org/what-is-a-levee.htm

[6] Rutledge, K., Ramroop, T., Boudreau, D., McDaniel, M., Teng, S., Sprout, E., Costa, H., Hall, H., Hunt, J., Crooks, M., Gunther, T., Evers, J., West, K., Wynne, N., & Caryl-Sue. (2011, January 21). Levee. National Geographic Society. Retrieved (2021, July 16), from https://www.nationalgeographic.org/encyclopedia/levee/

[7] The Constructor. Embankment Materials - Types, Characteristics, Properties, and Tests. Retrieved (2021, August 2), from https://theconstructor.org/building/embankment-materials-types-properties-characteristics/2281/

[8] U.S. Department of Transportation: Federal Highway Administration. (2016, March 8). User Guidelines for Waste and Byproduct Materials in Pavement Construction. Retrieved (2021, August 2), from https://www.fhwa.dot.gov/publications/research/infrastructure/structures/97148/app4.cfm