Levee
A levee is a structure, either natural or artificial, designed to hold back large bodies of water, predominantly rivers and oceans, to prevent flooding. Historically, levees have been utilized since ancient times, with evidence of their construction by civilizations like the Sumerians as early as 3500 BCE. These early levees were often made from clay and strategically designed to manage water flow for agricultural purposes. While levees can protect farmland and urban areas, they require careful engineering to ensure their safety and effectiveness.
Improperly built levees can erode, leading to catastrophic failures, exemplified by the 2005 Hurricane Katrina disaster in New Orleans, where levee breaches resulted in extensive flooding and loss of life. Modern levees are primarily constructed from earth, rock, metal, and concrete, and can be designed to be both functional and visually appealing. However, the construction of levees can have environmental consequences, such as increased erosion and alterations to local ecosystems. Understanding the balance between flood prevention and environmental impact is crucial in levee construction and maintenance.
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Levee
Levees are natural or artificial structures designed to hold back large bodies of water. While most levees are designed for rivers, levees are created for other bodies of water as well, such as oceans. Levees have been used to create farmland and stop flooding since ancient times. However, levees must be carefully constructed to be safe. If they are not, the silt and soil behind them can erode, causing the area to sink below sea level. This can have catastrophic consequences if the levees failed. This happened in 2005 during Hurricane Katrina when the levees protecting New Orleans burst and flooded the city.
Background
Artificial levees are not a modern creation. Archaeologists have discovered evidence that many ancient peoples built and maintained levees to protect their farmland and settlements. By 3500 BCE, the Sumerians had learned to control water through the use of canals and levees. They did this to strategically supply their farmlands with water, allowing them to grow enough crops to support large concentrations of people.
Sumerian levees were similar to modern-day earthen levees. The Sumerians piled and sculpted vertical clay walls next to rivers and canals and then landscaped a hill to support each wall. Many ancient levees were more than one-half mile long and almost twenty-five feet high. In later periods, the Sumerians used carefully prepared clay bricks to reinforce their levees against erosion. In some cases, Sumerian builders created special drainage systems in their levees. These systems allowed especially high floodwaters to pass through the levee and drain into nearby fields, giving those fields an annual source of fertilizing moisture.
Overview
Building cities near water has some natural advantages. A large body of water can serve as a convenient means of transportation to ship goods and a source of food and income. Additionally, a large body of water is aesthetically pleasing, prompting tourists to visit the area and new residents to relocate.
Unfortunately, large bodies of water can be dangerous and unpredictable. Storms and high tides can cause rivers and other waterways to overflow. Large quantities of moving water can be extremely dangerous to residents, their property, and the local ecosystem.
Levees can prevent flooding by holding back large bodies of water. Some levees form naturally around rivers. Moving water cuts a path through natural sediment, pushing it to the sides. Over many years, the sediment piles up, becoming higher than the river itself. This is how riverbanks are formed. In times of flooding, the banks help stop the river from spilling into surrounding territories.
However, in many cases, natural levees are not high enough or strong enough to contain a powerful river. Then an artificial levee must be built. Earth is the most common building material for manmade levees. Engineers design large slopes of packed earth and rocks along areas at risk of flooding. Earthen levees can be landscaped to look like a naturally occurring hill, making them preferable for many scenic and residential areas. However, they require periodic maintenance as dirt and rocks are gradually washed away.
In areas where the current is extremely powerful or large earthen hills are impractical, levees can be made out of other materials. Wood and plastic can be used to create large walls to hold back strong water. In some cases, levees are built to be retractable, allowing nearby residents and tourists access to the shore. When water levels begin to rise or heavy rainfall is expected, the levees can be closed to prevent flooding.
If an area is extremely prone to flooding, metal and concrete levees can be built. These materials are much stronger than wood, plastic, and earth but are not as attractive. Sometimes levees can be built that are both strong and attractive. For example, heavier levees are sometimes used in conjunction with earthen levees. The heavily reinforced metal or concrete levees are placed immediately next to the water, providing a strong barrier against flooding. Earthen levees are then built on top of the heavier levees, providing a scenic appearance as well as an additional level of protection against severe flooding.
In some scenarios, restricting the natural ebb and flow of a waterway can harm the local environment. The construction of a major levee system may stop new soil from being deposited. If erosion continues to take place from other sources, then the elevation level of the land behind the levee drops. This makes farmland, roads, and residential areas drop below sea level. Many cities, such as New Orleans, are below sea level because of this phenomenon. Levees can also narrow the path of water in a waterway, causing the water to move faster than unmodified waterways. This can increase erosion downstream and make flooding in those areas more difficult to contain.
When a levee fails, it can be disastrous for the surrounding area. Failures often result in major flooding that claims lives and causes irreparable damage to ecosystems, homes, and other structures. When the flooded area is below sea level, the situation is even worse. Water fills the basin and flows into the area for a longer time, causing exceptionally severe damage. This occurred in New Orleans during Hurricane Katrina in 2005. The city's levees were damaged by the waves from the storm and the levees burst, severely flooding most of the city and claiming more than 1,800 lives. A national state of emergency was declared as first responders rescued survivors from the roofs of their homes. Many areas of the city were flooded with more than twenty feet of water. After Katrina, extensive repairs and modifications were made to the New Orleans' levees, costing more than $14 billion. Among the modifications was the construction of an enormous storm surge wall. The levees were built deeper into the ground and designed to hold up even if water passed over them. The new levees protected the city during Hurricane Ida in 2021, a Category 4 storm.
Studies have shown that levee failures disproportionately affect disadvantaged communities in the United States. Additionally, studies showed that the levee systems throughout much of the United States were aging and had received inadequate maintenance throughout their lifetime. This became apparent in March 2023, when the Pajaro River breached its embankment, flooding the town of Pajaro, California.
Bibliography
"A Brief History of Levees." The Atlantic, 2015, www.theatlantic.com/technology/archive/2015/08/a-brief-history-of-levees/402119/. Accessed 13 Jan. 2025.
"Is New Orleans Safe?" The New York Times, 2015, https://www.nytimes.com/2015/08/02/opinion/sunday/is-new-orleans-safe.html?‗r=0. Accessed 13 Jan. 2025.
"Levees and the National Flood Insurance Program: Improving Policies and Practices." National Academies Press, 2013, https://www.nap.edu/read/18309/chapter/8. Accessed 13 Jan. 2025.
"New Orleans' Levees Break After Hurricane Katrina in 2005." Daily News, 2015. http://www.nydailynews.com/news/national/new-orleans-lost-city-teary-gov-orders-full-scale-evacua-article-1.571309. Accessed 13 Jan. 2025.
"Tokyo Building Enormous 'Super-Levees' to Hold Back Its River." Next City, 2013, https://nextcity.org/daily/entry/tokyo-is-building-enormous-super-levees-to-hold-back-its-river. Accessed 13 Jan. 2025.
"US Levee Failures Much More Likely to Affect Vulnerable Communities." Geographical, 20 Nov. 2023, geographical.co.uk/science-environment/us-levee-failures-more-likely-to-affect-vulnerable-communities. Accessed 13 Jan. 2025.