What is a Levee?

A levee is a natural or artificial flood bank that follows along a river or canal path. Natural ones are created when a river floods over the bank and deposits sediment, which causes the banks to be higher than the floodplain. Man-made barriers are created to prevent flooding, contain water flow, and/or increase water speed.

Also known as a stop wall, dike, dam, or storm barrier, a levee can be found along lakes, rivers, or the sea. Generally made of soil, some man-made levees are reinforced by rocks or concrete to prevent erosion. They are occasionally used as a military defense, as well. There is no set height for such a barrier; the height usually varies between 10 and 30 feet (3 to 10 m). An emergency levee, such as that to be used in the event of flood, can be created with sandbags.

In the Southern and Midwestern areas of the U.S., "levee" is the commonly used term. In Europe and Canada, this structure is most likely to be known as a dike. Although the terms are often used interchangeably, the definition is slightly different. In the Netherlands, a system of dikes diverts flood waters from large bodies of water. Along the Mississippi River, a system of levees restrains flooding waters from lakes and stream. These barriers might also be referred to as embankments.

A levee failure occurs when a break, also known as a breach, occurs. As part of the barrier breaks away, it allows water to flow through the opening. Another type of failure occurs when water flows over the top of the structure. Sand boils, which results when the rising pressure of the water flowing through the pores in the soil is stronger than the downward pressure of the soil, can also occur during a breach.

A levee is an embankment built to prevent the overflow of a river. It functions by providing a barrier between the water and the land, effectively raising the height at which a river can flow before it spills onto the floodplain. Levees are critical for flood protection in many riverine communities.

Levees are typically constructed using local materials like earth, sand, and rock. The process involves compacting these materials into a raised embankment, often with a core of clay for impermeability. Modern levees may also incorporate synthetic materials for added stability and erosion resistance.

While levees are designed to mitigate flood risk, they can also pose potential hazards. If a levee fails or is overtopped, the resulting flood can be catastrophic due to the sudden release of pent-up water. Additionally, levees can cause rivers to deposit sediment upstream, leading to elevated riverbeds and increased flood risk over time.

Levees can significantly alter natural water flow and sediment deposition, which can disrupt local ecosystems. They may lead to habitat loss for species that rely on floodplains and can also reduce the natural replenishment of nutrients in these areas, impacting plant and animal life and potentially reducing biodiversity.

Yes, environmentally friendly levee designs are possible. These "green levees" incorporate natural features like wetlands, which can provide habitat for wildlife and help filter water. They are designed to work with natural processes to provide flood protection while minimizing ecological disruption.

Levees remain a cornerstone of flood management, protecting lives and property in flood-prone areas. They are part of a broader strategy that includes other measures like floodwalls, diversion channels, and flood forecasting systems. Proper maintenance and regular upgrades are crucial to ensure levees function effectively in the face of increasingly unpredictable weather patterns.