Levee

Overview

A Levee is a natural or artificial embankment, usually earthen, designed to prevent the overflow of a river, protect against flooding, or to contain an area of water. This structure is often part of a larger flood control system in areas prone to high water levels. Levees are typically found along the coastline, around low-lying cities, and along rivers.

Etymology

The term "levee" originates from the French word "lever", meaning "to raise". It was first used in the English language in the late 15th century and referred to the practice of constructing embankments to control water levels.

Natural Levees

Natural levees are formed over time by the deposition of sediment during floods. When a river overflows its banks, the speed of the water decreases, causing heavier sediment to be deposited closest to the river bank. Over time, this leads to the formation of a natural levee.

Artificial Levees

Artificial levees, also known as man-made levees, are often constructed in areas prone to flooding. These structures are typically made from earth, but can also be constructed from concrete or stone. The design and construction of artificial levees require careful engineering to ensure they can withstand the pressure from high water levels.

A wide, flat earthen mound running parallel to a river, with a flat top wide enough for a small vehicle to drive on.

Design and Construction

The design and construction of a levee can vary greatly depending on the specific needs of the area it is protecting. Factors such as the size and flow rate of the river, the type of soil in the area, and the potential for flooding all play a role in the design process. The construction of a levee typically involves the following steps:

1. Site Selection: The location of the levee is chosen based on the area that needs protection and the characteristics of the local landscape. 2. Design: Engineers design the levee, taking into account factors such as the height and width needed to contain potential floodwaters. 3. Construction: The levee is built using earthmoving equipment to pile soil or other materials into the designed shape. 4. Reinforcement: The levee is often reinforced with materials such as rocks or concrete to prevent erosion. 5. Maintenance: Regular inspections and maintenance are necessary to ensure the levee remains effective.

Levee Failures and Breaches

Levee failures, also known as breaches, can occur when a levee is overtopped or eroded. This can lead to catastrophic flooding, as was seen during Hurricane Katrina in New Orleans in 2005. Levee breaches can be caused by a number of factors, including excessive rainfall, storm surge, erosion, poor design or construction, and lack of maintenance.

Levees and Ecosystems

While levees can provide important flood protection, they can also have significant impacts on local ecosystems. By altering the natural flow of water, levees can affect wetland habitats, fish populations, and water quality. These impacts must be carefully considered when planning and constructing levees.

Future of Levees

As climate change leads to rising sea levels and more intense storms, the role of levees in flood protection is likely to become even more important. However, there is also growing recognition of the need for more sustainable and ecologically sensitive approaches to flood management. This could include the use of natural floodplains and wetlands, as well as the construction of 'green' levees that incorporate natural features.