Similar to dams, levees and dikes have a simple but important job: they hold back water. Although they look similar and can be made of the same materials, levees and dikes have different uses. Levees keep rivers from flooding low-lying land. Dikes are used to take back land that is normally under water.

Physical features

Levees and dikes can be made from cement, stacked stones, or packed earth. They lie along the border between the water they hold back and the land they protect. They are usually wider at the bottom than they are at the top. They can be from 3 feet (1 meter) to 50 feet (15 meters) high.

Uses

A levee creates an extra high bank to keep a river contained during rainstorms. If the water level might rise higher than the levee, people stack bags of sand on the levee to make it taller. They also may break the levee at certain points to allow unpopulated areas to flood.

People build dikes to reclaim, or take back, land that is under water—for example, along the coast of a sea. First, engineers build a dike around the area to be reclaimed. The dike must be higher than the water level. Second, they pump out all the water from that area. The new area of dry land is called a polder.

Where levees are found

Levees are commonly found along rivers that can flood low-lying areas. Along the Mississippi River a system of levees, begun in the 18th century, protects low-lying farmland and cities. People in ancient Egypt built levees along the Nile River. Levees also protect the valleys around the Loire River in France and the Huang He in China.

Where dikes are found

A large part of The Netherlands used to be under the North Sea. From the 13th to the 20th century engineers built a series of dikes and dams along the sea. They created more than 2,500 square miles (6,470 square kilometers) of dry land for farms and growing towns. Dikes in Denmark, Germany, Poland, and Italy also have provided fertile land to farmers.