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Flowing over rapids and falls, the Mississippi River drops nearly 700 feet between its headwaters at Lake Itasca and the Twin Cities (Minneapolis and Saint Paul).
It keeps dropping until it reaches the Gulf of Mexico. The river also gets wider as it flows south. Its water level keeps changing, too. This makes it hard to keep the river safe for navigation. It also makes it hard to keep the shores safe for people to live there. But over the years, engineers have built dams, levees, and locks. These devices control the mighty Mississippi.
▲ Levees
Levees are banks made of earth. They are designed to contain, control, or turn water aside. They are built to protect areas from flooding. Levees must be able to withstand the force of fast-flowing water. The first levees were three-foot dikes built by French pioneers in 1718 to protect New Orleans. Today, some levees are more than 50 feet high.
Locks
The Upper Mississippi drops more than 400 feet from Minneapolis to St. Louis. The U.S. Army Corps of Engineers has constructed a series of 29 locks and dams between the two cities. They make it possible for all kinds of vessels to travel on this part of the river.
▲ Dredging
Soil and debris are continually deposited in the river. That clogs the waterway. To keep the river clear for shipping, it must be dredged often. Big barges are floated to the center of the river. These barges are equipped with giant shovel-like tools, huge suction devices, and other equipment. Sediment from the river bottom is sometimes blown through pipes back to shore. Then it is used to build levees to protect the shoreline from rising floodwaters.
▲ Flooding
In spring, melting snow and heavy rains send water into the Mississippi, sometimes causing floods. Flooding makes soil richer, but it can also cause damage. Dams on the Ohio and Missouri Rivers control how much water flows into the Mississippi. Levees and restraining walls contain rising water. Still, floods happen. In 1993, heavy rains in the upper Midwest caused the Mississippi and its tributaries to overflow. The result: $7 billion in property damage and $10 billion in crop loss.
