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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 broader as it flows south. Its water level continually changes, too. All these changes make it difficult to keep the river safe for navigation and its shores safe for habitation. But over the years, engineers have devised dams, levees, and locks to control the mighty Mississippi.
▲ Levees
Levees are earthen embankments designed to contain, control, or divert water. 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. To make it possible for all kinds of vessels to travel on this section of the river, the U.S. Army Corps of Engineers has constructed a series of 29 locks and dams along its length.
▲ Dredging
Soil and debris are continually deposited in the river, clogging the waterway. To keep the river clear for shipping, it must be frequently dredged, or have its bottom dug up. Big barges equipped with giant shovel-like tools, huge suction devices, and other equipment are floated to the center of the river. 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, while levees and restraining walls hold back the rising water. Still, floods occur. 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.
