I.

Introduction

Mississippi (Algonquian Misi sipi, “big river”), river, central United States, one of the longest rivers of North America. The Mississippi River system is mainly within the United States, with the headwaters of the Missouri River, the main Mississippi tributary, extending into Canada. The Mississippi is exceeded in length by the Missouri and Mackenzie rivers, but it discharges a greater volume of water than any other river on the North American continent. It drains most of the country’s central plains between the Rocky and Appalachian mountains, an area of about 3,256,000 sq km (1,257,000 sq mi).

In addition to the Missouri, the Mississippi is fed by the Red, Arkansas, and Ohio rivers and by about 250 other tributaries. The total length of the Mississippi is 3,779 km (2,348 mi), and the total navigable length of all the rivers in the system is about 25,900 km (16,100 mi). The Mississippi-Missouri-Red Rock river system is approximately 5,970 km (3,710 mi) long, making it the fourth longest river system in the world.

II.

Human Development

Nicknamed Old Man River, the Mississippi emerged as a key transport and trade route when paddle-wheel steamboats became common in the late 1800s. Today river barges pushed by tugboats carry millions of tonnes of freight each year—mostly agricultural products, coal, steel, and petroleum. The principal cities on the river are Minneapolis, St Paul, La Crosse, Dubuque, Davenport, Keokuk, Quincy, Hannibal, St Louis, Memphis, Vicksburg, Baton Rouge, and New Orleans. At several cities the river is crossed by bridges.

III.

Headwaters to Missouri

The Mississippi rises in the area of Lake Itasca in north-western Minnesota, about 512 m (1,680 ft) above sea level. As it issues from Lake Itasca the Mississippi is about 3.7 m (12 ft) wide and 0.5 m (1.5 ft) deep. The upper course of the river is steep and at times obstructed by winter ice and fog. Steep bluffs of sandstone and limestone flank much of the river in this section. It flows north-east and then turns south near Grand Rapids, Minnesota. At Minneapolis, where it drops 20 m (65 ft) over the Falls of St Anthony, the river is more than 305 m (1,000 ft) wide. This point is the head of river navigation on the Mississippi. After receiving the waters of the Minnesota and St Croix rivers, the Mississippi becomes the boundary between the states of Minnesota, Iowa, Missouri, Arkansas, and Louisiana on the west, and Wisconsin, Illinois, Kentucky, Tennessee, and Mississippi on the east.

On the Wisconsin boundary the river expands into Lake Pepin, and thereafter, with a width of about 1.6 km (1 mi), flows between bluffs 61 and 91 m (200 and 300 ft) high. Around obstructions to navigation at Rock Island, Illinois, Keokuk, Iowa, and north of St Louis, Missouri, the US government has constructed dams and locks to accommodate the thousands of barges carrying bulk commodities up and down the river.

Devastating floods above Cape Girardeau, Missouri, extending as far north as Wisconsin, still occur every decade or so, most notably in 1937, 1965, 1973, 1983, and 1993. The floods inundate some river towns and cities, destroy millions of acres of crops, and halt commercial river traffic. The 1993 flood is estimated to have caused US$10 billion of damage.

IV.

Missouri to Louisiana

From the mouth of the Ohio River the Mississippi is about 1,370 m (4,500 ft) wide, but as it approaches the Red River, it narrows to about 910 m (3,000 ft), and at New Orleans, Louisiana, is 760 m (2,500 ft) wide. The depth of the channel south from the Ohio is between 15 and 30 m (50 and 100 ft). A system of storage reservoirs near the headwaters of the Mississippi and a series of flood-control dams along the river and its tributaries help maintain a relatively even flow of water.

From the Missouri to the Gulf of Mexico, the Mississippi meanders through vast alluvial plains that vary in width from 64 to 113 km (40 to 70 mi), forming oxbow lakes. Although of great fertility, these lands have not been fully cultivated because of the dangers of flooding. Melting ice and snow in the upper basin swell the lower current from March to June. Levees or embankments now extend for more than 2,575 km (1,600 mi). Many of them were built by the federal government after the flood of 1927—the largest recorded up to that time—when the river reached a maximum height at Cairo, Illinois, of 17.2 m (56.4 ft).

V.

Mouth of the Mississippi

Below the Red River, the Mississippi flows through numerous bayous into the Gulf of Mexico. The main channel of the river runs south-east and divides into a delta of several passes. The average discharge of the Mississippi into the gulf is nearly 19 million litres (4.2 million gallons) of water per second. The sediment carried is estimated at about 300 million cu m (10.6 billion cu ft) per year. To overcome the silting caused by these vast deposits and the constant changes caused by floods, a system of jetties at the South Pass was built, beginning in 1875, and has proved successful in maintaining a depth exceeding 9 m (30 ft). The mouth of the Mississippi is essentially tideless.