Great Flood of 1993: The Mississippi and Missouri Rivers Overflow

The Great Flood of 1993 was one of the most damaging floods in United States history. From April to October 1993 the Mississippi and Missouri rivers and their tributaries rose again and again across nine Midwestern states, peaking in July and August. About 50 people died, tens of thousands lost their homes, and the damage, estimated at 15 to 20 billion US dollars, prompted a lasting shift away from relying on levees alone.

A wet year

The flood had its roots in the previous autumn. Heavy rain and snow in late 1992 and early 1993 left soils across the Upper Midwest saturated, and spring snowmelt filled the rivers. From June a stubborn weather pattern then parked a stationary front over the region, steering thunderstorm after thunderstorm across the same areas.

Between April and August, parts of Iowa, Missouri, Kansas, Minnesota and Illinois received two to three times their normal rainfall. Because the ground could absorb nothing more, almost every downpour ran straight into the rivers.

The rivers rise

Flooding began on the upper Mississippi in spring, but the worst came in July as the rivers crested one after another. At many gauges the water stayed above flood stage for weeks or months, far longer than in ordinary floods. Along stretches of the upper Mississippi and lower Missouri the peaks were the highest ever measured.

The flood control system was overwhelmed. More than 1,000 levees, most of them smaller agricultural levees built by local districts and farmers, failed or were overtopped. The large federal levees protecting cities generally held. The breaks flooded huge areas of farmland; estimates of the land affected range from about 6 to 8 million hectares (15 to 20 million acres).

Communities under water

Des Moines, Iowa, lost its water supply on 11 July when the Raccoon River flooded the city’s water works. About 250,000 people went without running water for nearly two weeks and without safe drinking water from the tap for longer.

At St. Louis the Mississippi crested on 1 August at 49.58 feet, a record. The city’s floodwall held, but the surrounding low-lying areas and suburbs were inundated. Nearby, the confluence of the Missouri, Illinois and Mississippi rivers spread into one vast lake.

Small towns suffered most. Grafton and Valmeyer in Illinois were largely submerged, and in July a levee break flooded Kaskaskia, an island town that was once Illinois’s first capital. Barge traffic on the Mississippi stopped for weeks, and flooded bridges, highways and rail lines cut transport links across the region.

The response

Thousands of National Guard troops, the US Army Corps of Engineers and volunteers from across the country filled and stacked sandbags. Many towns survived because emergency levees were raised just ahead of the crest; others lost the race.

Congress approved about 6 billion US dollars in emergency aid. The disaster also exposed the low take-up of flood insurance: many affected households had no cover under the National Flood Insurance Program.

A new approach: buyouts

The flood forced a debate about building on floodplains. In December 1993 Congress passed the Hazard Mitigation and Relocation Assistance Act, which raised the federal share of hazard mitigation grants and allowed the money to be used to buy flood-prone homes. Local governments then demolished the houses and kept the land as open space.

Thousands of properties in Missouri, Illinois, Iowa and other states were bought out in the following years. Valmeyer moved its entire town to higher ground on nearby bluffs. Some agricultural levees were not rebuilt, and parts of the floodplain were returned to wetlands.

In 1994 a White House committee led by Brigadier General Gerald Galloway published Sharing the Challenge, known as the Galloway Report. It argued that levees can encourage risky development and that floodplain management should combine structures, land-use planning, insurance and restored wetlands.

By the numbers

Timeline

• 1992, autumn: Heavy rain saturates soils across the Upper Midwest.
• 1993, April: Spring flooding begins on the upper Mississippi.
• 1993, June: A persistent weather pattern brings repeated heavy storms.
• 1993, 11 July: Floodwater knocks out the Des Moines water works.
• 1993, July: Levees fail along the Mississippi and Missouri, flooding towns including Kaskaskia.
• 1993, 1 August: The Mississippi reaches a record crest of 49.58 feet at St. Louis.
• 1993, December: Congress passes the Hazard Mitigation and Relocation Assistance Act.
• 1994: The Galloway Report calls for a broader approach to floodplain management.

Why it matters

The Great Flood of 1993 showed that even the extensive flood control works built along the Mississippi after the Great Mississippi Flood of 1927 could not hold back a truly exceptional season of rain. By pushing governments to buy out homes rather than simply rebuild levees, it changed American flood policy. Like Hurricane Andrew the year before, it also exposed how much the country’s disaster costs depend on where and how people build.