MEDC Natural Hazard Case Study :

Mississippi Floods (USA - 1993)

The Mississippi River is 3800km in length and flows through ten states of the USA. It has over 100 main tributaries, including the Missouri. Its drainage basin covers one third of the USA and also a small part of Canada. In an attempt to reduce the damage caused by flooding in major urban areas, the natural embankments or 'levees' which run alongside the river were strengthened and made higher. The levee at the city of St Louis is some 18km long and 16m high. Dams and storage reservoirs were also built. However they simply could not cope with the floods of 1993.

In April 1993, heavy rain had saturated the upper part of the Mississippi basin. Thunderstorms during June caused large amounts of surface run-off and flash flooding. During July, the severity of the storms increased and soon the Mississippi had reached an all-time high. Levees were put under immense strain and in many places they collapsed. In some rural areas, the river spread for 25km across the flood plain. A huge area, some 26 000km² was covered by water (see map).

The damage and cost was immense and wide-spread. Only one road bridge survived north of St Louis. The floods claimed a total of 43 lives and destroyed property. River traffic was brought to a stand-still. Even when the river levels began to fall, the problems did not stop. The ground was too wet for crops to grow, losing an estimated $2.5 billion in revenues. The contents of warehouses, houses and factories were ruined. The clearing-up operations went on for many months. Sewage washed into waterways increased the threat of disease. The overall damage was estimated at a staggering $12 billion.