BBHS - CASE STUDY - The causes and impacts of the 1993 Mississippi Flood

Mississippi - the Facts

  • The river basin is the fifth largest in the world

  • It is the third longest river in the world behind the Nile & the Amazon

  • The river discharges 584 million tonnes of sediment a year

  • The flood plain is 200km wide at its widest point

  • The Mississippi flows through 10 states

  • The river carries 13% of all freight traffic in the USA

  • Its main tributaries are the R. Ohio,  R. Kansas, R. Missouri & the Red River

The Causes of the 1993 Flood

  • Floods are normal in the mid-west - usually arriving in the spring when rain and snowmelt fill the streams & rivers that drain the upper Mississippi Basin

  • In 1993 as normal this happened - the soil was still saturated from spring rains. Normally this is followed by dry weather &has done so for the last 20 years

  • In 1993 Atmospheric conditions conspired to bring further torrential rains to the Mississippi Basin

 

a. A Jet stream swung South bringing Cool dry air
b. Warm air moved North causing Thunderstorms
c. Two high pressure systems developed blocking any movement of the thunderstorms
d. The rains continued throughout May, June and July.

 

  Human Causes of the 1993 Floods

  • Urbanisation of the Flood Plain - reducing infiltration rates etc

  • Poorly built non-federal levees

  • The development of unsuitable sites for development

  • The channelisation of the river - especially at St Louis

 The 1993 Flood Fact File

Primary Effects

  • 50 people died

  •  62,000 families were evacuated

  •  72,000 homes were flooded

  •  70% of levees were damaged

  •  55 towns were wrecked

  •  6 million acres of farmland was flooded

 

 Secondary Effects

  • River traffic halted for several months

  • Crop losses were put at $2.6 billion

  • Insurance pay-outs reached $12 billion in property alone

  • Stagnant water attracted mosquitoes and rats and there was a threat of disease

  • Electricity lines collapsed leaving many towns without power

 

Holding back the tide with sandbags

 Transport - Roads and Bridges affected

 

 

 Response to Flooding on the Mississippi

  • Dams & Reservoirs - 6 huge reservoirs have been built along the River Missouri to store excess water with a further 19 along the Tennessee River and its tributaries

  • Afforestation - The Tennessee Valley Authority has been increasing tree cover to delay run off into rivers

  • Levees - Have been strengthened with concrete mattresses to reduce erosion of the river banks

  • Diversionary Spillways - These are overflow channels which can store excess water in times of flood and release it after the risk of floods have passed

  • FEMA - The Federal Emergency Management Agency has published risk assessments and encourages at risk settlements to move off the flood plain

  • Flood Forecasting - The National Weather Authority are now responsible for flood warnings along the river

  • There are of course more - remember to look at your own case study notes