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
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