Background: |
Billed as the 'Great flood of 1993', this flood was the worst natural disaster in the United States since the Mississippi flooded in 1927. Heavy snowfall over the winter of 1992/3, coupled with a prolonged wet spring and early summer contributed to extremely high discharge in the Mississippi River, which burst its banks flooding an estimated 30,000 square miles.
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Physical Causes of the flood
- Heavy rainfall dumped between 400-750% above the monthly average precipitation in early-mid 1993 in the Upper Midwest USA contributed to water levels in the river being record-breakingly high.
- This followed extremely heavy snowfall during the previous winter, which when melting, added to the rainfall run off entering the river systems.
- A jet stream of cold air moved south whilst warm air from the south moved north, where they met, thunderstorms occured, and a high-pressure system developed blocking these thunderstorms from dissipating properly. They therefore continued through May, June and July.
Human causes of the flood
- Development of many urban areas along the river, reduced infiltration and increased the risk of damage done to buildings.
- Channelisation of the river in places like St Louis exaggerated problems further downstream.
- Many of the levees along the river were poorly built, and were breached easily, especially away from major settlements.
- One man, James Scott was imprisoned for life for causing a catastrophe, for his role in flooding of Quincy, Illinois after he removed sandbags from a levee which broke later that day, flooding 57 square kilometers of farmland.
Political Impacts
- Death toll - 50
- 72,000 homes flooded
- 62,000 families evacuated
- National Weather Service forced to improve their river forecasting systems, by upgrading their computer software and collecting more river data to bring more accurate forecast models in future.
Economic impacts
- Some locations along the river were flooded for between 100 and 200 days.
- As a major freight artery in the USA, the river could not be used for freight whilst it was flooded, at a loss of an estimated $2 million per day.
- $2.6 billion in crop losses.
- Insurance payouts for property losses alone stood at an estimated $12 billion.
- Over 1000 levees failed and had to be rebuilt and strengthened.
- Two whole towns: Valmeyer and Rhineland were completely destroyed and relocated to higher ground.
Environmental Impacts
- Stagnant floodwater increased the risk of water-bourne diseases.
- 700 privately built agricultural levees were destroyed.
- 15 million acres of farmland flooded overall.
- Billions of pounds of eroded materials deposited as flood waters receded.
Responses
In response to the flood of 1993, various strategies were put in place to reduce the severity of the effects of any future flood of similar size. Note that many were expensive strategies that could be afforded by one of the world's richest nations:
- Afforestation in many areas in an attempt to reduce surface run-off by increasing infiltration, most promenantly in the Tennessee Valley.
- Many levees were replaced with concrete buttresses to reduce erosion and strengthen them.
- The Federal Emergency Management authority published flood risk assessments and encouraged those settlements at risk to relocate.
- Diversionary spillways were built to hold excess water during floods and then release it at a later date when flood waters recede.
- 6 new reservoirs on the Missouri river and 19 on the Tennessee River to hold excess flood water.
Five key points
- Death Toll of 50, a low death toll for such a severe flood, a common feature of disasters in MEDC countries, compared to over 1000 in a similar sized flood in Bangladesh
- Insurance payout reached over $12 billion, again compared to an LEDC flood, there were the resources to effectively and efficiently rebuilt destroyed areas
- Described as the great flood, or the five hundred year flood, an event this large and devastating is incredibly rare
- 30,000 square miles flooded.
- Was caused by a combination of rare and unfortunate atmospheric events that allowed storms to become 'trapped', which resulted in prolonged periods of torrential rain.