Background information :
Within the USA 8% of the surface area is at risk of flooding and 35 million people live on flood plains which means that one sixth of floodplains in the USA are now urbanised however this has its problem every year between 47.6 and 89 people die due to flooding. This means that obviously the US government spends a considerable amount of money on flood defences $9000 is spent on flood control every year and $300 is spent on forecasting alone.
This brings me to my case study on the Mississippi floodplain; it is the fifth largest in the world and is 3,211,000 km2 in area. The river alone drains over 585 million tones of sediment per year. The Mississippi lies just above the Mississippi river delta in the gulf on Mexico and has many meanders; now like many floodplains it also has a large “corridor” of development down the bottom of the valley when urbanisation has occurred. Before this urbanisation had occurred the floodplains mainly consisted of fertile silt, which was deposited by heavy times of flooding.
Bellow is a diagram of he exact location of the Mississippi:
Cause of the flood in 1993:
Like many floods this flood was caused by large amounts of precipitation over a long period of time, in June and July of 1993 much of the area experienced over 150% of normal rainfall and parts of North Dakota, Kansas and Iowa (see diagram bellow) experienced more than double their normal rainfall.
On top of this individual storms frequently dumped large volumes of rain that could not be accommodated along with the other precipitation, the ground was already saturated not only by the previous rainfalls but during the previous year 1992 the weather conditions were considerably cooler which meant less evaporation and so there was less rainfall absorbed by the soils to start with.
There were changes in upper atmosphere wind flows, which caused more rainfall than usual, and the previous year the river system had been altered by the draining of the riverine wetland and construction of levees, which may have disrupted natural water cycles. Which was not help by the fact that there is the confluence of two large rivers at that point.
The other human causes are that unsuitable sites were developed on the floodplain, there was pressure on city space because of urbanisation and the levees were poorly built and not federally made.
Effects of the flood:
As a result of the floods a large amount of money has been spent on transforming 300 dams, storage reservoirs, diversion channels, floodwalls and artificial levees. There has subsequently been great economic loses to he region with property being damaged when flooded cars smashed and property floating away the worst hit by the economic losses have been des marines and Iowa.
As far as precaution, which have been taken levees, have been heightened and some meanders straightened, artificial levees have been reinforced with concrete. And when it comes to building on the floodplains there has now been regulation bought in concerning building improvements and risk assessments for public safety also there has been restrictions on the amount of building allowed in certain areas.
The has also been long term project set up in order to help such as the wet lands reserve project, where the floodplain is store floodwater, natural swamps, wet lands and agricultural land has been restored 600000 hectares so far.