GEOGRAPHY! (8 marks)
1* Building artificial levees or dykes
One of the ways to deal with repeated floods is to build artificial levees or dykes. These walls of sand, concrete and stone are built along the river banks which are prone to flooding, to increase the capacity of the river to hold water, thus reducing its chances of flooding. Prominent levee systems exist along the Mississippi River and Sacarmento River in the US
The Mississippi River levee system represents one of the largest of such systems in the world. They comprises over 5600km of levee extending some 1600km along the Mississippi, stretching from Cape Girardeau, Misouri to Mississippi Delta. This has helped to prevent floodings to the nearby country, New Orleans during heavy rains. Similarly in less developed parts of the region in chia, dykes have been built for centuries in the lower course of the yellow river to prevent flooding around the areas close to the yellow river.
However, these have not been very successful in preventing floods in china because of the constant deposition of sediment on river bed. The river bed become raised, making the river shallower. Over time, water levels rise higher than the dykes and overflow. Thus high dykes have to be built constantly.
2* Construction of dams
Another way of reducing flood is to control the amount of water flowing into the rivers through the construction of dams. The dam has gates to control how water is released from the man-made reservoir behind it. The reservoir increases the amount of water that the river can hold, thereby reducing the occurence of flood. For example, the Three Gorges Dam in china was constructed to overcome the frequent flooding of the Yangtze River. This help to protect the lives of people, farmland and property downstream of the Yangtze River. The Three Gorges Dam also helps to generate an estimated 84.6 kilowatts of electricity annually, which will benefit the country's economy. The use of hydroelectricity power also helps to gererate electricitiy thereby reducing environmental pollution.
However, the construction of dams can bring about its problem as well. For example, the construction of Aswan High Dam in Egypt has reulted in the loss of soil fertility since sediments and nutrients are now trapped in the reservoir the dam.
This cause the soil in areas along the lower course of the rivers to become less fertile, cities of the project also pointed out that more sediments will accumulate in the reservoir as the dam slows down the speed of water in the river. The build-up of sediments would raise the reservoir bed and cause unanticipated floods to occur in the future.
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