If we look at the history of mankind, we find many instances of great floods. The primitive man settled in the valleys that were close to rivers as it not only met his basic need for water but also made the land fertile after floods.
Now, the question arises — what is flood? Generally, when a river overflows its banks and water spreads out over the surrounding lands, a flood is said to have taken place. Floods can be terribly destructive. They often wash away the fertile top soil and may leave the land unfit for cultivation for years to follow or take a large toll of human and animal lives.
However, some floods are very useful to man. For example, the annual flooding of the Nile without which the great Egyptian civilization could not have existed. In fact, Egypt is called “The Gift of Nile”. From the beginning, the annual floods of the river were the basic mechanism of the economy and set the rhythm of life on river banks for the Egyptians.
But, what causes floods? Sometimes rainfall is unusually heavy and the river banks may not be able to contain it. Water from other streams or reservoirs also feed the rivers. Erosion of soil around river banks due to wanton deforestation also causes flood. Combined with all these factors, the river overflows. We also know that most of the rivers build up their natural banks by depositing heavy particles on its sides as they can’t be carried away by the river flow. These natural banks are called “levees”. One of the main causes of flood is the breaking of the so called “levees” due to heavy pressure of water.
There are several ways to control floods. One is to have levees or dikes to protect lowlands, where the river water tends to pile up. There must be some emergency channels, such as spillways or floodways to discharge out the excess water. Another method is to develop huge dams or reservoirs to hold back flood waters and release them in a regulated way. Another important method is the afforestations on the vicinity of river banks and embarkments to prevent soil erosion and also to make the river banks more compact.
