Flood is a natural disaster that strikes mankind from time to time. When a river overflows its banks and water spreads out over the surrounding lands, it is known as ‘flood’. Floods can be terribly destructive. It washes away the fertile topsoil and can leave the land unfit for cultivation for years to follow. Floods take a large toll of human and animal lives. 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. Strange as it may seem, sometimes, floods are beneficial to man. For example, it was the annual flooding of the Nile due to which the great Egyptian civilisation came about. Egypt is known as the ‘Gift of Nile’, because the annual floods of the river were the basic mechanism of the economy and set the rhythm of life on riverbanks for the Egyptians. What causes floods? Sometimes rainfall is unusually heavy and the riverbanks may not be able to contain it. Water from other streams or reservoirs also feed the rivers. Erosion of soil around riverbanks due to wanton deforestation also causes flood. When all these factors come together, the river begins to overflow. Most of the rivers build up their natural banks by depositing heavy particles on its sides as they cannot carried away by the flowing river. These natural banks are called ‘levees’ and 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. Emergency channels such as, spillways or flood ways, should be constructed to discharge the excess water. Developing huge dams or reservoirs to hold back flood waters and release them in a regulated way also helps in preventing floods. Another important method to control floods is the afforestation of the vicinity of river banks and embankments to prevent soil erosion. This would also make the river banks more compact.
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