The Drainage Basin - Bangladesh

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Meghna, Ganges, Brahmaputra

The Drainage Basin

Extensive, covering much of Bangladesh, parts of India, Nepal and China. The Himalayas and Tibetan Plateau form the rivers’ watershed. The river Brahmaputra detours over a thousand kilometres as the river has not been able to cut a valley through the resistant rock of the Himalayas. The flood plain covers about 50% of Bangladesh’s land area. The river erodes material in its upper course in China, India and Nepal, carrying huge amounts of sediment to be deposited as the river slows crossing the floodplain and delta of Bangladesh. The river enters the Bay of Bengal through its distributaries in the delta.

How and why does the river flood ?

  1. MONSOON & SNOWMELT : along the delta, huge tidal waves can be whipped up in the storm conditions of the Monsoon season (May to October). These waves can reach 7 metres in height and therefore have very destructive effects. Islands in the delta such as Sandwip island house the very poorest of people in Bangladesh. They are forced to live on the stretches of land with greatest flood risk. They argue that no one in government is interested in protecting their land.
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  1. DEFORESTATION: some scientists argue that large scale clearance of forests in the Himalayas for firewood, furniture and sporting equipment for other countries is one cause. Forest clearance exposes the soil to rainsplash which loosens soil particles and surface run off.
  1. OVERFLOW: The increase in soil erosion adds to the silt / sediment load of the river. The rivers in Bangladesh carry 1600 tonnes of silt per kilometre. River’s channel fills with debris & there is less room for water which overflows.
  1. CHANNEL STRAIGHTENING / CANALISATION: increasing control of the river through concreted ...

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