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AS Geography: River Environments - Bangladesh |
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Large scale Lower Catchment Management
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River Brahmaputra, Bangladesh
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Background
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Bangladesh lies in the lower floodplain and delta by three great rivers; Ganges, Brahmaputra, and Meghna. River Brahmaputra is 155 miles long and the river basin is between 200 to 400 miles wide. Each year the river is fed by snowmelt in the Himalayas and the summer monsoon rains reach their peak discharge in July-August. Usually 25% of Bangladesh is covered by up to 1 metre of water during this flood season. In most years this bring benefits for agriculture and fishing. However, some years the floods are more extensive and can have catastrophic consequences, destroying crops, damaging property and bringing disease and misery to millions of people.
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Causes of flooding
| Natural causes |
Human causes |
| Extremely heavy monsoon rainfalls between April and September |
Rapid growth in population.(2.5% increase per annum) This leads to lower infiltration rates |
| Melting snow in the high Himalayas during summer months |
Deforestation due to the greater demand for fuel, building material and land for agriculture. As a result, interception is reduced and run-off increases. Soil erosion results and the capacity of the river is reduced |
| Tectonic activity. Soil is loosened as is susceptible to erosion. Consequently, more soil and silt ends up in the rivers, leading to more flooding |
Urbanisation increases run-off due to the impermeable surfaces in populated areas. |
| Tropical cyclones over the Bay of Bengal in summer and autumn |
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Effects of last major flood:
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- Flooding often covers 80% of the land
- 7 million homes have been destroyed
- 25 million people made homeless
- 2379 people died
- 25% of the rice crop was destroyed
- Destruction of communication and infrastructure meant that it was impossible to deliver food and medical supplies.
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Possible solutions: Bangladesh Flood Action (FAP)
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- 5000 flood shelters built on stilts in areas most at risk
- Improved flood forecasting system using satellites and computer monitoring
- Construction of dams to control river flow and hold back monsoon rain water in reservoirs
- Complete and strengthen embankments along the main river channels to a height of up to 7 metres
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What are the costs and benefits of human intervention?
| Costs |
Benefits |
| Each dyke costs $5 million to build. It is expected that to build 3350 km of embankment will cost $10 billion. |
Impact of flooding reduced. Consequently the number of deaths should be reduced |
| All the work has to be done manually |
Water could be controlled and used for irrigation |
| Stone and bricks have to imported |
Reclaimed land could be used for agriculture. |
| High maintenance costs involved. $600 million will need to be spent each year to maintain the dykes. |
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D. Drake 2011
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