Earth Hazards: Coastal and River flooding KQ2

River Case Study 

Bangladesh (1998)

Between July-September 1998, Bangladesh suffered one of its worse ever floods.

Physical Factors causing flooding:

Height- 70% of its land area being less than 1m above sea level and 80% of it being floodplain.

Relief-  Bangladesh is a very low-lying country, monsoons over highlands. 

Drainage- Bangladesh receives large amounts of water from the Ganges and Brahmaputra which converge and form a Delta from silt deposited as it enters the sea.  Both rivers have large volumes of water flowing through them to the sea as they have large drainage basins which increasing the flood risk.

Climate- Bangladesh has a monsoon climate and the annual torrential rains. In the spring, melting snow from the Himalayas further increases the flood risks.

Vegetation- lack of vegetation (human deforestation)  in the headwaters increased soil erosion which led to silt being washed into the rivers and being deposited on the river bed, reducing channel capacity and increasing the likelihood of flooding.

Rock Type- Impermeable rock (run off Ganges).

Human Factors involved:

Settlement building- Increasing population pressure in the foothills of the Himalayas where the rain contributes to the source of the River Ganges and Brahmaputra has resulted in intense deforestation. reduction in interception has resulted in more water entering the rivers - indeed with 92%. 

Increasing population pressure in Bangladesh itself has resulted in the sinking of many new wells resulting in the lowering of the water table and the subsequent subsidence of land

Farming-  Dependancy of river for farming meant populated around, increased run-off. 

Deforestation- deforestation in the headwaters is also believed to be responsible for the increased soil erosion which has led to large amount of silt being washed into the rivers and subsequently being deposited on the river bed, reducing its channel capacity 

Drainage- Concreate causing surface run-off.

Resulting Impacts

Environmental-

 water for crops

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