Flooding in Bangladesh

Flooding in Bangladesh : 

Flooding in Bangladesh Objective: To understand the causes and effects of flooding in Bangladesh

Background : 

Background Two thirds of Bangladesh is less than 3 metres asl. Bangladesh is a located on the largest delta in the world, where the Ganges, Meghna & Brahamaputra rivers meet. It is a zone of distributaries and frequent floods, yet is home to 80% of Bangaldeshis.

Focus on the Ganges : 

Focus on the Ganges A long river – 2500km long Drainage basin = million sq km. Source is melt water from Himalayan glaciers. Highest levels meltwater = April – June Rainfall is variable – 6500mm (Upper Ganges – 2000m in delta region. 90% of rainfall occurs in July – October (Monsoon period) Variable & complex river regime – periods of low flow & extreme flood.

Politics make things difficult… : 

Politics make things difficult… An international drainage basin – headwaters originate in NW India, Bhutan, Nepal & Tibet. Flows into Bay of Bengal through Bangladesh. Disputes over right to water have taken place over last 2 decades

Water disputes : 

Water disputes Deforestation in Nepal & NW India – led to sedimentation of the river. Use of dams for HEP and irrigation e.g. Farraka dam in India, only 18km from border with Bangladesh

Population pressure : 

Population pressure Ganges basin = 0.12% of world’s land mass, but 10% of world’s population Population density in some areas exceeds 800 people per square km. 29 cities and 70 large towns along the river.

Flooding : 

Flooding Annual floods (barsha) are frequent, essential and desirable High magnitude floods (bonna) are destructive and cause millions of damage & serious loss of life High magnitude events forecast to be more frequent 120 million currently live there, forecast to reach 180 million by 2010

Causes of flooding – : 

Causes of flooding – Monsoon rainfall Synchronisation of flood peaks of 3 rivers Carrying capacity of river has fallen (sedimentation) Rising sea level (base level) & subsidence of the delta Urbanisation within the drainage basin

Managing flooding : 

Managing flooding Structural approaches Favoured by recent World Bank Scheme Flood Action Plan (FAP) requires tall embankments along rivers of delta, enormous drains and high value areas are compartmentalised by embankments Controlled flooding managed via intake from river and off takes through drains.

Concerns about the structural approach : 

Concerns about the structural approach Embankments cut river off from flood plain – prevents channel movement & sedimentaion – delta shrinks and subsides A 1 in 100 year flood could overtop embankments Silting would make embankments costly to maintain Takes up land needed for agriculture and prevents subsistence farmers from fishing

Other options – “non-structural” : 

Other options – “non-structural” Stream storage through dams, water retention basins Dredging of rivers – sediment could be used to help delta grow, capacity of rivers increased Improve preparedness – flood warning & shelters Improved river monitoring & measurement

The 2007 floods : 

The 2007 floods