Bangladesh (LEDC)

Flooding is a natural phenomenon in Bangladesh and occurs on an annual basis.  The rivers are huge by global standards, and can inundate over 30% of the land mass at a time.   The notes below should help you to understand the causes and consequences of flooding in Bangladesh.

Bangladesh is prone to serious and chronic flooding.  Even in an average year 18% of the landmass is inundated and previous floods have affected 75% of the country (as in 1988).  75% of the country is below 10m above sea level and 80% is classified as floodplain as Bangladesh is principally the delta region of South Asia’s great rivers. 

Bangladesh floods on a regular basis, RECENT notable and catastrophic floods have occurred in 1988 (return period of 1 in every 50 to 100 years), 1998, 2004, 2007 and 2010.

Causes of flooding in Bangladesh:

1.     Tectonic uplift of the Himalayas means that erosion rates of sediment increase as the rivers have more potential for erosion.  This mass of sediment is dumped in Bangladesh choking the river channels making them more inefficient and reducing hydraulic radius.  Sediment is dumped and flooding can occur.

2.     Monsoon rainfall – some parts of the Ganges basin receive 500mm of rainfall in a day during the monsoon.

3.     Deforestation of the Himalaya – reducing interception rates which means shorter lag time and higher peak discharges.

4.     Three massive rivers converge in Bangladesh – the Ganges, Brahmaputra and Meghna – massively swells discharges.

5.     Cyclones from the Bay of Bengal cause and contribute to coastal flooding.

6. Snow melt affects the rivers too, as ice and snow melting from glaciers and mountain peaks in the Himalaya works its way into rivers.

7. The Himalaya also forces relief or orographic rainfall, increasing rainfall totals and then river levels further.

Effects:

Erosion of chars (islands) by flooding rivers causes landlessness amongst Bangladesh’s poor; these people end up in major cities such as Chittagong and Dhaka.

Death – over 200,000 people died in a cyclone and flood in the 1970s.

Loss of agricultural land – a major problem in a country with high natural increase.

2004 Floods

The 2004 floods lasted from July to September and covered 50% of the country at their peak. At the time of the July 2004 floods 40% of the capital, Dhaka was under water. 600 deaths were reported and 30million people were homeless. 100,000 people alone in Dhaka suffered from diarrhoea from the flood waters. Bridges were destroyed, the death toll rose to 750 and the airport and major roads were flooded. This hampered relief efforts. The damage to schools and hospitals was estimated at $7billion. Rural areas also suffered, the rice crop was devastated as were important cash crops such as jute and sugar.

2007 Floods

In 2007 major flooding occurred across wider South Asia, affecting not only Bangladesh but parts of India, Bhutan and Pakistan.

In September 2007 (June the 30^th to 15^th of August)heavy rain and rivers carrying water from upstream exacerbated flooding

Impacts

1.       The monsoon flooding killed over 1,100 people in Bangladesh (source), and according to Forbes over 2000 people were killed across the South Asia region.

2.       2.2 million acres of damaged cropland

3.       At least 10.5 million people were estimated to have been displaced or marooned by the floods.  30 million across the whole South Asia region

4.       The main highway connecting Dhaka to the rest of the country was flooded isolating the capital

5.       The Brahmaputra and Ganges rivers, both which rise in the Himalaya, caused the floods by rising in Bangladesh at the same time. They disgorged water from seasonal wet monsoon rains and melting glaciers and snow in the Himalaya.  The Bangladesh flood centre said that the rivers were well above danger levels

6.       The Bangladeshi health Department said that the deaths were caused by Diarrhoea, drowning, landslides, snakebites and respiratory diseases.

7.       46 of the country’s 64 districts were flooded in this flood event

8.       The Flood Forecasting and Warning Centre (FFWC) said that conditions in the South Central part of the country continued to deteriorate 12 days after the onset of flooding

9.       By 11 August, the number of people with flood-related diseases was increasing  and about 100,000 people had caught dysentery or diarrhoea (source)

10.   Rice crops were devastated TWICE that year so farmers did not have time to recover their losses and replant

11.   $150 million of aid was sought by Bangladesh and Saudi Arabia pledged $50 million and 5 planes worth of food and medicine

12.   $290 million of crops were damaged in the initial floods

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Solutions

Flood action plan – a system of huge embankments along the coast and rivers reinforced by concrete.  They increase channel capacity and hydraulic radius but stop floods replenishing fields with nutrients and can stop rainwater escaping into fields. It also causes erosion downstream of the defences and prevents deposition.

Improved drainage canals – the clearing of old canals had allowed a more efficient drainage system allowing water to drain away more efficiently.

SPARSO and flood satellite imaging systems – allow more warning to be given to Bangladeshis by monitoring cloud cover, hydrographs and rainfall patterns across the river basins.

Sea level change:

If sea levels rise Eustatically and Bangladesh sinks Isostatically because of the loading of sediment on the delta there will be major impacts on the people of Bangladesh. A 1.5m rise in sea level would affect 17 million people and 22000km2 of land (16%).  Major fishing villages will be affected and agricultural land and rice paddies will suffer the effects of salinisation.  Coastal cities such as Chittagong face inundation and ever greater threats from cyclones (hurricanes) (3,000people died in a cyclone on 16^th November 2007).

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