Causes and Consequences of River Flooding in Bangladesh: A Case Study

The Natural and Human Causes and Consequences of River Flood: Flooding in Bangladesh (LEDC) 1998

Bangladesh has been formed by deposition from three main rivers: the Brahmaputra, the Ganges, and the Meghan. The sediment from these and over 50 other rivers forms one of the largest deltas in the world, with up to 80% of the country located on the delta. As a result, much of the country is just a few meters above sea level and is under threat from flooding and rising sea levels. Bangladesh has a very dense population growth (nearly 2.7% per annum). Almost all of Bangladesh's rivers have their source outside of the country. For example, the drainage basin of the Ganges and Brahmaputra covers 1.75 million km2 and includes the Himalayas, the Tibetan Plateau, and much of northern India. Total rainfall within the Brahmaputra, Ganges, and Meghan catchment is very high and very seasonal, occurring between June and September. The Ganges and the Brahmaputra carry snowmelt waters from the Himalayas. Peak discharges of the rivers are enormous, reaching up to 100,000 cumecs in the Brahmaputra. The rivers also carry vast quantities of sediment, which is deposited annually to form temporary islands and sandbanks.

Natural Causes

• Intense Monsoon Rain: High rainfall in the first two weeks of June. The high-intensity rainfall fell at a greater rate than the infiltration rate, resulting in a great overland flow.
• Cyclones in Bay of Bangladesh/Storm Surges: Causes coastal flooding.
• Melting Glacier: Himalayan glacier is retreating at a rate of 8m per year. The source of the river Brahmaputra is fed by melt-water from the glacier, causing stream discharge to increase.
• Relief: Low lying land. Due to the steep terrain of the valleys in the state of Uttarakhand, surface runoff travels downslope at a greater rate, resulting in less water being infiltrated and more water being drained by the Brahmaputra, the Ganges, and the Meghan.

Human Causes

• Deforestation of Indian Himalayas: Deforestation destabilizes slopes, reducing interception and infiltration. It also leads to soil erosion, which increases the amount of sediment in the river and reduces its hydraulic radius or efficiency.
• Dam Construction: 70 completed dams situated along the main rivers. Dams can cause changes in hydrology, and dam operators often release additional water upstream during periods of intense rainfall to safeguard the infrastructure of dams.
• Building on the Floodplain: Poor local planning. Development has occurred on the banks of the rivers as tourism to the region has risen (30 million tourists/year). Most tourists visit Bangladesh to see the temples. Rising tourism requires better infrastructure, which brings more impermeable surfaces that increase flood risk.

Advantages of Flooding

• Replenish groundwater reserves
• Provide nutrient-rich sediment for agriculture in the dry season
• Provide fish earnings (fish supply 75% of dietary protein and over 10% of annual exports)
• Reduce the need for artificial fertilizers
• Flush pollutants and pathogens away from domestic areas
• Silt/Alluvium
• Create jobs

Consequences + Impacts

• 4750 people were killed
• 66% of Bangladesh was flooded
• 23 million people were made homeless
• 660,000 ha of crops were damaged
• 400 factories were closed, impacting the economy
• 1000 schools were damaged and destroyed
• Climate change is making things worse
• No power/electricity
• No aids or help, resulting in an isolated community
• Roadways were flooded in several locations
• Food and water shortages
• Erosion and loss of land
• Environmental refugees
• Landslides due to deforestation
• Spread of disease
• Loss of tourism
• Unemployment
• International border conflict

Solutions

• Dredging (Government Corruption)
• Community preparedness
• Flood shelters
• Levees (soft engineering)
• Afforestation