Bangladesh River Floods: Causes, Impacts, and Mitigation (1998 Case Study)

Bangladesh River Flooding: 1998 Case Study

Geographical Context and Vulnerability

Bangladesh is formed by deposition from three major rivers: the Brahmaputra, the Ganges, and the Meghna. Sediment from these and over 50 other rivers forms one of the largest deltas in the world. Up to 80% of the country is located on this delta. As a result, much of the country is just a few meters above sea level and is highly vulnerable to flooding and rising sea levels.

Bangladesh is a densely populated country (an LEDC) with a high population growth rate (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.

Hydrological Characteristics

Total rainfall within the Brahmaputra, Ganges, and Meghna catchment is very high and highly seasonal, peaking between June and September (the monsoon season). The Ganges and the Brahmaputra carry significant snowmelt waters from the Himalayas. Peak discharges of these rivers are enormous, reaching up to 100,000 cubic meters per second (cumecs) in the Brahmaputra. The rivers carry vast quantities of sediment, which is deposited annually to form temporary islands and sandbanks.

Natural Causes of River Floods

Climatic Factors

• Intense Monsoon Rainfall

  High rainfall, such as that experienced in the first two weeks of June, often falls at a greater rate than the infiltration rate, resulting in significant overland flow.

• Cyclones and Storm Surges

  Cyclones originating in the Bay of Bengal often generate storm surges, causing severe coastal flooding.

Physical Geography

• Melting Glaciers (Himalayan Retreat)

  The Himalayan glacier is retreating at a rate of 8 meters per year. The source of the Brahmaputra River is fed by meltwater from this glacier, causing stream discharge to increase.

• Low-Lying Relief and Steep Terrain

  Bangladesh is predominantly low-lying land. Furthermore, due to the steep terrain of the valleys in the state of Uttarakhand (upstream), surface runoff travels downslope at a greater rate. This reduces water infiltration and increases the volume of water drained by the Brahmaputra, the Ganges, and the Meghna.

Human Causes Contributing to Flood Risk

Deforestation in the Indian Himalayas

Deforestation destabilizes slopes, significantly reducing interception and infiltration. It also leads to soil erosion, which increases the amount of sediment in the river. This sediment deposition reduces the river's hydraulic radius and efficiency, increasing flood risk downstream.

Dam Construction and Management

Approximately 70 completed dams are situated along the main rivers and their tributaries. Dams can cause changes in hydrology. Furthermore, dam operators often safeguard the infrastructure during periods of intense rainfall by releasing additional water upstream, exacerbating flooding downstream.

Urbanization and Floodplain Development

Poor local planning has allowed development to occur on the banks of the rivers and floodplains. This development is often driven by rising tourism (30 million tourists per year), with most visitors coming to see the temples. Rising tourism requires better infrastructure, which often involves creating more impermeable surfaces that increase surface runoff and flood risk.

Consequences and Impacts of the 1998 Flood

The 1998 flood was devastating, affecting 66% of Bangladesh. Key impacts included:

• Fatalities and Displacement: 4,750 people were killed, and 23 million people were made homeless.
• Economic Damage: 400 factories were closed, significantly impacting the economy.
• Infrastructure and Agriculture: 660,000 hectares of crops were damaged, and 1,000 schools were damaged or destroyed. Roadways were flooded in several locations.
• Social and Health Issues: Food and water shortages, spread of disease, loss of tourism, and unemployment.
• Environmental Impacts: Erosion leading to loss of land, landslides (due to deforestation), and the creation of environmental refugees.
• Governance and Aid: Lack of power/electricity and isolation meant limited aid or help reached affected communities.
• Long-Term Concerns: Climate change is making these events worse, potentially leading to international border conflict.

Benefits of Seasonal Flooding

While catastrophic floods are destructive, seasonal flooding provides several ecological and agricultural advantages:

• Replenishes groundwater reserves.
• Provides nutrient-rich sediment (silt/alluvium) essential for agriculture in the dry season, reducing the need for artificial fertilizers.
• Supports the fishing industry (fish supply 75% of dietary protein and account for over 10% of annual exports).
• Flushes pollutants and pathogens away from domestic areas.
• Creates jobs related to flood management and recovery.

Flood Mitigation and Solutions

Strategies implemented or proposed to manage flood risk include:

• Hard Engineering: Construction of levees (embankments).
• Soft Engineering: Afforestation (planting trees) to increase interception and infiltration.
• Infrastructure Management: Dredging rivers (though often hampered by government corruption).
• Community Resilience: Establishing flood shelters and improving community preparedness.