Unit 1 - Essays - Causes of River Floods

Question 1

With the aid of an example, assess the relative importance of the factors that caused a recent river flood event.

Answer 1

Main Body

1. Natural Causes: Rainfall and Snowmelt (Approx. 150 words)

Key Points:
Heavy monsoon rainfall (30% more than average) during the 1998 season.
The role of snowmelt from the Himalayas contributing to river overflow.
Large rivers like the Ganges and Brahmaputra overflowed, causing widespread flooding.
Development:
Explain the spatial and temporal impact of these natural factors on Bangladesh.
Use statistics (e.g., 68% of the country submerged).

2. Human Activities: Land Use and Urban Growth (Approx. 150 words)

Key Points:
Deforestation in the upper reaches of the river basin, especially in Nepal and India, increased runoff.
Unplanned urbanization in Bangladesh led to more impermeable surfaces, reducing water absorption.
Encroachment on wetlands worsened flooding.
Development:
Explain how these factors contributed to faster and more widespread flooding, particularly in cities like Dhaka.
Highlight specific examples of damage in urban areas (e.g., 1.5 million people affected in Dhaka).

3. Weak Flood Defenses and Poor River Management (Approx. 150 words)

Key Points:
Inadequate flood defenses, such as poorly maintained embankments and levees, failed during the flood.
Poor coordination with neighboring India regarding water release from upstream dams.
Development:
Explain the importance of both local and international cooperation for flood management.
Discuss how failed infrastructure and lack of regional planning worsened the situation.

4. High Population Density and Poverty (Approx. 150 words)

Key Points:
High population density in flood-prone areas increased vulnerability.
Widespread poverty made it difficult for people to recover from the floods.
30 million people affected, with significant economic and social consequences.
Development:
Explain how socio-economic factors exacerbated the impact of the flood, especially in urban and rural areas.
Discuss the implications of living in flood-prone areas without proper resources.

Conclusion (Approx. 50 words)

Summarize the key points: natural causes, human activities, poor infrastructure, and socio-economic factors.
Provide judgment on the relative importance: While natural factors triggered the flood, human activities and poor planning worsened the situation. Emphasize the need for better planning, infrastructure, and cooperation in managing flood risks.

Question 2

“Assess the view that rainfall intensity is the most important factor in causing a river to flood.”

Answer 2

Main Body:

1. Rainfall Intensity as the Primary Cause of Flooding

Example: Boscastle 2004 – discuss the 75mm of rain in two hours, leading to rapid flooding.
Mention the small catchment area and steep topography that made the area particularly vulnerable to heavy rainfall.
Explain how rainfall intensity directly contributed to the flash flood.
Point: Despite the intensity, human factors like poor infrastructure worsened the impacts.

2. Large-Scale Flooding and Prolonged Rainfall

Example: Pakistan 2010 – discuss the 200mm of rain in one day, leading to flooding in the Indus River basin.
Explain how the large scale of the river system meant rainfall had prolonged effects, flooding a large area and affecting millions.
Point: While rainfall was crucial, human factors (deforestation, poor infrastructure) intensified the flooding’s scale and duration.

3. The Impact of Geography and Land Use

Example: Bangladesh 1998 – discuss how 300mm of rain in a day overwhelmed the Ganges-Brahmaputra delta, leading to widespread flooding.
Highlight the flat terrain, poor drainage, and sedimentation that prevented the rivers from handling the excess water.
Point: Geography and land use were as important as rainfall intensity in determining the flood’s severity.

4. Comparing Spatial, Temporal, and Scale Variations

Compare smaller-scale events (like Boscastle) with larger-scale events (like Pakistan and Bangladesh).
Discuss how rainfall intensity impacts smaller catchments differently compared to large river systems.
Point: In small areas, rainfall intensity may be the most important factor, but in large areas, other factors (such as river management, topography, and land use) also play significant roles.

Conclusion

Summarize that while rainfall intensity is a key trigger for flooding, other factors like geography, land use, and river management are equally important in determining the scale and severity of floods.
Conclude that rainfall intensity is crucial but not the sole determinant.