2015年-世界发展银行全球_Flood_Risk_Management_in_Dhaka___A_Case_for_Eco-Engineering_Approaches_and_Institutional_Reform_148页_7mb

Summary of Flood Risk Management in Dhaka

Core Content

This document presents an in-depth analysis of flood risk management in Greater Dhaka, Bangladesh, emphasizing the need for eco-engineering approaches and institutional reform to address the growing urban and river flood risks. It outlines the city's vulnerability to flooding due to its geographical location, rapid urbanization, and climate change, and highlights the historical and current public sector responses, institutional challenges, and the case for a more integrated and sustainable approach to managing flood risks.

Main Points

1. Flood Risk in Dhaka

• Dhaka is one of the largest and most densely populated cities in South Asia, with a population of around 17.5 million in 2015 and expected to grow beyond 20 million by 2025.
• The city is highly vulnerable to water-related hazards, including urban flooding and river flooding, due to its low elevation, dense population, and proximity to rivers.
• Major flood events have occurred in 1954, 1955, 1962, 1966, 1974, 1987, 1988, 1998, 2004, and 2009, with the 1998 floods causing $171 million in damages.
• Dhaka East and the DND (Dhaka-Narayanganj-Demra) area are particularly vulnerable under future climate scenarios, while Dhaka West continues to suffer from waterlogging and drainage congestion.
• Climate change is expected to intensify flood risks, and poverty exacerbates the impact of flooding on the city's most vulnerable populations.

2. Public Sector Responses

• Public sector efforts have historically been reactive, initiated in response to extreme flood events rather than being integrated into urban planning.
• Embankments in the DND area were built after the 1954–1955 floods, and western embankments were constructed due to the 1980s floods.
• These structures have encouraged settlement in low-lying areas despite inadequate drainage systems.
• There is limited connectivity between the city’s internal waterways and the outer river system, due to poor maintenance and infrastructure development.
• Structural measures (e.g., embankments, pumping stations) have dominated flood management, with less attention given to non-structural approaches like zoning, planning, and early warning systems.

3. Institutional and Organizational Challenges

• No integrated flood risk management plan exists for Dhaka.
• The Structure Plan (1995–2015) and the Detailed Area Plan (2010–2016) have been used for land use decisions but lack a comprehensive implementation strategy.
• RAJUK, the main planning authority, has enormous powers but limited accountability to the public, and its regulatory and development roles are conflicting.
• DNCC and DSCC (Dhaka North and South City Corporations) have limited capacity for planning and flood management, with insufficient human and technical resources.
• Union Parishads and cantonment boards manage non-municipal areas, but their capacity for flood risk management is also limited.
• There is no coordination between agencies, and institutional constraints hinder effective flood and urban resilience planning.

4. Case for Institutional Reform

• A revised Town Improvement Act and coordinated governance are needed to improve planning and service delivery.
• Integration of flood risk into urban planning is essential to ensure sustainable development.
• Institutional reforms should include accountability mechanisms, clear roles, and inter-agency coordination.
• RAJUK should be restructured to ensure transparency and public accountability.

5. Eco-Engineering and Green Defense Approaches

• The report advocates for eco-engineering as a complementary strategy to traditional flood control infrastructure.
• Eco-engineering includes restoring natural waterways, bioretention systems, buffer zones, and green spaces to enhance flood resilience and ecosystem services.
• Examples of eco-engineering approaches include:
  • Excavation and revitalization of natural khals (canals).
  • Construction of buffer zones along major rivers.
  • Use of low embankments to protect urban areas.
  • Bioretention swales in walkways to manage stormwater.
  • Rainwater harvesting and green space protection to maintain groundwater levels.

6. Recommendations

• Institutional and organizational reforms are needed to improve governance and coordination.
• Eco-engineering should be promoted as a key component of flood risk mitigation.
• Early warning systems and non-structural measures should be prioritized to support sustainable urban development.
• Public-private partnerships and inter-institutional cooperation are necessary to enhance flood resilience.

Key Information

• Population density: Dhaka has one of the highest population densities in the world, with 34,000 people per square kilometer.
• Economic importance: Dhaka contributes about 34% of Bangladesh's GDP.
• Groundwater decline: Dhaka's groundwater level is decreasing by 3 meters per year, leading to serious water shortages in the dry season.
• Flood vulnerability: The DND area is expected to be the most vulnerable under future climate scenarios.
• Eco-engineering case studies are presented in Appendix A, including bioretention swales, buffer zones, and natural khals.
• Institutional structure is detailed in Appendix B, and excavation of khals is discussed in Appendix C.

Conclusion

This study highlights the urgent need for institutional reform and eco-engineering to address the complex and growing flood risks in Greater Dhaka. It emphasizes that flood risk management should be integrated into urban planning, rather than being a reactive measure. The report also underscores the importance of non-structural flood mitigation and sustainable development to protect the city’s most vulnerable populations and ensure long-term resilience.