2014年-世界发展银行全球_Ganges_Strategic_Basin_Assessment___A_Discussion_of_Regional_Opportunities_and_Risks_140页_8mb

Ganges Strategic Basin Assessment Summary

Core Content

The Ganges Strategic Basin Assessment (Ganges SBA) is a comprehensive report by the World Bank South Asia Water Initiative (SAWI), aimed at analyzing the opportunities and risks of managing the Ganges River Basin. The report is based on an integrated analysis of hydrological, economic, and social aspects of the basin, with the goal of promoting regional cooperation and evidence-based decision-making.

The Ganges River Basin is the most populous in the world, with 655 million inhabitants, and plays a vital role in providing water for drinking, agriculture, hydropower, navigation, and ecosystem services across over 1 million square kilometers. However, the basin also faces significant challenges, including devastating floods and periodic droughts, which threaten development and livelihoods.

The report addresses ten fundamental questions about the future of water management in the basin, using nested hydrological and economic models to evaluate the potential and impacts of various infrastructure and management strategies.

Main Findings and Key Insights

1. Upstream Reservoir Storage Potential

• The Ganges Basin has many potential sites for large water storage infrastructure.
• However, due to the steep terrain and mountain gorges, the amount of water that can be stored behind even very high dams is limited.
• The total active storage from all examined dams would be only about 18% of the basin’s annual average flow, which is insufficient to meaningfully regulate the entire river system.
• The sediment management of such dams remains uncertain, and their impact on flood control is limited.

2. Flood Control via Upstream Storage

• Upstream storage is not effective in controlling basinwide flooding.
• The full active storage capacity (existing + proposed) is only 25-30% of average annual flows, which is too small to regulate the full system.
• Most floods in Nepal and Bihar are caused by localized rainfall, high flows in small tributaries, and embankment failures, not by overtopping of major tributaries.
• Even large dams like the Kosi High Dam would only modestly reduce flood peaks and not address the majority of flood events.

3. Low Flow Augmentation

• Upstream reservoirs could increase low flows in the dry months, particularly in the Ganges Delta.
• If all large dams were built, low flows could be doubled in the driest months.
• However, the economic value of this augmentation is uncertain due to low agricultural productivity and localized waterlogging.
• The benefits could be significant for ecosystem services, saline intrusion management, and navigation in the delta.

4. Alternatives to Reservoir Storage

• Groundwater is a viable and underutilized alternative to reservoir storage.
• The central and lower Ganges Basin has vast, untapped groundwater resources that can be sustainably used.
• Combining groundwater and surface water systems could provide equivalent or greater water supply benefits than dams, at lower costs and with less environmental and social impact.
• A conjunctive-use strategy could help manage soil waterlogging and improve water supply reliability for downstream users.

5. Hydropower Potential

• The Ganges Basin has substantial hydropower potential, especially in the Himalayan headwaters.
• Nepal alone has over 40,000 MW of economically feasible hydropower potential, with less than 2% currently developed.
• The 23 largest dams under consideration would have an installed capacity of 25,000 MW, generating 65-70 TWh of power annually.
• The net economic value of this potential is estimated at US$5 billion annually, which is significant compared to Nepal's GDP in 2011.
• However, large-scale hydropower development requires substantial capital, long timeframes, and effective sediment management.

Regional Opportunities and Risks

• Enhanced regional cooperation is essential for sustainable water management.
• The current approach to development is project-based and sector-specific, with limited system-wide analysis.
• Climate change poses significant risks, including increased flood and drought frequency, rising sea levels, and changing precipitation patterns.
• Social vulnerability is high in flood- and drought-affected areas, with poverty and population density playing a critical role.
• The economic trade-offs between water uses (hydropower, irrigation, flood control) are significant, especially in India-Nepal negotiations.

Methodology and Tools

• The report uses hydrological models (MIKE BASIN, SWAT) and economic optimization models to simulate various scenarios.
• Data was collected from public sources in Bangladesh, India, and Nepal, as well as global datasets.
• The models are calibrated and validated using historical data and field observations.
• The analysis includes social vulnerability, climate change impacts, and water quality assessments.

Conclusion

The Ganges SBA highlights the need for system-wide understanding and cooperative management of the basin. It challenges long-held beliefs about the role of reservoirs in flood control and emphasizes the potential of groundwater and other alternatives. The report underscores that while hydropower development offers significant benefits, it must be approached with careful consideration of sediment and seismic risks. The economic and environmental trade-offs must be clearly understood to guide future development and policy decisions in the region.