2018-埃贝耶海岸带风险评估技术报告（英文版）-17mb

Coastal Risk Assessment for Ebeye

Core Content

The Coastal Risk Assessment for Ebeye is a technical report commissioned by The World Bank as part of project 1230829-001. The report focuses on the two main islands of Ebeye and Majuro in the Republic of the Marshall Islands (RMI), which are part of an atoll archipelago in the central Pacific Ocean. These islands are characterized by low-lying topography and limited land area, making them highly vulnerable to coastal hazards such as extreme waves, storm surges, typhoons, and tsunamis, as well as the impacts of climate change and sea level rise (SLR).

Main Hazards and Impacts

Hazards Analyzed

• Extreme waves from both the ocean and lagoon sides
• Storm surges
• Typhoons
• Tsunamis

Key Findings

• Swell waves and typhoons are the main contributors to inundation and coastal erosion.
• Tsunamis are considered a minor source of hazard due to their limited impact on RMI.
• Sea level rise significantly increases the vulnerability of the islands, especially for low return periods (e.g., 5 years), with inundation areas expected to expand by 3–4 times by 2100 under the RCP 8.5 scenario.

Inundation Analysis

• For a 10-year return period, the percentage of the island inundated by more than 20 cm of water is expected to increase from 30.2% (current SLR = 0 m) to 78.2% (RCP 8.5, 2100).
• Current SLR scenarios show that the ocean side is more prone to inundation than the lagoon side.

Coastal Erosion

• Storm-induced erosion and coastal retreat due to SLR are assessed.
• Coastal retreat is projected to increase with sea level rise, depending on the rate of SLR and available accommodation space.

Risk Assessment and Adaptation

Risk Assessment Methodology

• Risk is defined as the product of hazard, exposure, and vulnerability.
• Exposure data includes property values and population distribution.
• Vulnerability is assessed based on the damage potential of assets and infrastructure in case of inundation.

Risk Assessment Results

• Higher risks are observed on the ocean side compared to the lagoon side.
• The risk assessment is used to identify priority areas for intervention, particularly those with high exposure and low topographic elevation.

Hotspots for Intervention

• Two hotspots are identified on the ocean side: one in the north and one in the central part of the island.
• These areas are selected due to combined high exposure and vulnerability.

Adaptation Options and Cost Estimates

Proposed Solutions

• Revetment is identified as the most suitable coastal protection measure.
• A berm in front of the revetment is recommended to increase flexibility and adaptability to future conditions.
• Four adaptation options are evaluated based on budget constraints and coverage.

Cost and Effectiveness

• Costs per linear meter range from $16,000 to $25,000, depending on the material used (e.g., single-layer cubes vs. rocks).
• Cost estimates for four options are provided, with the most effective solutions being those protecting hotspots directly.
• Cost-benefit analysis is performed, showing the reduction in Expected Annual Damages (EAD) and Expected Annual Asset Protection (EAAP) for each option.

Recommended Solution

• A continuous revetment covering the entire ocean side and the southern tip is recommended.
• This design is flexible and adaptable to future sea level rise and increased wave heights.
• The causeway is also considered for protection, although its effectiveness is lower than the revetment options.

Key Recommendations

• Further data collection is recommended to reduce uncertainties in the flooding maps and optimize design.
• The developed methodology can be used for long-term adaptive planning.
• The study emphasizes the importance of integrating hazard, exposure, and vulnerability in risk assessments.
• Adaptation measures should be cost-effective and flexible, especially given the high vulnerability and limited adaptive capacity of the islands.

Conclusion

• The RMI is highly vulnerable to coastal hazards, especially inundation and erosion.
• Sea level rise and climate change are expected to increase the frequency and severity of these hazards.
• The risk assessment provides a basis for identifying intervention priorities and designing effective coastal protection.
• The study recommends a revetment with berm as the most suitable solution, with cost estimates and effectiveness evaluated for different scenarios and locations.