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Summary of "Reducing Coastal Flood Risk with a Lake Pontchartrain Barrier"

Core Content

This report evaluates the potential flood risk reduction benefits and induced damage effects of a proposed Lake Pontchartrain barrier in southeast Louisiana and coastal Mississippi. It is part of the RAND Corporation's research on coastal resilience and environmental policy, and was developed in collaboration with the engineering firm Arcadis. The research was funded by the Louisiana Coastal Protection and Restoration Authority (CPRA) and was designed to guide the selection of barrier configurations for the 2017 Coastal Master Plan.

The analysis uses the updated version of the Coastal Louisiana Risk Assessment (CLARA) model, which estimates flood risk based on storm surge and wave heights, flood depths, and economic damage. The study considers five proposed barrier configurations, each with different road and gate heights, and evaluates their impact on flood damage in both Louisiana and Mississippi.

Main Goals

• To assess the flood damage reduction benefits of a Lake Pontchartrain barrier.
• To estimate the potential induced damage effects on coastal Mississippi.
• To support the selection of a barrier configuration for the 2017 Coastal Master Plan.

Key Findings

Damage Reduction Benefits for Louisiana

• The Hwy90/10/10 and CSX/10/10 configurations provided the highest net damage reduction benefits.
• The Hwy90/0/2 configuration also produced significant damage reduction, with the lowest induced damage effects on neighboring areas.
• The median expected annual damage reduction for the best-performing configurations ranged from $1.2 billion to $1.4 billion per year.

Induced Damage Effects in Mississippi

• All barrier configurations increased flood damage in coastal Mississippi compared to a future without action.
• The induced damage was typically low, ranging from 1 to 2 percent of the total flood damage risk for the three Mississippi counties (Hancock, Harrison, and Jackson).
• The Hwy90/24.5/24.5 configuration resulted in the highest induced damage, with a projected increase of $84 million in expected annual damage.

Impact on Hurricane Protection Systems

• A barrier could reduce the design height requirements for the Greater New Orleans Hurricane and Storm Damage Risk Reduction System (HSDRRS) along the south shore of Lake Pontchartrain.
• However, it could also increase design heights on the eastern face of the system or require additional levee armoring in other locations.

Methodology

• The study used the CLARA model, which combines statistical storm sets with hydrodynamic simulations to estimate flood risk.
• The model was updated to reflect new data and assumptions, including sea level rise, land subsidence, and asset growth.
• The analysis included both Louisiana and Mississippi coastal areas, with a focus on the impact of the barrier on flood depths and economic damage.
• The CLARA 2.0 model was used to simulate flood conditions for a future scenario 50 years from now, considering different barrier alignments.

Data Sources and Assumptions

• The study incorporated asset inventory data for coastal Mississippi and Louisiana, including roads, buildings, and other infrastructure.
• It used storm surge and wave data from historical events and projected future conditions.
• The analysis assumed a 50-year future scenario, including sea level rise and land subsidence.
• The model also considered parametric and model uncertainties using Monte Carlo simulations and bootstrapping techniques.

Key Barrier Configurations

Conclusion

• The study supports the selection of a high-performing barrier alignment for inclusion in the 2017 Coastal Master Plan.
• The Hwy90/0/2 configuration was ultimately chosen by CPRA for implementation.
• The analysis highlights the importance of considering both benefits and disbenefits when evaluating coastal flood protection projects.
• It underscores the need for a comprehensive and integrated approach to coastal risk management, including the consideration of induced damage effects on neighboring regions.

Key Information

• The CLARA model is a key tool for estimating flood risk and damage.
• The Hwy90/0/2 configuration provides significant damage reduction with minimal induced damage.
• The 2017 Coastal Master Plan was informed by this analysis, which included both Louisiana and Mississippi coastal areas.
• The study was conducted in collaboration with Arcadis and Brown and Caldwell, and supported by the U.S. Army Corps of Engineers Mobile District.