Coastal Louisiana Risk Assessment Model

Technical Description and 2012 Coastal Master Plan Analysis Results

by Jordan R. Fischbach, David R. Johnson, David S. Ortiz, Benjamin P. Bryant, Matthew Hoover, Jordan Ostwald

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Appendix

Flood Depth Results From the Final 2012 Master Plan Analysis

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Research Questions

  1. How is the Coastal Louisiana Risk Assessment (CLARA) model structured?
  2. What are CLARA's inputs and outputs?
  3. How was CLARA used to support the development of Louisiana's 2012 Coastal Master Plan?
  4. How does Louisiana's 2012 Coastal Master Plan help to reduce storm surge flood damage over the next fifty years?

Abstract

Motivated by the devastating effects of Hurricanes Katrina and Rita in 2005 and Gustav and Ike in 2008, planners and policymakers in the State of Louisiana have updated the state's Comprehensive Master Plan for a Sustainable Coast (the "Master Plan"). The resulting Master Plan proposes a range of risk reduction and coastal restoration projects to reduce storm surge flood risks to coastal communities and address other objectives to help create a more sustainable coast over the next 50 years. To support this process, the Coastal Protection and Restoration Authority of Louisiana asked RAND to create an analytical model, the Coastal Louisiana Risk Assessment (CLARA) model, to estimate flood depths and damage that occurs as a result of major storms. CLARA made it possible to systematically evaluate potential projects for inclusion in the Master Plan on the basis of how well they reduce flood damage in Louisiana's coastal region. CLARA was also used to evaluate the flood damage reduction provided by the final Master Plan. Results from this analysis show that storm surge flood damage represents a major threat to coastal Louisiana and that, if no action is taken, this damage can be expected to grow substantially in the future. Implementing the Master Plan, however, could substantially reduce future damage. For instance, average annual damage is projected to increase to between $7 billion and $21 billion per year by 2061 in a future without action, but, with the Master Plan in place, this damage level is reduced to between $3 billion and $5 billion.

Key Findings

The Coastal Louisiana Risk Assessment (CLARA) Model Is Based on the Principles of Quantitative Risk Analysis

  • The risk is the product of the annual likelihood of storm surge flooding at different depths and the damage that results from this flooding.
  • Likelihood is divided into the threat, which represents the probability that a surge-producing storm will occur, and the vulnerability of the hurricane protection infrastructure.
  • The model simulates consequences for a "future without action" and a "future with the final Master Plan in place" in 2012, 2036, and 2061, for three scenarios that reflect different assumptions about future rates of sea-level rise and coastal subsidence.

CLARA Uses Several Types of Information to Estimate Flood Depths and Resulting Damage

  • Estimated surge and wave heights from 40 simulated storms across the Louisiana coast selected to best represent the range of possible coastal flooding threats.
  • Data that characterize the hurricane protection system.
  • An inventory of economic assets on the Louisiana coast, updated with information from the 2010 U.S. census.

CLARA Helped Louisiana Compare and Rank Projects for Inclusion in Its Master Plan

  • The results show that, if no action is taken, flood damage can be expected to grow substantially in the future.
  • The Master Plan can reduce flood damage in many areas of the coast through a combination of structural and nonstructural risk reduction investments and coastal restoration projects.
  • Damage reduction is notable across all scenarios considered.

Table of Contents

  • Chapter One

    Introduction

  • Chapter Two

    Overview of CLARA

  • Chapter Three

    Measuring Hurricane Hazard and Flood Recurrence

  • Chapter Four

    Calculating Surge and Wave Overtopping

  • Chapter Five

    Estimating Protection System Fragility

  • Chapter Six

    Calculating Interior Drainage in Protected Areas

  • Chapter Seven

    Assessing Economic Value, Growth, and Flood Damage

  • Chapter Eight

    Uncertainty in CLARA

  • Chapter Nine

    Supporting Master Plan Development with CLARA

  • Chapter Ten

    Results from the Final Master Plan Analysis

  • Chapter Eleven

    Conclusion

This research was sponsored by the Coastal Protection and Restoration Authority of the State of Louisiana and was conducted in the RAND Gulf States Policy Institute and the Environment, Energy, and Economic Development Program within RAND Infrastructure, Safety, and Environment.

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