This report describes the results of an evaluation of the potential benefits for coastal Louisiana from a barrier across the mouth of Lake Pontchartrain. Conducted in advance of Louisiana's 2017 Coastal Master Plan, it includes estimates of the reduction in storm surge and wave heights, flood depths, and economic damage with proposed barrier options in place. It also estimates potential induced economic damage in neighboring areas.

Cover: Reducing Coastal Flood Risk with a Lake Pontchartrain Barrier
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Reducing Coastal Flood Risk with a Lake Pontchartrain Barrier

by Jordan R. Fischbach, David R. Johnson, Edmundo Molina-Perez

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Research Questions

  1. What would be the flooding and damage with or without barrier alignment options in place?
  2. What are the potential benefits for coastal Louisiana from a barrier across the mouth of Lake Pontchartrain, including storm surge and wave heights, flood depth, and direct economic damage reduction from different barrier options in one future scenario reflecting sea level rise and coastal land subsidence conditions 50 years from today?
  3. What is the potential induced economic damage from the proposed barrier options to Hancock, Harrison, and Jackson Counties in Mississippi, as well as to Saint Bernard and Plaquemines Parishes in Louisiana?

This report describes the results of an evaluation conducted in advance of analysis supporting Louisiana's 2017 Coastal Master Plan. It includes estimates of the potential benefits for coastal Louisiana from a barrier across the mouth of Lake Pontchartrain, including reduced storm surge and wave heights, flood depths, and direct economic damage. The analysis compared five different barrier options in one future scenario reflecting sea level rise and coastal land subsidence conditions 50 years from today. It also includes new estimates of the potential induced economic damage from the proposed barrier options to Hancock, Harrison, and Jackson Counties in Mississippi, as well as to St. Bernard and Plaquemines Parishes in Louisiana.

Results show that a Lake Pontchartrain barrier could provide substantial damage reduction benefits for southeastern Louisiana, with median expected annual damage reduction benefits ranging from $1.2 billion to $1.4 billion per year. All barrier alignments considered increased flood damage in coastal Mississippi compared with a future without action, but damage inducement was typically low for the best-performing alignment options compared with total flood damage risk for the three Mississippi coastal counties. A barrier option that includes Highway 90 with its current crown and 2-ft. gates produces damage reduction nearly as high as alignments with higher crowns and higher gates, with the lowest induced damage effects on neighboring Louisiana parishes and Mississippi coastal counties. CPRA included the alignment as part of the formal 2017 assessment and ultimately selected this project for implementation as part of the final 2017 Coastal Master Plan.

Key Findings

A Barrier Could Substantially Reduce Damage in Southeastern Louisiana

  • A Lake Pontchartrain barrier could provide substantial damage reduction benefits for southeastern Louisiana, with median expected annual damage reduction benefits ranging from $1.2 billion to $1.4 billion per year.
  • A barrier could also lower future design height requirements for the Greater New Orleans hurricane protection system along the south shore of Lake Pontchartrain, although it could also increase design heights for the eastern face of the system or otherwise necessitate additional levee armoring in other locations.

A Barrier Could Somewhat Increase Damage Along the Mississippi Gulf Coast

  • All barrier alignments considered increased flood damage in coastal Mississippi compared with a future without action but at a level several orders of magnitude lower than the damage reduction benefits estimated for southeastern Louisiana.
  • Damage inducement was typically low for the best-performing alignment options compared with total flood damage risk for the three Mississippi coastal counties, with total damage increases ranging from 1 to 2 percent.

Overall, a Low Barrier Provides the Best Balance of Benefits and Induced Damage

  • A barrier option that includes Highway 90 with its current crown and 2-ft. gates yields median expected annual damage reduction of $1.2 billion, nearly as high as alignments with higher crowns and higher gates.
  • The low barrier also yields the least induced damage for coastal Mississippi, approximately $22 million in total across all three counties (1-percent increase).

Recommendation

  • Move the low barrier option forward for formal consideration as part of the 2017 Coastal Master Plan analysis.

Table of Contents

  • Chapter One

    Introduction

  • Chapter Two

    Methods and Data Sources

  • Chapter Three

    Results from Proposed Barrier Alignments

  • Chapter Four

    Discussion and Next Steps

The research reported here was funded by the Coastal Protection and Restoration Authority (CPRA) of Louisiana and conducted by the Infrastructure Resilience and Environmental Policy Program within RAND Justice, Infrastructure, and Environment.

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