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Southwest Coastal Louisiana, Coastal Storm Damage Risk Reduction/Ecosystem Restoration, 30 March 2016

ABSTRACT:  The project would provide nonstructural hurricane and storm surge damage risk reduction and ecosystem restoration across 4,700 square miles in Calcasieu, Cameron, and Vermilion Parishes along the southwest coast of Louisiana.  The non-federal sponsor is the Coastal Protection and Restoration Authority Board of Louisiana (CPRAB).

The people, economy, environment, and cultural heritage of coastal areas in Southwest Louisiana are at risk from damages caused by hurricane storm surge flooding. Southwest coastal Louisiana’s topography and  low elevation, proximity to the Gulf of Mexico, subsiding lands, and rising seas are all contributing factors  which cause coastal flooding, shoreline erosion, saltwater intrusion, and loss of wetland and Chenier (forested ridges) habitats.  These conditions are expected to continue to worsen.

The Recommended Plan consists of a National Economic Development (NED) Plan and a National Ecosystem Restoration (NER) Plan.  Neither plan would have significant adverse effects, and no mitigation measures are required.

NED PlanNational Economic Development (NED) Plan.  Planning to address hurricane storm surge risk reduction was primarily focused on communities and areas located north of the Gulf Intracoastal Waterway, but measures for all at-risk structures both inside and outside of the coastal zone were considered.  Evaluation of the focused array of nonstructural and six structural levee alternatives determined that the most cost-effective solution to reduce hurricane storm surge risk within the study area is through nonstructural measures. The NED Plan would provide hurricane storm surge risk reduction for all economically justified structures in the study area with a first-floor elevation at or below the 25-year stage based on predicted year 2025 hydrologic conditions.  The NED Plan reduces the risk of hurricane storm surge damage for a total of 3,961 structures.  The plan is completely voluntary and is comprised of raising 3,462 residential structures, flood-proofing 342 public buildings and commercial structures, and construction of localized storm surge risk reduction features around 157 warehouses.

Based on October 2015 price levels, the estimated first cost of the NED Plan is $906,091,000.  The Federal share would be $588,959,000 (65 percent), and the non-Federal share would be $317,132,000 (35 percent).  The cost of lands, easements, rights-of-way, and relocations is estimated at $61,970,000.  OMRR&R by the non-federal sponsor is estimated at $5,000 per year.  At a 3.125-percent discount rate and a 50-year period of analysis, the total equivalent average annual costs of the NED Plan are estimated to be $36,056,000.  The Recommended Plan is estimated to reduce average annual flood damages by about 93 percent.  The equivalent average annual benefits are estimated at $203,554,000, with net benefits of $167,498,000.  The benefit-cost ratio is approximately 5.65 to 1.

NER Plan WestNational Ecosystem Restoration (NER) Plan.  Planning measures for ecosystem restoration concentrated exclusively within the coastal zone.  Alternative plans were created by combining measure types into comprehensive strategies.  The measures include hydrologic and salinity control, marsh restoration, shoreline protection, and chenier reforestation.  The NER plan formulation evaluated the focused array containing a “No Action” alternative and 27 other plans that were based on 8 restoration strategies.  Benefits in the Calcasieu-Sabine Basin were considered separately from the Mermentau/Teche-Vermilion Basin.  Benefits were also considered jointly as comprehensive plans (covering both basins).  Alternatives were evaluated for cost effectiveness and incremental costs.

The Recommended NER Plan, also known as NER Plan CM-4, would restore coastal habitats at 49 locations, providing benefits in two estuaries.  The NER Plan is the least-cost, cost-effective, comprehensive ecosystem restoration plan that addresses land loss and ecosystem degradation.  The plan recommends Corps construction of 7 marsh restoration features, 5 shoreline protection features, reforestation of chenier ridges at 35 locations, and 10 years of post-construction monitoring.  The plan also recommends that the NER Plan EastUS Fish and Wildlife Service seek its own authorization and appropriations to restore and manage tidal marsh habitat at two sites partially located within two refuges owned and managed by the USFWS.

At October 2015 price levels, the estimated first cost of the Corps-constructed NER Plan (47 sites) is $2,188,186,000.  The Federal share would be $1,422,000,000 (65 percent), and the non-Federal share would be $765,865,000 (35 percent).  The cost of lands, easements, rights-of-way, and relocations is estimated at $10,130,000.  OMRR&R by the non-federal sponsor is estimated at $5,958,000 per year.  The NER Plan would reforest, protect and restore 15,448 acres producing 4,976 average annual habitat units.  The plan would directly, indirectly, and cumulatively benefit chenier forests, brackish and saline marsh, essential fish habitat, wildlife, fisheries, water quality, and recreation.  The plan would also restore and protect 335 acres of designated critical habitat (for threatened piping plover and rufus species of the red knot); enhance plant productivity; and reinforce and protect critical landscape features.  The Calcasieu Ship Channel Salinity Barrier and the Cameron-Creole Watershed Spillway are recommended as additional long-range studies.

REPORT DOCUMENTATION:  Pertinent documentation on the project, the results of the Civil Works Review Board, and subsequent Washington-Level Review Actions are listed below (items not linked will be provided when available):

  • CWRB Agenda
  • Project Map/Placemat
  • Project Summary
  • CWRB Briefing Slides
  • CWRB Lessons Learned
  • CWRB Meeting Record
  • State & Agency Review Comments Letters
  • Documentation of Review Findings
  • Signed Chief of Engineers Report
  • Advanced Copy to Congressional Committees
  • ASA (CW) Memo to OMB
  • OMB Response
  • ASA (CW) Transmittal to Congress
  • Signed Record of Decision
  • Authorization

ADDITIONAL INFORMATION: