Louisiana’s Coastal Master Plan – Projects to Protect Transportation Infrastructure

In 2012, Louisiana’s Coastal Protection and Restoration Authority (CPRA) developed a Coastal Master Plan to provide a system-wide plan for reducing hurricane flood risk and restoring land along the Louisiana coast. The Plan defines a set of coastal protection and restoration projects to be implemented by the state over the next 50 years.  Six of these projects create wetlands in order to protect sections of Louisiana’s highways. The criteria used for selecting projects consider future climate impacts.

The Plan is based on a 2-year analysis developed by a team of Louisiana state agencies, scientists, engineers, and local communities. Using this analysis, the Plan identifies a total of 109 projects. The projects are grouped into three categories: (1) land restoration, (2) structural risk reduction, such as levees, and (3) nonstructural risk reduction, such as elevating houses.  This case study will focus on the six projects that were identified in the Plan to protect transportation infrastructure.

Several Louisiana highways are vulnerable to flooding from hurricanes, including LA-27, LA-82, and LA-182. To shield these highways, the Plan selected six land restoration projects that will create protective wetland buffers.  One type of project involves hydrologic restoration, which repairs degraded wetlands by removing blockages to the natural flow of water. Restoration is accomplished by conveying water to areas that had been previously cut off by man-made levees or other built structures. In the Mermentau Basin, three projects will increase the flow of freshwater to wetlands adjacent to LA-27 near Creole and sections of LA-82 near Grand Chenier and Pecan Island. An additional project will increase connectivity among wetlands on either side of LA-182 in the Chacahoula Basin by the addition of three culverts. Connected wetlands will become more robust and provide a stronger natural barrier against shoreline erosion. Each of these four projects will cost approximately $7 million and be developed during the first Plan implementation period (2012-2032). 

To provide additional protection for LA-82, a marsh creation project was selected to establish new wetland habitat near Grand Chenier, along with a shoreline protection project to construct rock breakwaters along the Schooner Bayou Canal near North Prong. Breakwaters are walls that extend out into a body of water to protect a shoreline from the impact of waves. These breakwaters are intended to dampen wave energy and prevent degradation of existing wetlands adjacent to the highway. The Grand Chenier marsh creation project is expected to cost $708 million and occur during the first Plan implementation period, and the Schooner Bayou Canal project will be completed during the second Plan implementation period (2032-2061) at a cost of approximately $23 million.

Two primary factors drove decision-making about which projects to select for the Plan - flood risk reduction and capacity to build new land or sustain existing land. Project selection was also guided by a set of 9 secondary factors, including: (1) support of cultural heritage, (2) distribution of risk reduction across socioeconomic groups, (3) protection of historic properties, (4) protection of critical infrastructure, (5) support of navigation, (6) support of oil and gas, (7) use of natural processes, (8) operations and maintenance, and (9) overall sustainability.

To quantify these factors and evaluate potential projects, CPRA developed a series of predictive models. The predictive models performed two different functions. First, the models assessed how Louisiana’s coastal landscape may change and how much damage communities may face from flooding over the next 50 years if no action is taken. Second, the models assessed how coastal landscapes and flood risks could change over the next 50 years if certain restoration and risk-reduction projects are constructed.

CPRA accounted for climate change within these models by including variables for sea-level rise and hurricane frequency and intensity. When estimating sea-level rise, CPRA used data from the 2007 Intergovernmental Panel on Climate Change (IPCC) report as well as U.S. Army Corps of Engineers 2009 Sea Level Rise Guidance. Based on these sources, CPRA projected a range of sea-level rise between 0.39 and 2.13 feet over the next 50 years for the region.

When estimating hurricane frequency and intensity, CPRA relied on a wide literature review, including figures from the 2007 IPCC report. This literature review indicated that in general hurricanes are predicted to become less frequent but more intense in the future. However, because of warming sea-surface temperatures in the Gulf of Mexico, hurricanes in that region could become more frequent. Based on this information, CPRA projected -20% to +10% change from current hurricane frequency and 0% to +30% change from current hurricane intensity over the next 50 years.

The Plan was created as a mandate from the Louisiana legislature, which established CPRA in the wake of Hurricanes Katrina and Rita. CPRA is required to develop a coastal master plan every 5 years, and the process is already underway for developing the 2017 Coastal Master Plan. In developing the 2017 update to the Plan, CPRA has several key goals: focusing on flood risk reduction and resilience; incorporating new project ideas and information; improving models based on best available science; engaging communities; and expanding collaboration and partnerships.

While many of the selected projects from the 2012 Plan are already underway, the comprehensive timeline for implementing this Plan spans the next 50 years. The total cost of all 109 projects is estimated at $50 billion; in FY 2015, CPRA estimated spending $477 million to begin or continue construction on 59 projects. The Plan includes projections of future funding, which combine estimates of existing funding sources and possible sources of new funding. For example, one source of new funding is likely to be the Deepwater Horizon oil spill settlement.

 

This Adaptation Clearinghouse entry was prepared with support from the Federal Highway Administration. This entry was last updated on March 31, 2016. 

 

Publication Date: March 2012

Related Organizations:

  • Louisiana Coastal Protection and Restoration Authority

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