St. Tammany Parish Government Subconsultant to Stantec Lake Pontchartrain Barrier Gate Modeling Project

The State of Louisiana’s Coastal Protection and Restoration Authority (CPRA) began, as far back as 2013, an investigation of the potential coastal flood damage reduction benefits and the potential induced damage effects to both Louisiana and Mississippi from a proposed barrier across the mouth of Lake Pontchartrain in southeast Louisiana, as a part of the effort to advance the 2017 Coastal Master Plan. After performing the initial evaluation of proposals for a Lake Pontchartrain barrier using the Coastal Louisiana Risk Assessment (CLARA) model utilized in development of the 2017 Coastal Master Plan, Atkinson and Roberts (2015) prepared a report describing the preliminary design assessment and screening process used to identify a subset of barrier options to consider and Fischbach et al. (2017) prepared a report providing the analysis to guide the selection of a barrier option for formal consideration in the 2017 Coastal Master Plan analysis.

In these initial analyses, twelve different alternatives were evaluated for the project, in addition to a future without action alternative; These alternatives evaluated placing the closure structures at different locations that include U.S. 90 and the CSX railway, different gate heights that ranged from 0.6 meters up to 6.0 meters, and different barrier heights, that included no increase over the height of U.S.90 and a 3-meter increase in the elevation of U.S. 90. In Risk Reduction in Louisiana’s Coastal Master Plan: Lake Pontchartrain Barrier, Leadon, Atkinson, and Fischbach (2018) show that the potential to adversely impact water levels in the vicinity of Lake Borgne, and even in portions of western Hancock County, MS exists. Louisiana’s 2023 Coastal Master Plan includes the Lake Pontchartrain Barrier Project and describes it as consisting of the Construction of closure gates and weirs to an elevation of 2 feet NAVD88 across the passes at Chef Menteur and the Rigolets for storm surge risk reduction within the Lake Pontchartrain Basin.

Much of the coastal portions of the City of Slidell and several other communities in St. Tammany Parish, as well as portions of the City of New Orleans, that are outside of Hurricane Levee systems would see Flood Depth Reductions at year 50 of up to three feet with the completion of the project, as compared to a future without project scenario, for the storm events evaluated in the 2023 Master Plan. This would protect an additional approximately 5800 residences and would result in an estimated $680,000,000-$740,000,000 in avoided losses. Completion of this project could potentially eliminate the need for, or at least potentially reduce the scope and cost of other projects within the basin, providing for an additional resilience benefit.

Wingate Engineers, as a sub-consultant to Stantec is performing the following services:

• Developing a Rough Order of Magnitude (ROM) cost estimate for the construction of structures at Rigolets and Chef Menteur Pass.
• Quantifying and comparing reductions and increase in the number of flooded structures and resulting damages in project scenarios from Stantec’s preliminary inundation maps.
• Comparing the values of the damages to the costs of constructing the storm surge risk reduction structures.