Hurricane Protection-
- St. Bernard Parish – Hurricane Protection System (Chalmette Loop Levee) Engineering Alternatives Report
Chalmette, Louisiana
the challengeThe majority of levees in St. Bernard Parish (located in southwestern Louisiana, east of and adjacent to New Orleans) were overtopped or breached during Hurricane Katrina. The St. Bernard Parish Hurricane Protection System consists of approximately 25 miles of levees and floodwalls between the Bayou Bienvenue Control Structure (LPV 144) and the Mississippi River at Caernarvon (Chalmette Loop - LPV 145 to 149). The project evaluates and recommends engineering alternatives to the present system, which is required to maintain a level of protection against a storm event with a one percent probability of occurrence (100-year) for St. Bernard Parish. The US Army Corps of Engineers, New Orleans District Hurricane Protection Office (USACE-HPO), contracted with the Bioengineering Group to evaluate alternative levee alignments that would raise the existing levees to the federal system's design elevation level.
the interdisciplinary approachThe Bioengineering Group performed a site reconnaissance to become familiar with the existing structures and levees to identify any potential environmental issues that may affect the analysis and design alternatives. Various alternatives were investigated for the levees and floodwalls within the reaches to provide recommendations on the most feasible solutions to achieve the 100-year, level one protection, plus overbuild. The USACE-HPO provided historical data via original design memoranda, construction plans, as-built plans, Task Force Guardian construction plans, and existing survey data. All geotechnical analysis was performed using this data. This analysis included slope stability, seepage, pile capacities, settlement analysis, bearing capacity, earth pressures, and external stability as appropriate for each reach and alternative. Structural analysis included the following structures: T-walls, floodgates, a sector gate, and a sluice gate. All structures included a minimum of a 2-foot overbuild included in the 26-foot design elevation. All transmission poles will be raised to a distance equivalent to the change in levee elevation. Also, utility pipelines will be raised above the levee design section and supported on a pipe bridge in accordance with USACE-HPO criteria for crossing of levees and floodwalls.
the resultsBased on topography and subsurface soil conditions, a variety of alternatives were recommended for the reaches of this project. Optimization of the recommended alternative, including the estimates of probable cost, will be possible during the final design phase and shall be based on recent survey and subsurface data. The subsurface conditions in this region present challenging scenarios to provide flood protection to the required 100-year flood elevations. While this project presents viable and constructible alternatives, additional study and analysis should be undertaken to evaluate additional alternatives in an effort to reduce the overall cost, impact to the environment, and reduce the amount of ROW.