Flood Damage Reduction System at Chalmette Loop Levee

Client: U.S. Army Corps of Engineers, Hurricane Protection Office, New Orleans, Louisiana

The Challenge

A levee system nearly 30 miles long needed to be raised by 20 to 30 feet in order to provide suitable risk reduction for greater New Orleans after Hurricane Katrina. Chester Engineers was tasked with providing an Engineering Analysis Report, Alternatives Analysis, and detailed designs for a new T-walls and related structures atop an existing levee located on some of the weakest soils in North America. The heightened Chalmette Loop Levee system required new elements to achieve closure against storm surge, while allowing navigation. The levee system did not exist as stand-alone infrastructure, but instead tied in to existing and new elements including the Inner Harbor Navigation Canal Lake Borgne Surge Barrier, the Bayou Dupre and Bayou Bienvenue gates, and the Mississippi River levee. Six gas pipelines and overhead transition poles required relocation, as well as other sensitive features including river, coastal wetland, and dredged material management, requiring the evaluation of potential environmental impacts and opportunities for beneficial reuse.

The Interdisciplinary Approach

Chester Engineers provided site reconnaissance; a NEPA environmental analysis; geotechnical analysis; structural analysis and design of T-walls, floodgates, a sector gate, and a sluice gate; slope/stability analysis; and a design for an inverted T-wall on top of an earthen levee. The T-wall designs were used to add height to the levee while minimizing right-of-way and relocation changes to rebuild to an estimated 100-year level of hurricane risk reduction. Initial analyses also included design of a pontoon bridge and cross-over ramps constructed of earthen levees at the same wall height in order to provide vehicular access for maintenance. Geotechnical engineering services included geotechnical lab testing and cone penetration tests (CPT) data evaluation, determination of design shear strength, settlement analyses, analysis of steady state levee under seepage and slope stability analysis. Analysis results were included in a Geotechnical Engineering Report and used to guide the geotechnical design of various structures along the levee alignment. Engineers also performed an evaluation of cost and performance of deep soil mixing critical levee sections. Finally, Chester Engineers provided follow-on services with Norfolk Southern bridges along this levee.

The Sustainable Result

Tie-in designs for the T-walls which flank all structures provide scour protection for the transition zones. Plans and specifications included the design of coffer dams and dewatering systems necessary for the construction and Chester Engineers supported the solicitation of bids, contract administration, construction, and inspection allowing the project to be designed and executed, including environmental compliance, all within four years. The loop levee system functions as part of a multi-tier integrated system to provide a redundant and climate change adaptable level of risk management.

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    Project Highlights:
  • Risk based and climate change resilient strategy.
  • Levee design.
  • T-wall design.
  • Engineering alternatives report.
  • Sector gate design.
  • Deep soil mixing.
    Services Provided:
  • Civil, structural and geotechnical engineering.
  • Analysis of geotechnical data on subsidence and settlement of delta soil.
  • Development of geotechnical reports and alternatives analysis.
  • Follow on services for Norfolk Southern Rail bridges along the levee.