Trigon Associates, llc

Alternative Designs to Permanent Protection System for Outfall Canals

Client: Sewerage & Water Board of
New Orleans
Completed: 2010

Preparation of Opinion of Probable Cost

Trigon provided various services on this project, which included evaluating multiple options for providing increased flood protection along three (3) major outfall canals in New Orleans – the 17th Street, Orleans Avenue and London Avenue Canals – and developing opinions of probable cost.

These three outfall canals handle the majority of storm water runoff from the City of New Orleans and a portion of Jefferson Parish and connect pump stations located on the interior of the City to Lake Pontchartrain, where the storm water is discharged. Levees and floodwalls were constructed on both sides of the outfall canals as features of the Lake Pontchartrain and Vicinity Hurricane Protection System. Options are being evaluated to construct new permanent pump stations/control structures at the mouths of the canals and possibly eliminate the need for the interior pump stations by deepening the outfall canals to allow gravity flow all the way to the lake.

Trigon’s primary focus included the mechanical, electrical, geotechnical and real estate aspects of the project.

Trigon reviewed various previous reports and studies completed by the USACE, including previous geotechnical analyses, and utilized them as a baseline for this project. Trigon provided input to the conceptual designs of the pump stations and multiple canal cross-sections developed by the team for options requiring the outfall canals to be deepened (and widened in most instances).

The new canal cross-sections included such variations as concrete-lined and earthen/clay-lined canals. In addition, several options were evaluated for groundwater cutoff, including slurry walls, diaphragm walls, and steel sheet pile walls.

The 17th Street Canal was evaluated for a projected flow rate of 12,500 cubic feet per second (cfs); the Orleans Avenue Canal for 3,400 cfs; and the London Avenue Canal for 9,000 cfs.

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