Seabrook Sector Gate Complex

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

The Challenge

The existing levee and floodwall system provided protection against the project design hurricane that was defined for conditions before Hurricane Katrina. That level of protection provided for an El. of +15 feet along the Inner Harbor Navigational Channel (IHNC). The purpose of this project was to provide a 100-year level of protection from a storm that will be contained outside the IHNC in the area north of the project. The project reduces storm surge levels to which the existing floodwalls along the IHNC are exposed, thus, eliminating the need to strengthen or replace those floodwalls to provide the authorized level of protection. Chester Engineers prepared plans, specifications, and a Design Documentation Report for the improvement of hurricane protection in the IHNC in New Orleans, LA. The project design demanded engineering structures that could operate under and survive hurricane force winds, establishing a new standard for the region.

The Interdisciplinary Approach

Professional services included field investigations, surveys, soil borings, hydraulic modeling, and construction documents for the Seabrook Sector Gate Complex. Chester Engineers provided all structural design calculations and construction documents for concrete T-walls, vertical lift gate foundations, structural steel lift gate and concrete generator building. The Seabrook Sector Gate project involved the submission of multiple design deliverables over the course of the project. These deliverables included a Mechanical/Electrical Communication Plan; Design Quality Control Plan (DQCP); Design Criteria; Independent Technical Review (ITR) and certification; Biddability, Constructability, Operability, and Environmental (BCOE) Review and certification; calculations; quantity take-offs; cost estimates; Plans and Specifications (P&S); amendments during advertisement; engineering considerations and instructions (ECI); modifications during construction; and As-Built P&S and a periodic inspection design brochure.

The Sustainable Result

The floodgate system consisted of one 95-foot sector gate flanked by two 50-foot vertical lift gates, concrete T-walls that tied into the existing lines of protection, control buildings on the sector gate machinery blocks, needle beams and girders that provided for maintenance dewatering for the sector gate, a storage rack to contain the needle girders, and a generator building located on the west bank of the project. The 95-foot sector gate and the two 50-foot vertical lift gates provided a 95-foot navigable channel width through the sector gate opening and allowed for flow augmentation through the two lift gates. The system included a cofferdam, dewatering, tie-in T-wall monoliths to the lift gates, a steel pipe pile foundation, sheet pile cutoff walls, a concrete tremie seal within the cofferdam, a cast-in-place concrete slab, concrete walls, sector gate leafs, mechanical and electrical equipment, dewatering needle beams and girders, timber guide walls, and steel pile dolphins. The gate complex served critical functions within the overall multiple lines of defense strategy which allowed the Hurricane Storm and Damage Risk Reduction System to be completed rapidly, while also maintaining potential for adaptive management towards future sea level rise mitigation goals.

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    Project Highlights:
  • Floodwall design.
  • Structural steel vertical lift gate design.
  • Structural steel sector gate design.
  • Vertical lift gate foundation and tower design.
  • Generator building design.
  • Geotechnical analysis.
  • Concrete Foundation Design.
  • Structural Steel Design.