Island and Coastal Ecosystem Restoration

East and West Grand Terre Islands are located at the mouth of Barataria Bay, in Jefferson and Plaquemines Parish, Louisiana. Repeated hurricanes, overwash, and increased tidal prism have led to the breakup of Grand Terre Island and the development of Pass Abel, which now separates West Grand Terre Island from East Grand Terre Island. The islands have experienced gulfside erosion rates in excess of 50 feet per year over the last decade, with bayside erosion rates exceeding 6 feet per year. It is projected that East Grand Terre Island will disappear by the year 2050 without project planning and restoration implementation.

Restoration plans for East Grand Terre include creating 74 acres of dune and 211 acres of marsh habitat. The restoration of the barrier shoreline of West Grand Terre is expected to include constructing 40 acres of dune from the Lyle St. Amant Laboratory to the U.S. Army Corps of Engineers disposal area.

Project Goals

• Restore the gulfside shorelines on East and West Grand Terre Islands to a position that remains seaward of the preconstruction shoreline for at least 6 years following construction.
• Maintain average dune platform elevation on East and West Grand Terre Islands at or above the as-built elevation using vegetation planting and sand fencing.
• Construct a 211-acre wetland platform on East Grand Terre Island comprising 96% land and 4% water 1 year after construction; 82% land after 10 years; and 62% land after 20 years.
• Create habitat comprising wetland vegetation on the land portion of the wetland platform, of which 25% will have at least 80% cover in target year 1 and 100% will have at least 80% cover in target years 3, 10, and 20.

Engineering and Design Services

WESTON performed the topographic, bathymetric, and magnetometric surveys, collected geotechnical borings to determine borrow source characteristics, assisted the Louisiana Department of Natural Resources (LDNR) in obtaining access to affected properties, and performed cultural resource assessments and endangered species reviews.

WESTON reviewed dredge technologies and containment barriers to identify low-impact/high-efficiency technologies that were used to develop three alternate design strategies, which included diagrams and draft plans, costs, work process descriptions, and quantity estimates. At the client’s request, WESTON performed numerous one- and two-dimensional modeling using SBEACH, ADCIRC, COAST-L, and PSed. These and coastal modeling tools were used to drive sediment transport and shoreline/profile evolution models for evaluating profile and planned shoreline changes on the islands. WESTON prepared the Draft Preliminary Engineering and Design Report, which included alternatives analysis, preliminary cost estimates, site plans, existing cross-sections, bathymetric profiles, and sediment transport model results.