After Sandy: The Bay Park W.T.P. flood control project.-Paper

Paper

Pdf Summary

Hurricane Sandy inundated the low-lying Bay Park Sewage Treatment Plant on Long Island, flooding underground systems and releasing untreated effluent into nearby Hewlett Bay. To prevent a recurrence and account for projected sea-level rise, Nassau County developed a perimeter flood-protection system while keeping the plant operational.<br /><br />The barrier was designed to protect to elevation 17 ft (5.2 m) NAVD, incorporating projected sea-level rise and freeboard. Space constraints required three construction approaches: earthen levees where room allowed, pile-supported concrete T-walls in restricted areas, and I-walls where a smaller berm with a sheet-pile extension was suitable. Flood gates were included at the site entrances.<br /><br />Because the island’s soils are predominantly sand, clay for the levee cover and core had to be imported. Seepage control was provided by a deep, thin vibrated-beam cutoff wall filled with saltwater-resistant, low-permeability self-hardening slurry made from attapulgite clay and slag cement. The wall extended to approximately elevation −25 ft and connected to T-walls; jet-grouted panels sealed gaps beneath utilities.<br /><br />Construction required adapting the design to site conditions and material availability. Displacement piles were replaced with augered cast-in-place piles to reduce the risk of damaging the cutoff wall. Building the wall from a partially completed sand berm also reduced the amount of imported clay required. Utility conflicts, winter weather, and inconsistent water supply affected construction sequencing and production.<br /><br />The completed system included about 6,700 ft (2,042 m) of cutoff wall and 699 foundation piles. Material testing met project requirements. The project demonstrates how levees, structural walls, and seepage barriers can be combined to protect critical infrastructure where space and subsurface conditions constrain design.

Keywords

Hurricane Sandy

Bay Park Sewage Treatment Plant

flood protection

Long Island

sea-level rise

perimeter barrier

cutoff wall

levees

T-walls

seepage control