Significant areas of the 1,500-foot-long seawall at Fort Mott State Park had deteriorated and no longer provided necessary protection from heavy erosion caused by the Delaware River and tidal fluctuation. The risk of loss of land within the historical fort facility – part of the Harbor Defenses of the Delaware constructed between 1872-1902 –required comprehensive rehabilitation. An existing tide gate required repair.
Maintaining the historical nature of the wall, a critical project goal, required a thoughtful solution that not only satisfies permitting requirements of the state Historic Preservation Office, but produces a durable long-term solution.
Short sheetpile walls will be key to protecting the base of the walls from further erosion and undermining. For exposed stone face sections, dislodged stones will be reset using original stone or, if necessary, stone of comparable origin and appearance, to maintain the historic aesthetic. Joints will be cleaned and repointed, with pinnings or small stones set in the wider joints. Stitching and injection grouting will be considered where necessary. Concrete-faced sections will be thoroughly rehabilitated including: repairing cracks and deteriorated joints; installing dowels and reinforcements as needed; filling spalls and depressions with mortar; and re-coating appropriately. All materials will be suitable for the marine environment, to control future deterioration. A roadway collapse at the existing sluice gate will also be repaired and problematic sluice gate operation will be resolved to allow free exchange of water to the existing moat during high and low tide conditions. Construction will be phased to minimize disruption to the access road to the park.
GZA’s understanding of historic stone seawall construction and the specific existing conditions of this site allowed for the development of an innovative, yet practical and cost effective, solution for the park that durably preserves the historic appearance for years to come.