Winthrop Beach: Utilizing a Mixed Sediment Nourishment Regime to Restore an Urban Beach

Winthrop Beach faces the open ocean, is approximately 7,000 feet in length, and is situated along the east side of Winthrop between two glacial headlands or relic drumlins. To address the issues of shore protection and “sediment starvation” along the Winthrop Beach shoreline, a beach nourishment project has been designed to return the shoreline to historic conditions. Unlike most beach nourishment projects in the United States, the material proposed for restoration of Winthrop Beach consists of mixed cobble, gravel, and sand sediments. Due to the origin of the native beach (erosion of glacial drumlin deposits), the in situ beach material consists of poorly sorted materials ranging from fine sand to cobble. The total beach fill length was approximately 4,200 linear feet and the equilibrated berm width is designed at 100 feet. The total nourishment volume was approximately 460,000 cubic yards. Once the beach nourishment was completed in late 2014, the high tide shoreline was pushed more than 150 feet from the seawall, with a gradual slope extending approximately 350 feet offshore. Although shoreline change modeling indicated a design life of approximately 10 years, it is anticipated that the coarse fraction of the nourishment material will be naturally sorted by wave action and form a gravel/cobble berm along the upper portion of the beach (observed along the natural mixed sediment beaches of the New England coast). Initial monitoring results after the first complete year post-nourishment support this finding, as minimal sediment loss has occurred, despite an active nor’easter season in the winter of 2014-2015.