STATEN ISLAND BEACH MORPHOLOGY - IMPLICATIONS FOR SHORELINE RESPONSE TO STORM EVENTS

Staten Island’s beaches were shown to be vulnerable to storm surge during Hurricane Sandy, with severe inundation into neighborhoods along the eastern shoreline; the area chosen for this study, and the area in which the Army Corps of Engineers plan to start constructing a seawall. In order to determine a baseline against which future changes in beach morphology can be measured, the beaches in this area, South Beach, Midland Beach and New Dorp Beach, were surveyed during the summer of 2018. This survey consisted of measuring 9 transects from the low tide mark to the base of the dunes (most of which are man-made structures), and collecting sediments from the low tide mark, beach berm and boundary between the beach and the base of the dunes. Samples were dry sieved into different grain size fractions, to identify any significant relationships between grain size and location on the beach.

The beach profiles are all typical of a sandy, wave dominated beach. Variations along shore are partially the result of sand movement being restricted by groins, with a much wider overall beach profile being present where sand is accumulating on the up-current side of the structure. Analysis of both morphology and sand grain sizes suggests that this is a reflective shoreline. Such shorelines develop where there is sandy sediment and an average wave height of < 1 m, typical of locations similar to that of Staten Island in the mouth of the Hudson estuary. Reflective beaches generally change little over the course of a year because of this low wave height, but are extremely vulnerable to erosion during major storm events when wave heights are greatly increased. More dissipative beaches are much more variable, but less vulnerable, not least because their variability discourages close proximity development. If we are to plan for future storm events on Staten Island, it is essential that these beach morphodynamics are well understood, so that it is not a surprise when a seemingly stable beach can suddenly move.