DOWNDRIFT MIGRATION OF SHORELINE FACETS AT SANDY HOOK, EFFECTS OF BEACH NOURISHMENT, AND IMPLICATIONS FOR MANAGEMENT

Sandy Hook is a part of Gateway National Recreation Area (GATE) and occupies the northern portion of a barrier spit extending from the New Jersey Shore into the New York Harbor. At Sandy Hook three shoreline facets have been identified in the past, indicating a change in shoreline direction and sediment mobility (Allen 1981; Psuty et. al 2011). The southernmost facet had a negative sediment budget on the order of 20,000 – 40,000 m³/yr. To the north, the middle facet had a near equilibrium budget, and then (continuing downdrift) the third and northernmost facet had a positive sediment budget of about 30,000 m³ /yr (Psuty et. al 2011). However, the inflection points of these facets have been shifting downdrift (to the north). Shoreline position has been monitored since 1990 with GPS units, and seasonally beginning in 2006 following a consistently applied monitoring protocol, resulting in a 30-year shoreline record. During this time, the inflection point between facet 1 and facet 2 shifted about 450 m north at a rate of about 15m/yr. The boundary between facet 2 and facet 3 shifted about 800 m north at a rate of about 30 m/yr, and the tip of the Sandy Hook spit shifted about 680 m to the north at a rate of 27 m/yr. Whereas longshore sediment transport may be the primary reason for these facet shifts, several other drivers, including anthropogenic activities, affect the shoreline position at Sandy Hook. Beach nourishment has occurred directly on Sandy Hook and in the updrift communities from the 1940s to the present, a total of 44 million cubic yards. The boundary between facet 1 and facet 2 appears to have migrated north at a slower rate, possibly due to structures updrift and proximity to nourishment events. The location of nourishment placement relative to the park boundary affected the time taken to impact the shoreline position in the park. As the margins of these facets shift north, so does the sediment budget condition associated with each facet. Anthropogenic structures, including a seawall, are present in the southern portion of the site limiting the movement of the shoreline in some areas and affect sediment mobility. Shifting facets and areas of erosion in conjunction with hardened structures are of concern to park management as areas of erosion threaten different recreational activities and infrastructure within the park.