OLD STRUCTURES, NEW INSIGHT: ANALYSIS ON SEDIMENT TRANSPORT ALONG A HEAVILY ENGINEERED BAYSIDE BEACH

Bayside beach sediment transport is the product of a different set of morphodynamic processes than on oceanside beaches. The Kingman-Mills site is a 1.7 km stretch of fetch-restricted estuarine beach at the northern end of coastal New Jersey, part of the Sandy Hook Unit of Gateway National Recreation Area (GATE). The beach has multiple groins, seawalls, and bulkheads in various states of disrepair emplaced to protect the historical resources of WWI gun batteries and the main road on Sandy Hook. These hardened structures and sheltered position have made Kingman-Mills one of the most stable of segments of Sandy Hook. However, scarped dunes, undermining of the shore parallel road, and sinking of two ammunition bunkers on the beach face are tribute that the site is still vulnerable.

Silveira and Psuty (2009) studied the site from 2007-2008, and concluded that the site had a negative sediment budget derived from winter storms and erosional summer incident waves, separating it from the seasonal geomorphological evolution of an oceanside beach. Revisiting Kingman-Mills in Post Hurricane Sandy, using topographical field data collected from 2014-2019, the site now has an overall gain in volume (2,783 m³). A new compartmentalization model of the beach reveals the placement of hardened structures is influential in the sediment transport within this coastal system. The least engineered northernmost (updrift) 400 m of the site is responsible for ~73% of the overall volumetric gain, while erosive slumping and flanking features are present in parts of the site with hardened structures to the south. Analysis of wind data in this time interval provides support that winters with strong northwesterly winds, which in this fetch-restricted environment generate the largest oblique hitting waves, are a major component of sediment mobilization on the beach face and north to south alongshore transport on the bayside.