Spatial Variation of Shoreline Change along An Important Marine Corps Amphibious Training Ground, Onslow Beach, North Carolina; Part 2: Beach Morphology

Onslow Beach at Marine Corps Base Camp Lejeune, NC, is an important amphibious training area that is rapidly eroding in places. The beach extends 12 km from Brown's Inlet in the northeast to the New River Inlet in the southwest and from the shoreface toe at -10 m to the estuarine or Intracoastal Waterway shoreline. The beach consists of three zones, characterized by different morphologies and uses: 1) a southern zone, located adjacent to the New River Inlet, dominated by wash-over fans and used mainly by off-road recreational vehicles, 2) a middle zone with discontinuous low-elevation dunes (4-6 m) where military amphibious exercises occur, and 3) a northern zone dominated by continuous high dunes (8-11 m) used mainly for sunbathing and walking.

To sustain amphibious training activities at this site into the future, it is important to determine the underlying causes behind observed along-beach variations in erosion rates. Based on measurements from the North Carolina Department of Coastal Management, the southern beach zone is eroding at an average annual rate of 3-6 m per year while erosion rates decrease towards the north to less than 1 m per year. The impacts of variations in underlying geology, management, and land use on beach erosion are being examined using sediment core, seismic, remote sensing, granulometric, and minerologic data. Here, we present preliminary data and results from monitoring and research activities conducted over the past year. Gravel (shell hash) is generally more abundant towards the south and Pleistocene paleochannels intersect the southern beach zone. The contact between the Oligocene Belgrade (limestone and sandstone) and Silverdale (quartz sandstone) formations is near Brown's Inlet. Both of these formations are exposed seaward of the shoreface, where the bathymetry is irregular and likely influences coastal morphology.