Littoral processes on the Cape Lookout Cuspate Foreland, North Carolina: Wave refraction/diffraction modeling of longshore currents and sediment transport

The Cape Lookout cuspate foreland has undergone significant accretion since the first rudimentary field studies were conducted in the 1800s. Despite its wave-dominated setting, little is known about longshore currents and resulting sediment transport under the wide range of wave conditions that impact the complicated coastal geometry at the cape. This study examined littoral processes driven by longshore currents using a numerical wave refraction/diffraction model (REF/DIF 1) and through use of aerial photographs.; Results show that longshore current direction and speed, as expected, are highly variable depending primarily on incoming wave direction. Southerly longshore currents on Core Banks predominate under northeast and east wave approaches while weaker northerly currents are generated under southeast and east wave approach. These patterns provide a source of sediments to Cape Lookout Shoal.; The western limb of the system, including Cape Lookout spit, receives sediments that are released from the shoal and transported north by southeast, south, and southwest waves. Morphological changes at the spit, which represents the distal end of the littoral cell, correlate volumetrically quite well with the model results, which show 180,000–200,000 m3/yr supplying the spit. Sediments at Shackleford Banks do not notably influence spit growth due to net westerly longshore sediment transport. Based on these results, annual sediment input from Core Banks to the shoal was estimated to be 640,000–755,000 m3/yr.; Predicted longshore current patterns on the shoal indicated that repeated extension and retreat of Cape Lookout Point would result from the imbalance between the southerly longshore currents on the east side of the shoal and the northerly longshore currents on the west side.; Cape Lookout Shoal may play a role in protecting the study area by interfering with wave propagation and by allowing waves to concentrate energy onto their subaqueous portions. It is unclear, however, how sediments on the northern portion of the shoal continue being transported to the southern portion. Other physical processes such as storm-driven longshore currents, local wind- and wave-generated currents, and tidal currents on the shoal would transport sediments to the south, but further investigations will be needed to fully understand these processes.