Longshore Transport at Cape Lookout, North Carolina: Shoal Evolution and the Regional Sediment Budget

The Cape Lookout cuspate foreland has undergone significant offshore accretion since the first rudimentary field studies were conducted in the 1800s. Despite the wave-dominated setting, however, little is known about littoral processes under the wide range of wave conditions that impact the complicated coastal geometry at the cape. In this study we examined littoral processes, driven by longshore currents, using a numerical wave refraction/diffraction model (Ref/Dif 1) and through use of aerial photographs and nautical charts. Results show that longshore current direction and speed, as expected, are highly variable and depend primarily on incoming wave direction. Southerly longshore currents on Core Banks predominate under northeast and east wave approaches, whereas weaker northerly currents are generated under southeast and south wave approaches. The result of these patterns provides a source of sediments to Cape Lookout Shoal. Results show the sediment input from Core Banks to the shoal is of the order 512,000 to 581,000 m3/yr. The western limb of the system receives a portion of these sediments, which are released from the shoal and transported north by waves that approach from the southeast, south, and southwest. Predicted longshore currents on the shoal indicate that repeated extension and retreat of Cape Lookout Point would result from the imbalance between southerly longshore currents on the east side of the shoal and northerly longshore currents on the west side. Cape Lookout Shoal may play a role in protecting sections of adjacent barrier islands by interfering with shoreward wave propagation and by allowing waves to focus energy onto their offshore subaqueous areas. It is still unclear, however, how sediments on the northern proximal regions of the shoal are transported to the distal regions farther south.