ABSTRACT

A close relationship has been found between wave energy, longshore sediment supply, and the ebb-tidal delta morphology of North Inlet, South Carolina. Surf zone wave observations during seasonal studies have documented a pattern of dominantly southward wave energy flux, as expressed by the longshore energy flux factor (P_1s). Four stations were monitored, two on either side of the inlet, and the station just downdrift of the inlet was found to lie within a zone of energy flux reversal due to wave refraction around the ebb-tidal delta. Since the inlet stabilized in its present position in the 1930's, longshore sediment transport has been directed toward the inlet from both sides, budding up the ebb-tidal delta.

Comparison of volumetric changes in the ebb-tidal delta between 1925 and 1964 yields an estimated annual rate of accretion of 4.33 10⁵ m³ (5.66 10⁵ yd³). Net annual longshore energy flux factors of 157.0 joule/sec/m (35.3 ft-lbs/sec/ft) at the most updrift station and 128.1 joule/sec/m (28.8 ft.lbs/sec/ft) in the zone of transport reversal indicate an inlet-directed longshore sediment transport rate (Q) of 3.53 10⁵ m³/yr (4.6 10⁵ yd³/) utilizing the design relationship Q = (7.5 10³) P_1s. This value is 82 percent of the ebb-tidal delta accretion rate, indicating that the primary source of sediment for the ebb-tidal delta is the longshore transport system and that the ebb-tidal delta is an efficient trap for littoral drift. Low-intensity northeast storms, while contributing to beach erosion, may have an accretionary effect on the ebb-tidal delta by activating the sediment transport reversal.