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 x 10 5 m 3 (5.66 x 10 5 yd 3 ). 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 x 10 5 m 3 /yr (4.6 x 10 5 yd 3 /) utilizing the design relationship Q = (7.5 x 10 3 ) 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.

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