Wave climate, sand budget and shoreline alignment evolution of the Iluka–Woody Bay sand barrier, northern New South Wales, Australia, since 3000 yr BP

Abstract

Multi-centennial fluctuations in the northern New South Wales (NSW) coastline alignment are interpreted from a detailed reconstruction of the morphological and depositional evolution of the Iluka to Woody Bay barrier during the late Holocene. The regional coastline is aligned obliquely to the south-east, inner-shelf, modal wave direction, and hence sediment is transported obliquely on the shoreface with a net northward movement. On centennial to millennial time scales, the coastline is shown to have responded to fluctuations in mean wave direction, longshore gradients in sand transport and headland sand bypassing processes. Overall, barrier progradation has been punctuated by episodes of shoreline recession and realignment throughout the late Holocene. A prolonged shoreline recessional phase occurred at ∼ 1500 yr BP in response to a rotation in modal wave direction from more southerly, towards east–south–easterly. Subsequent to this realignment, renewed shoreline progradation occurred along the east aspect coastline after ∼ 1400 yr BP whilst the north-east aspect, coastline remained in a receded alignment until after ∼ 1000 yr BP, when renewed progradation occurred. Progradation rates increased throughout the past millennium, driven by changes to the alongshore gradient in sand transport, under an implied shift to a more southerly and energetic modal wave climate. In the past 50 yrs, the north-east aspect shoreline has experienced a rapid recessional trend, which is associated with a shift in modal wave climate, to a more east–southeasterly direction, and a reduction in headland sand bypassing, The average sand supply rate to the Iluka to Woody Head section of the northern NSW shoreline is 4.1 m 3/m/yr, since ∼ 3000 yr BP.