Alongshore variation in foredune height in response to transport potential and sediment supply: South Padre Island, Texas

The height and extent of coastal dune development can exhibit considerable variability over short distances, leading to variable storm impact alongshore. The source of this variation is not well understood in general, and in many cases is not easily explained by models that ascribe dune height and development to regional variations in sediment availability and foreshore slope. In this paper. LiDAR data collected in 2000 and 2005 from South Padre Island, Texas are used to characterize the alongshore variation in dune morphology, and to identify how the variation is related to foreshore morphology and nearshore state. Results of cross-wavelet analysis suggest that foredune height exhibits a statistically significant coherence with the surf similarity parameter at length scales of similar to 1300 of 2300 m. The resulting variation in beach state alongshore, from intermediate to dissipative, is the consequence of wave refraction and focusing by transverse ridges on the inner shelf. Dune height reaches a local maximum approximately halfway between the more intermediate and dissipative sections of the coast, where the volume of sediment in the backshore and in the foreshore bars are also at a maximum. The greater elevation of the foreshore and backshore also provides a wider fetch and potential for aeolian transport during the storm surge that tends to accompany storm winds. It is argued that the variation in dune morphology is not strictly the result of transport limitations as suggested by the fetch model, but rather depends on the alongshore coincidence of transport potential with an available supply of sediment in the backshore and on the foreshore. (C) 2010 Elsevier B.V. All rights reserved.