Abstract

Fourier shape analysis has been applied to quartz sand grains collected along the coastal regions around Port Stephens (150 km north of Sydney), with the intent to determine the dispersal patterns of the fluvial sand along this coast. By using a video-digitizing micro-processor controlled computer system, the outline of the quartz particles were defined in polar coordinates and a Fourier series in closed form was calculated. Twenty-four harmonics were obtained, each representing the contribution of elementary forms to the real shape of the grain. Selected distributions of harmonic amplitude were defined utilizing the maximum entropy method and chi-square statistic. The combined 15-24th harmonic amplitude distributions were submitted to unmixing analysis, allowing the definition of three main end-members to be made, each one related to smooth, angular and intermediate shaped grains. The proportion of these end-members in each sample has suggested the provenance and dispersion patterns for the study system. Three major sand types have been identified: flood reworked coastal plain sands, related to a mixture of river and mature coastal plain particles; fluvial-marine coastal sands, related to a sand mixture of fluvial and marine origin, found close to the area of the Hunter River mouth, and marine coastal sands in the northern portion of the study area, which show higher maturity than the other two types of sediment. Sands associated with headland erosion display shape characteristics similar to those of the fluvial material. The shape data suggests that the Hunter River supplies sediment at least in the southwest sector of the Newcastle Bight modern beach system, probably during higher discharge flood events. Additionally, this study indicates that textural characteristics of the river sediment are subjected to rapid changes in the coastal active zone, and hence generally make non-definitive indicators of source and dispersion of the sediment.

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