Analysis of grain size trends, for defining sediment transport pathways in marine environments

Abstract

An approach to grain size trend analysis is developed on the basis of a semi-quantitative filtering technique. Using this technique, grain size trends identified from a grid of surficial sediment samples are transformed into a "residual pattern" representing net sediment transport paths. The method assumes that the grain size trends used for the analysis have a higher frequency of occurrence in sediment transport directions than in the opposite directions, but such dominance does not exist if there is no exchange of material between the sampling sites. The proposed method is applied to the analysis of grain size trends over the Christchurch Bay area, southern England.

Mean grain size, sorting and skewness are used to form eight possible grain size trends; two of these are used to derive a residual pattern. The pattern obtained shows general agreement with transport patterns derived from other sediment dynamics investigations undertaken for the region. Further, a residual pattern similar to that of transport paths on the basis of estimates of longshore transport rates, for the Rh6ne Delta, is derived. The present investigation indicates that the feasibility of grain size trend analysis depends upon the selection of appropriate grain size trends and the analytical approach.

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