Characteristics of grain size distributions have been used as environmental indicators. The beach environment contains a double saltation population when the distribution is plotted on log-probability paper. This saltation break has been attributed to the swash-backwash action of waves. In order to study the double saltation population and its origin, a model beach was formed in a wave tank and individual swash and backwash movements of waves were sampled. Surface samples were taken from the swash zone of the resulting beach so that the combined effects of the swash and backwash movements could be compared. The grain size distribution of the surface samples showed the existence of the characteristic saltation break. The individual swash and backwash distribution curves showed no saltation breaks. When the swash and backwash distributions were combined into a composite, however, the saltation break was formed. This confirms that the saltation break may be formed by the swash-backwash action of waves as postulated.

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