Comparative median grain size assessment through three different techniques for sandy beach deposits on the Maltese Islands (Central Mediterranean)

Abstract

It is estimated that sandy beaches cover only 2.2 per cent of the Maltese coastline. Although small in size, Maltese pocket beaches exhibit complex geomorphological interactions. A granulometric analysis of Maltese beach deposits may thus shed further light on the understanding of these interactive processes and provide baseline information on how beach sediment size may relate geo-spatially and morphometrically. Surface (0-10cm) sand samples were collected from ninety sandy beaches in Sicily, circum-Sicilian islands and the Maltese Islands. The median grain size of these sediment samples was assessed through three different techniques: the conventional sieving technique, observation through stereo microscopy and through image processing. The two primary objectives of such work were firstly, to construct a repository of median grain size values for the entire stretch of Maltese sedimentary coastline (the first study ever to be done on such a comprehensive spatial scale), and secondly, to evaluate the degree of concordance between the three techniques. The highest Pearson correlation value (0.90) was recorded for the sieving-scanning match, although in many cases differences were large enough to result in a different sediment type classification. The highest level of agreement between the scanning and sieving technique was registered for the medium-fine (1.5-2.5phi) and very coarse categories (-0.5-0.0 phi). Median particle diameters measured through microscopy were those which diverged most from those of other techniques. This maybe due to the relatively small number of sediment grains which were analysed within such a technique.