Journal of Coastal Research, Special Issue No. 65, 2013 Comparative median grain size assessment through three different techniques for sandy beach deposits 1757 Comparative median grain size assessment through three different techniques for sandy beach deposits on the Maltese Islands (Central Mediterranean) Alan Deidun†, Ritienne Gauci‡, John A Schembri‡, Ela Šegina∞, Adam Gauci †, Fabrizio Gianni#, Juan Angel Gutierrez†, Arnold Sciberras§ and Jeffrey Sciberras§ †IOI-Malta Operational Centre University of Malta University Campus, Msida Malta MSD 2080 alan.deidun@um.edu.mt adam.gauci@um.edu.mt ‡ Department of Geography University of Malta University Campus, Msida Malta MSD 2080 ritienne.gauci@um.edu.mt john.a.schembri@um.edu.mt ∞ Ela Segina University of Nova Gorica, Department of Karstology Vipavska 13 SI-5000 Nova Gorica Slovenia #Faculté des Sciences, Université de Nice Sophia-Antipolis, EA 4228, ECOMERS, 06108 Nice cedex 2, France §131, `Arnest`, Arcade Str, Paola, Malta INTRODUCTION Measuring parameters like median particle size is of the utmost importance in achieving a better understanding of beach processes and the refinement of coastal models. In addition, sand particle size distribution is also a sensitive indicator of the ecological conditions pertaining on a particular beach (Little, 2000). In fact, broad typologies for a number of beach interstitial parameters, including porosity, permeability, dissolved oxygen, organic content and microbial populations, can be anticipated with some confidence from baseline information on sediment particle sizes. There are four basic techniques through which dimensional information on sediments can be gleaned: (1) conventional granulometric techniques, which permits the concurrent study of large volumes of sediment but is labour-intensive, (2) microscopic observation/analysis, which is accurate but which can be applied to small sediment volumes only, (3) laser diffraction, which is a robust and rapid technique but which requires expensive equipment and which cannot analyse large sediment size ranges and (4) image analysis, for which no single harmonized protocol has been described to date (Pina & Lira, 2009) and which requires highly skilled human resources. ABSTRACT Deidun, A., Gauci, R., Schembri, J.A., Šegina, E., Gauci, A., Gianni, J., Gutierrez, J.A., Sciberras, A. and Sciberras, J., 2013. Comparative median grain size assessment through three different techniques for sandy beach deposits on the Maltese Islands (Central Mediterranean) In: Conley, D.C., Masselink, G., Russell, P.E. and O’Hare, T.J. (eds.), Proceedings 12 th International Coastal Symposium (Plymouth, England), Journal of Coastal Research, Special Issue No. 65, pp. 1757-1761, ISSN 0749-0208. 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. ADDITIONAL INDEX WORDS: beach, granulometry, median, sieving, microscope, image analysis, correlation, Gradistat, MATLAB, Maltese Islands. . www.JCRonline.org www.cerf-jcr.org ____________________ DOI: 10.2112/SI65-297.1 received 07 December 2012; accepted 06 March 2013. © Coastal Education & Research Foundation 2013