ORIGINAL On the displacement of marked pebbles on two coarse-clastic beaches during short fair-weather periods (Marina di Pisa and Portonovo, Italy) Duccio Bertoni & Edoardo Grottoli & Paolo Ciavola & Giovanni Sarti & Giuliano Benelli & Alessandro Pozzebon Received: 3 April 2013 /Accepted: 6 September 2013 /Published online: 20 September 2013 # Springer-Verlag Berlin Heidelberg 2013 Abstract The aim of the investigation was to define the mechanisms of sediment transport in the swash zone of microtidal coarse-clastic beaches in the very short term by evaluating the displacement rates of marked pebbles under low-energy wave conditions. Tests were performed at two sites (Marina di Pisa, Ligurian Sea, and Portonovo, central Adriatic Sea) to check the consistency of the data over a range of different grain sizes. Two recovery campaigns were carried out at both sites, one 6 h and the other 24 h after the injection. During the experiments wave action was at a minimum (wave heights never exceeded 0.3 m). The results show that 20% of pebbles ranging in diameter from 30–90 mm moved signifi- cantly (more than 0.5 m) already 6 h after the injection, with some tracers being lost (3%). After 24 h, 40% of the pebbles were significantly displaced and 10% were lost. The prefer- ential downslope movement of tracers, which suggests that coarse sediment movement under low-energy conditions is mainly controlled by gravity processes enhanced by steep beachface slopes, represents the novelty of the results reported here. It would appear that swash processes on low-energy beaches cause a significant rate of pebble displacement through the destabilization induced by wave uprush and back- wash. Despite the microtidal range, the position of the mean water level plays a major role in changing the beach level at which swash processes can actually trigger pebble movement. The results of this study show that considerable, and mostly seaward-directed, coarse sediment transport takes place even during short fair-weather periods. Introduction Sediment transport along ocean shorelines is a foremost aspect in the morphological evolution of coastal environments, the factors responsible for sediment displacement driving the morphodynamics of a given beach between erosion and accre- tion in the process of achieving some form of equilibrium. To understand the principles of beach morphodynamics and, in particular, to trace the pathways of sediment movement has been a major objective of beach studies over past decades (e.g., Komar and Inman 1970; McCave 1978; Wright et al. 1985; Salomons and Mook 1987; Ciavola et al. 1997, 1998; White 1998; Short 1999; Benavente et al. 2005; Silva et al. 2007; Poizot et al. 2013; Sancho-García et al. 2013). Although more attention has generally been given to sandy beaches, mainly because it is easier to carry out field experiments on sand-sized sediments rather than gravel-sized ones (Buscombe and Masselink 2006), a renewed interest in the investigation of coarse-clastic beaches can be observed in recent years (e.g., Allan et al. 2006; Curtiss et al. 2009; Curoy 2010; Bertoni et al. 2010; Miller et al. 2011). The understanding of sediment transport in coastal envi- ronments has in recent years improved mostly because of novel technical solutions that solved many of the logistical problems encountered previously. For instance, the possibility of tracking individual pebbles by means of the RFID (radio frequency identification) technique provided a major boost toward the unraveling of coarse sediment displacement mech- anisms (Allan et al. 2006; Bertoni et al. 2010). In addition, the use of gravel and pebble beaches as a form of coastal protec- tion has progressively increased because they are more D. Bertoni (*) : E. Grottoli : P. Ciavola Department of Physics and Earth Sciences, University of Ferrara, via Saragat 1, 44100 Ferrara, Italy e-mail: duccio.bertoni@unife.it G. Sarti Department of Earth Sciences, University of Pisa, via Santa Maria 53, 56126 Pisa, Italy G. Benelli : A. Pozzebon Department of Information Engineering, University of Siena, via Roma 56, 53100 Siena, Italy Geo-Mar Lett (2013) 33:463–476 DOI 10.1007/s00367-013-0341-3