ABSTRACT In this paper pebbles marked by passive integrated transpon- ders from two artificial coarse-grained beaches at Marina di Pisa (Tuscany, Italy) were analyzed in order to measure the in situ abra- sion rate. The beaches (Cella 7 and Barbarossa) were set up in 2006 as a form of coastal protection. They are both composed of pebbles (30-to-90 mm diameter) and bounded longshore by huge groynes. They differ in length (250 m and 110 m respectively) and in the presence of an additional defense structure, a submerged breakwater 50 m off the coastline, at Cella 7. The aim of the study is to reckon the abrasion rate of individual pebbles and evaluate abrasion differences of pebbles released on Cella 7 and on Barbarossa. The RFID technology (Radio Frequency Identification) was used to track the pebbles due to its reliability and limited costs. The tracers were released on the beaches in March 2009 along closely-spaced cross- shore transects. The recovery campaign was carried out in May 2009. A total of 127 pebbles was detected, 83 of which were recov- ered. Huge beach reworking during the storms determined high burial rates and consequently the loss of a definite amount of tracers. The pebbles that were recovered showed a significant increase in roundness, in particular the tracers that were released on Bar- barossa. The average pebble weight loss measured at Cella 7 was slightly lower, which means lower mobilization rate at this site rather than at Barbarossa. The resulting values are significant considering the short time frame of the research (two months) and the limited energy of the storms occurred during the experiment. KEY WORDS: Abrasion, pebble, replenishment, coarse-clastic beach, tracer. INTRODUCTION Among the textural properties of coarse sediments, the abrasion rate is one of the most attractive mainly because it has a direct influence on practical activities, such as artificial beach replenishments. Gravel and peb- ble beach fills are progressively more used as a form of protection from coastal erosion, even where coarse parti- cles do not constitute the natural sediments of the area. The efficiency of an artificial replenishment is deter- mined in terms of the durability of the protection level it provides. Thus, the use of the most suitable grain-size is the primary requirement to fulfill the purpose of the intervention. However, the grain-size is connected to the abrasion rate to the point that it largely affects the out- come of a beach fill both in mid- and long-term. Underes- timating the abrasion rate might lead to a rather quick inefficiency of the artificial beach, which in turn implies the recurrence of additional fills along with cost swelling. The abrasion rate was firstly addressed with labora- tory experiments (KUENEN, 1964; LATHAM et alii, 1998; NORDSTROM et alii, 2008). MATTHEWS (1983) measured beach pebble attrition on pebbles of significantly different lithology relative to the native sediments using statistical methods, then compared the results to laboratory tests performed with the same lithology. Preliminary attempts on individual pebbles were performed by ZHDANOV (1958), but the technique implied the breakage of the peb- bles to identify them once recovered. DORNBUSCH et alii (2002) provided a remarkable impulse to this topic, mea- suring the in situ abrasion of individual pebbles without the need to break them. To allow both recognition and recovery of the marked samples, the rock types that were used in the experiment were different from the lithology of the study site, which constitutes the limit of the method. Recently the recognition of the pebbles was attained by means of the Radio Frequency Identification (RFID) technology, which enables to detect items that have been coupled to small devices (ALLAN et alii, 2006; CURTISS et alii, 2009). A later work by BERTONI et alii (2010) allowed to extend this technique to the underwater environment. The technique is reliable and cost-effective, and proved to be suitable for abrasion rate experiments on individual samples. In addition, it is easily repeatable on different scenarios. The aim of this research is to evaluate the in situ abrasion of individual pebbles that were collected from the backshore of an artificial coarse-clastic beach and injected in the very same beach after being marked. The resulting abrasion rates were sensible and the speed at which the tracers lost weight in a limited span of time was significant enough to not be neglected when replen- ishments are projected and then set up. STUDY AREA The artificial pebble beaches at Marina di Pisa (Tu- scany, Italy) were chosen as the study site because they match several of the needed requirements, such as the limited length and the defined boundaries. The Province of Pisa invested a lot of financial resources to set up these beaches in 2006 as part of a huge coastal defense scheme (*) Department of Earth Sciences, University of Pisa, Via S. Maria, 53 - 56126 Pisa (Italy). (**) Department of Earth Sciences, University of Pisa, Via S. Maria, 53 - 56126 Pisa (Italy). Corresponding author: tel.: +39 050 2215734; fax: +39 050 2215800; e-mail: sarti@dst.unipi.it (***) Department of Information Engineering, University of Siena, Via Roma, 56 - 53100 Siena (Italy). (****) Department of Information Engineering, University of Siena, Via Roma, 56 - 53100 Siena (Italy). In situ abrasion of marked pebbles on two coarse-clastic beaches (Marina di Pisa, Italy) DUCCIO BERTONI (*), GIOVANNI SARTI (**), GIULIANO BENELLI (***) & ALESSANDRO POZZEBON (****) Ital. J. Geosci. (Boll. Soc. Geol. It.), Vol. 131, No. 2 (2012), pp. 205-214, 8 figs., 6 tabs. (doi: 10.3301/IJG.2012.04) © Società Geologica Italiana, Roma 2012 Author’s personal copy