The abrasion rate of coarse sediments often draws the interest of sedimentologists mainly because it is a primary textural property. Firstly, this topic was assessed by laboratory experiments, which involved abrasion measurements of a number of samples though (Kuenen, 1964; Latham et al., 1998; Nordstrom et al., 2008). However, after first attempts performed by Zhdanov (1958), Dornbusch et al. (2002) reckoned in situ abrasion of individual pebbles. This methodology enables the assessment of abrasion rate on single samples by no statistical means. In the present research, pebbles marked by passive integrated transponders from two artificial coarse-grained beaches at Marina di Pisa (Tuscany, Italy) were analyzed in order to measure the in situ abrasion rate. The beaches (Cella 7 and Barbarossa) are similar in concept because they 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) allows to couple a transponder to coarse sediments, which are detected back by an antenna that transmits low frequency signals. The preparation procedures of the marked pebbles did not affect the textural properties of the tracers, thus making them suitable for abrasion rate measurements. The dry and wet weights of 198 marked pebbles were accurately measured. The tracers were photographed and then released on the beaches in March 2009 along closely-spaced cross-shore transects. Along the transects, the pebbles were placed on the fair-weather berm, on the beachface, and on the step crest. The recovery campaign was carried out in May 2009, after three intense storms struck the Pisa coast, which assured a high mobilization of the sediments constituting the beaches. A total of 127 pebbles was detected, 81 of which were recovered and weighted again. Huge beach reworking during the storms determined high burial rates and consequently loss of a definite amount of tracers (the transmission and reception range of the devices was about 50 em). The pebbles that were recovered showed a significant increase in roundness, in particular the tracers that were released on Barbarossa. As a matter of fact, these pebbles lost an average of 8% of their weight, with peak values of about 34 and 22%. The average pebble weight loss measured at Cella 7 was slightly lower, which means higher mobilization rate at this site rather than at Barbarossa. This notion is further backed by the growth of algae on several Cella 7 pebbles, which is never reported on Barbarossa samples. In conclusion, a weight loss of slightly less than 10% of the initial weight can be expected on such beaches, mostly attained by a significant smoothing of the angles. These results may be useful when it comes to set up defense scheme involving artificial coarse replenishments, which are progressively more used as a protection system even where coarse-grained beaches are not naturally present.

In situ abrasion of marble pebbles tracked by RFID technology on two artificial coarse-grained beaches (Marina di Pisa, Italy): preliminary data

Bertoni D.;SARTI, GIOVANNI;
2010-01-01

Abstract

The abrasion rate of coarse sediments often draws the interest of sedimentologists mainly because it is a primary textural property. Firstly, this topic was assessed by laboratory experiments, which involved abrasion measurements of a number of samples though (Kuenen, 1964; Latham et al., 1998; Nordstrom et al., 2008). However, after first attempts performed by Zhdanov (1958), Dornbusch et al. (2002) reckoned in situ abrasion of individual pebbles. This methodology enables the assessment of abrasion rate on single samples by no statistical means. In the present research, pebbles marked by passive integrated transponders from two artificial coarse-grained beaches at Marina di Pisa (Tuscany, Italy) were analyzed in order to measure the in situ abrasion rate. The beaches (Cella 7 and Barbarossa) are similar in concept because they 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) allows to couple a transponder to coarse sediments, which are detected back by an antenna that transmits low frequency signals. The preparation procedures of the marked pebbles did not affect the textural properties of the tracers, thus making them suitable for abrasion rate measurements. The dry and wet weights of 198 marked pebbles were accurately measured. The tracers were photographed and then released on the beaches in March 2009 along closely-spaced cross-shore transects. Along the transects, the pebbles were placed on the fair-weather berm, on the beachface, and on the step crest. The recovery campaign was carried out in May 2009, after three intense storms struck the Pisa coast, which assured a high mobilization of the sediments constituting the beaches. A total of 127 pebbles was detected, 81 of which were recovered and weighted again. Huge beach reworking during the storms determined high burial rates and consequently loss of a definite amount of tracers (the transmission and reception range of the devices was about 50 em). The pebbles that were recovered showed a significant increase in roundness, in particular the tracers that were released on Barbarossa. As a matter of fact, these pebbles lost an average of 8% of their weight, with peak values of about 34 and 22%. The average pebble weight loss measured at Cella 7 was slightly lower, which means higher mobilization rate at this site rather than at Barbarossa. This notion is further backed by the growth of algae on several Cella 7 pebbles, which is never reported on Barbarossa samples. In conclusion, a weight loss of slightly less than 10% of the initial weight can be expected on such beaches, mostly attained by a significant smoothing of the angles. These results may be useful when it comes to set up defense scheme involving artificial coarse replenishments, which are progressively more used as a protection system even where coarse-grained beaches are not naturally present.
File in questo prodotto:
Non ci sono file associati a questo prodotto.

I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.

Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11568/140388
 Attenzione

Attenzione! I dati visualizzati non sono stati sottoposti a validazione da parte dell'ateneo

Citazioni
  • ???jsp.display-item.citation.pmc??? ND
  • Scopus ND
  • ???jsp.display-item.citation.isi??? ND
social impact