TY - JOUR
T1 - On the displacement of marked pebbles on two coarse-clastic beaches during short fair-weather periods (Marina di Pisa and Portonovo, Italy)
AU - Bertoni, Duccio
AU - Grottoli, Edoardo
AU - Ciavola, Paolo
AU - Sarti, Giovanni
AU - Benelli, Giuliano
AU - Pozzebon, Alessandro
PY - 2013/12/31
Y1 - 2013/12/31
N2 - 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 significantly (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 preferential 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 backwash. 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.
AB - 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 significantly (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 preferential 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 backwash. 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.
KW - Beach
KW - Wave Height
KW - Pebble
KW - Significant Wave Height
KW - Beach Profile
UR - http://www.scopus.com/inward/record.url?scp=84887156060&partnerID=8YFLogxK
U2 - 10.1007/s00367-013-0341-3
DO - 10.1007/s00367-013-0341-3
M3 - Article
AN - SCOPUS:84887156060
SN - 0276-0460
VL - 33
SP - 463
EP - 476
JO - Geo-Marine Letters
JF - Geo-Marine Letters
IS - 6
ER -