Short term displacements of marked pebbles in the swash zone: Focus on particle shape and size

Edoardo Grottoli, Duccio Bertoni, Paolo Ciavola, Alessandro Pozzebon

Research output: Contribution to journalArticle

9 Citations (Scopus)

Abstract

In this paper, two short term experiments with tracers on a mixed beach are presented. The aim was to understand how the size and shape of pebbles can affect their transport under low energy conditions. Sediment transport was studied by means of RFID technology to univocally monitor every single marked pebble. A size subdivision of injected pebbles was conducted based on three classes ("Big" from - 5.5 to - 6.5 phi; "Medium", from - 5 to - 5.5 phi; and "Small", from - 4.5 to - 5 phi). Two recoveries were realised 6 and 24 h after the injection. During a single day, the wave motion was very low in the first experiment and low to moderate in the second (never exceeding 0.4. m). The results showed that discs are less dynamic than spheres but can cover greater distances. Regarding the sediment size, "Big" pebbles are less dynamic if compared to finer classes, and they move preferentially down the swash zone towards the step or do not move up-slope if already at the step. Very low and steady energy conditions facilitate cross-shore and offshore movement of pebbles, rather than a slight raise in wave height producing predominant longshore transport even with non-marginal displacements. Low to moderate energy conditions can also produce some trend displacement based on the pebble shape even though T-tests showed that shape was not statistically significant for pebble displacement. The displacements of "Medium" and "Small" sized pebbles show a statistical dissimilarity compared to the "Big" ones. To refine the velocity estimation necessary to initiate pebble movement, the threshold velocity formulas known up to now should involve the shape parameter, especially for the short term. Better knowledge of the relationship between the sediment's characteristics and dynamics is critical to forecast the durability of replenishment material and to establish the suitability of fill material relative to native beach material. Hence, a better understanding of the role of particle characteristics is necessary.

LanguageEnglish
Pages143-158
Number of pages16
JournalMarine Geology
Volume367
Early online date17 Jun 2015
DOIs
Publication statusPublished - 1 Sep 2015

Fingerprint

wave runup
pebble
Beaches
Sediments
Sediment transport
Radio frequency identification (RFID)
Durability
Experiments
Recovery
beach
longshore transport
energy
particle
wave height
durability
sediment
sediment transport
fill
experiment
tracer

Keywords

  • Gravel nourishments
  • Mixed beach
  • Particle shape
  • Sediment transport
  • Swash
  • Tracer

Cite this

Grottoli, Edoardo ; Bertoni, Duccio ; Ciavola, Paolo ; Pozzebon, Alessandro. / Short term displacements of marked pebbles in the swash zone : Focus on particle shape and size. 2015 ; Vol. 367. pp. 143-158.
@article{d226373dbcd94b1da04bdb21fbb85cde,
title = "Short term displacements of marked pebbles in the swash zone: Focus on particle shape and size",
abstract = "In this paper, two short term experiments with tracers on a mixed beach are presented. The aim was to understand how the size and shape of pebbles can affect their transport under low energy conditions. Sediment transport was studied by means of RFID technology to univocally monitor every single marked pebble. A size subdivision of injected pebbles was conducted based on three classes ({"}Big{"} from - 5.5 to - 6.5 phi; {"}Medium{"}, from - 5 to - 5.5 phi; and {"}Small{"}, from - 4.5 to - 5 phi). Two recoveries were realised 6 and 24 h after the injection. During a single day, the wave motion was very low in the first experiment and low to moderate in the second (never exceeding 0.4. m). The results showed that discs are less dynamic than spheres but can cover greater distances. Regarding the sediment size, {"}Big{"} pebbles are less dynamic if compared to finer classes, and they move preferentially down the swash zone towards the step or do not move up-slope if already at the step. Very low and steady energy conditions facilitate cross-shore and offshore movement of pebbles, rather than a slight raise in wave height producing predominant longshore transport even with non-marginal displacements. Low to moderate energy conditions can also produce some trend displacement based on the pebble shape even though T-tests showed that shape was not statistically significant for pebble displacement. The displacements of {"}Medium{"} and {"}Small{"} sized pebbles show a statistical dissimilarity compared to the {"}Big{"} ones. To refine the velocity estimation necessary to initiate pebble movement, the threshold velocity formulas known up to now should involve the shape parameter, especially for the short term. Better knowledge of the relationship between the sediment's characteristics and dynamics is critical to forecast the durability of replenishment material and to establish the suitability of fill material relative to native beach material. Hence, a better understanding of the role of particle characteristics is necessary.",
keywords = "Gravel nourishments, Mixed beach, Particle shape, Sediment transport, Swash, Tracer",
author = "Edoardo Grottoli and Duccio Bertoni and Paolo Ciavola and Alessandro Pozzebon",
year = "2015",
month = "9",
day = "1",
doi = "10.1016/j.margeo.2015.06.006",
language = "English",
volume = "367",
pages = "143--158",

}

Short term displacements of marked pebbles in the swash zone : Focus on particle shape and size. / Grottoli, Edoardo; Bertoni, Duccio; Ciavola, Paolo; Pozzebon, Alessandro.

Vol. 367, 01.09.2015, p. 143-158.

Research output: Contribution to journalArticle

TY - JOUR

T1 - Short term displacements of marked pebbles in the swash zone

T2 - Focus on particle shape and size

AU - Grottoli, Edoardo

AU - Bertoni, Duccio

AU - Ciavola, Paolo

AU - Pozzebon, Alessandro

PY - 2015/9/1

Y1 - 2015/9/1

N2 - In this paper, two short term experiments with tracers on a mixed beach are presented. The aim was to understand how the size and shape of pebbles can affect their transport under low energy conditions. Sediment transport was studied by means of RFID technology to univocally monitor every single marked pebble. A size subdivision of injected pebbles was conducted based on three classes ("Big" from - 5.5 to - 6.5 phi; "Medium", from - 5 to - 5.5 phi; and "Small", from - 4.5 to - 5 phi). Two recoveries were realised 6 and 24 h after the injection. During a single day, the wave motion was very low in the first experiment and low to moderate in the second (never exceeding 0.4. m). The results showed that discs are less dynamic than spheres but can cover greater distances. Regarding the sediment size, "Big" pebbles are less dynamic if compared to finer classes, and they move preferentially down the swash zone towards the step or do not move up-slope if already at the step. Very low and steady energy conditions facilitate cross-shore and offshore movement of pebbles, rather than a slight raise in wave height producing predominant longshore transport even with non-marginal displacements. Low to moderate energy conditions can also produce some trend displacement based on the pebble shape even though T-tests showed that shape was not statistically significant for pebble displacement. The displacements of "Medium" and "Small" sized pebbles show a statistical dissimilarity compared to the "Big" ones. To refine the velocity estimation necessary to initiate pebble movement, the threshold velocity formulas known up to now should involve the shape parameter, especially for the short term. Better knowledge of the relationship between the sediment's characteristics and dynamics is critical to forecast the durability of replenishment material and to establish the suitability of fill material relative to native beach material. Hence, a better understanding of the role of particle characteristics is necessary.

AB - In this paper, two short term experiments with tracers on a mixed beach are presented. The aim was to understand how the size and shape of pebbles can affect their transport under low energy conditions. Sediment transport was studied by means of RFID technology to univocally monitor every single marked pebble. A size subdivision of injected pebbles was conducted based on three classes ("Big" from - 5.5 to - 6.5 phi; "Medium", from - 5 to - 5.5 phi; and "Small", from - 4.5 to - 5 phi). Two recoveries were realised 6 and 24 h after the injection. During a single day, the wave motion was very low in the first experiment and low to moderate in the second (never exceeding 0.4. m). The results showed that discs are less dynamic than spheres but can cover greater distances. Regarding the sediment size, "Big" pebbles are less dynamic if compared to finer classes, and they move preferentially down the swash zone towards the step or do not move up-slope if already at the step. Very low and steady energy conditions facilitate cross-shore and offshore movement of pebbles, rather than a slight raise in wave height producing predominant longshore transport even with non-marginal displacements. Low to moderate energy conditions can also produce some trend displacement based on the pebble shape even though T-tests showed that shape was not statistically significant for pebble displacement. The displacements of "Medium" and "Small" sized pebbles show a statistical dissimilarity compared to the "Big" ones. To refine the velocity estimation necessary to initiate pebble movement, the threshold velocity formulas known up to now should involve the shape parameter, especially for the short term. Better knowledge of the relationship between the sediment's characteristics and dynamics is critical to forecast the durability of replenishment material and to establish the suitability of fill material relative to native beach material. Hence, a better understanding of the role of particle characteristics is necessary.

KW - Gravel nourishments

KW - Mixed beach

KW - Particle shape

KW - Sediment transport

KW - Swash

KW - Tracer

UR - http://www.scopus.com/inward/record.url?scp=84935006571&partnerID=8YFLogxK

U2 - 10.1016/j.margeo.2015.06.006

DO - 10.1016/j.margeo.2015.06.006

M3 - Article

VL - 367

SP - 143

EP - 158

ER -