Spectral wave-driven sediment transport across a fringing reef

Andrew Pomeroy, Ryan Lowe, A.R. Van Dongeren, Marco Ghisalberti, D. Roelvink

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Abstract

© 2015 Elsevier B.V. A laboratory experiment was conducted to investigate the dynamics of cross-shore sediment transport across a fringing coral reef. The aim was to quantify how a highly bimodal spectrum of high-frequency (sea-swell) and low-frequency (infragravity and seiching) waves that is typically present on coral reef flats, influences the various sediment transport mechanisms. The experiments were conducted in a 55. m wave flume, using a 1:15 scale fringing reef model that had a 1:5 forereef slope, a 14. m long reef flat, and a 1:12 sloping beach. The initial 7. m of reef flat had a fixed bed, whereas the back 7. m of the reef and the beach had a moveable sandy bed. Four seven-hour irregular wave cases were conducted both with and without bottom roughness elements (schematically representing bottom friction by coral roughness), as well as for both low and high still water levels. We observed that the wave energy on the reef flat was partitioned between two primary frequency bands (high and low), and the proportion of energy within each band varied substantially across the reef flat, with the low-frequency waves becoming increasingly important near the shore. The offshore transport of suspended sediment by the Eulerian mean flow was the dominant transport mechanism near the reef crest, but a wide region of onshore transport prevailed on the reef flat where low-frequency waves were very important to the overall transport. Ripples developed over the movable bed and their properties were consistent with the local high-frequency wave orbital excursion lengths despite substantial low-frequency wave motions also present on the reef flat. This study demonstrated that while a proportion of the sediment was transported by bedload and mean flow, the greatest contributions to cross-shore transport were due to the skewness and asymmetry of the high and low-frequency waves.
Original languageEnglish
Pages (from-to)78-94
JournalCoastal Engineering
Volume98
Early online date17 Feb 2015
DOIs
Publication statusPublished - Apr 2015

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Reefs
Sediment transport
Beaches
Surface roughness
Suspended sediments
Water levels
Frequency bands
Sediments
Experiments
Friction

Cite this

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title = "Spectral wave-driven sediment transport across a fringing reef",
abstract = "{\circledC} 2015 Elsevier B.V. A laboratory experiment was conducted to investigate the dynamics of cross-shore sediment transport across a fringing coral reef. The aim was to quantify how a highly bimodal spectrum of high-frequency (sea-swell) and low-frequency (infragravity and seiching) waves that is typically present on coral reef flats, influences the various sediment transport mechanisms. The experiments were conducted in a 55. m wave flume, using a 1:15 scale fringing reef model that had a 1:5 forereef slope, a 14. m long reef flat, and a 1:12 sloping beach. The initial 7. m of reef flat had a fixed bed, whereas the back 7. m of the reef and the beach had a moveable sandy bed. Four seven-hour irregular wave cases were conducted both with and without bottom roughness elements (schematically representing bottom friction by coral roughness), as well as for both low and high still water levels. We observed that the wave energy on the reef flat was partitioned between two primary frequency bands (high and low), and the proportion of energy within each band varied substantially across the reef flat, with the low-frequency waves becoming increasingly important near the shore. The offshore transport of suspended sediment by the Eulerian mean flow was the dominant transport mechanism near the reef crest, but a wide region of onshore transport prevailed on the reef flat where low-frequency waves were very important to the overall transport. Ripples developed over the movable bed and their properties were consistent with the local high-frequency wave orbital excursion lengths despite substantial low-frequency wave motions also present on the reef flat. This study demonstrated that while a proportion of the sediment was transported by bedload and mean flow, the greatest contributions to cross-shore transport were due to the skewness and asymmetry of the high and low-frequency waves.",
author = "Andrew Pomeroy and Ryan Lowe and {Van Dongeren}, A.R. and Marco Ghisalberti and D. Roelvink",
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Spectral wave-driven sediment transport across a fringing reef. / Pomeroy, Andrew; Lowe, Ryan; Van Dongeren, A.R.; Ghisalberti, Marco; Roelvink, D.

In: Coastal Engineering, Vol. 98, 04.2015, p. 78-94.

Research output: Contribution to journalArticle

TY - JOUR

T1 - Spectral wave-driven sediment transport across a fringing reef

AU - Pomeroy, Andrew

AU - Lowe, Ryan

AU - Van Dongeren, A.R.

AU - Ghisalberti, Marco

AU - Roelvink, D.

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N2 - © 2015 Elsevier B.V. A laboratory experiment was conducted to investigate the dynamics of cross-shore sediment transport across a fringing coral reef. The aim was to quantify how a highly bimodal spectrum of high-frequency (sea-swell) and low-frequency (infragravity and seiching) waves that is typically present on coral reef flats, influences the various sediment transport mechanisms. The experiments were conducted in a 55. m wave flume, using a 1:15 scale fringing reef model that had a 1:5 forereef slope, a 14. m long reef flat, and a 1:12 sloping beach. The initial 7. m of reef flat had a fixed bed, whereas the back 7. m of the reef and the beach had a moveable sandy bed. Four seven-hour irregular wave cases were conducted both with and without bottom roughness elements (schematically representing bottom friction by coral roughness), as well as for both low and high still water levels. We observed that the wave energy on the reef flat was partitioned between two primary frequency bands (high and low), and the proportion of energy within each band varied substantially across the reef flat, with the low-frequency waves becoming increasingly important near the shore. The offshore transport of suspended sediment by the Eulerian mean flow was the dominant transport mechanism near the reef crest, but a wide region of onshore transport prevailed on the reef flat where low-frequency waves were very important to the overall transport. Ripples developed over the movable bed and their properties were consistent with the local high-frequency wave orbital excursion lengths despite substantial low-frequency wave motions also present on the reef flat. This study demonstrated that while a proportion of the sediment was transported by bedload and mean flow, the greatest contributions to cross-shore transport were due to the skewness and asymmetry of the high and low-frequency waves.

AB - © 2015 Elsevier B.V. A laboratory experiment was conducted to investigate the dynamics of cross-shore sediment transport across a fringing coral reef. The aim was to quantify how a highly bimodal spectrum of high-frequency (sea-swell) and low-frequency (infragravity and seiching) waves that is typically present on coral reef flats, influences the various sediment transport mechanisms. The experiments were conducted in a 55. m wave flume, using a 1:15 scale fringing reef model that had a 1:5 forereef slope, a 14. m long reef flat, and a 1:12 sloping beach. The initial 7. m of reef flat had a fixed bed, whereas the back 7. m of the reef and the beach had a moveable sandy bed. Four seven-hour irregular wave cases were conducted both with and without bottom roughness elements (schematically representing bottom friction by coral roughness), as well as for both low and high still water levels. We observed that the wave energy on the reef flat was partitioned between two primary frequency bands (high and low), and the proportion of energy within each band varied substantially across the reef flat, with the low-frequency waves becoming increasingly important near the shore. The offshore transport of suspended sediment by the Eulerian mean flow was the dominant transport mechanism near the reef crest, but a wide region of onshore transport prevailed on the reef flat where low-frequency waves were very important to the overall transport. Ripples developed over the movable bed and their properties were consistent with the local high-frequency wave orbital excursion lengths despite substantial low-frequency wave motions also present on the reef flat. This study demonstrated that while a proportion of the sediment was transported by bedload and mean flow, the greatest contributions to cross-shore transport were due to the skewness and asymmetry of the high and low-frequency waves.

U2 - 10.1016/j.coastaleng.2015.01.005

DO - 10.1016/j.coastaleng.2015.01.005

M3 - Article

VL - 98

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EP - 94

JO - Coastal Engineering

JF - Coastal Engineering

SN - 0378-3839

ER -