Surface gravity wave transformation across a platform coral reef in the Red Sea

S. J. Lentz, J. H. Churchill, K. A. Davis, J. T. Farrar

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48 Scopus citations

Abstract

The transformation of surface gravity waves across a platform reef in the Red Sea is examined using 18 months of observations and a wave transformation model developed for beaches. The platform reef is 200 m across, 700 m long, and the water depth varies from 0.3 to 1.2 m. Assuming changes in wave energy flux are due to wave breaking and bottom drag dissipation, the wave transformation model with optimal parameters characterizing the wave breaking (γm = 0.25) and bottom drag (hydrodynamic roughness zo = 0.08 m) accounts for 75%-90% of the observed wave-height variance at four sites. The observations and model indicate that wave breaking dominates the dissipation in a 20-30 m wide surf zone while bottom drag dominates the dissipation over the rest of the reef. Friction factors (drag coefficients) estimated from the observed wave energy balance range from fw = 0.5 to fw = 5 and increase as wave-orbital displacements decrease. The observed dependence on wave-orbital displacement is roughly consistent with extrapolation of an empirical relationship based on numerous laboratory studies of oscillatory flow. As a consequence of the dependence on wave-orbital displacement, wave friction factors vary temporally due to changes in water depth and incident wave heights, and spatially across the reef as the waves decay.
Original languageEnglish (US)
Pages (from-to)693-705
Number of pages13
JournalJournal of Geophysical Research: Oceans
Volume121
Issue number1
DOIs
StatePublished - Jan 22 2016
Externally publishedYes

Bibliographical note

KAUST Repository Item: Exported on 2020-10-01
Acknowledged KAUST grant number(s): USA 00002, KSA 00011
Acknowledgements: The authors would like to thank Dr. Yasser Abualnaja, Dr.Abdulaziz Al-Suwailem, Haitham Aljahdali, Mohsen Aljahdali, Ramzi Aljahdali, WaelAlmoazen, Captain Evangelos G. Aravantinos, Yasser Kattan, and all the whaler crewfrom King Abdullah University of Sciences and Technology (KAUST) for providinglogistical and field support. We'd also like to thank C. Marquette, J. Kemp, J. Ryder, S.Whelan, J. Smith, P. Bouchard, J. Lord and the rigging shop, all of Woods HoleOceanographic Institution (WHOI), for their efforts in instrument preparation,deployment, and recovery. This research is based on work supported by Award Nos.USA 00002 and KSA 00011 made by King Abdullah University of Science andTechnology (KAUST). K. Davis was supported by a WHOI Postdoctoral Fellowship. T.Farrar was partly supported by NSF Grant OCE-1435665. S. Lentz was partly supportedby NSF Grants OCE-1332646 and OCE-1357290. Data is available from correspondingauthor (slentz@whoi.edu) upon request, subject to approval from KAUST. The authorsthank two anonymous reviewers for recommendations and comments that substantiallyimproved this manuscript.
This publication acknowledges KAUST support, but has no KAUST affiliated authors.

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