Harris, Daniel L., Vila-Concejo, A., Webster, J.M. and Power, H.E. (2015) Spatial variations in wave transformation and sediment entrainment on a coral reef sand apron. Marine Geology, 363 . pp. 220-229. DOI https://doi.org/10.1016/j.margeo.2015.02.010.

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Abstract

Waves are the main hydrodynamic force acting on coral reefs and are crucial in driving the evolution of reef systems. Previous research has mainly focused on wave breaking and transformation on the reef flat but often neglected the spatial variation of reformed wave characteristics once they have propagated into the back-reef environment. This study examines wave conditions on a reef flat and the adjacent back-reef sand apron specifically focusing on the transformation of wave height, period and spectra (including changes to long-period and incident wave height). The ability of reformed waves in the back-reef environment to entrain sediment is also investigated. Wave conditions were found to be distinctly different on the sand apron compared to the reef flat, with the majority of wave energy dissipated during initial breaking and transformation. Almost all incident waves are dissipated on the reef flat under a depth threshold of 0.5 m before reaching the back-reef with long-period motions dominating in the back-reef during these tidal stages. At higher tidal stages incident waves are capable of propagating into the back reef but they are very low energy with under 1% of all waves capable of entraining sediment. This suggests that higher energy events, such as high frequency storms, are required to significantly transport sediment and change reef geomorphology. Smaller scale spatial changes in wave height were observed on the sand apron that shows the influence of both cross- and along-reef attenuation processes. A distance parameter (Xpd) is introduced that combines the cross-reef distance from the reef crest (Xd) and the temporally specific along-reef distance from the first point of wave breaking on the reef rim (Xp, where Xpd = Xd + Xp). Xpd is shown to accurately describe the changes in wave height and sediment entrainment if deep water significant wave height, wave direction, and depth over the reef flat are known. The results in this study shows that wave conditions, sediment entrainment, and longer term trends in sediment characteristics can be predicted in back-reef environments from a few simple geomorphic inputs.

Document Type: Article
Research affiliation: Affiliations > Not ZMT
Biogeochemistry and Geology
Refereed: Yes
Open Access Journal?: No
DOI etc.: https://doi.org/10.1016/j.margeo.2015.02.010
ISSN: 00253227
Date Deposited: 25 Jul 2019 14:03
Last Modified: 01 Oct 2020 12:59
URI: http://cris.leibniz-zmt.de/id/eprint/2415

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