Current dynamics across a platform reef in the Red Sea near Jeddah, Saudi Arabia, are examined using 18 months of current profile, pressure, surface wave, and wind observations. The platform reef is 700 m long, 200 m across with spatial and temporal variations in water depth over the reef ranging from 0.6 to 1.6 m. Surface waves breaking at the seaward edge of the reef cause a 2-10 cm setup of sea level that drives cross-reef currents of 5-20 cm s-1. Bottom stress is a significant component of the wave setup balance in the surf zone. Over the reef flat, where waves are not breaking, the cross-reef pressure gradient associated with wave setup is balanced by bottom stress. The quadratic drag coefficient for the depth-average flow decreases with increasing water depth from Cda = 0.17 in 0.4 m of water to Cda = 0.03 in 1.2 m of water. The observed dependence of the drag coefficient on water depth is consistent with open-channel flow theory and a hydrodynamic roughness of zo = 0.06 m. A simple one-dimensional model driven by incident surface waves and wind stress accurately reproduces the observed depth-averaged cross-reef currents and a portion of the weaker along-reef currents over the focus reef and two other Red Sea platform reefs. The model indicates the cross-reef current is wave forced and the along-reef current is partially wind forced.
|Original language||English (US)|
|Number of pages||17|
|Journal||JOURNAL OF GEOPHYSICAL RESEARCH-OCEANS|
|State||Published - Jan 29 2016|
Bibliographical noteKAUST Repository Item: Exported on 2022-05-31
Acknowledged KAUST grant number(s): KSA 00011
Acknowledgements: The authors are grateful for the scientific and technical support provided by colleagues at King Abdullah University of Sciences and Technology (KAUST), in particular Yasser Abualnaja, Abdulaziz Al-Suwailem, Haitham Aljahdali, Mohsen Aljahdali, Ramzi Aljahdali, Wael Almoazen, Captain Evangelos G. Aravantinos, Yasser Kattan, and all the crew members of the Boston Whaler used in our field work. We also thank C. Marquette, J. Kemp, J. Ryder, S. Whelan, J. Smith, P. Bouchard, J. Lord and the rigging shop, all of Woods Hole Oceanographic Institution, for their efforts in instrument preparation, deployment, and recovery. This research is based on work supported by awards USA 00002 and KSA 00011 KAUST. K. Davis was supported by a WHOI Postdoctoral Fellowship. T. Farrar was partly supported by NSF grant OCE-1435665. S. Lentz was partly supported by NSF grants OCE-1332646 and OCE-1357290. Data are available from the corresponding author (email@example.com) upon request, subject to approval from KAUST. The authors thank two anonymous reviewers for comments and suggestions that improved the manuscript.
This publication acknowledges KAUST support, but has no KAUST affiliated authors.