Coral Reef Drag Coefficients - Water Depth Dependence

S. J. Lentz, K. A. Davis, J. H. Churchill, T. M. DeCarlo

Research output: Contribution to journalArticlepeer-review

35 Scopus citations


A major challenge in modeling the circulation over coral reefs is uncertainty in the drag coefficient because existing estimates span two orders of magnitude. Current and pressure measurements from five coral reefs are used to estimate drag coefficients based on depth-average flow, assuming a balance between the cross-reef pressure gradient and the bottom stress. At two sites wind stress is a significant term in the cross-reef momentum balance and is included in estimating the drag coefficient. For the five coral reef sites and a previous laboratory study, estimated drag coefficients increase as the water depth decreases consistent with open channel flow theory. For example, for a typical coral reef hydrodynamic roughness of 5 cm, observational estimates, and the theory indicate that the drag coefficient decreases from 0.4 in 20 cm of water to 0.005 in 10 m of water. Synthesis of results from the new field observations with estimates from previous field and laboratory studies indicate that coral reef drag coefficients range from 0.2 to 0.005 and hydrodynamic roughnesses generally range from 2 to 8 cm. While coral reef drag coefficients depend on factors such as physical roughness and surface waves, a substantial fraction of the scatter in estimates of coral reef drag coefficients is due to variations in water depth.
Original languageEnglish (US)
Pages (from-to)1061-1075
Number of pages15
JournalJournal of Physical Oceanography
Issue number5
StatePublished - May 1 2017
Externally publishedYes

Bibliographical note

KAUST Repository Item: Exported on 2022-06-03
Acknowledged KAUST grant number(s): KSA 00011, USA 00002
Acknowledgements: The authors thank Dr. Yasser Abualnaja, Dr. Abdulaziz Al-Suwailem, Haitham Aljahdali, Mohsen Aljahdali, Ramzi Aljahdali, Wael Almoazen, Captain Evangelos G. Aravantinos, Yasser Kattan, the whaler crew from King Abdullah University of Sciences and Technology (KAUST), and C. Marquette of Woods Hole Oceanographic Institution (WHOI) for providing logistical and field support. The Red Sea field program was supported by Awards USA 00002 and KSA 00011 made by KAUST to S. Lentz and J. Churchill. Data are available from corresponding author ( upon request, subject to approval from KAUST.; The authors thank George P. Lohmann, Kathryn A. Rose, Rebecca Belastock (all WHOI), Jay Andrew, Geory Mereb, Arius Merep, Dawnette Olsudong (all PICRC), Rodney Salm, and Elizabeth Mcleod (The Nature Conservancy). The Palau field program was funded by NSF Award OCE-1220529.; We thank Keryea Soong and the Dongsha Atoll Research Station; the Dongsha Atoll Marine National Park; the crew of the Ocean Researcher 3; Pat Lohmann (WHOI); Kathyryn Shamberger (Texas A&M University); Aryan Safie (UC Irvine); and Lisa Hou, Kuo-Yuan Lee, and Yao-Chu Wu (Academia Sinica) for assistance with fieldwork and logistics. The Dongsha field program was supported by NSF Award OCE-1220529 and by the Academia Sinica (Taiwan) through a thematic project grant to George Wong and Fuh-Kwo Shiah. CCMP Version-2.0 vector wind analyses are produced by Remote Sensing Systems. Data are available at S. Lentz was supported for the analysis by NSF Award OCE-1558343.
This publication acknowledges KAUST support, but has no KAUST affiliated authors.

ASJC Scopus subject areas

  • Oceanography


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