Hydrodynamics of a tidally forced coral reef atoll

Research output: Contribution to journalArticle

3 Citations (Scopus)

Abstract

The hydrodynamics of a tidally forced semi-enclosed coral reef atoll (North Scott) at the edge of the continental shelf of northwestern Australia were investigated by combining field observations and numerical modeling. The observations revealed that the spring tidal range outside the atoll reaches 4 m, and as the water level drops below mean sea level, the reef rim surrounding the shallow (~10–15 m) lagoon becomes exposed. During this time, the lagoon can only exchange with the open ocean through two narrow channels, resulting in highly asymmetric water levels and velocities that were most pronounced during spring tide. On average, the ebb tide duration was ~2 hr longer than the flood, with rapid flood velocities in the channel reaching 2 m/s. We applied an unstructured grid model Delft3D-Flexible Mesh to simulate the atoll hydrodynamics and were able to replicate the asymmetric water levels and complex velocities in the lagoon. The results revealed that at higher tidal stages, a dominant momentum balance exists between the pressure gradient (established by the propagation of the tide on the shelf) and the local flow acceleration of water throughout the interior of the atoll. At lower tidal stages, which coincided with a reversal of the offshore tidal pressure gradient, the lagoon became isolated from offshore dynamics and all momentum terms were negligible. This resulted in a tidally averaged residual westward flow within the lagoon that drove an asymmetric flushing pattern within the atoll, which we propose would be a common flushing mechanism within other tide-dominated atolls worldwide.

Original languageEnglish
Pages (from-to)7084-7101
Number of pages18
JournalJournal of Geophysical Research: Oceans
Volume123
Issue number10
DOIs
Publication statusPublished - Oct 2018

Fingerprint

coral reefs
lagoons
Reefs
atoll
Tides
hydrodynamics
coral reef
tides
lagoon
Hydrodynamics
Water levels
tide
surface water level
momentum
flushing
Pressure gradient
water level
Momentum
pressure gradients
pressure gradient

Cite this

@article{4620775040eb4739a460ec57f19ad4a6,
title = "Hydrodynamics of a tidally forced coral reef atoll",
abstract = "The hydrodynamics of a tidally forced semi-enclosed coral reef atoll (North Scott) at the edge of the continental shelf of northwestern Australia were investigated by combining field observations and numerical modeling. The observations revealed that the spring tidal range outside the atoll reaches 4 m, and as the water level drops below mean sea level, the reef rim surrounding the shallow (~10–15 m) lagoon becomes exposed. During this time, the lagoon can only exchange with the open ocean through two narrow channels, resulting in highly asymmetric water levels and velocities that were most pronounced during spring tide. On average, the ebb tide duration was ~2 hr longer than the flood, with rapid flood velocities in the channel reaching 2 m/s. We applied an unstructured grid model Delft3D-Flexible Mesh to simulate the atoll hydrodynamics and were able to replicate the asymmetric water levels and complex velocities in the lagoon. The results revealed that at higher tidal stages, a dominant momentum balance exists between the pressure gradient (established by the propagation of the tide on the shelf) and the local flow acceleration of water throughout the interior of the atoll. At lower tidal stages, which coincided with a reversal of the offshore tidal pressure gradient, the lagoon became isolated from offshore dynamics and all momentum terms were negligible. This resulted in a tidally averaged residual westward flow within the lagoon that drove an asymmetric flushing pattern within the atoll, which we propose would be a common flushing mechanism within other tide-dominated atolls worldwide.",
keywords = "atoll, coral reef, flushing, hydrodynamics, tide-dominated",
author = "Green, {Rebecca H.} and Lowe, {Ryan J.} and Buckley, {Mark L.}",
year = "2018",
month = "10",
doi = "10.1029/2018JC013946",
language = "English",
volume = "123",
pages = "7084--7101",
journal = "Journal of Geophysical Research C: Oceans",
issn = "2169-9275",
publisher = "American Geophysical Union",
number = "10",

}

Hydrodynamics of a tidally forced coral reef atoll. / Green, Rebecca H.; Lowe, Ryan J.; Buckley, Mark L.

In: Journal of Geophysical Research: Oceans, Vol. 123, No. 10, 10.2018, p. 7084-7101.

Research output: Contribution to journalArticle

TY - JOUR

T1 - Hydrodynamics of a tidally forced coral reef atoll

AU - Green, Rebecca H.

AU - Lowe, Ryan J.

AU - Buckley, Mark L.

PY - 2018/10

Y1 - 2018/10

N2 - The hydrodynamics of a tidally forced semi-enclosed coral reef atoll (North Scott) at the edge of the continental shelf of northwestern Australia were investigated by combining field observations and numerical modeling. The observations revealed that the spring tidal range outside the atoll reaches 4 m, and as the water level drops below mean sea level, the reef rim surrounding the shallow (~10–15 m) lagoon becomes exposed. During this time, the lagoon can only exchange with the open ocean through two narrow channels, resulting in highly asymmetric water levels and velocities that were most pronounced during spring tide. On average, the ebb tide duration was ~2 hr longer than the flood, with rapid flood velocities in the channel reaching 2 m/s. We applied an unstructured grid model Delft3D-Flexible Mesh to simulate the atoll hydrodynamics and were able to replicate the asymmetric water levels and complex velocities in the lagoon. The results revealed that at higher tidal stages, a dominant momentum balance exists between the pressure gradient (established by the propagation of the tide on the shelf) and the local flow acceleration of water throughout the interior of the atoll. At lower tidal stages, which coincided with a reversal of the offshore tidal pressure gradient, the lagoon became isolated from offshore dynamics and all momentum terms were negligible. This resulted in a tidally averaged residual westward flow within the lagoon that drove an asymmetric flushing pattern within the atoll, which we propose would be a common flushing mechanism within other tide-dominated atolls worldwide.

AB - The hydrodynamics of a tidally forced semi-enclosed coral reef atoll (North Scott) at the edge of the continental shelf of northwestern Australia were investigated by combining field observations and numerical modeling. The observations revealed that the spring tidal range outside the atoll reaches 4 m, and as the water level drops below mean sea level, the reef rim surrounding the shallow (~10–15 m) lagoon becomes exposed. During this time, the lagoon can only exchange with the open ocean through two narrow channels, resulting in highly asymmetric water levels and velocities that were most pronounced during spring tide. On average, the ebb tide duration was ~2 hr longer than the flood, with rapid flood velocities in the channel reaching 2 m/s. We applied an unstructured grid model Delft3D-Flexible Mesh to simulate the atoll hydrodynamics and were able to replicate the asymmetric water levels and complex velocities in the lagoon. The results revealed that at higher tidal stages, a dominant momentum balance exists between the pressure gradient (established by the propagation of the tide on the shelf) and the local flow acceleration of water throughout the interior of the atoll. At lower tidal stages, which coincided with a reversal of the offshore tidal pressure gradient, the lagoon became isolated from offshore dynamics and all momentum terms were negligible. This resulted in a tidally averaged residual westward flow within the lagoon that drove an asymmetric flushing pattern within the atoll, which we propose would be a common flushing mechanism within other tide-dominated atolls worldwide.

KW - atoll

KW - coral reef

KW - flushing

KW - hydrodynamics

KW - tide-dominated

UR - http://www.scopus.com/inward/record.url?scp=85054586478&partnerID=8YFLogxK

U2 - 10.1029/2018JC013946

DO - 10.1029/2018JC013946

M3 - Article

VL - 123

SP - 7084

EP - 7101

JO - Journal of Geophysical Research C: Oceans

JF - Journal of Geophysical Research C: Oceans

SN - 2169-9275

IS - 10

ER -