Shallow-water Frictional Effects in Island Wakes

Furukawa, Keita; Wolanski, Eric

doi:10.1006/ecss.1997.0301

Cited by 28 publications

(12 citation statements)

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“…Furukawa and Wolanski (1998) suggest that it is not possible to model unsteady island wakes correctly using classical fixed-grid models, justifying their use of a discrete vortex model. TFD, however, accurately reproduced the features of Beamer Rock wake, as confirmed by field observations.…”

Section: Discussionmentioning

confidence: 96%

Observations and simulations of an unsteady island wake in the Firth of Forth, Scotland

Neill

Elliott

2004

Ocean Dynamics

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Beamer Rock, a 50-m-wide island in the Firth of Forth, produces a distinctive von Ka´rma´n vortex street wake, the characteristics of which depend on the speed and direction of the tidal flow. ADCP (acoustic Doppler current profiler), CTD (conductivity-temperature-depth) and aerial photograph data were collected from the region during flood and ebb tidal flow under neap and spring conditions. Good agreement was found between the observations and the results from a fixedgrid depth-averaged numerical tidal model. The island wake parameter correctly predicted the unsteady nature of the wake, and the Strouhal number (defined in terms of flow past a circular cylinder) was found to give excellent predictions of the wake wavelength when scaled on the island width. Contrary to published results, the study shows that it is possible to accurately simulate an unsteady island wake using a relatively coarse fixed-grid numerical model.

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Section: Discussionmentioning

confidence: 96%

Observations and simulations of an unsteady island wake in the Firth of Forth, Scotland

Neill

Elliott

2004

Ocean Dynamics

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“…Settling rates of 3-62-m diameter quartz particles, as indicated by Stokes' Law, are 2-3 m h Ϫ1 and are of sufficient magnitude to explain the observed decline in light attenuance. Deep scour holes are reported in the region where island flanks are aligned normal to the incident flow (Wolanski et al 1984a;Furakawa and Wolanski 1998) and where coarse shell fragments are found on the seabed. Similar scour holes would be expected near the flanks of Derwent Island.…”

Section: Discussionmentioning

confidence: 98%

Entrainment and advection in an island's tidal wake, as revealed by light attenuance, zooplankton, and ichthyoplankton

Suthers

Taggart

Kelley

et al. 2004

Limnology & Oceanography

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Spatial and temporal patterns of light attenuance, zooplankton abundance, and larval fish assemblages observed at night in the flood tide wake of a 2-km-wide, steep-sided island within the Great Barrier Reef lagoon (40-45-m local depth) are compared with two simple models. Eddy upwelling is shown to be slow relative to erosion, vertical entrainment, and advection (EA) arising near the flanks of the island, where currents were accelerated to 1-2 m s Ϫ1 , approximately twice that in the free stream. Turbidity (particles Ͻ300-m equivalent spherical diameter [ESD], inferred from increased water column light attenuance of an optical plankton counter) and medium-sized zooplankton (700-1,000-m ESD) appeared to be entrained toward the surface, to form a V-shaped plume. The plume originated near the island's flanks and converged 4 km downstream. Here, light attenuance returned to the free stream conditions, presumably as sediments settled, leaving a patch of medium-sized zooplankton that had a three-to fourfold greater biomass concentration than the free stream. A decrease in the concentration of small zooplankton (300-500-m ESD, generally found in surface waters) is also consistent with vertical mixing by EA. Neuston net collections across the wake revealed two larval fish assemblages that were correlated with either the small surface zooplankton or with the deeper, medium-sized zooplankton, which included epibenthic taxa. If EA is a common process for patch formation in tidal waters, then the geometry of the associated plumes may predict larval settlement (recruitment ''hotspots'') in shallow tidal waters.Swirls of turbidity in the wakes of small islands are distinctive features within shallow, tidally energetic areas such as the Great Barrier Reef lagoon (Hamner and Hauri 1977; Wolanski et al. 1984a,b). Wakes of this nature may extend downstream several island diameters within the semidiurnal tidal excursion, and they may exist for periods of 4-5 h (Black and Gay 1986;Signell and Geyer 1991). Wakes may AcknowledgmentsWe are grateful to the crew and captain of the RV Franklin, along with the Commonwealth Scientific and Industrial Research Organisation personnel who contributed to the success of the cruise. We acknowledge constructive discussions with C. Reiss and K. Thompson at Dalhousie University and two anonymous reviewers. GeoScience Australia, the National Tidal Facility at Flinders University and B. Petrie assisted with bathymetry data and tidal interpretation. We thank R. Piola and S. Murray for the zooplankton analyses.Funding was provided by the Australian Research Council; the Department of Industry, Trade and Commerce; the Australian Geographic magazine; Focal Technologies; the Canada Department of Fisheries and Oceans; and the Natural Sciences and Engineering Research Council of Canada. enhance mixing (Townsend et al. 1983) and modify sediment transport, thus influencing the bathymetry. Wakes can also have biological consequences that affect species-diversity gradients and plankton patchiness Hauri...

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“…Much of the interest in island and headland wakes relates to their effects on the structure of marine ecosystems – from primary productivity to top predators – and has implications for fisheries, waste disposal, coastal development and geomorphology (Furukawa and Wolanski, 1998).…”

Section: Discussionmentioning

confidence: 99%

Flow‐field observations of a tidally driven island wake used by marine mammals in the Bay of Fundy, Canada

Johnston¹,

Read

2007

Fisheries Oceanography

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Correlations between fine-scale oceanographic features and aggregations of marine mammals are frequently reported, but the physical forces shaping these relationships are rarely explored. We conducted a series of oceanographic observations and remote sensing surveys of an oceanographic feature near Grand Manan Island known to attract marine mammals on flood tides. We tracked drift drogues from cliff-top with a theodolite and conducted boxtype surveys with an acoustic Doppler current profiler (ADCP) to assess flow patterns within the oceanographic feature. The feature was also visualized with Synthetic Aperture Radar (SAR) scenes. Drift drogues were advected towards a shear line originating near the northern tip of the island and entrained in one or more eddies downstream. ADCP surveys confirmed the presence of the shear line between rapid easterly flow and slower return flow. As the tide progressed, the shear line extended and manifested a single anti-cyclonic eddy at its distal end. As the flood tide progressed, northerly flow along the eastern shore of the island intensified and deflected the shear line northwards, shedding the eddy at slack high water. SAR images confirmed the presence of the shearline and eddy system, illustrating the evolution of a wake behind the island on flood tides. Profiles of flow direction and acoustic backscatter revealed secondary flows within the wake consistent with models and observations of other wakes. Oceanographic and remote sensing observations confirm that an island wake is generated by tidal flow past Grand Manan Island and provide an ecological context for the predictable aggregations of odontocete and mysticete cetaceans observed foraging within this region.

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Shallow-water Frictional Effects in Island Wakes

Cited by 28 publications

References 0 publications

Observations and simulations of an unsteady island wake in the Firth of Forth, Scotland

Observations and simulations of an unsteady island wake in the Firth of Forth, Scotland

Entrainment and advection in an island's tidal wake, as revealed by light attenuance, zooplankton, and ichthyoplankton

Flow‐field observations of a tidally driven island wake used by marine mammals in the Bay of Fundy, Canada

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