Observations of Bed Roughness of a Coral Reef

Nunes, V.B.; Pawlak, Geno

doi:10.2112/05-0616.1

Cited by 54 publications

(37 citation statements)

References 13 publications

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“…8, red lines). Pomeroy et al (2012) found essentially the same dependence on water depth for drag coefficients associated with infragravity wave motions over a coral reef (Fig. 8b in their paper).…”

Section: Depthsupporting

confidence: 55%

“…Previous studies in a variety of fields suggest the relationship between hydrodynamic and physical roughness is complex, depending, for example, on the ratio of roughness frontal area to bed area (e.g., Raupach et al 1991;Britter and Hanna 2003;Jimenez 2004; see also Monismith et al 2015). Consequently, determining a useful characterization of the physical roughness over coral reefs that is relevant to bottom stress is a major challenge (Nunes and Pawlak 2008;Zawada et al 2010;Rosman andHench 2011, Jaramillo andPawlak 2011;Hearn 2011). Accounting for the water depth dependence of the drag coefficients to get accurate estimates of hydrodynamic roughness is an important first step.…”

Section: Discussionmentioning

confidence: 99%

“…The dependence of C da on water depth was included in some early studies of nutrient uptake by corals (e.g., Atkinson and Bilger 1992;Hearn et al 2001), and a more recent laboratory study of flow over coral (McDonald et al 2006) indicates that the drag coefficient depends on water depth. However, studies estimating the drag coefficient over coral reefs using field measurements have not generally considered the dependence of the drag coefficient on water depth [though see Pomeroy et al (2012) and Lowe et al (2015) for two exceptions].…”

Section: Introductionmentioning

confidence: 99%

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Coral Reef Drag Coefficients – Water Depth Dependence

Lentz

Davis

Churchill

et al. 2017

Journal of Physical Oceanography

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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.

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Section: Depthsupporting

confidence: 55%

Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Coral Reef Drag Coefficients – Water Depth Dependence

Lentz

Davis

Churchill

et al. 2017

Journal of Physical Oceanography

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“…Traditionally, such models empirically estimate reef roughness by parameterizing conventional friction models based on a few in situ current measurements [Hearn, 1999]. The accuracy of such parameterizations decreases as roughness increases, and also as it exhibits spatial heterogeneity [Nunes and Pawlak, 2008]. This failure is attributable to the inherent topographic irregularities of the reef spanning multiple scales.…”

Section: Discussionmentioning

confidence: 99%

“…For reefs, greater topographic complexity has been shown to be positively correlated with high species diversity [Risk, 1972;Talbot, 1965], primary productivity [Barnes, 1988], and biomass density [Luckhurst and Luckhurst, 1978]; to provide refuge from predation [Idjadi and Edmunds, 2006;Steele, 1999]; and to supplement larval settlement space [Idjadi and Edmunds, 2006]. In addition, topographic complexity has profound hydrodynamic effects, dictating water flow around, over, and through the reef [Hearn, 2008;Monismith, 2007;Munk and Sargent, 1954;Nunes and Pawlak, 2008], as well as enhancing energy dissipation and, thereby, nutrient uptake and mass-transfer rates [Hearn et al, 2001;Shashar et al, 1996]. Given this range of influence, quantifying and mapping the spatial variability in topographic complexity over multiple spatial scales is important to understanding the functioning of a coral reef ecosystem.…”

Section: Introductionmentioning

confidence: 99%

Topographic complexity and roughness of a tropical benthic seascape

Zawada

Piniak²,

Hearn³

2010

Geophysical Research Letters

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[1] Topographic complexity is a fundamental structural property of benthic marine ecosystems that exists across all scales and affects a multitude of processes. Coral reefs are a prime example, for which this complexity has been found to impact water flow, species diversity, nutrient uptake, and wave-energy dissipation, among other properties. Despite its importance, only limited assessments are available regarding the distribution or range of topographic complexity within or between benthic communities. Here, we show substantial variability in topographic complexity over the entire inner-shelf seascape of a tropical island. Roughness, estimated in terms of fractal dimension, served as a proxy for topographic complexity, and was computed for linear transects (D T ), as well as the benthic surface (D S ). Spatial variability in both D T and D S was correlated with the known distribution of benthic cover types in the seascape. Transect roughness values ranged from 1.0 to 1.7, with features along the shelf edge being markedly anisotropic with an along-shore bias, whereas regions with high scleractinian coral cover were nearly isotropic and exhibited minimal directional bias. Surface-roughness values ranged from 2.0 in predominantly hardbottom areas with low coral cover to 2.5 in areas with high coral cover. Quantifying roughness across the substrates and biological communities for an entire seascape provides a synoptic view of its spatial variability at scales appropriate for numerous research efforts, including ecosystem studies, parameterizing hydrodynamic models, and designing monitoring programs. Citation: Zawada, D. G., G. A. Piniak, and C. J. Hearn (2010), Topographic complexity and roughness of a tropical benthic seascape, Geophys.

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Effects of waves on coastal water dispersion in a small estuarine bay

et al. 2014

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[1] A three-dimensional wave-current model is used to investigate wave-induced circulations in a small estuarine bay and its impact on freshwater exchanges with the inner shelf, related to stratified river plume dispersion. Modeled salinity fields exhibit a lower salinity surface layer due to river outflows, with typical depth of 1 m inside the bay. The asymmetric wave forcing on the bay circulation, related to the local bathymetry, significantly impacts the river plumes. It is found that the transport initiated in the surf zone by the longshore current can oppose and thus reduce the primary outflow of freshwater through the bay inlets. Using the model to examine a high river runoff event occurring during a high-energy wave episode, waves are found to induce a 24 h delay in freshwater evacuation. At the end of the runoff event, waves have reduced the freshwater flux to the ocean by a factor 5, and the total freshwater volume inside the bay is increased by 40%. According to the model, and for this event, the effect of the surf zone current on the bay flushing is larger than that of the wind. The freshwater balance is sensitive to incident wave conditions. Maximum freshwater retention is found for intermediate offshore wave heights 1 m < H s < 2 m. For higher-energy waves, the increase in the longshore current reduces the retention, which is two times lower for H s 5 4 m than for H s 5 2 m.

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Observations of Bed Roughness of a Coral Reef

Cited by 54 publications

References 13 publications

Coral Reef Drag Coefficients – Water Depth Dependence

Coral Reef Drag Coefficients – Water Depth Dependence

Topographic complexity and roughness of a tropical benthic seascape

Effects of waves on coastal water dispersion in a small estuarine bay

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