Marco Ghisalberti

Canopy Flow Analysis Reveals the Advantage of Size in the Oldest Communities of Multicellular Eukaryotes

Publisher: Elsevier BV

Date: 02-2014

DOI: 10.1016/J.CUB.2013.12.017

Water residence time controls the feedback between seagrass, sediment and light: Implications for restoration

Publisher: Elsevier BV

Date: 07-2018

DOI: 10.1016/J.ADVWATRES.2018.04.004

Particle capture by a circular cylinder in the vortex-shedding regime

Publisher: Cambridge University Press (CUP)

Date: 19-09-2013

DOI: 10.1017/JFM.2013.407

Abstract: Particle capture, whereby suspended particles contact and adhere to a solid surface (a ‘collector’), is an important mechanism for a range of environmental processes including suspension feeding by corals and ‘filtering’ by aquatic vegetation. In this paper, we use two- and three-dimensional direct numerical simulations to quantify the capture efficiency ( $\\eta $ ) of low-inertia particles by a circular cylindrical collector at intermediate Reynolds numbers in the vortex-shedding regime (i.e. for $47\\lt \\mathit{Re}\\leq 1000$ , where $\\mathit{Re}$ is the collector Reynolds number). We demonstrate that vortex shedding induces oscillations near the leading face of the collector which greatly affect the quantity and distribution of captured particles. Unlike in steady, low- $\\mathit{Re}$ flow, particles directly upstream of the collector are not the most likely to be captured. Our results demonstrate the dependence of the time-averaged capture efficiency on $\\mathit{Re}$ and particle size, improving the predictive capability for the capture of particles by aquatic collectors. The transition to theoretical high-Reynolds-number behaviour (i.e. $\\eta \\sim {\\mathit{Re}}^{1/ 2} $ ) is complex due to comparatively rapid changes in wake conditions in this Reynolds number range.

Relationships between trait impulsivity and cognitive control: the effect of attention switching on response inhibition and conflict resolution

Publisher: Springer Science and Business Media LLC

Date: 06-08-2015

DOI: 10.1007/S10339-015-0733-6

Abstract: This study examined the relationship between trait impulsivity and cognitive control, as measured by the Barratt Impulsiveness Scale (BIS) and a focused attention dichotic listening to words task, respectively. In the task, attention was manipulated in two attention conditions differing in their cognitive control demands: one in which attention was directed to one ear at a time for a whole block of trials (blocked condition) and another in which attention was switched pseudo-randomly between the two ears from trial to trial (mixed condition). Results showed that high impulsivity participants exhibited more false alarm and intrusion errors as well as a lesser ability to distinguish between stimuli in the mixed condition, as compared to low impulsivity participants. In the blocked condition, the performance levels of the two groups were comparable with respect to these measures. In addition, total BIS scores were correlated with intrusions and laterality index in the mixed but not the blocked condition. The findings suggest that high impulsivity in iduals may be less prone to attentional difficulties when cognitive load is relatively low. In contrast, when attention switching is involved, high impulsivity is associated with greater difficulty in inhibiting responses and resolving cognitive conflict than is low impulsivity, as reflected in error-prone information processing. The conclusion is that trait impulsivity in a non-clinical population is manifested more strongly when attention switching is required than during maintained attention. This may have important implications for the conceptualization and treatment of impulsivity in both non-clinical and clinical populations.

Retention time and dispersion associated with submerged aquatic canopies

Publisher: American Geophysical Union (AGU)

Date: 04-2007

DOI: 10.1029/2006WR005362

A One‐Dimensional Model for Turbulent Mixing in the Benthic Biolayer of Stream and Coastal Sediments

Publisher: American Geophysical Union (AGU)

Date: 12-2020

DOI: 10.1029/2019WR026822

Particle capture and low-Reynolds-number flow around a circular cylinder

Publisher: Cambridge University Press (CUP)

Date: 07-09-2012

DOI: 10.1017/JFM.2012.367

Abstract: Particle capture, whereby suspended particles contact and adhere to a solid surface (a ‘collector’), is an important mechanism in a range of environmental processes. In aquatic systems, typically characterized by low collector Reynolds numbers ( $\\mathit{Re}$ ), the rate of particle capture determines the efficiencies of a range of processes such as seagrass pollination, suspension feeding by corals and larval settlement. In this paper, we use direct numerical simulation (DNS) of a two-dimensional laminar flow to accurately quantify the rate of capture of low-inertia particles by a cylindrical collector for $\\mathit{Re}\\leq 47$ (i.e. a range where there is no vortex shedding). We investigate the dependence of both the capture rate and maximum capture angle on both the collector Reynolds number and the ratio of particle size to collector size. The inner asymptotic expansion of Skinner ( Q. J. Mech. Appl. Maths , vol. 28, 1975, pp. 333–340) for flow around a cylinder is extended and shown to provide an excellent framework for the prediction of particle capture and flow close to the leading face of a cylinder up to $\\mathit{Re}= 10$ . Our results fill a gap between theory and experiment by providing, for the first time, predictive capability for particle capture by aquatic collectors in a wide (and relevant) Reynolds number and particle size range.

Shallow Flows Over a Permeable Medium: The Hydrodynamics of Submerged Aquatic Canopies

Publisher: Springer Science and Business Media LLC

Date: 10-12-2008

DOI: 10.1007/S11242-008-9305-X

The Near‐Bed Flow Structure and Bed Shear Stresses Within Emergent Vegetation

Publisher: American Geophysical Union (AGU)

Date: 04-2023

DOI: 10.1029/2022WR032499

Abstract: The structure of the bottom boundary layer (BBL) in aquatic flows influences a range of biophysical processes, including sediment transport, hyporheic exchange, and biofilm formation. While the structure of BBL above bare sediment beds has been well studied, little is known about the complex near‐bed flow structure within aquatic vegetation. In this study, we used high‐resolution laboratory measurements and numerical Large Eddy Simulations to investigate the near‐bed mean and turbulent flow properties within staggered‐ordered emergent vegetation under a wide range of flow conditions and densities. There is strong spatial variability of key near‐bed flow characteristics on the scale of the vegetation elements. Measurement locations that provide single‐point flow characteristics closest to the spatially averaged values were identified. The spatially averaged BBL thickness is influenced strongly by vegetation density. This impact of vegetation density is engendered through its direct control of near‐bed turbulent kinetic energy (TKE), which in turn is negatively correlated with BBL thickness, both locally in a given flow and across the range of flow conditions studied here. A model based on the near‐bed TKE is developed to predict the BBL thickness and, ultimately, the bed shear stress. Model predictions were in close agreement with the experimental and numerical results. These findings provide new insights into the physical links between near‐bed flow variables and therefore contribute to the understanding of some of the complex biophysical processes present in vegetated flows.

Editorial: Coastal protection provided by ecosystems: Observations and modeling across scales

Publisher: Frontiers Media SA

Date: 12-08-2022

DOI: 10.3389/FMARS.2022.998923

Vertical mixing in coastal canopies

Publisher: Wiley

Date: 29-09-2016

DOI: 10.1002/LNO.10368

A Model for Mass Transport Across the Sediment‐Water Interface

Publisher: American Geophysical Union (AGU)

Date: 04-2018

DOI: 10.1002/2017WR022418

Wave‐Driven Mean Flow Dynamics in Submerged Canopies

Publisher: American Geophysical Union (AGU)

Date: 03-2020

DOI: 10.1029/2019JC015935

Abstract: The physical roughness (canopies) formed by organisms within aquatic ecosystems (e.g., seagrass, kelp, and mangroves) modifies the local wave‐driven hydrodynamics within coastal and estuarine regions. In wave‐dominated environments, an understanding of the mean wave‐driven flows generated within and above canopies is important, as it governs material transport (e.g., of nutrients, sediment, and biota). However, until recently the effect of submerged canopies on wave‐current interactions and the resulting mean (wave‐averaged) flow dynamics has received relatively little attention. In this study, a combination of wave flume experiments and numerical modeling is used to investigate the wave‐induced mean flow profiles in the presence of a submerged canopy. The measured velocities and vegetation forces were used to derive bulk drag and inertia coefficients, and to validate a nonhydrostatic 2DV wave‐flow model. The numerical model results were used to conduct an in‐depth analysis of the mean horizontal momentum terms responsible for driving the mean (horizontal) flow within and above the submerged canopies. We show that the mean canopy hydrodynamics are driven by vertical gradients in wave and turbulent Reynolds stresses, balanced by the mean canopy drag forces. The wave Reynolds stress gradient is the dominant force driving the in‐canopy mean flow and is directly related to the vorticity that is generated when the wave orbital motions become rotational near the canopy interface. This study provides new insight in the mechanisms responsible for wave‐driven mean flows within submerged canopies and guidance for how these hydrodynamics can be predicted in coastal wave‐circulation models.

Effect of instream logs on bank erosion potential: a flume study with a single log

Publisher: Informa UK Limited

Date: 20-11-2019

DOI: 10.1080/24705357.2019.1634499

Identifying, reducing, and communicating uncertainty in community science: a focus on alien species

Publisher: Springer Science and Business Media LLC

Date: 29-08-2022

DOI: 10.1007/S10530-022-02858-8

Abstract: Community science (also often referred to as citizen science) provides a unique opportunity to address questions beyond the scope of other research methods whilst simultaneously engaging communities in the scientific process. This leads to broad educational benefits, empowers people, and can increase public awareness of societally relevant issues such as the bio ersity crisis. As such, community science has become a favourable framework for researching alien species where data on the presence, absence, abundance, phenology, and impact of species is important in informing management decisions. However, uncertainties arising at different stages can limit the interpretation of data and lead to projects failing to achieve their intended outcomes. Focusing on alien species centered community science projects, we identified key research questions and the relevant uncertainties that arise during the process of developing the study design, for ex le, when collecting the data and during the statistical analyses. Additionally, we assessed uncertainties from a linguistic perspective, and how the communication stages among project coordinators, participants and other stakeholders can alter the way in which information may be interpreted. We discuss existing methods for reducing uncertainty and suggest further solutions to improve data reliability. Further, we make suggestions to reduce the uncertainties that emerge at each project step and provide guidance and recommendations that can be readily applied in practice. Reducing uncertainties is essential and necessary to strengthen the scientific and community outcomes of community science, which is of particular importance to ensure the success of projects aimed at detecting novel alien species and monitoring their dynamics across space and time.

Characterizing the Three‐Dimensional Flow in Partially Vegetated Channels

Publisher: American Geophysical Union (AGU)

Date: 2023

DOI: 10.1029/2022WR032570

Abstract: Partially obstructed shear flows, such as flows over submerged vegetation patches in river systems, are common in natural environments. Here, a model of a patchily‐vegetated river flow, using staggered arrays of rigid wooden dowels, is used to experimentally characterize the flow. Three‐component point velocity measurements in the cross sectional plane are used to investigate the highly nonuniform, 3D flow field in patchy vegetation and its effect on mass and momentum exchange. The cross‐sectional distribution of mean streamwise velocity varies as a consequence of the bed heterogeneity, being highly dependent on vegetation density. Asymmetric shear layers form at the vertical and lateral edges of the canopy, having different scales within the canopy and in the unvegetated region. Secondary flow cells form in the cross‐plane, with a size that decreases with increasing canopy density. The strength of the upward and downward motions is found to be greater for denser canopies. In addition to the secondary flow, additional rotating cells are observed both above the patch and next to it with increasing canopy density. A triple‐averaging procedure allowed for the quantification of the vertical advective dispersive stresses, which are up to 21% of the total shear stress. This demonstrates the significant role of secondary circulation generated by patchy vegetation in interfacial momentum exchange. Finally, the secondary circulation contribution to vertical scalar transport is estimated to be of the same order as that due to turbulent diffusion, highlighting the importance of understanding the impact of the secondary flow field on aquatic ecosystem function.

The use of Fick's First Law for predicting porewater nutrient fluxes under diffusive conditions

Publisher: Wiley

Date: 09-2001

DOI: 10.1002/HYP.297

Flow and transport in channels with submerged vegetation

Publisher: Springer Science and Business Media LLC

Date: 10-05-2008

DOI: 10.2478/S11600-008-0017-Y

The wave‐driven current in coastal canopies

Publisher: American Geophysical Union (AGU)

Date: 05-2017

DOI: 10.1002/2016JC012446

Abstract: Wave‐driven flows over canopies of aquatic vegetation (such as seagrass) are characterized by the generation of a strong, shoreward mean current near the top of the canopy. This shoreward drift, which is observed to be up to 75% of the RMS above‐canopy orbital velocity, can have a significant impact on residence times within coastal canopies. There have been limited observations of this current and an accurate formulation of its magnitude is still lacking. Accordingly, this study aims to develop a practical relationship to describe the strength of this current as a function of both wave and canopy characteristics. A simple model for the Lagrangian drift velocity indicates that the magnitude of the wave‐driven current increases with the above‐canopy oscillatory velocity, the vertical orbital excursion at the top of the canopy, and the canopy density. An extensive laboratory study, using both rigid and (dynamically scaled) flexible model vegetation, was carried out to evaluate the proposed model. Experimental results reveal a strong agreement between predicted and measured current velocities over a wide and realistic range of canopy and wave conditions. The validity of this model is also confirmed through available field measurements. Characterization of this wave‐induced mean current will allow an enhanced capacity for predicting residence time, and thus key ecological processes, in coastal canopies.

Coexistence of order and chaos in C major

Publisher: American Physical Society (APS)

Date: 17-10-2018

DOI: 10.1103/PHYSREVFLUIDS.3.100510

Spectral wave-driven sediment transport across a fringing reef

Publisher: Elsevier BV

Date: 04-2015

DOI: 10.1016/J.COASTALENG.2015.01.005

From grey to green: Efficacy of eco‐engineering solutions for nature‐based coastal defence

Publisher: Wiley

Date: 16-02-2018

DOI: 10.1111/GCB.14063

Abstract: Climate change is increasing the threat of erosion and flooding along coastlines globally. Engineering solutions (e.g. seawalls and breakwaters) in response to protecting coastal communities and associated infrastructure are increasingly becoming economically and ecologically unsustainable. This has led to recommendations to create or restore natural habitats, such as sand dunes, saltmarsh, mangroves, seagrass and kelp beds, and coral and shellfish reefs, to provide coastal protection in place of (or to complement) artificial structures. Coastal managers are frequently faced with the problem of an eroding coastline, which requires a decision on what mitigation options are most appropriate to implement. A barrier to uptake of nature-based coastal defence is stringent evaluation of the effectiveness in comparison to artificial protection structures. Here, we assess the current evidence for the efficacy of nature-based vs. artificial coastal protection and discuss future research needs. Future projects should evaluate habitats created or restored for coastal defence for cost-effectiveness in comparison to an artificial structure under the same environmental conditions. Cost-benefit analyses should take into consideration all ecosystem services provided by nature-based or artificial structures in addition to coastal protection. Interdisciplinary research among scientists, coastal managers and engineers is required to facilitate the experimental trials needed to test the value of these shoreline protection schemes, in order to support their use as alternatives to artificial structures. This research needs to happen now as our rapidly changing climate requires new and innovative solutions to reduce the vulnerability of coastal communities to an increasingly uncertain future.

Obstructed shear flows: similarities across systems and scales

Publisher: Cambridge University Press (CUP)

Date: 10-12-2009

DOI: 10.1017/S0022112009992175

Abstract: In this paper, I show that a range of environmental flows are inherently dynamically similar. These flows, which are partially obstructed by a permeable medium, are here termed ‘obstructed shear flows’. Ex les include aquatic flows over sediment beds, submerged vegetation canopies and coral reefs, as well as atmospheric flows over crop canopies, forests and cities (‘urban canopies’). While the density and geometry of the obstructions may vary, the drag in each system generates a velocity profile with an inflection point. This renders the flow unstable. Consequently, it is expected that ( a ) the dominant interfacial turbulent structure in obstructed shear flows will be a Kelvin–Helmholtz-type vortex, and ( b ) that this instability will engender hydrodynamic similarities among obstructed shear flows. Such similarities have been hypothesized but not yet fully explored. An extensive review of existing data confirms these dynamic similarities on scales of O (mm) to O (10 m). The extent of shear penetration into the obstruction, which is a primary determinant of residence time in the obstruction, scales upon the drag length scale. Other relationships that link the strength of turbulence and the ‘slip’ velocity at the top of the obstruction to the friction velocity ( u ∗) are also evident. The relationships presented here provide predictive capability for flow and transport in obstructed shear flows and suggest the possibility of a single framework to describe such flows on all scales.

Sediment transport in the presence of large reef bottom roughness

Publisher: American Geophysical Union (AGU)

Date: 02-2017

DOI: 10.1002/2016JC011755

Three-dimensionality of shallow island wakes

Publisher: Springer Science and Business Media LLC

Date: 04-02-2019

DOI: 10.1007/S10652-019-09661-5

A joint velocity-intermittency analysis reveals similarity in the vertical structure of atmospheric and hydrospheric canopy turbulence

Publisher: Springer Science and Business Media LLC

Date: 04-07-2019

DOI: 10.1007/S10652-019-09694-W

Shallow Flows Over a Permeable Medium: The Hydrodynamics of Submerged Aquatic Canopies

Publisher: Springer Science and Business Media LLC

Date: 07-2009

DOI: 10.1007/S11242-009-9434-X

Kelp beds as coastal protection: wave attenuation of Ecklonia radiata in a shallow coastal bay

Publisher: Oxford University Press (OUP)

Date: 19-08-2019

DOI: 10.1093/AOB/MCZ127

Abstract: Coastal protection from erosion and flooding is a significant ecosystem service provided by vegetated marine systems. Kelp beds are a dominant habitat-forming species on temperate reefs worldwide. While they are valued as hotspots of bio ersity, there is a paucity of information that supports their use in nature-based coastal defence. This includes the effectiveness of kelp beds in attenuating waves approaching the shore and how this influences sediment transport. Wave loggers were deployed at paired kelp bed and control (urchin barren) treatments at four sites in Port Phillip Bay, Australia. The significant wave height offshore (exposed side) to onshore (sheltered side) of the treatment were compared to determine wave attenuation. At three sites, the wave attenuation of kelp beds was significantly less than the control. This result was consistent across the environmental conditions recorded in this study. At the fourth site, on average there was no significant difference in wave transmission between kelp and control. However, wave attenuation at kelp beds was 10% greater than the control during periods of northerly winds. We highlight the importance of disentangling the effects of the reef substratum and kelp when evaluating the efficacy of kelp at providing coastal protection. We have highlighted a significant gap in the research on ecosystem services provided by kelp beds. A greater understanding is needed on which kelp species are able to provide coastal protection, and under what conditions. Such future research is essential for providing managers and policy makers with actionable information on sustainable and cost-effective solutions for coastal defence when faced with a changing climate.

On predicting particle capture rates in aquatic ecosystems

Publisher: Public Library of Science (PLoS)

Date: 22-12-2021

DOI: 10.1371/JOURNAL.PONE.0261400

Abstract: Recent advances in understanding the capture of moving suspended particles in aquatic ecosystems have opened up new possibilities for predicting rates of suspension feeding, larval settlement, seagrass pollination and sediment removal. Drawing on results from both highly-resolved computational fluid dynamics (CFD) simulations and existing experimental data, we quantify the controlling influence of flow velocity, particle size and collector size on rates of contact between suspended particles and biological collectors over the parameter space characterising a erse range of aquatic ecosystems. As distinct from assumptions in previous modeling studies, the functional relationships describing capture are highly variable. Contact rates can vary in opposing directions in response to changes in collector size, an organism’s size, the size of particles being intercepted (related to diet in the case of suspension feeders), and the flow strength. Contact rates shift from decreasing to increasing with collector diameter when particles become relatively large and there is vortex shedding in the collector wake. And in some ranges of the ecologically relevant parameter space, contact rates do not increase strongly with velocity or particle size. The understanding of these complex dependencies allows us to reformulate some hypotheses of selection pressure on the physiology and ecology of aquatic organisms. We discuss the benefits and limitations of CFD tools in predicting rates of particle capture in aquatic ecosystems. Finally, across the complete parameter space relevant to real aquatic ecosystems, all quantitative estimates of particle capture from our model are provided here.

The three-dimensionality of obstructed shear flows

Publisher: Springer Science and Business Media LLC

Date: 20-12-2009

DOI: 10.1007/S10652-009-9161-4

Editorial: Canopies in Aquatic Ecosystems: Integrating Form, Function, and Biophysical Processes

Publisher: Frontiers Media SA

Date: 15-11-2019

DOI: 10.3389/FMARS.2019.00697

Living in the Canopy of the Animal Forest: Physical and Biogeochemical Aspects

Publisher: Springer International Publishing

Date: 2017

DOI: 10.1007/978-3-319-21012-4_14

The variation of flow and turbulence across the sediment–water interface

Publisher: Cambridge University Press (CUP)

Date: 06-07-2017

DOI: 10.1017/JFM.2017.345

Abstract: A basic framework characterising the interaction between aquatic flows and permeable sediment beds is presented here. Through the permeability Reynolds number ( $Re_{K}=\\sqrt{K}u_{\\ast }/\\unicode[STIX]{x1D708}$ , where $K$ is the sediment permeability, $u_{\\ast }$ is the shear velocity and $\\unicode[STIX]{x1D708}$ is the fluid viscosity), the framework unifies two classical flow typologies, namely impermeable boundary layer flows ( $Re_{K}\\ll 1$ ) and highly permeable canopy flows ( $Re_{K}\\gg 1$ ). Within this range, the sediment–water interface (SWI) is identified as a transitional region, with $Re_{K}$ in aquatic systems typically $O(0.001{-}10)$ . As the sediments obstruct conventional measurement techniques, experimental observations of interfacial hydrodynamics remain extremely rare. The use of refractive index matching here allows measurement of the mean and turbulent flow across the SWI and thus direct validation of the proposed framework. This study demonstrates a strong relationship between the structure of the mean and turbulent flow at the SWI and $Re_{K}$ . Hydrodynamic characteristics, such as the interfacial turbulent shear stress, velocity, turbulence intensities and turbulence anisotropy tend towards those observed in flows over impermeable boundaries as $Re_{K}\\rightarrow 0$ and towards those seen in flows over highly permeable boundaries as $Re_{K}\\rightarrow \\infty$ . A value of $Re_{K}\\approx 1{-}2$ is seen to be an important threshold, above which the turbulent stress starts to dominate the fluid shear stress at the SWI, the penetration depths of turbulence and the mean flow into the sediment bed are comparable and similarity relationships developed for highly permeable boundaries hold. These results are used to provide a new perspective on the development of interfacial transport models at the SWI.

Sludge accumulation and distribution impact the hydraulic performance in waste stabilisation ponds

Publisher: Elsevier BV

Date: 03-2017

DOI: 10.1016/J.WATRES.2016.11.031

Abstract: Waste stabilisation ponds (WSPs) are used worldwide for wastewater treatment, and throughout their operation require periodic sludge surveys. Sludge accumulation in WSPs can impact performance by reducing the effective volume of the pond, and altering the pond hydraulics and wastewater treatment efficiency. Traditionally, sludge heights, and thus sludge volume, have been measured using low-resolution and labour intensive methods such as 'sludge judge' and the 'white towel test'. A sonar device, a readily available technology, fitted to a remotely operated vehicle (ROV) was shown to improve the spatial resolution and accuracy of sludge height measurements, as well as reduce labour and safety requirements. Coupled with a dedicated software package, the profiling of several WSPs has shown that the ROV with autonomous sonar device is capable of providing sludge bathymetry with greatly increased spatial resolution in a greatly reduced profiling time, leading to a better understanding of the role played by sludge accumulation in hydraulic performance of WSPs. The high-resolution bathymetry collected was used to support a much more detailed hydrodynamic assessment of systems with low, medium and high accumulations of sludge. The results of the modelling show that hydraulic performance is not only influenced by the sludge accumulation, but also that the spatial distribution of sludge plays a critical role in reducing the treatment capacity of these systems. In a range of ponds modelled, the reduction in residence time ranged from 33% in a pond with a uniform sludge distribution to a reduction of up to 60% in a pond with highly channelized flow. The combination of high-resolution measurement of sludge accumulation and hydrodynamic modelling will help in the development of frameworks for wastewater sludge management, including the development of more reliable computer models, and could potentially have wider application in the monitoring of other small to medium water bodies, such as channels, recreational water bodies, and commercial ports.

Density-ratio effects on the capture of suspended particles in aquatic systems

Publisher: Cambridge University Press (CUP)

Date: 15-10-2015

DOI: 10.1017/JFM.2015.557

Abstract: Particle capture, whereby suspended particles contact and adhere to a solid surface (a ‘collector’), is important in a range of environmental processes, including suspension feeding by corals and ‘filtering’ by aquatic vegetation. Although aquatic particles are often considered as perfect tracers when estimating capture efficiency, the particle density ratio ( ${\\it\\rho}^{+}$ ) – the ratio of the particle density to the fluid density – can significantly affect capture. In this paper, we use a numerical analysis of particle trajectories to quantify the influence of ${\\it\\rho}^{+}$ on particle capture by circular collectors in a parameter space relevant to aquatic systems. As it is generally believed that inertia augments the capture efficiency when the Stokes number ( $\\mathit{St}$ ) of the particles exceeds a critical value, we first estimate the critical Stokes number for aquatic-type particles and demonstrate its dependence on both ${\\it\\rho}^{+}$ and the Reynolds number ( $\\mathit{Re}$ ). Second, we analyse how efficiently circular collectors can capture neutrally buoyant ( ${\\it\\rho}^{+}=1$ ), sediment-type ( ${\\it\\rho}^{+}=2.6$ ) and weakly buoyant ( ${\\it\\rho}^{+}=0.9$ ) aquatic particles. Our analysis shows that, for ${\\it\\rho}^{+} $ , inertia can either augment or diminish capture efficiency, and inertial effects appear well before the critical Stokes number is reached. The role of particle inertia is maximised at Stokes numbers above the critical value and, for sediment-type particles, can result in as much as a fourfold increase in the rate of capture relative to perfect tracers of the same size. Similar but opposite effects are observed for weakly buoyant particles, where capture efficiency can decrease by 60 % relative to the capture of perfect tracers.

Model and laboratory study of dispersion in flows with submerged vegetation

Publisher: American Geophysical Union (AGU)

Date: 05-2007

DOI: 10.1029/2006WR005229

Video: The Coexistence of Order and Chaos in C-major

Publisher: American Physical Society

Date: 19-11-2017

DOI: 10.1103/APS.DFD.2017.GFM.V0053

The Structure of the Shear Layer in Flows over Rigid and Flexible Canopies

Publisher: Springer Science and Business Media LLC

Date: 06-2006

DOI: 10.1007/S10652-006-0002-4

Predicting Bed Shear Stresses in Vegetated Channels

Publisher: American Geophysical Union (AGU)

Date: 11-2018

DOI: 10.1029/2018WR022811

Seagrass Meadows Reduce Wind-Wave Driven Sediment Resuspension in a Sheltered Environment

Publisher: Frontiers Media SA

Date: 31-01-2022

DOI: 10.3389/FMARS.2021.733542

Abstract: Seagrass meadows are prominent in many coastal zones worldwide and significant contributors to global primary production. The large bottom roughness (or canopy) created by seagrass meadows substantially alters near-bed hydrodynamics and sediment transport. In this study, we investigate how a seagrass meadow in a low-energy environment (forced by local winds) modifies near-bed mean and wave-driven flows and assess how this relates to suspended sediment concentration (SSC). A two-week field study was conducted at Garden Island in southwestern Australia, a shallow and sheltered coastal region subjected to large diurnal sea-breeze cycles, typical of many low-energy environments where seagrasses are found. The mean and turbulent flow structure, along with optical estimates of SSC, were measured within both a seagrass canopy and over an adjacent bare bed. Near-bed mean current velocities within the seagrass canopy were on average 35% of the velocity above the canopy. Oscillatory wave velocities were less attenuated than mean current velocities, with near-bed values on average being 83% of those above the canopy. Mean and maximum shear velocities inferred from currents and waves above the canopy frequently exceeded the threshold for sediment resuspension, but no significant variation was observed in the SSC. However, a significant correlation was observed between SSC and bed shear stress estimated using near-bed velocities inside the canopy. When sediment was resuspended, there were substantial differences between the SSCs within and above the canopy layer, with higher levels confined within the canopy. This study demonstrates the importance of measuring near-bed hydrodynamic processes directly within seagrass canopies for predicting the role seagrass meadows play in regulating local rates of sediment resuspension.

Spatial Variability of Sediment Transport Processes Over Intratidal and Subtidal Timescales Within a Fringing Coral Reef System

Publisher: Wiley

Date: 05-2018

DOI: 10.1002/2017JF004468

A framework to quantify flow through coral reefs of varying coral cover and morphology

Publisher: Public Library of Science (PLoS)

Date: 18-01-2023

DOI: 10.1371/JOURNAL.PONE.0279623

Abstract: Flow velocities within coral reefs are greatly reduced relative to those at the water surface. The in-reef flow controls key processes that flush heat, cycle nutrients and transport sediment from the reef to adjacent beaches, all key considerations in assessments of reef resilience and restoration interventions. An analytical framework is proposed and tested with a suite of high-resolution numerical experiments. We demonstrate a single parameter that describes the total coral frontal area explains variation of horizontally averaged velocity within a reef canopy across morphologies, densities, and flow depths. With the integration of existing data of coral cover and geometry, this framework is a practical step towards the prediction of near-bed flows in erse reef environments.

Vortex generation in oscillatory canopy flow

Publisher: American Geophysical Union (AGU)

Date: 03-2013

DOI: 10.1002/JGRC.20073

Cylinder wakes in shallow oscillatory flow: the coastal island wake problem

Publisher: Cambridge University Press (CUP)

Date: 04-07-2019

DOI: 10.1017/JFM.2019.441

Abstract: Topographic complexity on continental shelves is the catalyst that transforms the barotropic tide into the secondary and residual circulations that dominate vertical and cross-shelf mixing processes. Island wakes are one such ex le that are observed to significantly influence the transport and distribution of biological and physical scalars. Despite the importance of island wakes, to date, no sufficient, mechanistic description of the physical processes governing their development exists for the general case of unsteady tidal forcing. Controlled laboratory experiments are necessary for the understanding of this complex flow phenomenon. Here, three-dimensional velocity field measurements of cylinder wakes in shallow-water oscillatory flow are conducted across a parameter space that is typical of tidal flow around shallow islands. The wake form in steady flows is typically described in terms of the stability parameter $S=c_{f}D/h$ (where $D$ is the island diameter, $h$ is the water depth and $c_{f}$ is the bottom boundary friction coefficient) in tidal flows, there is an additional dependence on the Keulegan–Carpenter number $KC=U_{0}T/D$ (where $U_{0}$ is the tidal velocity litude and $T$ is the tidal period). In this study we demonstrate that when the influence of bottom friction is confined to a Stokes boundary layer the stability parameter is given by $S=\\unicode[STIX]{x1D6FF}^{+}/KC$ where $\\unicode[STIX]{x1D6FF}^{+}$ is the ratio of the wavelength of the Stokes bottom boundary layer to the depth. Three classes of wake form are observed with decreasing wake stability: (i) steady bubble for $S\\gtrsim 0.1$ (ii) unsteady bubble for $0.06\\lesssim S\\lesssim 0.1$ and (iii) vortex shedding for $S\\lesssim 0.06$ . Transitions in wake form and wake stability are shown to depend on the magnitude and temporal evolution of the wake return flow. Scaling laws are developed to allow upscaling of the laboratory results to island wakes. Vertical and lateral transport depend on three parameters: (i) the flow aspect ratio $h/D$ (ii) the litude of tidal motion relative to the island size, given by $KC$ and (iii) the relative influence of bottom friction to the flow depth, given by $\\unicode[STIX]{x1D6FF}^{+}$ . A model of wake upwelling based on Ekman pumping from the bottom boundary layer demonstrates that upwelling in the near-wake region of an island scales with $U_{0}(h/D)KC^{1/6}$ and is independent of the wake form. Finally, we demonstrate an intrinsic link between the dynamical eddy scales, predicted by the Ekman pumping model, and the island wake form and stability.

The limited growth of vegetated shear layers

Publisher: American Geophysical Union (AGU)

Date: 07-2004

DOI: 10.1029/2003WR002776

Modeling the Effects of Turbulence on Hyporheic Exchange and Local‐to‐Global Nutrient Processing in Streams

Publisher: American Geophysical Union (AGU)

Date: 09-2018

DOI: 10.1029/2018WR023078

The effect of instream logs on bank erosion potential: a flume study with multiple logs

Publisher: Informa UK Limited

Date: 23-11-2019

DOI: 10.1080/24705357.2019.1669495

Impact of hydrodynamic reconfiguration with baffles on treatment performance in waste stabilisation ponds

Publisher: MDPI AG

Date: 27-01-2018

DOI: 10.3390/W10020109

The Impact of Plant Oscillation on Dispersion in Emergent Aquatic Canopies

Publisher: American Geophysical Union (AGU)

Date: 03-2023

DOI: 10.1029/2022WR032035

Abstract: Flexible canopies bend and oscillate in both the in‐line and cross‐flow directions due to periodic forcing associated with vortex shedding. The resultant plant motion impacts the vegetation wake structure and, thus, the rate of lateral dispersion in these environments. Despite significant improvements in our understanding of dispersion in rigid canopies, a reliable framework to predict mixing in oscillating canopies is still lacking. This research demonstrates how plant oscillation can profoundly impact rates of lateral mixing in steady flows. The lateral dispersion coefficients were evaluated experimentally, using photographs of injected dye plumes within two types of emergent flexible model vegetation. Results revealed a significant increase in the rates of lateral dispersion (by up to 45%) due to the plant oscillation. A predictive model, based on a redefined vegetation density that incorporates the impact of plant oscillation, was developed that can accurately predict dispersion in emergent canopies. A quantitative prediction of dispersion in oscillating flexible vegetation is a significant step toward a more accurate description of material transport in aquatic environments.

Living in the Canopy of the Animal Forest: Physical and Biogeochemical Aspects

Publisher: Springer International Publishing

Date: 2016

DOI: 10.1007/978-3-319-17001-5_14-1

Unifying Advective and Diffusive Descriptions of Bedform Pumping in the Benthic Biolayer of Streams

Publisher: American Geophysical Union (AGU)

Date: 27-10-2020

DOI: 10.1029/2020WR027967

Mass Transport in Vegetated Shear Flows

Publisher: Springer Science and Business Media LLC

Date: 12-2005

DOI: 10.1007/S10652-005-0419-1

A new model for predicting the drag exerted by vegetation canopies

Publisher: American Geophysical Union (AGU)

Date: 04-2017

DOI: 10.1002/2016WR020090

Mixing layers and coherent structures in vegetated aquatic flows

Publisher: American Geophysical Union (AGU)

Date: 02-2002

DOI: 10.1029/2001JC000871

Canopy resistance on oscillatory flows

Publisher: Elsevier BV

Date: 10-2019

DOI: 10.1016/J.COASTALENG.2019.04.014

Modelling wave attenuation through submerged vegetation canopies using a subgrid canopy flow model

Publisher: Elsevier BV

Date: 09-2022

DOI: 10.1016/J.COASTALENG.2022.104153

MECHANICS OF SEDIMENT SUSPENSION AND TRANSPORT WITHIN A FRINGING REEF

Publisher: WORLD SCIENTIFIC

Date: 15-04-2015

DOI: 10.1142/9789814689977_0086

The Hydrodynamic Response of the Sediment‐Water Interface to Coherent Turbulent Motions

Publisher: American Geophysical Union (AGU)

Date: 04-10-2018

DOI: 10.1029/2018GL079850

Abstract: Unique observations of the hydrodynamics across the sediment‐water interface are used to quantify the instantaneous response of the interstitial fluid to the passage of coherent turbulent motions in the overlying flow. Over a range of permeability Reynolds numbers (where K is the sediment permeability, u ∗ is the shear velocity, and ν is the fluid viscosity), the passage of these turbulent motions create velocity fluctuations and momentum fluxes at the sediment‐water interface to greatly exceed their mean values. Sweep motions are observed to penetrate into the sediment bed and induce instantaneous momentum fluxes that can be an order of magnitude larger than the mean bed shear stress. By penetrating into the sediment bed, the turbulent motions increase the effective roughness experienced by the flow and therefore the flow resistance. The properties of the mean flow alone are thus insufficient to describe the interaction of the overlying flow with the sediments.

Feedback between sediment and light for seagrass: Where is it important?

Publisher: Wiley

Date: 24-06-2016

DOI: 10.1002/LNO.10319

Predicting current-induced drag in emergent and submerged aquatic vegetation canopies

Publisher: Frontiers Media SA

Date: 04-12-2018

DOI: 10.3389/FMARS.2018.00449

The impact of flexibility on flow, turbulence, and vertical mixing in coastal canopies

Publisher: Wiley

Date: 06-08-2018

DOI: 10.1002/LNO.11008

Massachusetts Institute Of Technology

Location: United States of America

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University Of Western Australia

Location: Australia

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University Of Melbourne

Location: Australia

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Performance Of Waste Stabilisation Ponds: Controlling Factors, Novel Performance Indicators, And Risk Assessment

Start Date: 2013

End Date: 2016

Funder: Australian Research Council

Predictive Capability For Particle Capture In Aquatic Ecosystems

Start Date: 2015

End Date: 2017

Funder: Australian Research Council

(Extreme Tidal Forcing Of A Topographically Complex Coastal Region: The Kimberley, Western Australia)

Start Date: 2010

End Date: 2012

Funder: Australian Research Council

The Role Of Herbivory And Hydrodynamics In Ameliorating The Effects Of Nutrient Enrichment In Marine Ecosystems

Start Date: 2009

End Date: 2010

Funder: Commonwealth Scientific and Industrial Research Organisation

Redefining Sediment Transport Predictions In Benthic Ecosystems

Start Date: 2017

End Date: 2019

Funder: Australian Research Council

(A New Framework For Flow And Mixing At The Sediment-water Interface)

Start Date: 2012

End Date: 2014

Funder: Australian Research Council

A Predictive Framework For The Flow Control Of Environmental Roughness

Start Date: 2021

End Date: 2023

Funder: Australian Research Council

Discovery Projects - Grant ID: DP1095294

Start Date: 2010

End Date: 12-2013

Amount: $430,000.00

Funder: Australian Research Council

Discovery Projects - Grant ID: DP150102638

Start Date: 2015

End Date: 12-2017

Amount: $286,100.00

Funder: Australian Research Council

Discovery Projects - Grant ID: DP210103131

Start Date: 2022

End Date: 12-2024

Amount: $370,000.00

Funder: Australian Research Council

Discovery Projects - Grant ID: DP200101545

Start Date: 04-2020

End Date: 10-2024

Amount: $564,507.00

Funder: Australian Research Council

Linkage Projects - Grant ID: LP130100856

Start Date: 07-2013

End Date: 03-2017

Amount: $412,000.00

Funder: Australian Research Council

Linkage Projects - Grant ID: LP210100386

Start Date: 04-2022

End Date: 04-2025

Amount: $433,540.00

Funder: Australian Research Council

Discovery Projects - Grant ID: DP170100802

Start Date: 2017

End Date: 12-2019

Amount: $285,000.00

Funder: Australian Research Council

Discovery Projects - Grant ID: DP120102500

Start Date: 2012

End Date: 12-2016

Amount: $153,000.00

Funder: Australian Research Council