1642 research outputs found
Sort by
Coupling fragmentation to a size-selective sedimentation model can quantify the long-term fate of buoyant plastics in the ocean
No full textPlastic pollution in the ocean is a global environmental issue, with buoyant debris accumulating at the surface and posing long-term ecological threats. Although sediments are the ultimate sink for plastics, a mismatch between observed surface concentrations and estimated inputs implies the understanding of vertical sedimentation mechanisms and rates are inaccurate. Here, we present a coupled fragmentation–sedimentation model that quantitatively predicts the vertical transport and long-term fate of buoyant plastic debris and microplastics (MPs, less than 5 mm). Using a representative 10 mm polyethylene (PE) particle, we show that fragmentation into small MPs is essential for their incorporation into marine snow aggregates (MSAs) and subsequent settling. Even after 100 yr, ca. 10% of the initial plastic mass still remains at the surface providing a continual source of small MPs to ocean surface waters. This study provides the first mechanistic framework linking large plastic degradation to size selective sedimentation, demonstrating that plastic pollution will persist at our ocean surfaces for over a century even if inputs cease. Our findings highlight the need for mitigation strategies beyond input reduction and ocean clean-up, addressing the long-term removal of existing ocean plastics
Detecting coastal sewage spills using earth observation technologies
No full textSewage spills into coastal waters pose serious environmental and public health concerns. These events are typically caused by overwhelmed sewerage systems, failures at wastewater treatment facilities, or the complete absence of treatment infrastructure. The resulting pollution can degrade water quality, harm marine ecosystems, and pose risks to human health. This project investigated the potential of Earth Observation (EO) technologies to detect sewage spills from a variety of system types, across different geographic regions, and under varying oceanographic conditions. We used multispectral data and synthetic aperture radar (SAR) due to their different properties and machine learning techniques to identify the spills. For example, fats, oils, and greases, which are components of sewage, can form surface slicks, which can dampen wave activity in a manner similar to oil spills, which in turn can be identified using SAR. We present the results of these evaluations, highlighting both the strengths and the limitations of each approach
Analysis of deformable bi-cuspid valve dynamics in pulsatile flow using a coupled peridynamics–lattice Boltzmann-immersed boundary framework
No full textMulti-leaflet valves enable passive, one-way fluid transport and are increasingly applied in biological systems, soft robotics, and other industrial applications to prevent backflow. Despite extensive studies on biological valves, understanding the coupled fluid–structure dynamics of biological and synthetic bi-cuspid valves under material degradation and flow conditions remains limited. This work investigates operational modes of bi-cuspid valves using a strongly coupled framework combining the cascaded lattice Boltzmann method for fluid flow and bond-based peridynamics for solid mechanics modeling. The scheme is validated against other numerical data and applied to two-dimensional valve models subjected to pulsatile inlet conditions. Systematic variations in Young's modulus (E) and Reynolds number (Re) reveal their influence on leaflet deformation, aperture size, and flow features such as jet formation, recirculation zones, and inversion during reverse flow. Flexible leaflets (low E) exhibit larger apertures and higher variability, with increased risk of wall contact and asymmetry, while stiffer valves (high E) promote regular motion but reduce opening, enlarging stagnation regions. Higher Re amplifies the aperture and jet velocity, altering downstream flow separation. Simulations highlight the necessity of multi-cycle analysis to capture transient dynamics and inversion phenomena. These findings offer insights into the design of robust soft valves for applications that require controlled unidirectional flow under complex operating conditions
Comparative analysis of floc measurement setups for characterising settling velocities and size distributions
No full textFloc size distribution and settling velocities are crucial parameters for characterising cohesive sediments, as they influence how these sediments behave in various environmental settings. The accurate measurement of these properties is essential, with different methods available depending on the scope of the study. For long-term monitoring, in situ techniques based on laser diffraction are commonly used, while video microscopy techniques are preferred for shorter studies due to their ability to provide detailed information on individual particles. This study compares two high-magnification digital video camera setups, LabSFLOC-2 and FLOCCAM, to investigate the impact of particle concentration on settling velocity in flocculated sediments. Flocculated clay was introduced into settling columns, where both the size and settling velocities of the flocs were measured. The results obtained from both setups are in line with each other, even though the FLOCCAM was slightly more efficient at capturing images of small particles (of size less than 50 microns) and LabsFLOC-2 was better at detecting large size fraction particles (having a low contrast due to the presence of organic matter). Floc size and settling velocity measurements from both setups however exhibit mostly similar trends as a function of clay concentration and the same order of magnitudes for the recorded settling velocities
Shielding effects of neighbor particles on flocculation dynamics of cohesive sediment
No full textThe shielding effects of neighboring particles on the flocculation dynamics of cohesive sediment in homogeneous isotropic turbulence is investigated using a two-phase particle-unresolved, but turbulence-resolved, Euler–Lagrange simulations. A coupled CFD-DEM (Computational Fluid Dynamics-Discrete Element Method) framework was applied, in which the discrete element method model captures collisional interactions among particles. The high-resolution grid used in the CFD resolves all the turbulent scales. The primary particles are substantially smaller than the Kolmogorov length scale, therefore, flow around particles is not resolved and the fluid–particle interactions are modeled by force models. The present work employs the semiempirical force model of Kim and Lee (KL), in which the multibody interactions between the particles that makeup a floc are modeled as functions of pairwise interactions among particles. In comparison, the widely used free-draining approximation (FDA) uses Stokes drag of individual particles and completely ignores all inter-particle interactions within the floc. Most importantly, we observe that by allowing more accurate hydrodynamic interactions among the fractal floc members, the KL method predicts much larger flocs at equilibrium. By including the intra-floc shielding effects, the KL model predicts the floc settling velocity to substantially increase with floc size, in contrast to the FDA model. The aggregation and breakup kernels follow qualitatively similar patterns for both the FDA and KL models. For future work, a computationally efficient and accurate force model for fractal floc shapes needs to be developed for better predictions of the flocculation processes of cohesive sediment
On modelling of offshore scour protection rock berms under seismic loading
No full textUnderstanding the behaviour of rock-scour protection berms under seismic liquefaction will be key to the construction and service of newly planned windfarms in the west coast of North America and Southeast Asia. These farms will play a crucial role in harnessing the abundant and indispensable source of renewable energy which recently has seen rapid expansion. This paper compares dynamic, saturated centrifuge tests in which the rock berm was modelled using scaled individual rocks and for comparison the rock berm was modelled using an aluminium plate to represent a continuum. The results show that the two methods (rock berm vs. plate foundation) result in very different behaviour due to the ingress of sand in between the rocks seen in the physical experiments is not replicated in the continuum-based plate foundation models. It is seen that excess pore water pressure dissipation under the rock is much faster than that of the plate foundation, due to reduced drainage paths. In addition, there are differences in the resulting settlements depending on the size of the input motion and number of cycles in the earthquake. For large motions, the rocks forming the rock berm settle more. For smaller input motions, the rocks settle less compared to a continuum-based plate foundation. In addition, finite element based numerical analyses were carried out. The results of these analyses show that these rock berms might not be modelled as plate foundations. All in all, this has implications for numerical studies on the behaviour of rock berms under seismic liquefaction
The OVERCOME project: overall perspective and progress
No full textThe OVERCOME project is an applied research project that aims to provide the dam and dike engineering profession with an easy-to-use, physically based numerical tool that represents overtopping erosion and failure of homogeneous embankments made up of coarse-grained, gap-graded soils. This project began in 2018 and is scheduled for completion in 2028, and was initiated by EDF and CNR, who are the two main owners of embankment dams in France. To achieve this objective, the OVERCOME project is based on an extensive program of experimental tests of various dimensions. The interpretation of these tests will be used to define a numerical model that will be implemented in the TELEMAC 2D open-source code. This numerical model will be validated on the basis of large-scale tests. This article presents an overview of the project's progress, and then focuses on two major issues: the evaluation of a method for LIDAR measurement of the evolution of the geometry of the downstream face of the embankment during erosion tests, and the characterization of the erosion resistance parameters of coarse-grained soils with spread granulometry using the Jet Erosion Test
EO4Biodiversity: Applying GeoAI to improve habitat mapping for biodiversity net gain
No full textBiodiversity is essential to ecosystem health, supporting clean water, food security, medicine, and resilience to climate change. Reducing biodiversity loss and enhancing habitats through mechanisms such as biodiversity net gain (BNG) is becoming increasingly important. Accurate habitat mapping is central to these efforts, yet existing landcover and habitat datasets often lack the classification detail and spatial accuracy required to support robust BNG assessments.
EO4Biodiversity combines Earth Observation (EO) data with existing datasets and GeoAI techniques to refine habitat classification for Standardised Biodiversity Unit (SBU) calculations required for environmental planning in the UK. The project uses satellite imagery, elevation models, soil data, vector data and ground data alongside machine learning to improve the identification of habitat types.
As the project is in its early stages, we will outline the approach taken to integrate and evaluate these data sources, share initial insights into classification performance, and discuss the challenges and opportunities of applying EO and GeoAI to support biodiversity-sensitive development planning
A critical review of closure depth theories and uncertainties: implications for shoreline modelling and coastal management
No full textThe sustainability of coastal systems is being increasingly compromised as a result of climate-related coastal hazards and increasing human occupation of coastal zones. Shoreline models play an important role in predicting and understanding coastal systems behaviour, informing coastal resilience and adaptation strategies. A critical parameter in these models is the depth of closure (
), which defines the seaward extent of significant cross-shore sediment transport and shoreline morphodynamics. There are considerable uncertainties associated with estimating and identifying the
, which has implications for the accuracy of shoreline predictions and ensuing coastal management decisions. We, therefore, provide a critical literature review of existing theories and methods for defining and estimating the
, highlighting the complexities, uncertainties, and challenges. We also explore the role of the
in shoreline models, paying particular attention to their applicability across variations in timescale and coastal environments while considering the associated implications for coastal management decisions. Our findings highlight the need for standardised estimation methods and a better understanding of the
to improve the reliability and applicability of shoreline models across coastal morphologies and tidal environments. Our findings also emphasise the need for a paradigm shift in practice – from continuing to develop and apply flawed shoreline models to addressing the uncertainties underpinning the formulation and specification of key model parameters, of which the
is arguably the most critical. This shift is needed to enhance the predictive power and reliability of shoreline models, to better inform decision-making for coastal management and governance
Briefing: The Indian Ocean tsunami 20 years on – driving change and changing lives
No full textMore than 20 years have passed since the tragic 2004 Indian Ocean earthquake and tsunami, which killed over 227 000 people and devastated the coastlines of 14 countries surrounding the Indian Ocean. This tragic event kickstarted a worldwide effort in advancing knowledge towards mitigating the catastrophic effects of future tsunami. The ensuing research has greatly enhanced our understanding of tsunami, informing better infrastructure design and risk mitigation practices