Hydrodynamic Processes Research Articles

Sources, pathways, and abatement strategies of macroplastic pollution: an interdisciplinary approach for the southern North Sea

The issue of marine plastic pollution has been extensively studied by various scientific disciplines in recent decades due to its global threat. However, owing to its complexity, it requires an interdisciplinary approach to develop effective management strategies. The multidisciplinary scientific approach presented here focuses on understanding the sources and pathways of macroplastic litter and developing abatement strategies in the southern North Sea region. Over 2.5 years, more than 63,400 biodegradable wooden drifters were deployed with the help of citizen science to study the sources, pathways, and accumulation areas of floating marine litter. Rivers act as sinks of most of the floating marine litter released within their waterways. Short-term field experiments were also conducted to analyse the hydrodynamic and atmospheric processes that govern the transport of floating litter particles at the sea surface. Numerical models were used to examine the transport of virtual litter particles in the entire North Sea and in coastal regions. It was found that there are no permanent accumulation areas in the North Sea, and the Skagerrak and fronts can increase the residence times of floating marine litter and favour sinking. Field surveys revealed that the majority of litter objects originate from fisheries and consumer waste. To develop effective abatement strategies, the key stakeholder landscape was analysed on a regional level. The interdisciplinary approach developed in this study highlights the importance of synergizing scientific resources from multiple disciplines for a better understanding of marine plastic pollution and the development of effective management strategies.

INVESTIGATION OF THE ENERGY CHARACTERISTICS OF CENTRIFUGAL PUMPS

A hydraulic device that is used to suck up liquid, move it under pressure or pump it, is called a pump. As a rule, any movement of a liquid by similar aggregates is carried out due to the transfer of potential or kinetic energy to it. Depending on the technical indicators, different types of pumps are used. At the same time, they differ in efficiency, power, volumes of fluid pumped per unit time, maximum head and resulting pressure. The most used group of pumps are vane pumps. Their distinctive feature is the impeller rotating in a fixed housing, equipped with blades. Depending on the warehouse of the impeller and the conditions for moving fluid through it, vane pumps are divided into centrifugal and vortex. With a centrifugal pump, liquid is supplied due to the centrifugal force that appears when the impeller rotates. She is carried away by the blades and, under the action of centrifugal force, moves from the middle of the wheel to the edges along the blades. The blades of the impellers are bent in the direction of rotation backwards. The number of blades is usually from 6 to 8 pieces. But special pumps for impure liquids, in order to increase the cross section of the channels in the wheel, are installed with a smaller number of blades from 2 to 4 pieces. Centrifugal pumps are usually installed above the liquid level in the receiving tank, so they must be filled before use. The pump is filled with a check valve on the suction line through the filling funnel until the gas is completely expelled from the suction pipeline and the pump housing. In the absence of a check valve, for filling, air is forced out of the pump housing with the valve closed by a special vacuum pump. The same is done when filling large pumps. Centrifugal pumps are characterized by a rather high efficiency, compactness and durability of use. Based on the numerical modeling of hydrodynamic processes, a substantiation of adjustment of the design of the working wheels of centrifugal pumps is given. Mathematical modeling of the fluid flow in the running part of the centrifugal pump is performed. The results of the CFD calculation are analyzed, after which an experimental work wheel is created, and its tests are carried out. There is a process of comparing a serial and experimental pump. Keywords: Centrifugal pumps, numerical modeling, mathematical model, energy characteristics, hydrodynamic processes, dynamic characteristics, power engineering, working wheel, working fluid, working wheel vanes.

Differential-difference systems in the analysis of weak solvability of initial-boundary value problems with a spatial variable in a network-like domain

In the work, the approach and the corresponding methods, which make it possible to construct a priori estimates of weak solutions of a differential-difference system with a spatial variable varying in a multidimensional network-like domain are indicated. Such estimates in spaces of summable functions are used to find solvability conditions for boundary value problems of various types for differential-difference systems. In addition, a priori estimates are used to justify the application of the method of discretization with respect to the time variable (semi-discretization) to the analysis of the weak solvability of initial-boundary value problems and the subsequent construction of approximations of weak solutions. The rationale for the approach used is the fact that in a fairly wide class applied analysis of the problems of transporting continuous media networks-like carriers, the representation of mathematical models of the process using the formalisms of differential-difference systems is the only tool for effectively solving these problems. For example, the reduction of a differential system (initial-boundary value problem) to the corresponding differential-difference system makes it possible not only to significantly simplify the analysis of problems of optimal control of a differential system (since this analysis reduces to studying the problem of optimal control of a system of elliptic equations), but also, using classical methods of control theory for elliptic systems, algorithmize the original problem. The reduction used often facilitates establishing the conditions for the existence and uniqueness of optimal control of a differential system. These problems also include a fairly large range of studies of non-stationary network-like hydrodynamic processes and flow phenomena. As an illustration of the approach used and the results obtained, the analysis of the solvability of the linearized Navier–Stokes system is given and the ways of studying the nonlinear Navier–Stokes system are indicated.

Impact of magmatic intrusion on diagenesis of shallow marine sandstones: An example from Qasim Formation, Northwest Saudi Arabia

Igneous intrusions are common in sedimentary basins, and their occurrence can significantly affect the diagenesis and reservoir quality evolution of sandstones, thereby strongly impacting their hydrocarbons-, geothermal-, and CO2-storage potentials. The Qasim sandstones in the Tabuk region (NW Saudi Arabia) experienced shallow burial diagenesis (<2 km) when the Tertiary magma intruded to form basaltic sills (0.4–4 m thick). The sedimentology, tectono-stratigraphic framework, provenance, and chemostratigraphy of the Qasim Formation have been extensively covered in the literature. However, the impact of the magmatic intrusion on diagenesis and reservoir quality evolution of the sandstones remains enigmatic. This study employed thin-section petrography, QEMSCAN, XRD, SEM, and energy-dispersive spectrometer analyses to investigate the role of magmatic intrusion on diagenesis and reservoir quality of the Qasim sandstones. The results of the study indicate that reservoir porosity is principally influenced by primary depositional characteristics (grain size and sorting), diagenetic alterations, and magmatic intrusions. Sandstones with coarser grain size and better sorting have the best intergranular porosity and vice versa. The “normal” diagenetic processes that have significantly affected the reservoir porosity of the sandstones occurred during both shallow burial (eodiagenesis) and uplift (telodiagenesis). The eogenetic alterations include mechanical compaction, early diagenetic cementation by calcite, pyrite, and kaolinite, whereas the telogenetic alterations include the formation of kaolinite, goethite, hematite. Overall, mechanical compaction is the main driver for porosity loss in the sandstones. The intrusion-related diagenetic processes include the dissolution of quartz grains, rounded quartz overgrowths, and calcite cement, and the transformation of kaolinite into dickite and chlorite. Detrital quartz and rounded quartz overgrowths have undergone dissolution due to acidic pore fluids from magma and high temperature. The transformation of kaolinite into dickite occurred in a dissolution-recrystallization fashion, and the amounts of kaolinite and dickite increase in fine-grained sediments away from sill contact due to hydrodynamic processes that deposited muscovite (which form kaolinite) in low energy environments. The chloritization of kaolinite was localized, and the magma-induced dissolution of goethite likely supplied the requisite high Fe content. Additionally, the intrusion has resulted in the dissolution of the early calcite and increase in porosity towards the sill contact. However, values for compactional porosity loss have relatively remained similar both at and away from the sill contact, as the sill is too thin to exert significant vertical loading. This study has relevance to understanding hydrocarbon exploration and exploitation in sediment-lava sequences, and to understanding the development of sediment-lava systems.

Spray impact onto a hot solid substrate: Film boiling suppression by lubricant addition

Spray cooling of solid substrates is one of the methods used in various industrial processes such as forging, quenching or other metallurgical applications, electronics, pharmaceutical industry, medicine, or for cooling of powerful electrical devices. Spray cooling is governed by various hydrodynamic and thermodynamic processes, like drop impact, heat conduction in the substrate and convection in the spreading drops, and different regimes of boiling. The problem of modeling spray cooling becomes even more challenging if the liquid is multicomponent. The presence of components with various physicochemical properties (surfactants, binders, dispersed particles, etc.) can significantly affect the entire process of spray impact, as well as the outcome of the known cooling regimes and could lead to a formation of a thin deposited layer on the substrate. In this experimental study, spray impact onto a substrate, initially heated to temperatures significantly exceeding the liquid saturation point, is visualized using a high-speed video system. The heat transfer associated with spray impact is characterized using an array of thermocouples installed in a thick metal target. As a working fluid, a mixture of a distilled water and industrial white lubricant was used. It is observed that the presence of very small concentrations of lubricant augments the heat flux dramatically, particularly at high wall temperatures, at which usually film boiling is observed for spray cooling by using distilled water. Three main mechanisms lead to the increase of heat flux and shift of the Leidenfrost point. They are caused by the significant viscosity increase of the evaporating lubricant solutions, by an increase of the substrate wettability and by the emergence of stable liquid sheets between bubbles, preventing their coalescence and percolation of the vapor channels.

Design of hydrodynamic cavitation-based advanced oxidation process for degradation of recalcitrant micropollutants originating from tertiary effluent streams: a case study with norfloxacin

Abstract Treatment of micropollutants even after tertiary treatment and developing cost-effective, sustainable and energy-efficient technology for the same still remains an active area of research. The present study reports the feasibility and efficacy of hydrodynamic cavitation (HC)-based advanced oxidation process (AOP) for the degradation of norfloxacin. Experiments using HC were carried out in a sequential manner starting with the optimization of the cavitating device (orifice plate) using computational fluid dynamics (CFD) followed by optimizing the operational parameters such as pH, inlet pressure and initial concentration. An experimental study revealed that under optimized conditions of pH – 2, inlet pressure – 6 bar and initial conc – 250 μg/L, NRF degradation of 22.26% was obtained using HC in an experimental run of 60 min. For further improvement of the HC process, experiments were carried out by integrating with H2O2, O3 and Fenton's reagent. Under the optimized conditions, integrating with H2O2, O3 and Fenton's reagent enhanced the extent of NRF degradation. The energetics of the process was further evaluated to understand the techno-economic viability. The study revealed that HC + H2O2 consumed less energy of 8.01 kWh/m3 at the economics of Rs. 82.53/m3. Thus, HC combined with oxidizing agents can be a novel technique in the genre of AOP for the degradation of micropollutants.

Assessing 40 Years of Flood Risk Evolution at the Micro-Scale Using an Innovative Modeling Approach: The Effects of Urbanization and Land Planning

The present work is aimed at assessing the change in time of flood risk as a consequence of landscape modifications. The town of San Donà di Piave (Italy) is taken as a representative case study because, as most parts of the North Italy floodplains, it was strongly urbanized and anthropized in the last several decades. As a proxy for flood risk, we use flood damage to residential buildings. The analysis is carried out at the local scale, accounting for changes to single buildings; GIS data such as high-resolution topography, technical maps, and aerial images taken over time are used to track how the landscape evolves over time, both in terms of urbanized areas and of hydraulically relevant structures (e.g., embankments). Flood hazard is determined using a physics-based, finite element hydrodynamic code that models in a coupled way the flood routing within the Piave River, the formation of levee failures, and the flooding of adjacent areas. The expected flood damage to residential buildings is estimated using an innovative method, recently proposed in the literature, which allows estimating how the damage evolves during a single flood event. The decade-scale change in the expected flood damage reveals the detrimental effect of urbanization, with flood risk growing at the pace of a fraction of urbanized areas. The within-event time evolution of the flood damage, i.e., how it progresses in the course of past or recent flood events, reflects changes in the hydrodynamic process of flooding. The general methodology used in the present work can be viewed as a promising technique to analyze the effects on the flood risk of past landscape evolution and, more importantly, a valuable tool toward an improved, well-informed, and sustainable land planning.

The quantitative response of pollutant spatial distribution and mixing dynamics to confluent conditions in an asymmetric open-channel confluence

River confluences are key nodes of pollutant transport in fluvial ecosystems and they are accompanied by complex hydrodynamic and mixing processes. The generalization and quantitative response of mixing to highly variable confluent conditions remain unclear. This studyinvestigates the spatial distribution and mixing process of pollutants through a series of meticulous experiments in an asymmetric open-channel confluence. Furthermore, we propose quantitative responses and characterization equations for the mixing rate and mixing metric for various confluent conditions, namely junction angle, momentum flux ratio, and width-depth ratio. The spatial distribution of pollutants have a strong three-dimensional structure, with a narrow-long pollution belt near the tributary and an almost vertical mixing interface adjacent to the downstream junction corner; this interface exhibits a logarithmic growth trend downstream and is affected by shear layer distortion. The standard deviation of the cross-sectional pollutant concentration at the confluence decreases gradually along with the downstream mixing of convergent flows, and the fitting curve slope increases as the junction angle, momentum ratio, and width-depth ratio increase. The mixing rate is promoted by the enhancements of helical motion, lateral advection, and turbulent diffusion caused by the strengthening of mutual deflection and lateral momentum flux under a large junction angle and momentum ratio, as well as the reductions of vertical velocity gradient and cross-sectional area under large width-depth ratio conditions. Sufficient and complete mixing occurs under a larger momentum ratio condition of >1 within a short distance of 4–5 widths of the main channel. In addition, the mixing metric shows a strong linear relationship with each of the three confluent conditions. In summary, the significant (p < 0.001) quantitative responses of the mixing rate and mixing metric can be characterized by a polynomial equation. These results have major implications for the systematic understanding of the three-dimensional distribution characteristics, mixing patterns, and mixing dynamics of pollutants at asymmetric confluences, as well as for the prediction or calculation of the downstream mixing metric.

A Probabilistic Model for Evaluation of the Dynamic Behavior of a Concrete Gravity Dam considering the Fluid-Structure Interaction

Regarding the importance of the interaction effect in the dynamic behavior of a concrete dam and reservoir, the process of hydrodynamic wave propagation in the reservoir and its effects on the response of a concrete gravity dam are examined in this article by presenting a new probabilistic model. For this purpose, a program has been written in an APDL environment of Ansys software capable of dynamic analysis of a system and presenting probabilistic models. The Monte Carlo method with the LHS method has been applied for the probabilistic model, in which the essential parameters in the dam-reservoir interaction problem include excitation frequency, reservoir height, and reservoir length as input variables, and the effect of their changes on the hydrodynamic wave propagation process in the reservoir and the dynamic response of the dam are evaluated. For a better understanding of the dam-reservoir interaction concept and to show the capability of the presented model, two simple and isolated models of the concrete gravity dam and reservoir system have been considered. According to the results, the distribution trend of hydrodynamic pressure along the reservoir can be obviously recognized. Also, the results present the dependence of the responses and the propagation status on the excitation frequency and its relationship with the system frequency and the reservoir natural frequency.

A novel computational model and OpenFOAM solver for simulating thermal energy storages based on granular phase change materials: Advantages and applicability

In this paper, we consider hydrodynamic and heat transfer processes in thermal energy storages based on granular or encapsulated phase change materials. Such heat storages can be applied in renewable and conventional energy, safety systems, civil building, and so on. A computational model, which is based on the assumption of interpenetrating interacting continua, has been developed to simulate the processes of phase transitions, heat transfer and fluid flow in the packed bed latent heat storages. To implement this model, we chose OpenFOAM – the leading free, open source software for computational fluid dynamics and heat transfer. Solver porousHeatTransferFoam, which is based on the SIMPLE algorithm, and additional libraries have been developed in the OpenFOAM framework. The solver and the libraries allow one to model granular materials with complex enthalpy-temperature diagrams during phase transitions, thus expanding the applicability of OpenFOAM. The advantage of the solver is high computational speed – its calculation time varies from a minute to a few minutes for 1D simulations and from a few minutes to a few hours for 2D simulations depending on the mesh sizes. Comparison between numerical results obtained and known experimental data has shown that the model based on the assumption of interpenetrating interacting continua adequately describes the heat transfer processes in the packed bed latent heat storages not only for the large ratio of the storage characteristic size to the particle diameter, but also for the small one (about 7–8). In contrast to many existing computational models, which applicability is usually limited to rather narrow class of the processes, our model covers a variety of hydrodynamic and heat transfer problems in the thermal energy storages based on granular phase change materials. This computational model and OpenFOAM solver developed allow one to simulate incompressible and compressible (liquid or gaseous) flows through the packed bed latent heat storages under various boundary conditions, with isothermal and non-isothermal phase transitions, with various properties of granular materials and coolant, in wide ranges of flow velocities, operating temperatures and particle sizes.

Spatial Discrepancy of Hydrodynamics‐Driven Impacts on Organic Biomarkers Deposition and ′ and TEX86 Temperature Proxies Applications

AbstractThere is evidence that sedimentary organic matter is prone to lateral transport under hydrodynamic processes before its final deposition on the seafloor, restricting the applicability of molecular proxies. In this study, we examine the abundances of marine and terrestrial biomarkers in bulk and the grain‐size fractionated samples (&lt;20, 20–63, and &gt;63 μm fractions) from surface sediments in the South Yellow Sea to decipher the spatial influences of hydrodynamic processes on the biomarker distributions and molecule‐proxies' applications. Our results show that spatial deviations between proxies‐derived sea surface temperature (SST; the ′ and TEX86 indexes) and satellite‐derived annual mean SST may result from the lateral transportation of the alkenones and isoprenoid Glycerol Dialkyl Glycerol Tetraethers driven by dominated nearshore coastal currents. We propose a spatial‐SST correction approach to obtain more accurate SST information by removing the hydrodynamically introduced SST bias. Our investigations imply that hydrodynamic processes could be an important factor for controlling the spatial distribution of biomarkers in the ocean, further influencing the applications of biomarker‐based proxies for paleo‐environmental reconstruction. We suggest that this investigation would shed new light on the biogeochemical dynamics of sedimentary organic carbon pump in the shallow ocean, particularly in the passive continental marginal seas with strong hydrodynamic conditions.

Визуализационный анализ результатов континуально-атомистического моделирования кулоновского взрыва в металлах под влиянием ультракороткого (fs, ps) лазерного воздействия

A continuum-atomistic model that describes nonequilibrium thermal, hydrodynamic, and electronic processes in metals that occur under the action of ultrashort (fs, ps) laser radiation has been developed. A detailed study of two mechanisms of ultrashort laser ablation of Cu was carried out: fast - Coulomb, determined by Coulomb forces, and slow - thermal, realized in the unloading wave after the end of the laser pulse. Modeling showed that the excess nonequilibrium pressure of collectivized electrons plays a leading role in the formation of a strong electric field at the metal-vacuum interface. This effect can be taken as the basis for the Coulomb explosion in metals. The main feature of the work is the widespread use of modern visualization tools for processing and presenting simulation results.

Estimating coastal slope of sandy beach from ICESat-2: a case study in Texas

Coastal slope is a fundamental land characteristic that can influence the hydrodynamic and morphological processes, which is the essential parameter to calculate the wave setup and wave run up for further estimating extreme coastal water levels. Slope information of coastal zones also plays a key role in estimating the coastline erosion and evaluating the coastal vulnerability under sea level rise. However, accurate estimates of coastal slopes are currently limited, especially over sparsely populated and remote areas. The recent ICESat-2 photon-counting lidar provides unprecedented along-track dense and accurate height measurements in coastal zones. This study aims to demonstrate the potential of ICESat-2 measurements to estimate coastal slope of sandy beach at a large scale, and the proposed method is tested in Texas, USA. The validation with local airborne lidar data (with an average slope of 0.023 in Texas) indicates that, the ICESat-2 derived coastal slopes (0.026) have much better accuracy than current large-scale coastal slopes (0.0032) derived from SRTM and MERIT DEMs. With globally covered ICESat-2 datasets, this method can be expanded to estimate coastal slopes even at a global scale.

Mixed depositional processes in coastal to shelf environments: Towards acknowledging their complexity

The intricate development of coastal to shelf environments and their deposits is dominantly driven by the interplay of river, wave and tide hydrodynamic processes. These processes are, in turn, impacted by several additional factors including aeolian processes, contour currents, seasonal ice cover, the nature and mechanical characteristics of the substrate, confinement and physiography of the basin, climate oscillation and relative sea-level fluctuations. Consequently, the depositional record of these mixed-process interactions is complex and challenging to decipher. Because coastal and shallow-marine areas around the world are densely populated and subject to intense and increasing natural and anthropogenic stresses, a better understanding of these depositional systems will benefit their sustainable protection and development. In this special issue, contributors present their newest research on mixed-energy depositional processes and how they control the dynamics and sedimentary record of coastal to shelf environments.

Modeling Of Polymer Melt Flow In The Annular Channel Of A Disk Extruder

Purpose. Polymer products are used in industry due to their performance properties. The homogeneity of the melt is essential for the quality of the final product. Uniform distribution of components and properties ensures homogeneity of the product's physical and mechanical characteristics. Insufficient homogeneity can lead to defects in the product. The homogenization zone plays an important role in ensuring a homogeneous melt. In a disc extruder, the homogenization zone consists of four consecutive channels. In order to describe the flow for the entire homogenization zone, it is necessary to model the first channel first. Therefore, the main purpose of this work is to model hydrodynamic and thermal processes during the flow of a non-Newtonian fluid in a straight annular channel in a non-isothermal regime, as well as to create a general procedure for further calculations for other channels. Methodology. The analysis of publications was carried out. The procedure for calculating the velocity and shear rate of the longitudinal and tangential melt flow, the effective melt viscosity, and the calculation of the melt temperature change along the length of the annular gap in an analytical form was developed. Findings. In accordance with the developed procedure, the values of tangential and longitudinal velocities and shear rates were calculated. The graphical dependences of the distribution of tangential and longitudinal velocities and shear velocities of the melt flow along the width of the annular channel, the distribution of pressure and the temperature of the polymer melt averaged over the width of the gap along the length of the annular channel are presented. Originality. In this work, a stationary flow in a straight annular channel was modeled for LDPE of the 15803-020 grade in a non-isothermal regime. A general procedure for further calculations for other channels of the homogenization zone has been developed. Practical value. The given calculation procedure can be applied to the following channels of the homogenization zone, which allows describing the melt flow for the entire homogenization zone.

Original article Spatial-three-dimensional wave processes’ modeling in shallow water bodies taking into account the vertical turbulent exchange features

Introduction. Reliable prediction of indicators of turbulent flows is a very difficult task, which is explained by the exceptional physical complexity of turbulence, in particular its probabilistic nature, a wide space-time spectrum and a fundamentally three-dimensional non-stationary nature. Despite conducting a wide range of studies focused on the problem under consideration, they did not fully reflect the totality of various factors and processes affecting the structure and parameters of vertical turbulent mixing. This indicates the need for a systematic analysis of the problem and modeling of such complex formalized systems. The aim of the work is to construct a scenario of changes in hydrodynamic wave processes of the coastal zone, based on an improved mathematical model of wave processes.Materials and methods. The article is devoted to the study of spatial-three-dimensional wave processes in shallow water bodies, taking into account the features of turbulent exchange depending on the source and localization in the column of liquid, as well as the study of the influence of regular wave processes on turbulent exchange and vertically using a mathematical model of wave processes based on the system of Navier-Stokes equations, including three equations of motion in the with dynamically changing geometry of the computational domain.The results of the study. Based on the developed software package, a scenario of changes in hydrodynamic wave processes of the coastal zone is constructed, the formation of vortex structures is predicted. Discussion and conclusions. The separation of the wave flow into a near-surface macroturbulent layer caused by wave motion and a lower layer with background hydrodynamic turbulence is proved, the strength and intensity of turbulence changed synchronously with wave oscillations, demonstrating a pronounced asymmetry of turbulence generation throughout the water column.

Erosion and accretion patterns on intertidal mudflats of the Yangtze River Estuary in response to storm conditions

Understanding of erosion and accretion patterns over intertidal mudflats during storm periods is vital for the management and sustainable development of coastal areas. This study aimed to investigate the effect of the 2014 storm Fung-wong on the erosion and accretion patterns of the Nanhui intertidal mudflats in the Yangtze estuary, China, based on field measurements and Delft3D numerical modeling. Results show that prolonged easterly winds during the storm enhance the flood velocity, weaken the ebb velocity, and even change the current direction. The current velocity, wave heights, and bed-level changes increased by 1–1.43 times, 2.40–3.88 times, and 2.28–2.70 times than those of normal weather, respectively. The mudflats show a spatial pattern of overall erosion but increasing erosion magnitude from the high (landward) mudflat to the low (seaward) mudflat during the storm. The magnitude of bed-level change increases with increasing wind speed, but the spatial pattern of erosion and accretion remains the same. The main reason for this pattern is the longer submersion duration of the low mudflat compared with the high mudflat, so the hydrodynamic process is longer and stronger, leading to an enhancement in bed shear stress and sediment transport rate. Wind speed increases the hydrodynamic intensity but does not affect on the submersion duration over each part of the intertidal mudflat. This study is helpful to improve the understanding of physical processes during storms on intertidal mudflats and provides a reference for their protection, utilization, and management, as well as for research in related disciplines.

Bioclastic bottom‐current deposits of a Devonian contourite terrace: Facies variability and depositional architecture (Tafilalt Platform, Morocco)

ABSTRACTThe study examines bioclastic carbonate contourites that arise from the broad spectrum of bottom‐current related sedimentary processes ranging from deposition to erosion. The result of the intermittent accumulation of sediment are thin and condensed successions with abundant hiatuses. Such bottom‐current deposits are poorly known, since the broadly accepted contourite‐facies model, the bi‐gradational sequence, characterizes environments of contourite depositional systems as a continuous accretion of fine‐grained siliciclastic sediments. To increase current understanding of the carbonate facies within hiatal contourite records, the Eifelian–Frasnian of the Tafilalt Platform in Morocco was investigated. The succession is divided into five facies associations that are interpreted to reflect pelagic sedimentation and deposition from bottom currents on a contourite terrace, a gently inclined section of the upper slope of Gondwana shaped by a water‐mass interface. Contourite deposition was mainly controlled by oxic clear‐water currents (documented by moderately to completely bioturbated limestones with abundant hydrogenetic ferromanganese nodules, and low organic‐carbon contents), at times also by an anoxic water mass (featured by organic‐rich coquinas with absent to sparse bioturbation and predominantly syngenetic framboidal pyrites). Biostratigraphic data and the overall depositional architecture display palaeoceanographic hydrodynamic processes associated with a shifting water‐mass interface. The inner terrace was characterized by an alongslope contourite channel and a small mounded drift at its downslope margin. Energetic bottom currents furthermore caused abraded surfaces, i.e. plain areas of non‐deposition and localized erosion, and sandy condensation layers. The microfacies reflects repeated alternation between suspension deposition, winnowing of fines, bedload traction, dynamic sediment bypassing and reworking, together with concomitant seafloor cementation. Coquinas of mainly planktonic and nektonic organisms are identified as integral parts of bi‐gradational contourite sequences showing inverse and normal grading. Hiatal lag concentrations of carbonate intraclasts, ferromanganese nodules and conodonts often drape hardgrounds and erosional surfaces at the midpoint of these frequently incomplete sequences. This Devonian case provides the opportunity to investigate the spatial and temporal variability of the bed‐scale contourite sequence, also with regard to the drift‐scale depositional architecture. In addition, the identified high‐resolution record is a starting point for unravelling the pattern of oceanic circulation in the Devonian greenhouse world.

A partitioned model for predicting the spatial development of flow in ecological vegetated rivers with submerged vegetation

The evolution of the velocity caused by submerged vegetation in river courses with regular cross sections has been poorly investigated using analytical methods. Fully understanding the longitudinal profiles of the velocity is significant and essential to study the hydrodynamic processes taking place in wetland ecosystems, which is the most important indicator of energy transfer and material exchange in fluvial ecosystems. Based on the experimental data in the literature, the streamwise velocity gradually is found to decrease in the submerged vegetation and increase in the free surface layer. A four-panel analytical model derived from exponential decay theory was developed to predict the streamwise velocity occurring both upstream and within vegetation along the main flow direction in a rectangular open channel with a submerged vegetation patch. We aim at the development of velocity, which is averaged across the vegetation and free surface layers separately, and the length scales shown in the velocity evolution. The explicit calculation expression for each parameter in the analytical model was provided, and sensitivity analysis was conducted by changing the parameters to check how the predicted velocity changed. The change in the drag coefficient of vegetation (CD) and the velocity at the leading edge of the vegetation (U0) influenced the development of velocity. The former mainly enlarges the velocity difference between the vegetation and free surface layers after the leading edge as it increases, and the latter mainly diminishes the velocity difference before the leading edge as it increases. The error statistics is conducted and shows that the predicted and measured velocities are consistent within a relative error of 11%, indicating that the partitioned model is applicable in predicting longitudinal velocity in flows with submerged vegetation of various flexibility. The theoretical analysis of velocity development paves the way for the future studies on the flow turbulent structure and sediment transport in partially vegetated rivers.

Examining the commonalities and knowledge gaps in coastal zone vegetation simulation models

AbstractModels can be powerful tools to help scientists, policymakers, and practitioners forecast vegetation dynamics and inform management decisions in a variety of ecosystems. In coastal environments, vegetation moderates physical and hydrodynamic processes that conversely affect vegetation dynamics. Coastal management and the implementation of nature‐based solutions in the coastal environment requires models that can predict vegetation dynamics that are driven by ecological processes as well as physical processes (e.g., storms, sea level rise). To determine models that are capable of simulating biomass dynamics and assess their ability to make predictions within the context of climate change and environmental management, we reviewed coastal dynamic vegetation simulation models across the following coastal zone habitats: tidal wetlands (salt marsh, mangroves, and freshwater wetlands), seagrass beds, coastal forests (maritime and floodplain forests), and dune habitats. Fifty‐four models met the review criteria and were examined to assess their ability to simulate relevant ecological processes and the spatiotemporal scales at which they are applied. These models included a variety of exogenous and endogenous processes and integrate complex ecogeomorphological feedbacks affecting plant and soil community, hydrodynamic, and sediment transport dynamics. Most models reviewed utilized implicit approaches to predicting vegetation biomass and simulated a limited number of processes based on the principal drivers of habitat of interest. Key gaps identified were the exclusion of below‐ground biomass dynamics, limited inclusion of processes such as competition, facilitation, and succession, and the inability to simulate management actions. Future models should seek to move towards process‐based approaches where appropriate to enable their application to different systems and facilitate their use under novel environmental conditions.