Hydrodynamic Scenarios Research Articles

Numerical Modeling of the Dispersion Characteristics of Pollutants in the Confluence Area of an Asymmetrical River

It is challenging to investigate the transport and dispersion of contaminants in river confluence areas due to the complex flow dynamics. In recent studies on the flow dynamics in river confluence areas, it has been revealed that changes in inflow conditions (discharge ratio, width-depth ratio and concentration difference) can greatly influence pollutant diffusion. In this study, an asymmetric confluence-type river is modeled by a three-dimensional hydrodynamic water quality model, and three hydrodynamic scenarios are numerically simulated. The results show that a higher discharge ratio and width-depth ratio led to an increase in the lateral diffusion area of pollutants, deviation in the trajectory line of the mixing interface towards the opposite bank of the interchange, and an increase in the mixing rate of pollutants. For R = 0.267 and b/h = 3.75, the pollutants at the bottom are completely mixed in the exit end section. However, the difference in the pollutant concentration slightly affects the area, length and shape of the pollutant dispersion zone and notably affects only the concentration in each section.

Hydrodynamic numerical simulations based on residual cooperative neural network

As a gridless computational method, physics-informed neural networks (PINNs) have been widely applied and are a research hotspot in the field of numerical simulation due to their potential to provide approximations that are infinitely close to the analytical solutions. To address the complex hydrodynamic simulation scenarios with a large solution domain, where the conventional PINNs are not fully applicable, we propose a residual cooperative neural network (RCNN) embedded with hard constraints and optimized by the automatic mixed-precision (AMP) computational technique. To perform extreme condition hydrodynamic simulations, we provide smooth surrogate functions for each of the point-source and step conditions. The applicability and advantages of the RCNN model are verified with a total of four typical hydrodynamic cases. The results show that the RCNN performs better than the conventional PINN in terms of convergence, applicability, and fitting accuracy, with an overall goodness-of-fit of over 0.99. The computational cost of the RCNN model can be significantly reduced by the AMP technique, with the average computation time and occupied GPU memory reduced by 45.77% and 43.16%, respectively. The RCNN can effectively address the gradient explosion and gradient disappearance problems in complex hydrodynamic simulations with a large solution domain.

Zoning the suitability of the western Mekong Deltafor paddy rice cultivation and aquaculture under current and future environmental conditions.

Ca Mau and Kien Giang, the two provinces of the Mekong Delta bordering the Gulf of Thailand, are facing major environmental challenges affecting the agriculture and aquaculture sectors upon which many livelihoods in this region depend on. This study maps the suitability of these two provinces for paddy rice cultivation and shrimp farming according to soil characteristics and current and future environmental conditions for variables found to significantly influence the yield of those two sectors, i.e., the level of saltwater intrusion, water availability for rainfed agriculture, and the length of the growing period. Future environmental conditions were simulated using the MIKE 11 hydrodynamic model forced by four hydrodynamic scenarios, each one representing different extents of saltwater intrusion during both the dry and rainy seasons, while also considering the availability of water resources for rainfed agriculture. The suitability zoning was performed using a GIS-based analytic hierarchy process (AHP) approach, resulting in the categorisation of the land according to four suitability levels for each sector. The analysis reveals that paddy rice cultivation will become more suitable to Kien Giang province while shrimp farming will be more suitable to Ca Mau province if the simulated future environmental conditions materialise. A suitability analysis is essential for optimal utilisation of the land. The approach presented in this study will inform the regional economic development master plan and provide guidance to other delta regions experiencing severe environmental changes and wishing to consider potential future climatic and sea level changes, and their associated impacts, in their land use planning.

Experimental Carbon Emissions From Degraded Mediterranean Seagrass (Posidonia oceanica) Meadows Under Current and Future Summer Temperatures

AbstractPosidonia oceanica beds are recognized to be an essential carbon sink in the Mediterranean Sea. However, when seagrass cover disappears, seagrass sediments may become net carbon sources contributing to the CO2 atmospheric increase. Determining CO2 efflux from degraded seagrass beds is required to understand potential emissions from this Mediterranean ecosystem. This study presents one of the very first experimental CO2 efflux estimates from P. oceanica degraded seagrass sediments under future warming and hydrodynamic scenarios. Sediments were sampled from a P. oceanica seagrass meadow in Pollença, a sheltered bay on Mallorca Island. Sediment samples were kept in mesocosms for 98 days at five different temperatures (26, 27.5, 29, 30.5, and 32) and two treatments (agitation/repose). CO2 effluxes were higher in the agitated treatments (0.75 μM m−2 s−1) than in repose (0.51 μM m−2 s−1). CO2 efflux clearly increased with temperature in repose treatments, while treatments under agitation presented larger variation. Our results indicate that exposure to hydrodynamics plays a key role in the remineralization of organic carbon (Corg) under climate change conditions and that denuded seagrass meadows have the potential to emit in a single summer season (3 months) the amount of carbon (C) that a healthy meadow sequestrates during an entire year. This study provides brand new information required to quantify the dynamics of Corg stock loss and CO2 emissions in degraded seagrass meadows.

Compound Effects of Flood Drivers, Sea Level Rise, and Dredging Protocols on Vessel Navigability and Wetland Inundation Dynamics

Maritime transportation is crucial to national economic development as it offers a low-cost, safe, and efficient alternative for movement of freight compared to its land or air counterparts. River and channel dredging protocols are often adopted in many ports and harbors of the world to meet the increasing demand for freight and ensure safe passage of larger vessels. However, such protocols may have unintended adverse consequences on flood risks and functioning of coastal ecosystems and thereby compromising the valuable services they provide to society and the environment. This study analyzes the compound effects of dredging protocols under a range of terrestrial and coastal flood drivers, including the effects of sea level rise (SLR) on compound flood risk, vessel navigability, and coastal wetland inundation dynamics in Mobile Bay (MB), Alabama. We develop a set of hydrodynamic simulation scenarios for a range of river flow and coastal water level regimes, SLR projections, and dredging protocols designed by the U.S. Army Corps of Engineers. We show that channel dredging helps increase bottom (‘underkeel’) clearances by a factor of 3.33 under current mean sea level and from 4.20 to 4.60 under SLR projections. We find that both low and high water surface elevations (WSEs) could be detrimental, with low WSE (< -1.22 m) hindering safe navigation whereas high WSE (> 0.87 m) triggering minor to major flooding in the surrounding urban and wetland areas. Likewise, we identify complex inundation patterns emerging from nonlinear interactions of SLR, flood drivers, and dredging protocols, and additionally estimate probability density functions (PDFs) of wetland inundation. We show that changes in mean sea level due to SLR diminish any effects of channel dredging on wetland inundation dynamics and shift the PDFs beyond pre-established thresholds for moderate and major flooding. In light of our results, we recommend the need for integrated analyses that account for compound effects on vessel navigation and wetland inundation, and provide insights into environmental-friendly solutions for increasing cargo transportation.

Nonlinear stiffness enhancement of submerged wave energy device in high fidelity model

A three degree of freedom submerged wave energy converter with a nonlinear stiffness mechanism was modelled using both linear and nonlinear hydrodynamics. The linear hydrodynamics scenario used linear potential flow methods to predict the fluid–structure interaction, while the nonlinear hydrodynamic scenario use computational fluid dynamics (OpenFOAM). The potential energy of the nonlinear stiffness mechanism was varied relative to the potential energy of the incident wave. The wave energy converter was excited using regular and irregular waves. The nonlinear stiffness scenarios were compared to scenarios with optimised linear control parameters. When compared to optimal conditions, models using linear hydrodynamics to emulate both regular and irregular waves showed no improvement in power generation. In the regular wave nonlinear hydrodynamic scenarios, the nonlinear stiffness showed inconsistent improvements to power production and significant detuning at different levels of nonlinearity. The irregular wave scenario using nonlinear hydrodynamic methods demonstrated a small improvement compared to optimised linear control parameters when the nonlinear stiffness potential energy peak was less than half the potential energy of the incident wave. The nonlinear stiffness improved the robustness of the wave energy converter, and was an effective method for detuning the system, depending on the degree of nonlinearity.

Hydrodynamics and water renewal in the Pearl River Estuary, China: A numerical study from the perspective of water age

The time required for water renewal in an estuary is closely related to its self-purification ability and environment degree. A FVCOM-based water age (WA) model was conducted to investigate the renewal timescale in the Pearl River Estuary (PRE) under various hydrodynamic scenarios. Model sensitivities revealed the depth-averaged WA during the summer was significantly smaller than that during the winter; meanwhile, the region with vertically significant variations in the WA varied from almost the whole estuary to the downstream. It can be explained that the seaward residual currents became stronger and narrowed the region of vertical circulations by impeding salinity invasion and stratification. During typhoon Hagupit, the depth-averaged WA was apparently increased in the most of the estuary because the horizontal water circulations between the estuary and open sea were significantly decreased by the strong up-estuary surge-waves. Moreover, the vertical WA distribution almost became a single-layer structure with the severely weakened vertical circulations. After reclamations, the variable shorelines in the PRE significantly affected the hydrodynamic characteristics and water circulations, thus the depth-averaged WA complicatedly changed, and the vertical difference of the WA values slightly increased in narrowed waterways and their downstream due to the limited effects on the vertical circulations.

Numerical Prediction of Oil Mineral Aggregates Dispersion in the Estuary Of ST-Lawrence River

As part of the environment of the St-Lawrence River, the Canadian Coast Guard team and the URPEI research team at Ecole Polytechnique de Montreal carried out a numerical simulation based on the Eulerian-Lagrangian formulation for the dispersion of oil-mineral aggregates (OMA) in a turbulent flow produced by a propeller ship. This study is part of a larger project to assess the effectiveness of using fine clay minerals as a natural dispersant of petroleum in ice. The interest is to study the effect of an ice cover on the dispersal potential of a typical winter flow field. To highlight the potential dispersion, two hydrodynamic scenarios are chosen, with and without the presence of an ice cover. For each scenario, the calculation results are presented for a selection of particle densities in order to assess the model by comparison of the OMA distribution statistics in the water column.

Resistance of salt marsh substrates to near‐instantaneous hydrodynamic forcing

AbstractSalt marshes deliver vital ecosystem services by providing habitats, storing pollutants and atmospheric carbon, and reducing flood and erosion risk in the coastal hinterland. Net losses in salt marsh areas, both modelled globally and measured regionally, are therefore of concern. Amongst other controls, the persistence of salt marshes in any one location depends on the ability of their substrates to resist hydrodynamic forcing at the marsh front, along creek margins and on the vegetated surface. Where relative sea level is rising, marsh elevation must keep pace with sea‐level rise and landward expansion may be required to compensate for areal loss at exposed margins. This paper reviews current understanding of marsh substrate resistance to the near‐instantaneous (seconds to hours) forcing induced by hydrodynamic processes. It outlines how variability in substrate properties may affect marsh substrate stability, explores current understanding of the interactions between substrate properties and erosion processes, and how the cumulative impact of these interactions may affect marsh stability over annual to decadal timescales.Whilst important advances have been made in understanding how specific soil properties affect near‐instantaneous marsh substrate stability, less is known about how these properties interact and alter bulk substrate resistance to hydrodynamic forcing. Future research requires a more systematic approach to quantifying biological and sedimentological marsh substrate properties. These properties must then be linked to specific observable erosion processes, particularly at the marsh front and along creek banks. A better understanding of the intrinsic dynamics and processes acting on, and within, salt marsh substrates will facilitate improved prediction of marsh evolution under future hydrodynamic forcing scenarios. Notwithstanding the additional complications that arise from morphodynamic feedbacks, this would allow us to more accurately model the future potential protection from flooding and erosion afforded by marshes, while also increasing the effectiveness of salt marsh restoration and recreation schemes. © 2020 The Authors. Earth Surface Processes and Landforms published by John Wiley & Sons Ltd

Using qualitative network models to assess the influence of mussel culture on ecosystem dynamics

The expansion of the aquaculture industry in the last several decades has raised concerns about potential ecological impacts of the industry. Bivalve culture, particularly mussel farming, relies on naturally occurring plankton and numerous studies have demonstrated top-down control on phytoplankton, increased nutrients through excretion of metabolic wastes and remineralization of faeces and pseudofaeces, and bottom-up effects on predators and scavengers through mussel fall-off. However, results are inconsistent between studies, and hydrodynamic conditions and nutrient availability are thought to play an important role in the magnitude and the direction of the ecological effects of mussel culture on the surrounding ecosystem. We used qualitative network models (QNMs), to outline a general model that integrates these environmental conditions and (1) evaluated the ability of different model configurations to reproduce known responses to perturbations, (2) analyzed the behaviour of key components to contrasting hydrodynamic and nutrient condition scenarios, and (3) identified the most influential features of the derived scenarios. The model that included uncertain linkages to characterize unknown relationships performed best based on predetermined validation criteria; the addition of semi-quantitative information on the relative strength of certain linkages improved accuracy and sign determinacy of outcomes. The presence of suspended mussel culture negatively affected primary producers, zooplankton and deposit-feeders, and had a positive effect on predators and scavengers, especially in low-energy environments. Hydrodynamic conditions were shown to have a major impact on the response of the community to mussel culture, while nutrient availability had a very minor impact.

Simplification bias: lessons from laboratory and field experiments on flow through aquatic vegetation

AbstractWe present a critical analysis of experimental findings on vegetation–flow–sediment interactions obtained through both laboratory and field experiments on tidal and coastal environments. It is well established that aquatic vegetation provides a wide range of ecosystem services (e.g. protecting coastal communities from extreme events, reducing riverbank and coastal erosion, housing diverse ecosystems), and the effort to better understand such services has led to multiple approaches to reproduce the relevant physical processes through detailed laboratory experiments. State‐of‐the‐art measurement techniques allow researchers to measure velocity fields and sediment transport with high spatial and temporal resolution under well‐controlled flow conditions, yielding predictions for hydrodynamic and sediment transport scenarios that depend on simplified or bulk vegetation parameters. However, recent field studies have shown that some simplifications on the experimental setup (e.g. the use of rigid elements, a single diameter, a single element height, regular or staggered layout) can bias the outcome of the study, by either hiding or amplifying some of the relevant physical processes found in natural conditions. We discuss some observed cases of bias, including general practices that can lead to compromises associated with simplified assumptions. The analysis presented will identify potential pathways to move forward with laboratory and field measurements, which could better inform predictors to produce more robust, universal and accurate predictions on flow–vegetation–sediment interactions. © 2020 John Wiley & Sons, Ltd.

Numerical Modelling of Heavy Metal Dynamics in a River-Lagoon System

This paper describes the development of a two-dimensional water quality model that solves hydrodynamic equations tied to transport equations with reactions mechanisms inherent in the processes. This enables us to perform an accurate assessment of the pollution in a coastal ecosystem. The model was developed with data drawn from the ecosystem found in Mexico’s southeast state of Tabasco. The coastal ecosystem consists of the interaction of El Yucateco lagoon with Chicozapote and Tonalá rivers that connect the lagoon with the Gulf of Mexico. The results of pollutants transport simulation in the coastal ecosystem are presented, focusing on toxic parameters for two hydrodynamic scenarios: wet and dry seasons. As it is of interest in the zone, the transport of four metals is studied: Cadmium, Chromium, Nickel, and Lead. In order to address these objectives, a self-posed mathematical problem is solved numerically, which is based on the measured data. The performed simulations show how to characterise metals transport with an acceptable accuracy, agreeing well with measured data in total concentrations in four control points along the water body. Although for the accurate implementation of the hydrodynamic-based water quality model herein presented boundary (geometry, tides, wind, etc.) and initial (concentrations measurements) conditions are required, it poses an excellent option when the distribution of solutes with high accuracy is required, easing environmental, economic, and social management of coastal ecosystems. It ought to be remarked that this constitutes a robust differential equation-based water quality model for the transport of heavy metals. Models with these characteristics are not common to be found elsewhere.

Spatial preferences of Iberian barbel in a vertical slot fishway under variable hydrodynamic scenarios

Fish require access to multiple habitats to persist. Therefore, obstacles blocking a fish’s volitional ability to move between habitats can lead to its decline. A common way of addressing this problem is the construction of fishways. The design criteria of fishways are based on steady, uniform flows with the assumption that the water levels remain the same across the fishway. However once constructed, fishways are fundamentally dynamic systems exhibiting different hydrodynamic scenarios. These scenarios are classified as uniform and non-uniform water level profiles and are driven by changes in the up- and downstream water levels caused by operational and hydrological variability.In this paper, we demonstrate the need to consider a wider range of fishway hydrodynamic scenarios for an integral assessment of fishways. To do this, the spatial distribution of Iberian barbel (Luciobarbus bocagei) in a full-scale model of a vertical slot fishway under three different hydrodynamic scenarios is investigated. Video tracking was used to analyze the fish’s spatial distribution, and an acoustic Doppler velocimeter and lateral line probe were applied to characterize the local hydrodynamic conditions of each scenario. Spatial differences were tested using Syrjala's test and the relation with hydrodynamic variables analyzed by means of zero-inflated Poisson models. This study revealed three significant findings: 1) Fish made broader use of the fishway pool in scenarios with lower water drops, which are highly correlated with regions of overall lower turbulence and velocity magnitude. 2) The relative importance of physical variables varied between scenarios. Specifically, the protection offered by walls was found to be a determining factor in the spatial usage. 3) It is shown that a vertical slot fishway designed with the standard dimensions for fish passage under the assumption of uniform flow conditions may result in an adverse hydrodynamic environment for fish swimming under non-uniform conditions.

Stream flow simulation and verification in ungauged zones by coupling hydrological and hydrodynamic models: a case study of the Poyang Lake ungauged zone

Abstract. To solve the problem of estimating and verifying stream flow without direct observation data, we estimated stream flow in ungauged zones by coupling a hydrological model with a hydrodynamic model, using the Poyang Lake basin as a test case. To simulate the stream flow of the ungauged zone, we built a soil and water assessment tool (SWAT) model for the entire catchment area covering the upstream gauged area and ungauged zone, and then calibrated the SWAT model using the data in the gauged area. To verify the results, we built two hydrodynamic scenarios (the original and adjusted scenarios) for Poyang Lake using the Delft3D model. In the original scenario, the upstream boundary condition is the observed stream flow from the upstream gauged area, while, in the adjusted scenario, it is the sum of the observed stream flow from the gauged area and the simulated stream flow from the ungauged zone. The experimental results showed that there is a stronger correlation and lower bias (R2 = 0.81, PBIAS = 10.00 %) between the observed and simulated stream flow in the adjusted scenario compared to that (R2 = 0.77, PBIAS = 20.10 %) in the original scenario, suggesting the simulated stream flow of the ungauged zone is reasonable. Using this method, we estimated the stream flow of the Poyang Lake ungauged zone as 16.4 ± 6.2 billion m3 a−1, representing ∼ 11.24 % of the annual total water yield of the entire watershed. Of the annual water yield, 70 % (11.48 billion m3 a−1) is concentrated in the wet season, while 30 % (4.92 billion m3 a−1) comes from the dry season. The ungauged stream flow significantly improves the water balance with the closing error decreased by 13.48 billion m3 a−1 (10.10 % of the total annual water resource) from 30.20 ± 9.1 billion m3 a−1 (20.10 % of the total annual water resource) to 16.72 ± 8.53 billion m3 a−1 (10.00 % of the total annual water resource). The method can be extended to other lake, river, or ocean basins where observation data is unavailable.

ALARIC: An algorithm for constructing arbitrarily complex initial density distributions with low particle noise for SPH/SPMHD applications

A method is presented to obtain initial conditions for Smoothed Particle Hydrodynamic (SPH) scenarios where arbitrarily complex density distributions and low particle noise are needed. Our method, named ALARIC, tampers with the evolution of the internal variables to obtain a fast and efficient profile evolution towards the desired goal. The result has very low levels of particle noise and constitutes a perfect candidate to study the equilibrium and stability properties of SPH/SPMHD systems. The method uses the iso-thermal SPH equations to calculate hydrodynamical forces under the presence of an external fictitious potential and evolves them in time with a 2nd-order symplectic integrator. The proposed method generates tailored initial conditions that perform better in many cases than those based on purely crystalline lattices, since it prevents the appearance of anisotropies.

Light Particle Tracking Model for Simulating Bed Sediment Transport Load in River Areas

In this work a fast computational particles tracer model is developed based on Particle-In-Cell method to estimate the sediment transport in the access zone of a river port area. To apply the particles tracer method, first it is necessary to calculate the hydrodynamic fields of the study zone to determine the velocity fields in the three directions. The particle transport is governed mainly by the velocity fields and the turbulent dispersion. The mechanisms of dispersion and resuspension of particles are based in stochastic models, which describes the movement through a probability function. The developed code was validated using two well known cases with a discrete transformation obtaining a max relative error around 4.8% in both cases. The simulations were carried out with 350,000 particles allowing us to determine under certain circumstances different hydrodynamic scenarios where the zones are susceptible to present erosion and siltation at the entrance of the port.

Density profiles around A+B→C reaction-diffusion fronts in partially miscible systems: A general classification.

Various spatial density profiles can develop in partially miscible stratifications when a phase A dissolves with a finite solubility into a host phase containing a dissolved reactant B. We investigate theoretically the impact of an A+B→C reaction on such density profiles in the host phase and classify them in a parameter space spanned by the ratios of relative contributions to density and diffusion coefficients of the chemical species. While the density profile is either monotonically increasing or decreasing in the nonreactive case, reactions combined with differential diffusivity can create eight different types of density profiles featuring up to two extrema in density, at the reaction front or below it. We use this framework to predict various possible hydrodynamic instability scenarios inducing buoyancy-driven convection around such reaction fronts when they propagate parallel to the gravity field.

Simulation of hydrodynamic interaction forces acting on a ship sailing across a submerged bank or an approach channel

A solution is proposed to handle complex water boundaries based on the panelled moving patch method, in which the moving patch on the seabed is dynamically meshed by an optimized version of the paving algorithm and smoothed by a hybrid smoother. Using this approach, two typical hydrodynamic interaction scenarios with the non-even seabed are studied, and numerical results are obtained for a variety of values of the relative ship course as well as of characteristics of the seabed.

What drives nearshore sediment transport controls on the depletion of beach placers at Manavalakurichi, Southwest Coast of India?

An in-depth analysis has been made to simulate hydrodynamic scenarios for understanding the nearshore sediment transport controls of placer mineral depletion at Manavalakurichi, India. From the analyses of topographic configuration (extracted from Hydrographic Nautical Chart No. 2048 and data generated during year 2010), we inferred that the 5-m isobaths had broadened and exhibited shallowness. Distances between the coastline and the isobaths were found to have increased significantly over the past five decades. Along with this, the 10 and 20-m contours were found to have shifted about 35–100 m horizontally landward. These changes led to severe sediment deposition in these regions due to the changed wave energy levels and refraction patterns. Numerical simulations linking bathymetry, hydrodynamics, sediment load, and significant wave heights revealed that changes in bathymetry would amplify the wave heights and convergence of wave energy. Associated removal of sand from the high-energy zones will eventually lead to sediment starvation situations and depletion of placers in the adjacent beaches. As the observed trends of depletion generate great concern, detailed oceanographic investigations should be taken up immediately in the region. Fine-resolution hydrodynamic data-sets should prove useful for further evaluating the physical responses of the system to the altered geometry and for exploring remedial measures for restoring the heavy mineral content of the beach sand.

Developing a self‐consistent description of Titan's upper atmosphere without hydrodynamic escape

AbstractIn this study, we develop a best fit description of Titan's upper atmosphere between 500 km and 1500 km, using a one‐dimensional (1‐D) version of the three‐dimensional (3‐D) Titan Global Ionosphere‐Thermosphere Model. For this modeling, we use constraints from several lower atmospheric Cassini‐Huygens investigations and validate our simulation results against in situ Cassini Ion‐Neutral Mass Spectrometer (INMS) measurements of N2, CH4, H2, 40Ar, HCN, and the major stable isotopic ratios of 14N/15N in N2. We focus our investigation on aspects of Titan's upper atmosphere that determine the amount of atmospheric escape required to match the INMS measurements: the amount of turbulence, the inclusion of chemistry, and the effects of including a self‐consistent thermal balance. We systematically examine both hydrodynamic escape scenarios for methane and scenarios with significantly reduced atmospheric escape. Our results show that the optimum configuration of Titan's upper atmosphere is one with a methane homopause near 1000 km and atmospheric escape rates of 1.41–1.47 ×1011 CH4 m−2 s−1 and 1.08 ×1014 H2 m−2 s−1 (scaled relative to the surface). We also demonstrate that simulations consistent with hydrodynamic escape of methane systematically produce inferior fits to the multiple validation points presented here.