Flow Pathways Research Articles

Vertical Structure and Energetic Constraints for a Backscatter Parameterization of Ocean Mesoscale Eddies

AbstractMesoscale eddies modulate the stratification, mixing, tracer transport, and dissipation pathways of oceanic flows over a wide range of spatiotemporal scales. The parameterization of buoyancy and momentum fluxes associated with mesoscale eddies thus presents an evolving challenge for ocean modelers, particularly as modern climate models approach eddy‐permitting resolutions. Here we present a parameterization targeting such resolutions through the use of a subgrid mesoscale eddy kinetic energy budget (MEKE) framework. Our study presents two novel insights: (a) both the potential and kinetic energy effects of eddies may be parameterized via a kinetic energy backscatter, with no Gent‐McWilliams along‐isopycnal transport; (b) a dominant factor in ensuring a physically‐accurate backscatter is the vertical structure of the parameterized momentum fluxes. We present simulations of 1/2° and 1/4° resolution idealized models with backscatter applied to the equivalent barotropic mode. Remarkably, the global kinetic and potential energies, isopycnal structure, and vertical energy partitioning show significantly improved agreement with a 1/32° reference solution. Our work provides guidance on how to parameterize mesoscale eddy effects in the challenging eddy‐permitting regime.

Multiphase flow simulation of fractured karst oil reservoirs applying three-dimensional network models

The characteristics of karst reservoirs are extremely varied and anisotropic, exhibiting notable differences in porosity, permeability, and corresponding fluid flow pathways. Fractured karst petroleum reservoirs, such as distinct caverns and fractures, are an example of a typical discrete media type. The traditional reservoir modeling approach and discrete fracture-like local refinement models are unsuitable for field application of fractured karst oil reservoirs due to the needs of high fidelity geological description and huge computing efforts. Based directly on the spatial characteristics of seismic surveys, a numerical simulation model in three dimensions, akin to a node-like network, is presented here for cracked karst oil reserves. First, the watershed image processing technique and the automatic connection identification procedure are used to extract the three-dimensional node-network model. After that, automatic differentiation is used to build the numerical finite volume scheme, and the proper gradient-based adjoint approach is used to conduct the related historical matching rapidly. After validation by a synthetic model in a commercial simulator, this proposed three-dimensional network numerical model is used for a field reservoir block of deep formation in the Tarim basin to demonstrate its computational efficiency and viability for enormously comparable karst oil reservoirs.

Afforestation improves soil organic carbon and total nitrogen stocks mainly through increasing > 2 mm aggregate fractions and stimulating carbon and nitrogen transformations within aggregates in subtropical karst region

Vegetation restoration can significantly increase soil organic carbon (SOC) and total nitrogen (TN) stocks, however, the response of SOC and TN stocks, as well as their distribution, transformation, and stability within aggregates, to afforestation in fragile karst ecosystems remains unclear. In this study, soil samples were collected from orchards, 10-, 20-, and 40-year Dodonaea viscosa plantations after afforestation following orchard abandonment in a karst rocky desertification area. A natural succession shrubland soil served as the control. Aggregate size distribution, SOC and TN contents, and δ13C and δ15N values in bulk soils and aggregate fractions were determined. The results showed that 0.25–2 mm aggregates were the main contributors to SOC and TN stocks, amounting to 47.7 %-55.6 % and 43.0 %-51.7 %, respectively. Compared to orchards, D. viscosa afforestation significantly increased SOC and TN stocks by 160 %-393 % and 184 %-416 %, respectively, more obviously with prolonged afforestation. This effect was mainly attributed to the increases in > 2 mm aggregate fractions and their associated SOC and TN contents. In addition, δ13C and δ15N values decreased with decreasing aggregate size in afforested and shrubland soils. The C flow pathways followed the trend from < 0.053 mm to 4–8 mm following afforestation, but this was not the case for orchard soils exhibiting pathways from 2-4 mm to < 0.053 mm progressively. These results indicated that large aggregates showed a faster turnover rate and contributed to higher SOC and TN contents following afforestation. The significant and positive relationships between SOC and TN contents and magnesium, aluminium and iron oxides suggested the stimulatory effect on SOC and TN accumulation. Noticeably, although SOC and TN stocks in bulk soils following 40-year afforestation reached the level of shrubland, the proportion of > 2 mm aggregates and the geometric mean diameter remained significantly lower than those of shrubland soils. Soil aggregate stability following D. viscosa afforestation may take longer to reach natural restoration levels.

Evaluation of Urban–Rural Total Factor Flow Efficiency Based on Multiple Symbiosis: Insights from 27 Provinces in China

The rational flow of production factors is crucial for promoting benign interactions between urban and rural areas. To unveil the intrinsic mechanisms of factor flow pathways promoting mutual symbiosis between urban and rural areas, this study, based on symbiosis theory, takes total factor flow including land, technology, capital, and labor as inputs and urban–rural symbiosis level as output. Utilizing the Super-Efficiency Slack-Based Measure (SBM) model, this study calculates the urban–rural total factor flow efficiency of 27 provinces in China from 2011 to 2021 and explores specific improvement directions of urban–rural factor flow based on projection analysis. This study revealed the following findings: (1) The overall efficiency of urban–rural total factor flow in China shows a fluctuating upward trend but has not yet reached an effective state. There are significant regional disparities, with 8 provinces such as Guangdong and Fujian reaching Pareto optimality, while the remaining 19 provinces exhibit varying degrees of inefficiency. (2) Provinces with insufficient symbiotic production are mainly concentrated in the central and western regions and the northeast region, with 14 provinces including Inner Mongolia showing the inadequate transformation of urban–rural symbiosis. However, except for Hainan, the situation is gradually improving in other regions annually. (3) There is input redundancy in total factor, where land, labor, and capital redundancy are the main reasons for the inefficiency of urban–rural total factor flow in China. However, trends show that the redundancy of land, labor, and capital elements is improving annually, while technology redundancy is worsening. (4) Through a comprehensive analysis of input redundancy, output deficiency, symbiosis coefficient, and efficiency, this study categorizes the impact of factor flow on urban–rural symbiosis level into basic matching, redundancy, and comprehensive scarcity types. The research provides scientific guidance for promoting sustainable development through the rational flow of total factors and offers valuable insights for similar countries.

Subsurface flow pathway and hydrochemistry of a geographically isolated depression wetland in the Serra Geral Diabase Formation, São Paulo State, Brazil

Connectivity among water bodies is crucial for hydrological and ecological processes and fundamental for water management. Hydrochemistry and potentiometric studies on an isolated wetland allow to assess landscape influence, flow pathways, and subsurface connection. This study focuses on an isolated wetland over diabase on a topographic depression, with no visible river connection, and aims to determine the influence of rainfall and landscape on water composition and investigate subsurface flow toward the Santa Gertrudes stream. Water levels were monitored, and samples were collected from four wells during wet and dry seasons. Physical and chemical water parameters were measured, and ion concentrations determined. Pearson’s correlations highlighted codependence between physical and chemical parameters and ions and Piper’s diagram classified water composition. Six potentiometric maps were generated using interpolated hydraulic loads from monitoring campaigns. The findings show fluctuations in water level (0.11 to 0.93 m during wet periods and 1.25 to 1.79 m during dry periods), indicating rainwater directly affects water availability. Water composition was categorized as Sodium Bicarbonate and electrical conductivity values (greater than 100 µS/cm) may indicate that upstream wells are retaining salts from the surrounding crops. Strong positive correlation between sodium, bicarbonate and carbonate, and sulfate with electrical conductivity suggests simultaneous release of ions due to rock and soil mineral alteration. Potentiometric data reinforce the hypothesis of a subsurface connection between the studied area and the Santa Gertrudes stream. Future studies could benefit from expanding the monitoring network to include more GIWs and applying additional methods, such as isotope tracers.

Using subtle variations in groundwater geochemistry to identify the proximity of individual geological structures: a case study from the Grimsel Test Site (Switzerland)

Understanding groundwater flow and the evolution of groundwater chemistry in networks of fractures in crystalline rock is of fundamental interest for geothermal projects, nuclear waste disposal, and groundwater resources. Groundwater chemistry at a given location is typically conceived of being of a specific ‘type’ (e.g. meteoric, juvenile, connate, marine), with associated chemical types controlled through water–rock interactions. Minor chemical variations between groundwater sample locations with the same chemical type are generally considered as ‘noise’ in the geochemical data. Here, we argue that this noise contains useful information on the mineral phases encountered by the groundwater as it travels through specific flow pathways. We analyse the spatial variability of groundwater chemistry around the Grimsel Test Site (GTS), Switzerland, where groundwater is hosted in two lithologies: the Central Aar Granite and the Grimsel Granodiorite, where flow occurs predominantly in a fracture network created by brittle reactivation of ductile shear zones. Groundwater chemistry is analysed using principal component and hierarchical cluster analyses, which identify two groundwater types based on their chemistry. The primary control on groundwater type is the host rock lithology (granite/granodiorite). While the spatial variability of groundwater chemistry within each of the two lithologies is small, statistical analysis of the data shows similar groundwater chemistry in borehole intervals that are crosscut by similar geological structures, implying a structural control on groundwater chemistry. Our research shows that subtle chemical variations in groundwater provide information on fracture network connectivity and the proximity of geological features, that specific volumes of groundwater has interacted with.

Multi-objective optimisation framework for Blue-Green Infrastructure placement using detailed flood model

Designing city-scale Blue-Green Infrastructure (BGI) for flood risk management requires detailed and robust methods. This is due to the complex interaction of flow pathways and the need to assess cost-benefit trade-offs for various BGI options. This study aims to find a cost-effective BGI placement scheme by developing an improved approach called the Cost OptimisatioN Framework for Implementing blue-Green infrastructURE (CONFIGURE). The optimisation framework integrates a detailed hydrodynamic flood simulation model with a multi-objective optimisation algorithm (Non-dominated Sorting Genetic Algorithm II). The use of a high-resolution flood simulation model ensures the explicit representation of BGI and other land use features to simulate flow pathways and surface flood risk accurately, while the optimisation algorithm guarantees achieving the best cost-benefit trade-offs for given BGI options. The current study uses the advanced CityCAT hydrodynamic flood model to evaluate the efficiency of the optimisation framework and the impact of location and size of permeable interventions on the optimisation process and subsequent cost-benefit trade-offs. This is achieved by dividing permeable surface areas into intervention zones of varying size and quantity. Furthermore, rainstorm events with 100-year and 30-year return periods are analysed to identify any common optimal solutions for different rainfall intensities. Depending on the number of intervention locations, the automated framework reliably achieves optimal BGI implementation solutions in a fraction of the time required to find the best solutions by trialling all possible options. Designing and optimising interventions with smaller sizes but many permeable zones save a good fraction of investment. However, such a design scheme requires more computational time to find optimal options. Furthermore, the optimal spatial configuration of BGI varies with different rainstorm severities, suggesting a need for careful selection of the rainstorm return period. Based on the results, CONFIGURE shows promise in devising sustainable urban flood risk management designs.

Forest restoration effects on soil preferential flow in the paleo-periglacial eastern liaoning mountainous regions, China

To provide a practical reference index for the protection of water conservation forests and the establishment of vegetation in different forest restoration areas, we seek to clarify the preferential flow development and its influencing factors under different rainfall events in the forest restoration areas of paleo-periglacial landform in eastern Liaoning Province of China. To quantify the preferential flow development (PFI) in soil profile-scale through soil profile indexes, we carried out dual-tracer experiments with dyeing in two types of forest restoration lands (plantation forest, PF, and natural secondary forest, NSF) in the paleo-periglacial landform forestland to obtain the soil water infiltration trajectories and water-solute transport characteristics. The indexes of preferential flow morphology and pathway diversity (solute migration) were integrated to construct a more complete evaluation system of the PFI. In addition, we explored factors affecting the PFI through soil physical properties and root characteristics. The results showed that: (1) There were obvious preferential flows in both PF and NSF. Compared with NSF, preferential flow in PF diverged earlier, had greater non-equilibrium degree, more paths and higher development degree, and preferential flow was the main infiltration form. (2) Changes in infiltration amount played a key role in altering the PFI, i.e., increasing infiltration amount reduced the PFI, especially in PF (p < 0.05); (3) After water infiltration, the solute Br− diffusion range of the soil profile was wider than that of Brilliant Blue tracer, thus the development of preferential flow was better synthetical reflected by the indexes of water flow morphology and solute distribution characteristics; (4) Differences in the PFI can be explained by variations in clay content, total porosity (TP), and root volume density (RVD), with total path coefficients of 0.824, 0.462, and 0.624, respectively. In addition to establishing different forest restoration types in similar areas, it would be worthwhile to strengthen the prevention and control measures of soil and water loss in NSF, and properly manage PF in a near-natural model to enhance ecologically sustainable development of forest land. The results of this study contribute to the understanding of the hydrological processes of forest ecosystems in paleo-periglacial landforms, and provide theoretical support for the proposed forest management strategies.

Indications of preferential groundwater seepage feeding northern peatland pools

Groundwater seepage from underlying permeable glacial sedimentary structures, such as eskers, has been hypothesized to directly feed pools in northern peat bogs. These hypotheses directly contradict classical peat bog models for ombrogenous systems, wherein meteoric water is the sole water input to these systems. Variations in the underlying mineral sediment in contact with the peat imply that unrecognized hydrogeologic connectivity may exist with pools in northern peat bogs, particularly where high permeability materials are in contact with the peat. Seepage dynamics originating from these structural variations were investigated using a suite of thermal and hydrogeophysical methods deployed around pools in a peat bog of northeastern Maine, USA. Thermal characterization methods mapped anomalies that were confirmed as matrix seepage or preferential flow pathways (PFPs). Geochemical methods were employed at identified thermal anomalies to confirm upwelling of solute-rich groundwater. Conduits around pools were associated with surficial terminations of suspected peat pipes, based on the inference of pathways extending down into the peat, that focus flow through PFPs in the peat matrix. Discharge also occurred through the peat matrix adjacent to suspected pipe structures and matrix seepage rates were quantified using analysis of diurnal temperature signals recorded at multiple depths. Seepage rates, with a maximum of nearly 0.4 m/d, were measured at localized points around pools. Periods of synchronized temperatures paired with highly muted diurnal temperature signals, recorded in diurnal temperature with depth data, were interpreted qualitatively as activation of strong upward discharge rates through suspected peat pipes. These time periods correlated strongly with local precipitation events around the peatland. Ground-penetrating radar surveys revealed discontinuities in the low permeability glacio-marine clay at the mineral sediment-peat interface, interpreted to be regional glacial esker deposits, which were located beneath and around pools. Heat tracing, specific conductance contrasts, seepage rates, and trace metal concentrations all imply groundwater seepage originating from underlying permeable glacial esker deposits and directly sourcing pools. Preferential groundwater inputs into northern peat bogs may play a key role in developing and maintaining pool systems, with enhanced solute transport impacting peatland ecology, water resources, and carbon cycling.

Geothermo‐mechanical alterations due to heat energy extraction in enhanced geothermal systems: Overview and prospective directions

AbstractGeothermal energy from deep underground (or geological) formations, with or without its combination with carbon capture and storage (CCS), can be a key technology to mitigate anthropogenic greenhouse gas emissions and meet the 2050 net‐zero carbon emission target. Geothermal resources in low‐permeability and medium‐ and high‐temperature reservoirs in sedimentary sequence require hydraulic stimulation for enhanced geothermal systems (EGS). However, fluid migration for geothermal energy in EGS or with potential CO2 storage in a CO2‐EGS are both dependent on the in situ flow pathway network created by induced fluid injection. These thermo‐mechanical interactions can be complex and induce varying alterations in the mechanical response when the working fluid is water (in EGS) or supercritical CO2 (in CO2‐EGS), which could impact the geothermal energy recovery from geological formations. Therefore, there is a need for a deeper understanding of the heat extraction process in EGS and CO2‐EGS. This study presents a systematic review of the effects of changes in mechanical properties and behavior of deep underground rocks on the induced flow pathway and heat recovery in EGS reservoirs with or without CO2 storage in CO2‐EGS. Further, we proposed waterless‐stimulated EGS as an alternative approach to improve heat energy extraction in EGS. Lastly, based on the results of our literature review and proposed ideas, we recommend promising areas of investigation that may provide more insights into understanding geothermo‐mechanics to further stimulate new research studies and accelerate the development of geothermal energy as a viable clean energy technology.

Holistic evaluation of inlet protection devices for sediment control on construction sites

To address the deleterious impacts of excess soil erosion from the construction sites, the United States Clean Water Act requires that erosion and sediment control measures (ESCs) be implemented on construction projects disturbing more than 0.4 ha. Inlet protection devices (IPDs) are a common ESC utilized on construction projects to reduce the amount of sediment entering storm sewers. In Ohio, regulatory agencies use approved, non-proprietary IPDs made from commonly available materials (e.g., silt fence, geotextile, lumber, and aggregate) to mitigate sediment on construction projects; however, these IPDs often rely on extended ponding to remove sediment and require frequent maintenance making these unsuitable for road construction projects. Commercially manufactured (i.e., proprietary) IPDs which rely on filtration to quickly dewater following rainfall may prove more practical for road construction projects. However, little research which quantitatively compares the holistic performance of these two types of IPDs in field settings has been performed to date. To address this knowledge gap, the performance of 24 proprietary IPDs was evaluated at field-scale using simulated construction site runoff and compared to three non-proprietary IPDs currently approved for use in Ohio. Bypass flows, which typically occurred due to poor IPD fit to standard drainage inlets used in Ohio transportation settings, significantly increased effluent total suspended solids (TSS) and turbidity compared to tests of IPDs where bypass did not occur. Overflow, or intentional bypass around primary IPD flow pathways during high flows, did not significantly impact effluent water quality. Despite differences in treatment mechanisms (i.e., sedimentation versus filtration), the water quality performance of non-proprietary and proprietary IPDs were not statistically different, indicating comparable sediment removal was provided by both categories. Findings from this research can provide design engineers and state regulatory agencies the necessary tools to evaluate IPD performance in road construction settings and, ultimately, alleviate the impact of excess sediment discharged from construction sites.

Causal Drivers of Land‐Atmosphere Carbon Fluxes From Machine Learning Models and Data

AbstractInteractions among atmospheric, root‐soil, and vegetation processes drive carbon dioxide fluxes (Fc) from land to atmosphere. Eddy covariance measurements are commonly used to measure Fc at sub‐daily timescales and validate process‐based and data‐driven models. However, these validations do not reveal process interactions, thresholds, and key differences in how models replicate them. We use information theory‐based measures to explore multivariate information flow pathways from forcing data to observed and modeled hourly Fc, using flux tower data sets in the Midwestern U.S. in intensively managed corn‐soybean landscapes. We compare multiple linear regressions, long‐short term memory, and random forests (RF), and evaluate how different model structures use information from combinations of sources to predict Fc. We extend a framework for model predictive and functional performance, which examines a suite of dependencies from all forcing variables to the observed or modeled target. Of the three model types, RF exhibited the highest functional and predictive performance, correctly capturing strong dependencies between radiation and temperature variables with Fc. Regionally trained models demonstrate lower predictive but higher functional performance compared to site‐specific models, suggesting superior reproduction of observed relationships at the expense of predictive accuracy. This study shows that some metrics of predictive performance encapsulate functional behaviors better than others, highlighting the need for multiple metrics of both types. This study improves our understanding of carbon fluxes in an intensively managed landscape, and more generally provides insight into how model structures and forcing variables translate to interactions that are well versus poorly captured in models.

Fracture evaluation of the plutonic basement in the Upper Magdalena Basin: Implications for the development of naturally fractured reservoirs in the Northern Andes

Plutonic rocks typically have negligible matrix porosity and permeability. However, fractures and mineral alterations create storage space and flow pathways that turn plutonic rocks into fluid reservoirs. Despite significant hydrocarbon discoveries, naturally fractured reservoirs in plutonic rocks have been poorly studied. In most Colombian basins, the crystalline basement has undergone multiple deformational events and is thrust over the Cretaceous to Cenozoic source and reservoir rocks of the conventional petroleum system. This structural configuration is ideal for the migration of oil into a fractured basement. A multiscale fracture analysis, including field, petrographical and petrophysical techniques was conducted on the Permian and Jurassic plutonic basement of Upper Magdalena Basin in order to understand the controls on brittle deformation, the development of fracture networks and their potential to form hydrocarbon reservoirs. The results indicate that protolith textures and structures, including magmatic and mylonitic foliation, favours fracturing. Dykes exhibit higher fracture density (7–48 fractures/m), porosity (mean = 0.4%) and permeability (mean = 125,818.75 mD) than the host rock (2–25 fractures/m; 0.23%; 12,066.09 mD). Intersection zones from regional faults, are characterized by the highest fracture and lineament intensity. Our results suggest that dyke swarms and interacting damage zones can significantly enhance the reservoir quality of plutonic rocks by providing storage in fractures and fluid pathways to the host rock.

Flow Pathways in Fractured Basalt under Challenging Environmental Conditions: A Synergistic Approach of Electrical Resistivity Tomography and Seismic Refraction Imaging

Flow Pathways in Fractured Basalt under Challenging Environmental Conditions: A Synergistic Approach of Electrical Resistivity Tomography and Seismic Refraction Imaging

Application of quantum dot light-emitting diode harvest by quantum dot solar cells

Recent progress in photovoltaic (PV) cell usage has been hindered due to a shortage of suitable materials that emit adequate wavelengths of light energy and convert it to electricity. Quantum dot light-emitting diodes (QLEDs) and quantum dot solar cells (QDSCs) have been identified as promising artificial light sources and PV cell types to nicely fit into this solution, not only complying with that but also being controllable, flexible, portable, and lightweight. The purpose of this study is to provide a review of the application of how QLEDs can be collected for QDSCs. First, we introduce QLEDs as artificial light sources, briefly outline their mechanics and benefits, and compare them to other light sources for QDSC harvesting. Then, we summarize the mechanisms that occur when a QDSC absorbs a photon from a QLED, as well as how these energy flow pathways influence artificial light energy harvest. Finally, we explore the optoelectronic properties of lead sulphide (PbS) and lead selenide (PbSe) as appropriate quantum dots (QDs) materials for current applications in QDSC and QLED technologies. We anticipate that the literature will be comprehensive and relevant to the scientific community interested in creating artificial light energy harvesting and thus researching the most recent alternative method of getting healthy energy.

Effects of the freeze–thaw process on sources and pathways of subsurface flow in an alpine hillslope on the northeastern Qinghai-Tibet Plateau

The impact of the freeze–thaw process on the active layer is reflected in the changed subsurface flow (SSF) process in cold alpine regions. Identifying sources and pathways of SSF in the freeze–thaw process is critical but difficult, and the related dominant factors and mechanisms are still unknown. In this paper, the effective identification and analysis of SSF are promoted based on field sampling data from the thawing (June) to freezing (September) period of 2022 in the Qinghai Lake basin on the northeastern Qinghai-Tibetan Plateau. By the proposed method with a high sampling frequency and refined sampling spatial scale, the sources and pathways of SSF are clearly identified. The results are as follows: (1) The soil temperature is considered the most fundamental factor affecting the SSF pathways, it influences water infiltration to the deep layer and the effect is extended to the saprolite and weathered bedrock layers. (2) Thawing promotes water to infiltrating into deep layer. 30 cm soil water contributes the most to SSF (2 %–86 %) in the thawing period, while the contribution difference of the water from the 30 cm, 60 cm, and 90 cm layers is small (ranging from 32 %–33 %, 24 %–26 %, and 32 %–35 %, respectively) in the thawed period. (3) Meanwhile, the soil water from different slope positions contribute differently to SSF, and the SSF from deep soil layer is transit in prolong paths and depths. It is caused by the out-of-sync water transit process in the hillslope. With continuing climate warming, we propose that the differences in the water sources of SSF across soil layers may decrease, while the differences in the transit processes of SSF across soil layers may increase.

Upscaling the reaction rates in porous media from pore- to Darcy-scale

Modeling and prediction of reactive transport in porous media are challenging due to the complexity of the characterization of reactions across spatial and time scales. The application of reaction rates obtained from batch experiments to porous media is not valid because it disregards the influences of flow pathways, distribution of residence time, transport limitations within the porous media, as well as neglecting the impact of surface mineralogy heterogeneity. In this study, we presented how the pore-scale modeling can help to improve the Darcy-scale simulations. First, the reactive transport was simulated in a pore-network model and was validated against the experiments. Then, the pore-network results were averaged to obtain the effective reaction rates as a function of pore velocity, the inlet concentration, and the resident concentration. The upscaled function was incorporated into the Darcy-scale model and showed a significant improvement in predicting the concentration profiles. Notably, the use of batch reaction rates in the Darcy model (ADRE-batch) led to significant underestimation, up to 93%, of the required pore volume injection for complete contaminant removal from the simulation domain.

Flow and contaminant transport dynamics in clay-amended barriers through flushing experiments and multi-porosity-based modeling

Clay-amended barriers are widely used to prevent hazardous leachate percolation from landfill to subsurface. The performance of these barriers is mostly evaluated through numerical simulations with limited experimental investigation through leachate flushing experiments. To bridge this gap, contaminant loading and its flushing experiments were carried out to assess the performance of clay-amended composite materials as landfill liners. River sand (Sa), loamy soil (Ns), and alternative waste materials like fly ash (Fa) and flushed silt (Si) were used to prepare the composites. Composites fulfilling the hydraulic conductivity (<10−7 cm/s) and compressive strength (200 kPa) criteria were selected for contaminant loading and its flushing experiments to understand the fate of fluoride ions. The experimentally determined hydraulic conductivity (Ks) values for all the composites were in the order of 10−8 cm/s. The experimental breakthrough curves exhibited skewed shape, long tailing, and dual peaks. Dual porosity and dual permeability with immobile water models were employed to simulate these curves, revealing that preferential flow pathways and random chemical sorption sites significantly affect solute transport in clay-amended barriers. Further, scanning electron microscopy and energy-dispersive X-ray spectroscopy were employed to trace the preferred path of fluoride ions through the barrier. The removal efficiency and temporal moments were used to determine the percentage mass retained, mean arrival time, and spreading within the barrier. The highest solute mass was retained by sand-clay barrier (SaB30) (91%), followed by loam-clay barrier (NsB30) (59%), fly ash-clay barrier (FaB30) (38%), and silt-clay barrier (SiB30) (4%) with the least mass. The lowest mean arrival time was calculated for NsB30 (269 h) and the highest for SaB30 (990 h), with FaB30 (384 h) and SiB30 (512 h) having values in between. This study concludes that validating the design hypothesis of clay-amended barriers through contaminant loading and its flushing studies leads to an effective and sustainable design.

Uncertainty and sensitivity analysis of a travel‐time distribution‐based stream water electrical conductivity model

AbstractIn this paper, we analyse the uncertainty and parameter sensitivity of a conceptual water quality model, based on a travel time distribution (TTD) approach, simulating electrical conductivity (EC) in the Duck River, Northwest Tasmania, Australia for a 2‐year period. Dynamic TTDs of stream water were estimated using the StorAge Selection (SAS) approach, which was coupled with two alternate methods to model stream water EC: (1) a solute‐balance approach and (2) a water age‐based approach. Uncertainty analysis using the Differential Evaluation Adoptive Metropolis (DREAM) algorithm showed that: 1. parameter uncertainty was a small contribution to the overall uncertainty; 2. most uncertainty was related to input data uncertainty and model structure; 3. slightly lower total error was obtained in the water age‐based model than the solute‐balance model; 4. using time‐variant SAS functions reduced the model uncertainty markedly, which likely reflects the effect of dynamic hydrological conditions over the year affecting the relative importance of different flow pathways over time. Model parameter sensitivity analysis using the Variogram Analysis of Response Surfaces (VARS‐TOOL) framework found that parameters directly related to the EC concentration were most sensitive. In the solute‐balance model, the rainfall concentration Crain and in the age‐based model, the parameter controlling the rate of change of EC with age (λ) were the most sensitive parameter. Model parameters controlling the age mixes of both evapotranspiration and streamflow water fluxes (i.e., the SAS function parameters) were influential for the solute‐balance model. Little change in parameter sensitivity over time was found for the age‐based concentration relationship; however, the parameter sensitivity was quite dynamic over time for the solute‐balance approach. The overarching outcomes provide water quality modellers, engineers and managers greater insight into catchment functioning and its dependence on hydrological conditions.

Modeling the Seepage-induced Damage in Water-Rich Fault Zones at Tunnel Faces by Double Point Material Point Methods

During tunnel construction, crossing water-rich fault fracture zones leads to water influx hazards at the tunnel face. Excavation exposes the fault, causing disturbances and changes in the hydraulic gradient. Thus, the tunnel face becomes a low hydraulic head surface. The naturally high permeability of the fracture zone provides a pathway for groundwater flow, resulting in water seepage along the fracture zone and subsequent water influx at the tunnel face. To investigate this interaction, a two-phase double-point material point method was employed aimed at developing a coupled fluid-solid numerical model for excavating submarine fault tunnels. The model incorporates solid-liquid phase interaction, including rock mass permeability, water viscosity, and tunnel geometry. It analyzes the changes in the liquid-phase flow velocity, pore water pressure, and particle trajectories in the fractured zone ahead of the working face after the fracture zone is exposed, revealing the dynamic evolution of water influx following excavation. Additionally, this study discusses the impact of the solid-liquid phase permeability coefficients on the range of water influx hazards. The research findings demonstrate that the two-phase double-point material point method effectively captures the seepage and water influx processes, offering valuable insights into the mechanisms of sudden water influx in tunnel engineering.