Matrix Flow Research Articles

Distribution pattern of rainwater in soil under vertical deep rotary tillage in dryland farmland

In semi-arid areas, drought is the main limiting factor for rainfed agriculture. Vertical rotary subsoiling (VRT) has been shown to effectively increase soil water storage and so allow crops to resist seasonal drought. However, there is a lack of reports on the infiltration path and distribution pattern of rainwater in soil under VRT practice. The present study used simulated rainfall and visualized the soil profile water distribution and path of VRT, subsoiling tillage (SS) and conventional tillage (CT) practices. Twenty-four hours after applying simulated rain, vertical soil profiles were photographed and staining features used to indicate the infiltration path and distribution of rainwater in the soil. Our results showed that when rainwater infiltrated into the soil, matrix and preferential flows occurred concomitantly under VRT practice, and mainly matrix flow for SS and CT practices. The VRT increased water infiltration into the soil, occurrence of preferential flow and water storage in the soil profile, while the soil of SS and CT somewhat hindered the infiltration of water. The VRT decreased soil bulk density (BD) by 9.2–10.3 % and increased soil saturated hydraulic conductivity (Ks) by 50.4–70.4 % compared with SS and CT. Moreover, VRT significantly increased potato tuber yield by 22.9–36.0 % compared with SS and CT in two consecutive years. Structural equation modeling (SEM) further revealed that VRT increased potato yield was mainly caused by decreasing BD and increasing Ks, and then increasing water storage in the soil profile. These findings suggest that decreased BD and increased Ks in VRT practice could be particularly important for infiltration, sustaining and supplying of soil water in rainfed areas worldwide, which is important for production practices in these areas.

Experimental on physical properties of shale gas under low-velocity seepage and stress sensitivity environment

Shale gas reservoirs have complex pore structures, consisting not only of nanopores within and between organic grains but also of microcracks distributed randomly within the matrix. Although free gas and adsorption gas coexist, free gas is stored in pore spaces, and adsorption gas is stored in organic matter and clay minerals. Due to the presence of organic matter and heterogeneity in shale, the gas transfer mechanism is complicated involving multiple scales. Gas flow in shale does not conform to the characteristics of linear seepage at the low-velocity stage given the occurrence and flow state of different gases under different pressures. Meanwhile, very few studies have been performed on the low-velocity seepage characteristics of different gases in shale. Therefore, it is important to present experimental evidence for the low-velocity seepage law of different gases in shale. The present study uses experimental simulations of gas mass transfer at multi-scales to investigate the low-velocity gas flow and stress sensitivity of shale core samples. The results indicate that the shale matrix has a strong adsorption capacity, and that its helium flow capacity is 1.5–2.0 times greater than that of methane without backpressure. With increasing pore pressure, the combined action of gas adsorbed to the cavity and free gas leads to first an increase and then a decrease in the flow capacity of methane. With a low confining pressure, the permeability decreases exponentially. On the other hand, as the net confining pressure increases, the core fracture closes, causing the gas slip effect to increase permeability. The results of the study may provide valuable guidance in understanding gas flow in shale matrix and in the development of gas reservoirs.

Weak Galerkin coupled with conforming finite element method for hybrid-dimensional fracture model

In this paper, we propose the weak Galerkin coupled with conforming finite element method to solve the hybrid-dimensional fracture problem, which couples n-dimensional Darcy flow in the porous matrix with (n−1)-dimensional flow in the fracture. The generalized Robin type interface conditions present in the coupling scheme. We derive the optimal error estimates for L2 and energy norms with arbitrary degree polynomials. The error rate obtained by numerical examples agrees with the analysis results on both polygonal mesh and nonmatching mesh. Results of numerical examples also show that the proposed scheme is robust to the parameters in the reduced fracture model.

Buoyant heat transfer of nanofluids in a vertical porous annulus: a comparative study of different models

PurposeThis study aims to numerically study the buoyant convective flow of two different nanofluids in a porous annular domain. A uniformly heated inner cylinder, cooled outer cylindrical boundary and adiabatic horizontal surfaces are considered because of many industrial applications of this geometry. The analysis also addresses the comparative study of different porous media models governing fluid flow and heat transport.Design/methodology/approachThe finite difference method has been used in the current simulation work to obtain the numerical solution of coupled partial differential equations. In particular, the alternating direction implicit method is used for solving transient equations, and the successive line over relaxation iterative method is used to solve time-independent equation by choosing an optimum value for relaxation parameter. Simpson’s rule is adopted to estimate average Nusselt number involving numerical integration. Various grid sensitivity checks have been performed to assess the sufficiency of grid size to obtain accurate results. In this analysis, a general porous media model has been considered, and a comparative study between three different models has been investigated.FindingsNumerical simulations are performed for different combinations of the control parameters and interesting results are obtained. It has been found that the an increase in Darcy and Rayleigh numbers enhances the thermal transport rate and strengthens the nanofluid movement in porous annulus. Also, higher flow circulation rate and thermal transport has been detected for Darcy model as compared to non-Darcy models. Thermal mixing could be enhanced by considering a non-Darcy model.Research limitations/implicationsThe present results could be effectively used in many practical applications under the limiting conditions of two-dimensionality and axi-symmetry conditions. The only drawback of the current study is it does not include the three-dimensional effects.Practical implicationsThe results could be used as a first-hand information for the design of any thermal systems. This will help the design engineer to have fewer trial-and-run cases for the new design.Originality/valueA pioneering numerical investigation on the buoyant convective flow of two different nanofluids in an annular porous domain has been carried out by using a general Darcy–Brinkman–Forchheimer model to govern fluid flow in porous matrix. The results obtained from current investigation are novel and original, with numerous practical applications of nanofluid saturated porous annular enclosure in the modern industry.

Microstructure, properties and strengthening mechanism of Cu-TiB2-Al2O3 composite prepared by liquid phase in-situ reaction casting

A dual-phase reinforced Cu-0.75 wt% Al 2 O 3 -0.75 wt% TiB 2 composite ingot was prepared by liquid phase in- situ reaction casting method and then processed by hot rolling and cold rolling. The microstructure and property evolution of the composite during processing were investigated, and the strengthening mechanism was determined. Spherical Al 2 O 3 particles with a size of 50～500 nm and irregular polygonal TiB 2 particles with a size of 50 nm～1.5 µm were formed in the Cu matrix. When the cold rolling reduction exceeded 80%, the strengthening particles flowed with the plastic flow of the Cu matrix. The violent shear action between the particles and the Cu matrix made the particle agglomerations separate, which enhanced the uniform dispersion of strengthening particles. For the reduction of 90%, the tensile strength, yield strength, hardness, elongation and electrical conductivity were 477 MPa, 452 MPa, 158 HV, 5.7% and 80.0%IACS respectively. The strengthening mechanisms were dislocation strengthening, dispersion strengthening and subgrain strengthening in descending order. Liquid phase in-situ reaction casting combined with large-deformation rolling is a promising process for the preparation of dual-phase reinforced dispersion strengthened copper matrix composite. • A Cu-0.75 wt% Al 2 O 3 -0.75 wt% TiB 2 composite ingot is prepared by liquid phase in-situ reaction casting method. • The combination of hot working and high cold working can effectively improve the particle distribution of the composite. • The strengthening mechanisms are dislocation, dispersion and grain boundary strengthening in descending order.

Optimization of hydraulic fracturing treatment parameters to maximize economic benefit in tight oil

The optimizations of hydraulic fracturing treatment parameters are widely studied. Three optimization goals are usually pursued, i.e., uniform fracture propagation, stimulated reservoir volume (SRV) or fracture area maximization, and economic benefit maximization. However, when we pursue uniform fracture propagation or SRV maximization, can we also obtain the maximum economic benefit? Since the simulation of fracturing and production are usually-two separate methods, few studies have simultaneously investigated the relationship between fracturing treatment parameters and these three optimization goals. Therefore, the novelty of this work is that these relationships are systematically revealed under four different geological conditions, i.e., homogeneous and heterogeneous properties, hydraulic fracture turning, and induced secondary fractures. In comparison with previous hydro-mechanical model, our model can not only simultaneously simulate fracturing and production, but also consider some characteristics of tight oil reservoir, including nonlinear flow in tight matrix, dynamic capillary pressure, hydraulic fracture turning, and induced secondary fractures. Furthermore, simulation results of orthogonal experimental design are applied to fit 3D surfaces showing the relationship between fracturing treatment parameters and net present value (NPV). These 3D surfaces provide optimal fracturing treatment parameters. The results indicate that, in homogeneous reservoirs, pursuing uniform fracture propagation or maximum fracture area can obtain the highest NPV. However, in heterogeneous, hydraulic fracture turning, and induced secondary fracture cases, pursuing uniform propagation or maximum SRV usually cannot obtain the highest NPV. Our models serve as very useful tools for optimizing fracturing treatment parameters in different types of tight oil reservoirs, which play an increasingly significant role in the improving economic benefit of tight oil development.

Evaluation of lost gas in the borehole drilling stage: Implication for the direct method of coalbed methane content determination

The current direct method of coalbed methane (CBM) content determination may underestimate the CBM content due to the negligence of lost gas in the borehole drilling stage of coal sampling, thus causing inaccurate evaluation of CBM reserves. In this work, considering the gas flow in coal body around the borehole before the coal sample is drilled down and exposed to air, the advanced lost gas in the borehole drilling stage of coal sampling is quantitatively calculated. First, a dual-porosity model coupling coal deformation and gas flow in the coal matrix and fractures is proposed to describe the dynamical behavior of gas flow in the borehole drilling stage. The field logging data in previous references are used to verify the dual-porosity model. Then, the variations of advanced lost gas as well as gas pressure at the sampling location with the drilling depth and drilling time are numerically simulated and discussed in detail. Furthermore, the effects of model parameters such as permeability, drilling velocity and borehole diameter on the advanced lost gas are investigated. The results show that the advanced lost gas accounts for about 10% of the original CBM content. The relationship between the advanced lost gas and the drilling time can be well fitted by the exponential function. It is revealed that over 90% of advanced lost gas is lost within the last 5% of the drilling time. The borehole diameter cannot affect the drilling depth where the gas begins to lose, but largely affects the amount of the advanced lost gas. Finally, an improved method of CBM content determination is conceptualized, which regards the CBM content as the sum of the advanced lost gas in the borehole drilling stage, the lost gas in the sampling stage, the measured gas and the residual gas. The results contribute to improving the accuracy of CBM content determination.

Processes of preferential flow in a eurasian steppe under different scenarios

The control mechanisms of temporal and small-scale spatial characteristics on different types of preferential flow (PF) processes during infiltration are still lacking. Two-year high-resolution in situ soil moisture profiles were used to investigate the controls of PF processes and its interaction with moisture and vegetation dynamics, which covers three hillslope positions (upslope–14˚, midslope–9˚, and downslope–4˚) and three vegetation treatments (bare ground, stubble grassland and natural grassland) in a typical semi-arid grassland of Eurasia. Two types of PF were identified. Non-sequential response (NSR) was taken as one indication of PF using the disordered response of soil moisture profiles to rainfall. Fast preferential flow in sequence response (PF-rate) was taken as another indicator when a measured maximum pore water rate higher than saturated hydraulic conductivity. The conditions for the occurrence of the two PFs were inconsistent and different from the studies which showed the higher probability of PFs under dryer conditions and with higher rainfall intensities. Small rainfall events with low rainfall intensity and relatively low soil moisture at most locations showed higher NSR frequency, which further highlight the strong dependence of NSR on hydrophobicity and macropore structure of the topsoil. Whereas a higher rainfall intensity increased PF-rate under wet conditions. Meanwhile, the occurrence of PF-rate was also significantly controlled by vegetation coverage, soil texture and saturated hydraulic conductivity of 5–10 cm soil layer. Furthermore, the frequency of PF was 15.9%–44.5%, and its contribution to the total infiltration was >50%. The water recession rate of NSR and PF was slower and faster than that of matrix flow, respectively. This demonstrates the importance of PF to water replenishment in scarce rain areas and the influence of combinations of spatial–temporal factors on different flow processes.

Characterization of soil drainage dynamics on karst terrains by developing a site-specific reservoir cascade scheme hydrological model with preferential flows

Models provide quantitative solutions that enable better understanding of karst soils hydrology. A location in central Spain was selected to implement a 1-D hydrological model that uses a reservoir cascade scheme (RCS) approach to simulate soil water content (SWC) at daily resolution. The model simulates SWC for six soil layers and includes additional modules to reproduce preferential flow regime. The soil profile in the model is 0.5 m deep, developed in silt loam soil on top of dolomite marbles. Three different configurations of the model were considered. Configuration 1 considers a basic RCS module, whereas other configurations include preferential flows. Thus, Configuration 2 considers RCS module together with a continuous preferential flow module, where 1 to 5% of available SWC from each layer is drained every day along preferential pathways. Configuration 3 contains a discontinuous preferential flow module in addition to previous modules. The discontinuous preferential flow is only activated during rainfall events occurring after long dry periods. Simulated SWC values are compared with measured SWC values, so model parameters are iteratively adjusted to optimize the model results. The model produces the best simulations implementing the Configuration 3, when matrix flow and two preferential flow regimes are considered. The model shows that preferential flows significantly contribute to recharge and should not be neglected in soil hydrological models and recharge estimations in karst areas.

Graded regulation technology for enhanced oil recovery and water shutoff in pore-cavity-fracture carbonate reservoirs

• Clarified the types of chemical agents for graded regulation of pore-vug-fracture carbonate reservoirs. • Plugging effect and oil–water selectivity of gel and nanospheres. • Wetting modifiers improve the efficiency of injection water to wash the oil are investigated. • Comprehensively discussed the synergistic mechanism of profile control and water shutoff and improving the efficiency of oil washing with injected water. Although a single type of chemical agent (eg, gels, microspheres, surfactants, etc.) has achieved some effects in enhanced oil recovery of carbonate reservoirs, for pore-cavity-fracture carbonate reservoirs, the use of a single type of chemical agent does not perform well. The main objective of this study is to study the effect of different types of chemical agents in enhanced oil recovery of complex carbonate reservoirs. In order to determine the screening principle of chemical agents, the types of water channeling in the North Troyes reservoir were analyzed. For complex fractures, step by step plugging, multi-agent and multi-slug comprehensive intervention is carried out to ensure the plugging of high-permeability channels and inhibit the seepage of large channels. It can plug channeling fracture channel, adjust secondary dominant channel and reduce matrix flow resistance, so as to expand macroscopic swept volume and improve microscopic water flooding efficiency. The results show that it is difficult to comprehensively control water channeling in pore-cave-fracture carbonate reservoir, and the reservoir heterogeneity in the test area can be improved by mixing different types of control and flooding agents and carrying out deep profile control. The plugging rate of gel is 97.18 %, and the oil–water selection ratio is 0.45 in fractured core; the expansion rate of nano - microspheres is more than 3 times; the wetting modifier can improve the imbibition oil displacement efficiency by 14.76%, and the test result shown that nano - microspheres and wetting modifier have good synergistic oil displacement effect. The field application result shown that daily oil production of oil well in the test area increased by 5.0 m 3 /d and the daily water rate decreased by 19.0% compared with that before the control flooding. The findings of this study can help for better understanding of enhanced oil recovery in pore-cave-fracture carbonate reservoir.

Fluidic Flow Enhances the Differentiation of Placental Trophoblast-Like 3D Tissue from hiPSCs in a Perfused Macrofluidic Device.

The human placenta serves as a multifunctional organ to maintain the proper development of a fetus. However, our knowledge of the human placenta is limited due to the lack of appropriate experimental models. In this work, we created an in vitro placental trophoblast-like model via self-organization of human induced pluripotent stem cells (hiPSCs) in a perfused 3D culture macrofluidic device. This device allowed cell seeding, in situ trophoblast lineage differentiation, and formation of trophoblast-like tissues from hiPSCs in a biomimetic microenvironment. It incorporated extracellular matrix (ECM) and fluid flow in a single device. After trophoblast lineage differentiation, we were able to generate the 3D clusters with major cell types of the human placenta, including trophoblast progenitor cytotrophoblasts (CTBs), differentiated subtypes, syncytiotrophoblasts (STBs), and extravillous trophoblasts (EVTs) under long-term 3D culture (∼23 days). Moreover, the formed tissues exhibited enhanced expressions of CTB-, STB-, and EVT-related markers at the level of genes and proteins under a dynamic culture compared with static conditions. RNA-seq analysis revealed the higher expression of trophoblast-specific genes in 3D tissues, indicating the essential role of fluid flow to promote the trophoblast differentiation of hiPSCs. The established placental 3D model combined a bioengineering strategy with developmental principles, providing a promising platform for the study of placental biology in a biomimetic microenvironment in health and disease.

Water Liberating/Sealing effects on shale gas Extraction: A fully coupled multidomain and multiphysics model

Whether the gas in kerogen is liberated/sealed by water, is a crucial issue for successful shale gas reservoir exploitation. Although this issue has been recognized, no tools are developed to evaluate the impact of this gas liberation/sealing on gas production under in-situ conditions. In this work, a concept named kerogen threshold differential pressure (KTP) is proposed to describe the mass transport influenced by the wettability at the heterogeneous kerogen interface with external/connate water. KTP is defined as a critical pore pressure difference between inside and outside of kerogen pores. It corresponds to the energy barrier needed to remove the liquid film at the kerogen surface so that the gas in kerogen can flow out. Based on this definition, whether kerogen supplies gas to its surroundings or not is controlled by an on/off mechanism which is incorporated into a fully coupled, multidomain, and multiphysics model to simulate gas extraction from stimulated shale reservoirs. Gas flow in kerogen, gas–water-two-phase flowback in inorganic matrix and fractures, shale deformation, and gas sorption are considered in the model. The proposed model is verified against a set of gas production data from the field and the simulation results published by a previous study. Furthermore, a sensitivity analysis is performed to investigate the effects of important influencing factors on gas and water production. The results suggest four main findings: (1) Shale gas production behaviour is dependent on the combination of gas-supplying capabilities of the different components in different domains of shale reservoir. (2) Water influences shale gas extraction in two aspects including two-phase flow and on/off gas supplying mechanism. The former aspect affects the gas flow in inorganic matrix and fractures, while the latter aspect controls the gas liberation from kerogen and thus, the sustainability of gas extraction. (3) The shapes of the gas/water relative permeability curves of different components of shale reservoir are influenced by formation damage and stimulation operation. They mainly affect early-period water production. (4) Gas recovery is enhanced by decreasing KTP, which can be achieved by using appropriate surfactants and/or water-free fracking fluids to alleviate/eliminate formation damage.

Extracellular Microenvironmental Control for Organoid Assembly.

Organoids, which are multicellular clusters with similar physiological functions to living organs, have gained increasing attention in bioengineering. As organoids become more advanced, methods to form complex structures continue to develop. There is evidence that the extracellular microenvironment can regulate organoid quality. The extracellular microenvironment consists of soluble bioactive molecules, extracellular matrix, and biofluid flow. However, few efforts have been made to discuss the microenvironment optimal to engineer specific organoids. Therefore, this review article examines the extent to which engineered extracellular microenvironments regulate organoid quality. First, we summarize the natural tissue and organ's unique chemical and mechanical properties, guiding researchers to design an extracellular microenvironment used for organoid engineering. Then, we summarize how the microenvironments contribute to the formation and growth of the brain, lung, intestine, liver, retinal, and kidney organoids. The approaches to forming and evaluating the resulting organoids are also discussed in detail. Impact statement Organoids, which are multicellular clusters with similar physiological function to living organs, have been gaining increasing attention in bioengineering. As organoids become more advanced, methods to form complex structures continue to develop. This review article focuses on recent efforts to engineer the extracellular microenvironment in organoid research. We summarized the natural organ's microenvironment, which informs researchers of key factors that can influence organoid formation. Then, we summarize how these microenvironmental controls significantly contribute to the formation and growth of the corresponding brain, lung, intestine, liver, retinal, and kidney organoids. The approaches to forming and evaluating the resulting organoids are discussed in detail, including extracellular matrix choice and properties, culture methods, and the evaluation of the morphology and functionality through imaging and biochemical analysis.

Characterizing the hierarchical groundwater flow systems in Karstic Xiangxi River Basin, West Hubei, Central China

Karstification degree is a key factor in controlling the characteristics of karst GFP. In this study, hydrogeology, karst development, hydrograph, artificial and natural tracers and hydrochemistry were integrated to characterize the groundwater flow patterns (GFP) in the Cambrian-Ordovician karst aquifer in Xiangxi River Basin. Groundwater samples were collected from three karst groundwater points: Wulongdong spring (WLD), Shuimoxi spring (SMX), and groundwater exposed by Borehole ZK03 (ZK03), which have different discharge variations. The hydrogeological analysis and the artificial tracer tests showed that groundwater runoff channel for WLD, SMX and ZK03 are dominated by conduits, fracture networks and micro fissures-matrix, respectively. The natural responses (discharge, electrical conductivity and temperature) of WLD to rainfall indicated that flow in this system is discharged by conduit, fracture and matrix, respectively. Stable isotopes (2H, 18O) of precipitation and groundwater suggested that the WLD and SMX recharge at the adjacent zone with mean elevations of 878 m and 676 m, respectively; while ZK03 recharge at mean elevations of 1338 m from thousands of meters away. Mean residence times calculated by artificial and natural tracers (18O, CFC) of conduit flow in WLD (7–19 h), fracture flow in WLD and SMX (243 and 600 days), and matrix flow in ZK03 (41 years) were obviously increased gradually. Hydro-chemical analysis shows that ZK03 has higher concentrations of ions that related to carbonate dissolution, indicating groundwater in ZK03 has longer time to interact with rocks. The results show that GFP in study aquifer are characterized by local fast conduit flow, local intermediate fracture networks flow and regional slow matrix flow with progressively slower groundwater refresh rate. The conceptual model was also proposed to enable a better understanding of groundwater circulation, water resources and vulnerability of the karst system in Central China.

Extrinsic Behavior Prediction of Pedestrians via Maximum Entropy Markov Model and Graph-Based Features Mining

With the change of technology and innovation of the current era, retrieving data and data processing becomes a more challenging task for researchers. In particular, several types of sensors and cameras are used to collect multimedia data from various resources and domains, which have been used in different domains and platforms to analyze things such as educational and communicational setups, emergency services, and surveillance systems. In this paper, we propose a robust method to predict human behavior from indoor and outdoor crowd environments. While taking the crowd-based data as input, some preprocessing steps for noise reduction are performed. Then, human silhouettes are extracted that eventually help in the identification of human beings. After that, crowd analysis and crowd clustering are applied for more accurate and clear predictions. This step is followed by features extraction in which the deep flow, force interaction matrix and force flow features are extracted. Moreover, we applied the graph mining technique for data optimization, while the maximum entropy Markov model is applied for classification and predictions. The evaluation of the proposed system showed 87% of mean accuracy and 13% of error rate for the avenue dataset, while 89.50% of mean accuracy rate and 10.50% of error rate for the University of Minnesota (UMN) dataset. In addition, it showed a 90.50 mean accuracy rate and 9.50% of error rate for the A Day on Campus (ADOC) dataset. Therefore, these results showed a better accuracy rate and low error rate compared to state-of-the-art methods.

Study on Soil Water Infiltration Process and Model Applicability of Check Dams

As the primary ecological construction measure on the Loess Plateau, check dams play an essential role in developing agricultural production, improving people’s production and life, and replenishing groundwater. Soil water infiltration is the most important way to replenish groundwater in the dam land. In order to investigate the water infiltration process of check dams, an empirical model suitable for the simulation of the dam land infiltration process was selected. The soil water infiltration process of the check dam was studied by a field test and a model simulation. The results showed that there were few macropores in the dam, and the water mainly moved downwards in the form of matrix flow. Moreover, the stable infiltration rate of the dam site was low, and its infiltration process could be divided into three stages: rapid infiltration, fluctuating infiltration, and stable infiltration. In addition, the infiltration rate of a non-silted dense layer was 2.4~5 times that of a silted dense layer. The Horton model had a good fitting effect on the water infiltration process of the check dam and thus was suitable for the simulation and prediction of the water infiltration process of the dam. The results can provide a theoretical basis for efficient soil water utilization and infiltration simulation of check dam land.

A Note on Riccati Matrix Difference Equations

Discrete algebraic Riccati equations and their fixed points are well understood and arise in a variety of applications, however, the time-varying equations have not yet been fully explored in the literature. In this article we provide a self-contained study of discrete time Riccati matrix difference equations. In particular, we provide a novel Riccati semigroup duality formula and a new Floquet-type representation for these equations. Due to the aperiodicity of the underlying flow of the solution matrix, conventional Floquet theory does not apply in this setting and thus further analysis is required. We illustrate the impact of these formulae with an explicit description of the solution of time-varying Riccati difference equations and its fundamental-type solution in terms of the fixed point of the equation and an invertible linear matrix map, as well as uniform upper and lower bounds on the Riccati maps. These are the first results of this type for time varying Riccati matrix difference equations.

Review of groundwater flow and contaminant transport modelling approaches for the Sherwood Sandstone aquifer, UK; insights from analogous successions worldwide

Sandstones are characterized by different hydraulic behaviours and need to be modelled in various ways to represent groundwater flow and contaminant transport. This review shows how sandstone aquifers within the UK Triassic Sherwood Sandstone Group can be represented using three modelling approaches: the Conduit Network, Discrete Fracture Network and Equivalent Porous Medium. The Sherwood Sandstone aquifer is dominated by matrix flow in the Eastern England Shelf, Worcester, Needwood and Staffordshire basins. Here, the aquifers are modelled as Equivalent Porous Media at different spatial scales. Fractures represent the principal flow pathways in the Cheshire Basin. In this basin, Discrete Fracture Network models that account for diffusivity in the matrix can be used where the domain scale is small. The Sherwood Sandstone aquifer across northwestern England shows evidence of intense groundwater alteration and high flow velocities in solutionally enlarged fractures. Turbulent flowing pipe-elements can be inserted in the modelling domain represented by Equivalent Porous Medium at specific sites. The review shows how the Sherwood Sandstone aquifer as well as other siliciclastic deposits across the world need to be represented using a range of modelling approaches, as they behave as matrix or fracture flow aquifers, or in specific cases show a karst-like behaviour. Thematic collection: This article is part of the Hydrogeology of Sandstone collection available at: https://www.lyellcollection.org/cc/hydrogeology-of-sandstone

Laboratory Observations of Preferential Flow Paths in Snow Using Upward-Looking Polarimetric Radar and Hyperspectral Imaging

The infiltration of liquid water in a seasonal snowpack is a complex process that consists of two primary mechanisms: a semi-uniform melting front, or matrix flow, and heterogeneous preferential flow paths. Distinguishing between these two mechanisms is important for monitoring snow melt progression, which is relevant for hydrology and avalanche forecasting. It has been demonstrated that a single co-polarized upward-looking radar can be used to track matrix flow, whereas preferential flow paths have yet to be detected. Here, from within a controlled laboratory environment, a continuous polarimetric upward-looking C-band radar was used to monitor melting snow samples to determine if cross-polarized radar returns are sensitive to the presence and development of preferential flow paths. The experimental dataset consisted of six samples, for which the melting process was interrupted at increasing stages of preferential flow path development. Using a new serial-section hyperspectral imaging method, polarimetric radar returns were compared against the three-dimensional liquid water content distribution and preferential flow path morphology. It was observed that the cross-polarized signal increased by 13.1 dB across these experiments. This comparison showed that the metrics used to characterize the flow path morphology are related to the increase in cross-polarized radar returns spanning the six samples, indicating that the upward-looking polarimetric radar has potential to identify preferential flow paths.

Watershed approach for studying soil preferential flow: A case study

Preferential flow (PF) is a generic term used for water flow paths through biopores, fractures and macro pores. Many studies and models were already established to describe the PF. In semi-arid regions, the connecting aboveground and below ground processes to investigate how soil redistribute rainfall and nutrient and their impact on subsurface flow, is a fairly overlooked phenomenon. In this era of fast changing climate, erratic rainfall and rain water management, soil constitution plays an important role. In semi-arid regions, watershed is the basic hydrologic unit which gives study of the soil preferential flow a holistic look. In this regard, a study was conducted in Hayath nagar micro-watershed, Hyderabad, during 2020-2021.results revealed that the micro-watershed mainly comprises of heterogeneous matrix flow and fingering at surface while at sub surface macropore flow with low and mixed interaction prevails. This suggested that subsurface soils were mainly responsible for spatial redistribution of flows and generating lateral flow than vertical flow. Thus, the watershed under study requires better management practice to harvest water and check runoff at the time of high intensity rainfall. The results and the methodology of the present study have relevance in studying the preferential flow of diverse watersheds.