Lateral Flows Research Articles

Earth’s longest preserved linear volcanic ridge generated by a moving Kerguelen hotspot

Recent seismic tomography unveiled complex mantle plume structures diverging from the originally proposed single, narrow, and vertically-oriented plume conduits, which necessitates new perspectives on the mechanism of hotspot motion. While several recent endeavours have focused on Pacific hotspots’ motion, knowledge of others remains limited. Here we constrain the motions of the Kerguelen hotspot within the Indian Ocean by obtaining robust 40Ar/39Ar ages for the Ninetyeast Ridge, Earth’s longest linear volcanic ridge. These data indicate varying volcanic progression rates along the ridge, contrasting to a constant rate as previously documented. Combined with constraints on the Indian Plate motion and seafloor spreading, we reveal four periods of motions of the hotspot caused by its interactions with the Indian–Antarctic spreading ridge. This suggests that mantle plume lateral flows are susceptible to changes in shallow mantle convection due to the existence of horizontal ponding zones and vertical conduits, especially in the shallow asthenosphere.

Variable speed limit control strategy considering traffic flow lane assignment in mixed-vehicle driving environment

To accurately predict traffic flow and optimize the operations of freeway bottleneck areas in a mixed-vehicle driving environment, this paper proposes a traffic prediction model and a variable speed limit (VSL) cooperative control strategy. Firstly, a lane-level short-term traffic prediction model, physics informed Transformer and cell transmission model (PIT-CTM), is constructed by combining the Transformer neural network and lane-level cell transmission model (CTM) based on the physics-informed deep learning framework. On this basis, the accuracy and transferability of PIT-CTM are analysed. Secondly, a lane assignment decision model is presented, which enables the dynamic planning of the optimal traffic distribution across lanes. Furthermore, a lane-level VSL control model is constructed based on the model predictive control (MPC) framework. The model induces vehicles to change lanes earlier by setting the speed limit difference between lanes. By regulating the input flow in the bottleneck area of the freeway, it reduces conflicts between mainline vehicles and ramp vehicles. Finally, the feedback regulation between the lane assignment decision model and the lane-level VSL control model promotes the cooperative optimisation of the lateral and longitudinal flows and adapts the control strategy to the dynamic traffic characteristics. A three-lane freeway merging zone is selected, the numerical experiment is conducted and compared with differential lane-level VSL. The results show that the strategy can effectively optimise the mixed-vehicle traffic state and maintain better control performance under any connected and autonomous vehicle (CAV) penetration rates.

Enhanced Acoustic Mixing in Silicon-Based Chips with Sharp-Edged Micro-Structures

The small dimensions of microfluidic channels allow for fast diffusive or passive mixing, which is beneficial for time-sensitive applications such as chemical reactions, biological assays, and the transport of to-be-detected species to sensors. In microfluidics, the need for fast mixing within milliseconds arises primarily because these devices are often used in fields where rapid and efficient mixing significantly impacts the performance and outcome of the processes. Active mixing with acoustics in microfluidic devices involves using acoustic waves to enhance the mixing of fluids within microchannels. Using sharp corners and wall patterns in acoustofluidic devices significantly enhances the mixing by acoustic streaming around these features. The streaming patterns around the sharp edges are particularly effective for the mixing because they can produce strong lateral flows that rapidly homogenize liquids. This work presents extensive characterizations of the effect of sharp-edged structures on acoustic mixing in bulk acoustic wave (BAW) mode in a silicon microdevice. The effect of side wall patterns in different angles and shapes, their positions, the type of piezoelectric transducer, and its amplitude and frequency have been studied. Following the patterning of the channel walls, a mixing time of 25 times faster was reached, compared to channels with smooth side walls exhibiting conventional BAW behavior. The average locally determined acoustic streaming velocity inside the channel becomes 14 times faster if sharp corners of 10° are added to the wall.

A numerical study of the effects of lateral flow and retention in open tubular vortex chromatography

Axial dispersion in chromatographic columns is responsible for a reduced separation efficiency. In the present research macrotransport theory is used to predict the phenomenological constants related to axial dispersion. We evaluate the efficacy of lateral flow induced by alternating current (AC) in the presence of retaining walls on the separation resolution. Results show that lateral flows induced by laterally applied potentials as low as 0.3 V reduce C-term dispersion by a factor of 5.0 for unretained conditions (k = 0) and 2.7 for retained (k = 5) conditions, with a diffusion coefficient (Dm) of 10–11m2/s. The present paper further contributes to the understanding of the use of secondary lateral flows for dispersion reduction and offers practical guidance for designing future vortex chromatographic columns. It appears that a maximal performance gain is attained at low aspect ratios (AR=1), with the gain reduced from a factor of 5 to 1.6 for AR=4 for unretained conditions, and from 2.7 to 1.4 for retained conditions (k = 5)

The water cycle of small catchments impacted with tailings mudflows: A study in the Ferro-Carvão watershed after the breakup of B1 dam in Brumadinho

The B1 tailings dam of Córrego do Feijão iron-ore mine owned by Vale, S.A. company collapsed in 25 January 2019 releasing to the Ferro-Carvão stream watershed (32.6 km2) as much as 11.7 Mm3 of mine waste. A major share (8.9 Mm3) has been deposited along the stream channel and margins forming a 2.7 km2 patch. The main purpose of this study was to question whether the tailings deposit impacted the local water cycle and how. Using the Soil and Water Assessment Tool (SWAT) hydrologic model, the water balance components of 36 hydrologic response units (HRU) were calculated for pre- (S1) and post- (S2) B1 dam rupture scenarios represented by appropriate soil, land use and tailings cover. The results revealed an increase of evapotranspiration from S1 to S2, related to the sudden removal of vegetation from the stream valley and replacement with a blanket of mud, which raised the exposure of Earth's surface to sunlight and hence soil evaporation. For 11 HRU (10.3 km2) located around the tailings deposit, a decrease in lateral flow was observed, accompanied by an increase in percolation and a slight increase in groundwater flow. In this case, the water balance changes observed between S1 and S2 reflected a barrier effect imposed to the lateral flows by the tailings, which shifted the flows towards the vertical direction (percolation). Thus, the water followed an easier vertical route until reaching the shallow aquifer and being converted into groundwater flow. As per the modelling outcomes, the hydrologic impacts of B1 dam rupture are relevant because they affected 1/3 of Ferro-Carvão stream watershed, and hence claim for the complete removal of the tailings.

Chaotic mixing induced by chevron pattern surfaces: Application to reverse osmosis filtration

This study numerically investigates the chaotic mixing induced by chevron patterns and examines its influence on enhanced reverse osmosis (RO) filtration. The primary design variables include the dimensionless groove depth (dp*) and the dimensionless overlapped span (S*) of the patterns. The Reynolds number (Re) varies from 100 to 1000, within laminar flow conditions. We analyze the mixing characteristics using Poincaré sections and quantify mixing progress through the intensity of segregation (Id). For each Re value, a specific combination of dp* and S* induces chaotic mixing. Filtration performance is evaluated based on the permeate flux, total flow rate through the membrane, and Sherwood number. Our study reveals that both chaotic advection and intensified lateral flows near the patterns are essential for enhanced RO filtration. Patterns that induce globally chaotic mixing do not always correlate with optimal filtration performance, highlighting that the degree of chaotic mixing is not directly related to concentration polarization (CP) mitigation or filtration enhancement. Rather, it is the intense lateral flow near the patterns that acts as the decisive factor in achieving superior filtration performance, particularly at higher S* values (S*≥0.75) and with deeper grooves (dp*≥0.2). In terms of energy efficiency, patterned membranes demonstrate superior performance compared to their flat counterparts.

The impact of thixotropic behavior on microfluidic mixing in a staggered-herringbone mixer

This study numerically explores the influence of thixotropy on flow and mixing in a staggered-herringbone micromixer (SHM), employing a structure-kinetics model to simulate the microstructure formation and breakup in thixotropic fluids. This study represents the first of its kind to incorporate a thixotropic fluid model into microfluidic mixing in channels with patterned grooves. Specifically, we examine the effects of the destruction factor (kd) and the thixotropy number (Th) on microstructure, flow, and mixing in the SHM, covering extensive ranges (0.01≤kd≤10 and 0.01≤Th≤100). Higher values of kd and Th, particularly for kd>1 and Th>1, lead to larger spatial variations of the structure parameter (λ) and viscosity (η), with a notable decrease in λ near the groove tops, leading to the lowest viscosity in these areas. Conversely, at the groove bottoms, where shear deformation is minimal, there is less reduction in λ, leading to increased viscosity and higher flow resistance. The viscosity variations inside the grooves impede lateral flows, adversely affecting mixing in the higher kd and Th regimes. Therefore, an in-depth understanding of the complex thixotropic behaviors, as influenced by kd and Th near the grooves, is essential for achieving effective mixing in the SHM when using thixotropic fluids. Our results suggest that lowering the channel height, for a given groove depth, slightly improves the mixing of thixotropic fluids. Further enhanced mixing is achieved by combining a reduced channel height with double-sided groove patterns.

Enhancing Image Alignment in Time-Lapse-Ground-Penetrating Radar through Dynamic Time Warping

Ground-penetrating radar (GPR) is a rapid and non-destructive geophysical technique widely employed to detect and quantify subsurface structures and characteristics. Its capability for time lapse (TL) detection provides essential insights into subsurface hydrological dynamics, including lateral flow and soil water distribution. However, during TL-GPR surveys, field conditions often create discrepancies in surface geometry, which introduces mismatches across sequential TL-GPR images. These discrepancies may generate spurious signal variations that impede the accurate interpretation of TL-GPR data when assessing subsurface hydrological processes. In responding to this issue, this study introduces a TL-GPR image alignment method by employing the dynamic time warping (DTW) algorithm. The purpose of the proposed method, namely TLIAM–DTW, is to correct for geometric mismatch in TL-GPR images collected from the identical survey line in the field. We validated the efficacy of the TLIAM–DTW method using both synthetic data from gprMax V3.0 simulations and actual field data collected from a hilly, forested area post-infiltration experiment. Analyses of the aligned TL-GPR images revealed that the TLIAM–DTW method effectively eliminates the influence of geometric mismatch while preserving the integrity of signal variations due to actual subsurface hydrological processes. Quantitative assessments of the proposed methods, measured by mean absolute error (MAE) and root mean square error (RMSE), showed significant improvements. After performing the TLIAM–DTW method, the MAE and RMSE between processed TL-GPR images and background images were reduced by 96% and 78%, respectively, in simple simulation scenarios; in more complex simulations, MAE declined by 27–31% and RMSE by 17–43%. Field data yielded reductions in MAE and RMSE of >82% and 69%, respectively. With these substantial improvements, the processed TL-GPR images successfully depict the spatial and temporal transitions associated with subsurface lateral flows, thereby enhancing the accuracy of monitoring subsurface hydrological processes under field conditions.

A new 2D ESPH bedload sediment transport model for rapidly varied flows over mobile beds

A 2D Eulerian meshless bedload sediment transport model is developed using smoothed particle hydrodynamics (SPH) to simulate rapidly varied flows over mobile beds. In the developed model, we adopt a weakly coupled numerical approach to explicitly solve the governing equations, including 2D shallow water equations for fluid flow motion and the Exner equation for bed sediment movement at the same time step. A defined virtual bedload velocity in a weakly coupled approach is involved in the calculation of time step sizes. However, nonphysical virtual bedload velocities, which often occur in cases with nearly flat beds, require extremely small time step sizes. A formulation of the lower and upper bounds of information propagation speeds for an HLLC approximate Riemann solver is thus proposed to remedy the problem. Four case studies involving dam break flows in prismatic and erodible channels, knickpoint migration, dam erosion due to overtopping flow and dam-break flow in an erodible channel with an abrupt expansion are adopted to validate the developed model. In addition, to compare the performances of different particle interaction configurations under Cartesian uniform particle arrangements, four and eight interacting particles are obtained by changing the smoothing length. Against the measured results, the case of eight interacting particles shows more accurate predictions of erosion peaks along the measured cross-sections because the lateral flows are significant. The good agreement between the simulated and measured results shows that the developed 2D Eulerian SPH bedload sediment transport model with eight interacting particles is well suited for simulating complicated flow-induced bed erosion.

Generation and Evolution of Internal Solitary Waves in a Coastal Plain Estuary

Abstract Large-amplitude internal solitary waves were recently observed in a coastal plain estuary and were hypothesized to evolve from an internal lee wave generated at the channel–shoal interface. To test this mechanism, a 3D nonhydrostatic model with nested domains and adaptive grids was used to investigate the generation of the internal solitary waves and their subsequent nonlinear evolution. A complex sequence of wave propagation and transformation was documented and interpreted using the nonlinear wave theory based on the Korteweg–de Vries equation. During the ebb tide a mode-2 internal lee wave is generated by the interaction between lateral flows and channel–shoal topography. This mode-2 lee wave subsequently propagates onto the shallow shoal and transforms into a mode-1 wave of elevation as strong mixing on the flood tide erases stratification in the bottom boundary layer and the lower branch of the mode-2 wave. The mode-1 wave of elevation evolves into an internal solitary wave due to nonlinear steepening and spatial changes in the wave phase speed. As the solitary wave of elevation continues to propagate over the shoaling bottom, the leading edge moves ahead as a rarefaction wave while the trailing edge steepens and disintegrates into a train of rank-ordered internal solitary waves, due to the combined effects of shoaling and dispersion. Strong turbulence in the bottom boundary layer dissipates wave energy and causes the eventual destruction of the solitary waves. In the meantime, the internal solitary waves can generate elevated shear and dissipation rate in local regions. Significance Statement In the coastal ocean nonlinear internal solitary waves are widely recognized to play an important role in generating turbulent mixing, modulating short-term variability of nearshore ecosystem, and transporting sediment and biochemical materials. However, their effects on shallow and stratified estuaries are poorly known and have been rarely studied. The nonhydrostatic model simulations presented in this paper shed new light into the generation, propagation, and transformation of the internal solitary waves in a coastal plain estuary.

Structures of Lateral Flow and Turbulence in a Breaking Tidal Bore Rushing through a Curved Channel of the Qiantang Estuary

Abstract Tidal bores form in distinct funnel-shaped estuaries and bays initially and cause unique flow and turbulence dynamics when passing through meandering channels, such as in the Qiantang Estuary, Amazon River Estuary, and Seine River Estuary. To understand the lateral currents and turbulence processes of tidal bores in curved channels, velocity profiles and free-surface elevations are sampled for four semidiurnal tidal cycles in a curved channel located upstream of the Qiantang Estuary. During flood tides, the evolution of lateral currents experiences three distinct phases: first, there are inner-bank-toward lateral currents at the front of tidal bores, followed by two-layer helical currents in the middle of the flood tides, and finally, outer-bank-pointing lateral currents at the end of flood tides. Tidal bore breaking creates outbursts of turbulent kinetic energy. The enhanced turbulence emerges above the middle layers and persists for more than 10 minutes after the breaking front. The lateral momentum balance indicates that the decreasing lateral barotropic pressure gradient (LBTPG) and the increasing summation of centrifugal and Coriolis acceleration give rise to the variation in lateral currents. The phase lead of bores near the outer bank induced by shoal-channel topography generates an inner-bank-pointing LBTPG at the bore front and then gradually weakens it. Significant turbulence following bore breaking may be induced via the wave-induced turbulence mechanism by violent secondary waves. This research shows that complicated lateral currents are an important component of tidal bores flowing through meandering channels and that secondary waves after bore breaking can continually feed turbulence. Significance Statement The purpose of this study is to discern and explain the variation in lateral flows and turbulence when tidal bores rush through a curved estuarine channel. Lateral currents and turbulence play important roles in momentum exchange, scalar dispersion, and transverse topography evolution. Moreover, the discussion on lateral flows is necessary to extend the understanding of tidal bore hydrodynamics from the x–z dimension to the x–y–z dimension. In situ observations reveal that a complicated but regular pattern of lateral currents occurred in every tidal cycle and that there was significant turbulence at the tidal bore front. Our findings show that the lateral difference in tidal bore propagation speed caused by shoal-channel topography in the curved bend is an essential reason for the generation of lateral currents and that the secondary waves simulated by bore breaking can continuously feed tidal bore turbulence.

Talus and its cooling effects on the thermal regime of permafrost: A review

AbstractTalus, as the product of movement and accumulation along the slope after the cracking of cliffs or steep rock walls, is a common landform in the mountain periglacial environment. Significant thermal anomalies within talus have been widely reported to be a result of cooling effects. During the cold season, the increased temperature difference between talus and the ambient environment strengthens the intensity of convection (vertical flows) and transforms into upward advection (lateral flows) and exhausts the internal warm current. During the warm season, heat is concentrated on the surface of the talus, and the internal dominant cold current moves downward along the slope by advection. The principle of the proactive cooling effects of talus has been widely utilized in railway construction within permafrost regions as embankments to alleviate degradation of the underlying permafrost. However, limited model studies have examined the cooling effects of blocky debris in nature, and in situ observations are rare. Therefore, it will be important to increase observations and develop process‐based models that couple heat conduction, convection/advection, water transfer processes, and even the latent heat of phase change. This will help to better understand the extent of the cooling effects and its impact on the thermal regime of permafrost.

Analysis and prediction of SWM feed spacer performance based on CFD results with an emphasis on the effect of micro-scale lateral and longitudinal washing flows

In reverse osmosis applications, feed spacers are used in spiral wound membranes to separate the membrane surfaces and enhance mass transfer while incurring an acceptable pressure drop. In this study, an attempt has been made to understand the effect of spacer characteristics, such as arrangement and size, on mass transfer and pressure drop. Power-law equations were successfully developed to describe different spacer performance measures as a function of Reynolds number (Re), where both the multiplier of the Re term and the Re exponent vary for each spacer arrangement. Although at the macro level, it was not possible to adequately correlate the equation parameters with the spacers’ geometrical parameters (such as porosity), examining the post-processed CFD results at the micro level led to explanations for the observed concentration profiles, trends in spacer performance and changes in the equation parameters. A key observation was the importance of lateral flow recirculation, which was termed side-washing. Overall, based on the Spacer Configuration Efficacy performance measure and by assessing the trade-off between Sherwood number and pressure drop, the Woven configuration shows the best performance among the spacer arrangements and range of flowrates studied.

Hydrological modeling of the Silala River basin. 2. Validation of hydrological fluxes with contemporary data

AbstractA companion paper in this Special Issue reviewed the development of a hydrological model of the Silala River basin, using long‐term data (1969–1992) to determine the basin's water balance and plausible groundwater recharge scenarios. In the context of a remote river basin with limited in situ data, this article reviews the potential of in situ and remotely collected data, available for a relatively short period (2018–2019), to validate various aspects of the hydrological model performance. These include the spatiotemporal evolution of snow cover areal fraction (SCF), actual evapotranspiration (ETa) in the basin's extensive alluvial deposits, and wetland ETa. The observed SCF dynamics are well represented by the model at annual and monthly timescales, with monthly mean simulated SCF biases between −5.6% and 8%. At daily timescales, the model successfully captures snowstorm occurrence, although there are limitations on snow spatial patterning. Simulated ETa over alluvial deposits agrees with in situ observations during periods of high ETa, although the simulated values underestimate site‐specific observations during low ETa periods, due to the presence of lateral subsurface flows. In the wetlands, satellite‐based ETa estimates follow the seasonal pattern of in situ observations, but with values ~50% higher than those determined from elevation‐corrected eddy‐covariance (EC) measurements. Nonetheless, this difference is within the expected precision of the remote sensing method. Although based on a limited period, the validation results are encouraging, and demonstrate the utility of satellite tools and limited period in situ data for watersheds with scarce long‐term data.This article is categorized under: Science of Water > Hydrological Processes

Influence of distributor plate design on mixing characteristics of rice husk biomass in a bubbling fluidized bed gasifier: An experimental and CFD study

This study investigates the mixing characteristics of rice husk biomass in a bubbling fluidized bed gasifier (BFBG) using different distributor plates: perforated, 45° slotted, and hybrid plates. The study explores the fluidization characteristics of a biomass/sand mixture using three distributor plates, observing the maximum difference in initial minimum fluidization velocity (Umf,i) and final minimum fluidization velocity (Umf,f) for perforated plate, indicating axial mixing and segregation, while the 45° slotted plate represents uniform bed expansion and fluidization, and the hybrid plate exhibits an intermediate behavior. Axial and lateral biomass distribution is also studied, and it is found that with the 45° slotted plate the highest axial distribution of rice husk is observed at the lower portion due to lateral and swirling flow whereas perforated plate causes the highest deviation at the lower portion but approaches ideal mixing at the mid and upper sections due to axial dominant flow. The hybrid plate exhibits a blend of axial and lateral flows, resulting in intermediate axial distribution at lower and upper section of gasifier. Radially, the perforated plate has the highest concentration of biomass at maximum height whereas the 45° slotted plate has concentration near the walls, and the hybrid plate has optimal mixing throughout. The hybrid plate also achieves the highest mixing index at all air velocities. Overall, the study provides insights into biomass mixing in BFBGs and highlights the superior performance of the hybrid distributor plate.The CFD study also carried out to complement the experimental results in terms of pressure drop and mixing behavior by employing different distributor plats. Multiphase two fluid model (TFM) with kinetic theory of granular flow has been employed for CFD simulations with the engagement of k-epsilon turbulence model. The simulation results are in good agreement with experimental results in terms of bed pressure drop quantitatively and mixing characteristics of rice husk biomass qualitatively.

Stratification Breakdown in Antarctic Coastal Polynyas. Part II: Influence of an Ice Tongue and Coastline Geometry

Abstract This is Part II of a study examining wintertime destratification in Antarctic coastal polynyas, focusing on providing a qualitative description of the influence of ice tongues and headlands, both common geometric features neighboring the polynyas. The model of a coastal polynya used in Part I is modified to include an ice tongue and a headland to investigate their impacts on the dispersal of water formed at the polynya surface, which is referred to as Polynya Source Water (PSW) here. The model configuration qualitatively represents the settings of some coastal polynyas, such as the Terra Nova Bay Polynya. The simulations highlight that an ice tongue next to a polynya tends to break the alongshore symmetry in the lateral return flows toward the polynya, creating a stagnant region in the corner between the ice tongue and polynya where outflow of the PSW in the water column is suppressed. This enhances sinking of the PSW and accelerates destratification of the polynya water column. Adding a headland to the other side of the polynya tends to restore the alongshore symmetry in the lateral return flows, which increases the offshore PSW transport and slows down destratification in the polynya. This work stresses the importance of resolving small-scale geometric features in simulating vertical mixing in the polynya. It provides a framework to explain spatial and temporal variability in rates of destratification and Dense Shelf Water formation across Antarctic coastal polynyas, and helps understand why some polynyas are sources of Antarctic Bottom Water while others are not.

Impacts of Evaporation‐Induced Groundwater Upwelling on Mixing Dynamics in Shallow Wetlands

AbstractGroundwater mixing dynamics play a crucial role in the biogeochemical cycling of shallow wetlands. In this paper, we conducted groundwater simulations to investigate the combined effects of evaporation and local heterogeneity on mixing dynamics in shallow wetland sediments. The results show that evaporation causes groundwater and solutes to upwell from deep sediments to the surface. As the solute reaches the surface, evaporation enhances the accumulation of the solute near the surface, resulting in a higher solute concentration than in deep sediments. Mapping of flow topology reveals that local heterogeneity generates spatially varied mixing patterns mainly along preferential flow pathways. The upwelling of groundwater induced by surface evaporation through heterogeneous sediments is likely to create distinct mixing hotspots that differ spatially from those generated by lateral preferential flows driven by large‐scale hydraulic gradients, which enhances the overall mixing in the subsurface. These findings have strong implications for biogeochemical processing in wetlands.

A 3D Microfluidic Device with Vertical Channels toward In Vitro Reconstruction of Blood-Brain Barrier.

This paper reports a three-dimensional microfluidic device with an array of vertical channels to enable regulated, continuous, vertical flows to emulate the environment for in vitro culturing of brain and blood vessel organoids. This is expected to ultimately lead to in vitro reconstruction of the blood-brain barrier that is of high interest to studies on mental illness mechanisms and drug delivery to the brain. Twelve vertical microfluidic channels, each with 300 µm diameter and 5 mm height, were formed in the high-permeability agar gel surrounding the organoid to realize the vertical circulation flows and to allow lateral diffusion flows. The combined vertical flow rate of all channels ranges from 2.1 to 6.8 mL/min under different control parameters. A 30-day-old human blood vessel organoid was planted into the device for initial culturing and flow function tests. The result indicates that the organoid was properly activated with effective flow generation in the culturing site of the device.

Hydrochemical evolution of groundwater in northwestern part of the Indo-Gangetic Basin, India: A geochemical and isotopic approach

The present study aims to understand the hydrochemical evolution of groundwater in the Ghaggar River Basin, representing a zone of excessive abstraction of groundwater in the northwestern Indo-Gangetic Basin. The study comprises a regional scale and high-resolution sampling of groundwater during pre- and post-monsoon seasons of 2013 and their analyses for major ions, δ18O, δ2H, and 3H. Variation in hydrochemical and isotopic data is found both in spatial and vertical scales. The significant vertical variation of TDS, NO3− and K+ allowed the classification of the aquifer system into two major groups: shallow (depth < 80 m bgl) and deep (depth > 80 m bgl). The depthwise variations of δ18O and δ2H support this categorization of the aquifers. The Ca-HCO3 and Ca-Mg-Na-HCO3 water facies with higher values of 3H in the proximal part of the basin characterize recharge areas under humid conditions. The dominance of Mg-Na-HCO3 and Na-HCO3 facies in shallow and deep aquifers in central part of the basin, illustrate the intermediate to advanced stages of hydrochemical evolution in the system. Dominance of brackish Ca-Mg-Cl-SO4 and Na-Cl-SO4 water types in the discharge areas is due to the prevailing geological conditions and anthropogenic activities. Geochemical modelling supports the reverse cation exchange and mixing during lateral and vertical flows, weathering of silicate minerals, dissolution of crustal salts, and evaporative enrichment are the natural processes governing the evolution of groundwater chemistry along the flowpaths. The developed process-based conceptual model will aid in the formulation of a suitable plan for groundwater resource management in the region.

Changes of preferential flow in short-rotation eucalyptus plantations: field experiments and modeling

As an important part of the hydrological cycle, preferential flow significantly improves infiltration properties and limits the ability of soil to store, filter, and buffer water. However, the effect of roots on the preferential flow infiltration process in forest ecosystems is still unclear. This study measured the preferential flow infiltration process in short-rotation eucalyptus plantations (four forest ages of 1, 2, 3, and 5 years) with the surface-positioned double-ring infiltrometer in south subtropical area, China. Overall, the cumulative infiltration (CI), initial infiltration rate (IIR), and stable infiltration rate (SIR) increased with forest age. The CI, IIR, and SIR of the 5-year-old eucalyptus plantation were the highest in four aged eucalyptus plantations. Correlation analysis showed that root biomass was positively and significantly correlated with CI (p < 0.05), IIR (p < 0.01), and SIR (p < 0.01), which showed that the preferential flow increased with root biomass. However, the correlations between total porosity (TP) and IIR, SIR, and CI were all not significant (p > 0.05). The dye coverage of the inner and outer ring tangents, which were used to observe the strength of lateral preferential flows, was significantly and positively correlated with CI (p < 0.01), IIR (p < 0.01), and SIR (p < 0.01). The dye coverage of the outer ring tangent was significantly and positively correlated with root biomass (p < 0.05). So, the lateral preferential flows depended on root biomass and increased with forest age. The Horton model, which had higher stability and accuracy than the Kostiakov and Philip models, was the most suitable model to describe the preferential flow infiltration process in eucalyptus plantations. As important factors influencing the evolution of preferential flow in eucalyptus plantation, root biomass was used in predicting the parameters of the Horton model through regression analysis. Then, a unified model predicting the preferential flow infiltration process in short-rotation eucalyptus plantations was proposed and verified. This study achieved the quantitative measurement of preferential flow infiltration process, explored the importance of roots in the production of preferential flow channels, and found the lateral preferential flow played an important role in infiltration in forests. These results can provide a theoretical basis for improving the efficiency of water resource management in plantation, and optimizing the model of preferential flow infiltration process in plantation.