Anisotropic Hydraulic Conductivity Research Articles

Analytical analysis of the leachate flow to a horizontal well in dual-porosity media

Horizontal wells are gradually used for dewatering at municipal solid waste (MSW) landfills in recent years. A theoretical model of leachate flow to horizontal well is required to better evaluate its dewatering performance. In this study, a dual-porosity model of the leachate flow to a horizontal well in MSW landfills is established. The proposed model divides waste into fracture and matrix domains. Leachate in these two domains flows horizontally and vertically into a horizontal well together with leachate exchange occurring between them. An analytical solution of leachate level drawdown under horizontal well draining is obtained through Laplace integral transformation and Separation of variables. The analytical solution is verified with the numerical solution obtained by finite element method in COMSOL Multiphysics software. A sensitivity analysis is performed to investigate the effect of model key parameters, including anisotropy of hydraulic conductivity kr/kz, hydraulic conductivity ratio of fracture domain to matrix domain kfr/kmr, and proportion of fracture domain in total domain wf, on leachate level drawdown. A case study of the horizontal well draining test at the Tianziling landfill indicated that the dual-porosity model performed better than the single-porosity model in leachate level drawdown estimation, especially near the horizontal well. The average value of hydraulic conductivity ratio of fracture domain to matrix domain kfr/kmr is fitted to be 419 for typical MSW with high kitchen waste content in China.

Characterization of macropore structure of remolded loess and analysis of hydraulic conductivity anisotropy using X-ray computed tomography technology

The pore structure of loess is crucial for understanding the transport of water in soil and affects soil permeability. In this study, X-ray computed tomography (X-ray CT) technology was used to establish the macropore structure of remolded loess, and analyze the influence of macropore on permeability. A new specific and efficient workflow for constructing macropore structure of loess samples was established. The workflow improves the precision of image segmentation and provides a new method for creating 3D soil macropore structure. The macropore structure showed that the macro-porosity variation of loess sample was clearly anisotropic. Based on the macropore structure model, a modified Kozeny–Carman equation was suggested to investigate the hydraulic conductivity anisotropy of the loess sample. Subsequently, permeability test was used to verify the results calculated by equation. Both the results showed that hydraulic conductivity was positively correlated with the uniformity of the porosity changes in each direction. It provides a new method to estimate the anisotropy of hydraulic conductivity based on macropore structure model.

On Inflow to a Tunnel in a Fractured Double-Porosity Aquifer.

Inflow to a tunnel is a great public concern and is closely related to groundwater hydrology, geotechnical engineering, and mining engineering, among other disciplines. Rapid computation of inflow to a tunnel provides a timely means for quickly assessing the inflow discharge, thus is critical for safe operation of tunnels. Dewatering of tunnels is another engineering practice that should be planned. In this study, an analytical solution of the inflow to a tunnel in a fractured unconfined aquifer is obtained. The solution takes into account either the spherical or slab-shaped matrix block and the unsteady state interporosity flow. The instantaneous drainage water table and anisotropic hydraulic conductivities of the fractures network are also considered. Both uniform flux and uniform head boundary condition are considered to simulate the constant head boundary condition in the tunnel. The effects of the hydraulic parameters of the fractured aquifer on the inflow variation of the tunnel are explored. The application of the presented solution to obtain the optimum location and discharge of the well to minimize the inflow to a tunnel is illustrated.

Groundwater flow to a well in a strip-shaped unconfined-fractured aquifer system with a transition zone

Semi-infinite unconfined-fractured strip shaped aquifer systems are common in alluvial plain margins, but have received little attention in the hydrogeological community. Thus, the aim of this study is to present semi-analytical solutions of flow to a well in these aquifer systems. Two conceptual models are considered: 1-An unconfined aquifer with a lateral fractured aquifer and a pumping well installed in the unconfined aquifer (model I); 2-An unconfined aquifer with a lateral fractured aquifer and a pumping well installed in the fractured aquifer (model II). A transition zone is considered between two aquifers. Three-dimensional groundwater flows are considered in unconfined, fractured and transition zone aquifers. Homogeneous, anisotropic hydraulic conductivity and instantaneous drainage water table condition are assumed first but can be relaxed to accommodate delayed drainage water table condition if needed. The point sink/source solutions are obtained via finite and infinite Fourier transforms for space and Laplace transform for time. The line sink/source solutions are obtained via integration along the desired direction. The uniform flux and uniform head boundary conditions are considered for the pumping well. The vertical distribution of the flux toward the well screen is explored. The effects of inner well condition on the variation of the dimensionless drawdown and boundary depletion volume are investigated. We investigate the influences of the hydraulic parameters of the transition zone on the spatial and temporal variations of the sensitivity of the drawdown to hydraulic parameters of the aquifer system. Furthermore, the influences of the transition zone on the spatial distribution of the drawdown are explored. The results of this study can be utilized to evaluate head distribution in the aquifer system; to calculate the water budget of the alluvial aquifers near a fractured one; to analyze the influences of a transition zone on the head and flow distribution in the aquifer system.

Anisotropy of subsoil pore characteristics and hydraulic conductivity as affected by compaction and cover crop treatments

AbstractThe natural and cover crop (CC)‐induced anisotropy of subsoil pore characteristics is important in assessments of soil compaction but, until recently, has received limited attention. This study aims to quantify the anisotropy of soil pore characteristics and hydraulic conductivity in subsoils subjected to compaction and CC treatments in a split‐plot field experiment on temperate sandy loam soils. The main factor was ±compaction and the split‐plot factor was ±CC with fodder radish (Raphanus sativus L.). The compacted plots were heavily trafficked for 4 yr (2010–2013). After 4 yr under CC (2013–2016), core samples were collected at 0.3 m. The samples were taken vertically and horizontally to quantify the anisotropy of air‐filled porosity (εa) and air permeability (ka), saturated hydraulic conductivity (ksat), and bulk density (ρb). The results showed isotropic behavior for ρb and εa and significant anisotropic behavior (p < .05) for ka, pore geometry index (PO1) (ka/εa), ratio of non‐Darcian to Darcian ka (R‐ratio), and ksat. For parameters with significant anisotropy, higher values occurred vertically than horizontally for all compaction –CC combinations, except for R‐ratio. This indicates that pre‐existing vertical continuous pores dominated the pore system in the control subsoil. A nonsignificant trend of higher values of ka, PO1, and ksat in the +CC than in the compacted –CC plots suggest that CC could contribute to the formation of vertical biopores. Including an autumn CC in rotation with a summer cereal crop for a longer period may significantly affect the anisotropy of the soil pore and hydraulic properties.

Optimization Strategies for in Situ Groundwater Remediation by a Vertical Circulation Well Based on Particle‐Tracking and Node‐Dependent Finite Difference Methods

AbstractBoth theory and application of multispecies reactive transport for in situ groundwater bioremediation involving a vertical circulation well (VCW) are not fully understood despite its importance and common usage in aquifer remediation practices. This study proposes novel approaches including two methods for design and remediation prediction of a VCW system, which involves multispecies, multiphase, and microbially enhanced reactive transport process. One is particle‐tracking method, which depicts the trajectories of particles released from an injection chamber; the other is node‐dependent finite difference (NDFD) method, which describes the advection‐dispersion process based on the inflow and outflow directions at each node. The numerical results demonstrate that the particle‐tracking method works well by yielding a useful index, that is, the recovery ratio, which helps optimize the in situ preliminary remediation screening. When biochemical parameters, dispersivities, and in situ contaminated conditions are known after the preliminary screening, the NDFD method performs better than the conventional Laplace transform finite difference method in terms of describing multispecies reactive transport with multiple phases in a VCW system. The proposed particle‐tracking method and NDFD methods are employed to elucidate different effects of factors such as injection mode, hydraulic conductivity anisotropy ratio, distance between injection and extraction screened intervals, and injection/extraction rate on recovery and removal ratios. Our findings suggest that both methods are effective tools for optimization and prediction of VCW remediation in an anisotropic aquifer.

Deformation and Stability Characteristics of Layered Rock Slope Affected by Rainfall Based on Anisotropy of Strength and Hydraulic Conductivity

The strength and hydraulic conductivity anisotropy of rock slopes have a great impact on the slope stability. This study took a layered rock slope in Pulang, Southwestern China as a case study. The strength conversion equations of the seriously weathered rock mass were proposed. Then, considering the anisotropy ratio and anisotropy angle (dip angle of bedding plane) of strength and hydraulic conductivity, the deformation and stability characteristics of rock slope were calculated and compared with field monitoring data. The results showed that the sensitivity analysis of strength and hydraulic conductivity anisotropy could successfully predict the occurrence time, horizontal displacement (HD), and the scope of the rock landslide. When the anisotropy ratio was 0.01 and the dip angle was 30°, the calculated HD and scope of the landslide were consistent with the field monitoring data, which verified the feasibility of the strength conversion equations. The maximum horizontal displacement (MHD) reached the maximum value at the dip angle of 30°, and the MHD reached the minimum value at the dip angle of 60°. When the dip angle was 30°, the overall factor of safety (FS) and the minimum factor of safety (MFS) of the rock slope were the smallest. By assuming that the layered rock slope was homogeneous, the HD and MHD would be underestimated and FS and MFS would be overestimated. The obtained results are likely to provide a theoretical basis for the prediction and monitoring of layered rock landslides.

Event-Driven Hyporheic Exchange during Single and Seasonal Rainfall in a Gaining Stream

This study combined a reach-scale field survey and numerical modelling analysis to reveal the pattern of transient hyporheic exchange driven by rainfall events in the Zhongtian River, Southeast China. Field observations revealed hydrodynamic properties and flux variations in surface water (SW)/ groundwater (GW), suggesting that the regional groundwater recharged the study reach. A two-step numerical modelling procedure, including a hydraulic surface flow model and a groundwater flow model, was then used to interpret the transient hyporheic flow system. The hyporheic exchange exhibited strong temporal evolution in the study reach, as indicated by the rainfall event-driven hyporheic exchange. The reversal of the hydraulic gradient and transient hyporheic exchange were simulated using numerical simulation. Anisotropic hydraulic conductivity is the key to generating transient hyporheic exchange. A revised conceptual model was used to interpret the observed temporal patterns in hyporheic exchange. The seasonal rainfall events generate transient hyporheic exchange, and the pattern of transient hyporheic exchange indicates that transient hyporheic exchange appears only after an increased phase of the river stage but does not last long. The temporal pattern of hyporheic exchange can significantly affect the hydrodynamic exchange and the evolution of hydrology in the hyporheic zone for a gaining stream, and these results have important guiding significance for the comprehensive management of surface water and groundwater quantity and quality.

Sensitivity Analyses of the Seepage and Stability of Layered Rock Slope Based on the Anisotropy of Hydraulic Conductivity: A Case Study in the Pulang Region of Southwestern China

In the study of the seepage characteristics of layered rock slope under rainfall conditions, the majority of previous research has considered the hydraulic conduction to be isotropic, or only considered the anisotropy ratio of the hydraulic conductivity, ignoring the anisotropy angle. In the current study, a layered rock slope in the Pulang region was selected as an example. Then, based on the fitting parameters of the Van Genuchten model, pore water pressure sensitivity analyses of the layered rock slope were carried out. The anisotropy ratio and anisotropy angle were used to analyze the sensitivity of the seepage and stability of the layered rock slopes. The results show that as the anisotropy angle of hydraulic conductivity of layered rock slope decreased, the maximum volume water content of surface (MWCS) of layered rock slope gradually increased. Additionally, as the anisotropy ratio decreased and the anisotropy angle increased, the rising heights of the groundwater (RHG) of layered rock slope gradually increased. When the hydraulic conduction of layered rock slope was considered isotropic, the factor of safety (FS) tended to be overestimated. As the anisotropy ratio decreased and the anisotropy angle increased, the factor of safety (FS) of layered rock slope decreased. Prevention should be the objective for rock slopes with larger dip angles in the bedding plane in the Pulang region. This study provides feasible schemes for the evaluation of the seepage and stability of layered rock slopes in Pulang region of southwestern China.

Why tracer migration experiments with a pressure gradient do not always allow a correct estimation of the accessible porosity in clays

For assessing the radionuclide transport parameters, the apparent diffusion coefficient and the rock capacity factor ηR (being the product of the accessible porosity η and the retardation factor R) in host rocks used for nuclear waste disposal, mainly two classes of experiments are used: pure diffusive experiments e.g. through-diffusion, and experiments where next to a concentration gradient also a pressure gradient is applied e.g. pulse injection experiments. In Boom Clay, through-diffusion and pulse injection experiments lead to similar values for the accessible porosity of tritiated water (HTO), while for another unretarded tracer, iodide, significantly higher values are obtained by pulse injection. Similarly, in recompacted Na-illite, for chloride (another unretarded anion), lower accessible porosity values are observed by through-diffusion than by pulse injection. The difference increases while lowering the ionic strength.The reason for the discrepancy lies in the models used for analysing the migration experiments with a pressure gradient. Experiments with a pressure gradient allow fitting the apparent velocity Vapp of a tracer. The rock capacity factor is estimated as the ratio VDarcy/Vapp of the Darcy velocity VDarcy and Vapp. This is correct for HTO, but not for anions because the water flow through anion inaccessible porosity is neglected. Making a correct water flow mass balance by taking the water flow through inaccessible porosity into account, demonstrates that the rock capacity factor is given by the product FVVDarcy/Vapp with FV the fraction (0 ≤ FV ≤ 1) of the Darcy velocity flowing through tracer accessible porosity. Previously determined ηR values are in reality the ratio ηR/FV and overestimate ηR. In agreement with the experimental results, a lower ionic strength leads for (unretarded) anions to a lower accessible porosity η and consequently a lower FV and more overestimation of η. Besides charge related inaccessible porosity, porosity can also be inaccessible because of the size of the transported species: the accessible porosity becomes zero in case the particle size approaches the pore throat.Because the intention of experiments with a pressure gradient is to know ηR, we propose two models, which are basically two tracer distributions over a pore, for estimating FV. Considering Poiseuille flow, we calculate a typical pore radius, the hydraulic conductivity and for both distributions the accessible porosity, the fraction FV and the fitted ratio ηR/FV. Application to experimental data shows anisotropy in the pore radius, corresponding to the observed anisotropy in hydraulic conductivity. For anion exclusion, the model describes qualitatively the experimentally observed evolution as a function of double layer width.Because also for cations there is presently no valid relation between Vapp and ηR, migration experiments with a pressure gradient only provide a reasonable estimate for the rock capacity factor ηR in case of small (with respect to the average pore size) neutral particles like HTO.

Groundwater Throughflow and Seawater Intrusion in High Quality Coastal Aquifers

High quality coastal aquifer systems provide vast quantities of potable groundwater for millions of people worldwide. Managing this setting has economic and environmental consequences. Specific knowledge of the dynamic relationship between fresh terrestrial groundwater discharging to the ocean and seawater intrusion is necessary. We present multi- disciplinary research that assesses the relationships between groundwater throughflow and seawater intrusion. This combines numerical simulation, geophysics, and analysis of more than 30 years of data from a seawater intrusion monitoring site. The monitoring wells are set in a shallow karstic aquifer system located along the southwest coast of Western Australia, where hundreds of gigalitres of fresh groundwater flow into the ocean annually. There is clear evidence for seawater intrusion along this coastal margin. We demonstrate how hydraulic anisotropy will impact on the landward extent of seawater for a given groundwater throughflow. Our examples show how the distance between the ocean and the seawater interface toe can shrink by over 100% after increasing the rotation angle of hydraulic conductivity anisotropy when compared to a homogeneous aquifer. We observe extreme variability in the properties of the shallow aquifer from ground penetrating radar, hand samples, and hydraulic parameters estimated from field measurements. This motived us to complete numerical experiments with sets of spatially correlated random hydraulic conductivity fields, representative of karstic aquifers. The hydraulic conductivity proximal to the zone of submarine groundwater discharge is shown to be significant in determining the overall geometry and landward extent of the seawater interface. Electrical resistivity imaging (ERI) data was acquired and assessed for its ability to recover the seawater interface. Imaging outcomes from field ERI data are compared with simulated ERI outcomes derived from transport modelling with a range of hydraulic conductivity distributions. This process allows for interpretation of the approximate geometry of the seawater interface, however recovery of an accurate resistivity distribution across the wedge and mixing zone remains challenging. We reveal extremes in groundwater velocity, particularly where fresh terrestrial groundwater discharges to the ocean, and across the seawater recirculation cell. An overarching conclusion is that conventional seawater intrusion monitoring wells may not be suitable to constrain numerical simulation of the seawater intrusion. Based on these lessons, we present future options for groundwater monitoring that are specifically designed to quantify the distribution of; (i) high vertical and horizontal pressure gradients, (ii) sharp variations in subsurface flow velocity, (iii) extremes in hydraulic properties, and (iv) rapid changes in groundwater chemistry. These extremes in parameter distribution are common in karstic aquifer systems at the transition from land to ocean. Our research provides new insights into the behaviour of groundwater in dynamic, densely populated, and ecologically sensitive coastal environments found worldwide.

Assessing the Hydraulic Conductivity Anisotropy and Skin-Effect Based on Data of Slug Tests in Partially Penetrating Wells

A semianalytic and approximate analytical solution is given to the problem of slug test in a partially penetrating well in a confined or unconfined anisotropic aquifer. An asymptotic solution is given to the problem of slug test in a partially penetrating well in an unconfined aquifer. The latter solution, unlike the semiempiric Bouwer–Rice method, takes into account hydraulic conductivity anisotropy and skin effect. Levenberg–Marquardt algorithm was used to develop a method for determining hydraulic conductivity anisotropy and skin effect based on data of slug tests in partially penetrating wells in confined or unconfined aquifer.

Improving Groundwater Model in Regional Sedimentary Basin Using Hydraulic Gradients

Groundwater flow systems are strongly influenced by heterogeneity and anisotropy of hydraulic conductivity (K). Particularly in stratified clastic sedimentary aquifers, the vertical hydraulic gradient (dh/dz) is often very high, due to the low vertical hydraulic conductivity (Kv) or high anisotropy (Kh/Kv). However, data on the vertical hydraulic gradient to calibrate the anisotropy is seldom available. We investigated the relationship between the variable Kh/Kv and the dh/dz computed by a groundwater flow model to improve the regional parameterization using an extensive data base on 3D distribution of hydraulic head. Although it is commonly assumed that the value of Kh/Kv is 10, our values typically ranged between 10 and 105, because the maximum Kh/Kv was 105 in this regional basin. The simulations used MODFLOW-2000. We found that the high Kh/Kv contributed to high dh/dz, while identifying locations of potentially good vertical connectivity between the aquifer zones, where dh/dz is very low and difficult to measure sufficiently accurately. Sensitivity analysis of dh/dz to recharge and pumping from wells showed that recharge led to change in inflow of groundwater that led to head change, which in turn led to change in dh/dz. While, pumping contributed to aquifer outflow, as change in head drawdown around the influence zone, in turn changed dh/dz. Additionally, dh/dz in a shallower aquifer was more strongly affected by recharge and pumping.

Influence of time-dependent ground surface flux on aquifer recharge with a vadose zone injection well

Vadose zone well (VZW) injection is an effective method for aquifer recharge in semiarid and arid regions where groundwater table is deep or sufficiently permeable soils and/or sufficiently large land areas for surface infiltration are not available. Several analytical and numerical models have been developed for the injection well in the vadose zone. However, those models usually ignore the ground surface flux (GSF) generated by infiltration or evapotranspiration, which may cause errors and hinder the success of artificial recharge and groundwater management. This study takes GSF generated by these two processes into consideration with the purpose of understanding their influences on the hydraulic responses and recharge efficiency. An innovative mathematical model is established based on a three-dimensional (3D) governing equation for saturated flow and a linearized 3D Richards’ equation for unsaturated flow. The Laplace-Hankel transforms are applied to derive solutions for the hydraulic head increments and recharge rate. The solutions are tested by a finite-element numerical model developed using COMSOL Multiphysics. The obtained solutions are utilized to assess the influences of time-dependent GSF generated by infiltration or evapotranspiration. The magnitude of these influences depends on unsaturated and saturated aquifer properties and the value of GSF. The impacts of three important properties are investigated: the constitutive exponent of the unsaturated zone ω, the specific yield Sy, and the hydraulic conductivity anisotropy KD=KzKr. Smaller values of dimensionless constitutive exponent ωD and dimensionless specific yield SyD lead to larger changes of hydraulic head increments in both unsaturated zone (uD) and saturated zone (sD) when GSF is the same. A small value of KD can delay the changes of uD and sD, but the value of KD does not affect the final values of uD and sD. Larger values of GSF generated by surface infiltration lead to larger increases of uD and sD; larger absolute values of GSF generated by evapotranspiration lead to larger decreases of uD and sD. The proposed semi-analytical solutions can be used to improve the feasibility and efficiency of artificial recharge in semiarid and arid regions.

Sensibility Analysis of the Hydraulic Conductivity Anisotropy on Seepage and Stability of Sandy and Clayey Slope

Evaluation of slope stability under rainfall is an important topic of Geotechnical Engineering. In order to study the influence of anisotropy ratio (kr = kx/ky) and anisotropy direction (α) on the seepage and stability of a slope, the SEEP/W and SLOPE/W modules in Geo-studio were utilized to carry out the numerical analysis of a homogeneous slope in Luogang District, Guangzhou City, China, which is based on the theory of unsaturated seepage and stability. Two kinds of soils (clay and sand) were included. Results show that: For sandy soil slope, the increase of kr promotes the rainfall infiltration, and the decrease of α prevents the rainfall infiltration. The maximum water content of the surface (MWCS) reaches maximum with the increase of kr and α. The rising height of groundwater (RHG) is −3–4 m and the safety factor (SF) is 1.3–1.7. For clayey soil slope, variations of kr and α have little impact on the seepage characteristics and slope stability. The MWCS remains almost the same. The rainfall infiltration depth (RID) is 0.5–1 m and the SF is about 1.7. Therefore, for sandy soil slope, it is not only necessary to consider the influence of kr, but also the influence of α. For clayey soil slope, it can be treated as isotropic material to simplify calculation.

Prediction of discharge flow rate beneath sheet piles using gene expression programming based on scaled boundary finite element modelling database

Sheet piles are of general water retaining structures. The discharge flow rate beneath sheet plies is an important parameter in the design of these structures. In this study, the Gene Expression Programming (GEP) as an Artificial Intelligence (AI) method is used for developing a model to predict the discharge flow rate. The input parameters include the sheet pile height, upstream head and hydraulic conductivity anisotropy ratio. In order to achieve better performance, the flow rate is normalized and selected as an output of the model. A database including 1000 cases are created from the Scaled Boundary Finite Element Method (SBFEM) for the seepage beneath sheet plies is employed to develop the model. The GEP-based model predictions demonstrate a reasonable agreement with the simulated data, which indicates the efficiency of the developed model. The results of the sensitivity analysis indicate that the upstream head is the most influential parameter in the discharge flow rate beneath the sheet piles. Furthermore, the outputs of the parametric analysis show the reasonable performance of the model in the prediction of normalized discharge flow rate.

Piecewise-linear large-strain model for radial consolidation with non-Darcian flow and general constitutive relationships

A piecewise-linear large-strain radial consolidation model, called VRCS1, is developed for soft soil stabilized by prefabricated vertical drain (PVD) assisted by vacuum-surcharge combined preloading incorporating non-Darcian flow and nonlinear compressibility and permeability relationships. VRCS1 accounts for large strain, soil self-weight, smear effect, partial drain penetration, time-dependent surcharge loading, time- and depth-dependent vacuum pressure, unload/reload effects, radial and vertical flows, hydraulic conductivity anisotropy, non-Darcian flow and nonlinearly varying relationships of compressibility and permeability. The compressibility and permeability constitutive relationships are specified using discrete data points and, as a result, VRCS1 is more flexible than other existing models in terms of considering a variety of different constitutive relationships. VRCS1 shows excellent agreement with other exiting solutions and field measurements involving Darcian flow and non-Darcian flow, surcharge loading and surcharge-vacuum combined loading, and small and large strains. A series of numeric examples indicates that compressibility and permeability relationships can have significant effect on the rate of radial consolidation. Results also indicate that solutions based on small-strain theory can be in significant error for large strain conditions, especially when non-Darcian flow and nonlinear constitutive relationships are encountered.

Effect of depth-dependent hydraulic conductivity and anisotropy on transit time distributions

The paper presents exact closed-form analytical solutions describing a two-dimensional profile confined groundwater flow induced by areal recharge in a laterally bounded aquifer with anisotropic permeability, which decreases with depth. The mathematical formulation of the problem for a rectangular flow domain in terms of hydraulic head and stream function are free of the limitation of the Dupuit–Forchheimer assumption. Two different types of outflow boundary conditions associated with the aquifer discharge area, Dirichlet and Neumann, are explored. Analytical solutions with respect to stream function allow examining the distribution of recharge over depth (between contouring streamlines) for a variety of flow parameter combinations. The solutions are extended to allow the groundwater transit time distribution (TTD) to be calculated. It was found that the dependence of the transit time function on hydraulic conductivity anisotropy and depth-decay coefficients may exhibit non-monotonic behavior. The mathematical models introduced in the article are accompanied by computational simulations.

Anisotropic features of natural Teguline clay

In general, due to their geological formation by deposition, natural stiff clays exhibit anisotropic thermo-hydro-mechanical behaviour. This behaviour is important to be considered in geological and geo-environmental engineering. In this study, natural stiff Teguline clay was extracted at different depths and the thermal conductivity, compressibility and hydraulic conductivity were determined on samples along various orientations with respect to the bedding plane. Significant thermal and hydraulic conductivity anisotropies were evidenced with higher values along the bedding plane, indicating that both heat and water transfers preferentially occurred along the direction parallel to the bedding plane. Moreover, the compression index in the horizontal direction were found lower than in the vertical direction, while opposite phenomenon was observed for the yield stress. The degrees of thermal conductivity anisotropy ηΤ, compression index anisotropy ηCc1, yield stress anisotropy ησ'y and hydraulic conductivity anisotropy ηk1 were found comparable, indicating that bedding is a good indicator of the inherent thermo-hydro-mechanical anisotropy for natural stiff clays. Upon loading in oedometer after the yield stress, the inherent anisotropy changed: for the vertical sample (loading direction normal to the bedding plane), loading led to more and more anisotropy, while for the horizontal sample (loading direction parallel to the bedding plane), the inherent anisotropy disappeared first; then, the induced anisotropy was developed. These findings provided useful information for analyzing the thermo-hydro-mechanical anisotropy of natural soils in geotechnical and geo-environmental engineering.

Bulk density optimization to determine subsurface hydraulic properties in Rocky Mountain catchments using the GEOtop model

AbstractIntegrated watershed models can be used to calculate streamflow generation in snow‐dominated mountainous catchments. Parameterization of water flow is often complicated by the lack of information on subsurface hydraulic properties. In this study, bulk density optimization was used to determine hydraulic parameters for the upper and lower regolith in the GEOtop model. The methodology was tested in two small catchments in the Dry Creek Watershed in Idaho and the Libby Creek Watershed in Wyoming. Modelling efficiencies for profile‐average soil–water content for the two catchments were between 0.52 and 0.64. Modelling efficiencies for stream discharge (cumulative stream discharge) were 0.45 (0.91) and 0.54 (0.94) for the Idaho and Wyoming catchments, respectively. The calculated hydraulic properties suggest that lateral flow across the upper–lower regolith interface is an important driver of streamflow in both the Idaho and Wyoming watersheds. The overall calibration procedure is computationally efficient because only two bulk density values are optimized. The two‐parameter calibration procedure was complicated by uncertainty in hydraulic conductivity anisotropy. Different upper regolith hydraulic conductivity anisotropy factors had to be tested in order to describe streamflow in both catchments.