Horizontal Hydraulic Conductivity Research Articles

Effect of chemical modification on hydraulic conductivity of stratified porous media

ABSTRACT Understanding hydraulic conductivity is essential in porous media as it dictates the capacity of fluids to permeate through these substances. This research investigated the impact of chemical modification using fly ash on hydraulic conductivity. The coefficient of hydraulic conductivity along the bedding plane at different angles of orientations was predicted by employing machine learning techniques such as gene expression programming (GEP), artificial neural networks (ANNs), and regression tree (RT), considering various influencing parameters. As the amount of fly ash in the porous medium rises, the hydraulic conductivity decreases. The statistical results demonstrate that the proposed ANN model effectively forecasted the horizontal hydraulic conductivity. It achieved the highest R2 value (0.989), the lowest mean absolute percentage error value (5.772), the lowest scatter index value (0.040), and the lowest Akaike Information Criterion value (−2,359.914) compared to the GEP, RT, and previously established approaches. Moreover, a novel equation has been proposed for determining horizontal hydraulic conductivity, which can be used for any stratified medium, distinguishing this work from previous ones. These findings can inform global practices in mitigating groundwater contamination, enhancing irrigation efficiency, and improving the design of subsurface fluid flow systems, making it a valuable contribution to both academic and practical applications worldwide.

Very‐Near‐Field Coseismic Fault Pressure Drop and Delayed Postseismic Cross‐Fault Flow Induced by Fault Damage From the 2018 M6.3 Hualien, Taiwan Earthquake

AbstractEarthquakes can produce rock damage, poroelastic deformation, and ground shaking that modify fault zone hydrogeologic properties. Coseismic and postseismic hydrologic response to the ruptured fault can serve as constraints on hydrogeologic property changes. Here, we document fluid pressure responses to the 2018 M6.3 Hualien, Taiwan earthquake and model the postseismic fault zone hydrology inferred from very‐near‐fault data. Two groundwater wells located ∼180–250 m from the fault damage zone experienced 10–15 m of groundwater level decline followed by a prolonged (>6 months) recovery. Poroelastic models indicate that strain dilation in the fault's hanging wall can produce water level reductions of several meters. However, the model cannot explain groundwater level change in the footwall nor the delayed postseismic recovery, suggesting fault zone damage played a primary role in both the coseismic and postseismic water level reductions. Fluid flow models incorporating the effects of coseismic fault damage on the temporal evolution of hydrologic fault properties show enhanced hydraulic anisotropy after the earthquake. The best‐fit models show that while both vertical hydraulic conductivity and specific storage likely increased within the fault zone, the horizontal hydraulic conductivity is low, suggesting the fault zone behaves as a hydraulic barrier to cross‐fault flow with modeled diffusivities as low as ∼10−3 m2/s. High‐fidelity hydrologic measurements in the very‐near‐field of fault zones (e.g., within a few hundred meters) may be a useful tool to constrain the spatial and temporal evolution of fault zone properties before, during, and after rupture.

Confined seepage analysis of saturated soils using fuzzy fields

Seepage refers to the flow of water through porous materials. This phenomenon has a crucial role in dam, slope, excavation, tunnel, and well design. Performing seepage analysis usually is a challenging task, as one must cope with the uncertainty associated with the parameters such as the hydraulic conductivity in the horizontal and vertical directions that drive this phenomenon. However, at the same time, the data on horizontal and vertical hydraulic conductivities are typically scarce in spatial resolution. In this context, so-called non-traditional approaches for uncertainty quantification (such as intervals and fuzzy variables) offer an interesting alternative to classical probabilistic methods, since they have been shown to be quite effective when limited information on the governing parameters of a phenomenon is available. Therefore, the main contribution of this study is the development of a framework for conducting seepage analysis in saturated soils, where uncertainty associated with hydraulic conductivity is characterized using fuzzy fields. This method to characterize uncertainty extends interval fields towards the domain of fuzzy numbers. In fact, it is illustrated that fuzzy fields are an effective tool for capturing uncertainties with a spatial component, since they allow one to account for available physical measurements. A case study in confined saturated soil shows that with the proposed framework, it is possible to quantify the uncertainty associated with seepage flow, exit gradient, and uplift force effectively.

Investigating soil properties and their effects on freeze-thaw processes in a thermokarst lake region of Qinghai-Tibet Plateau, China

Soil parameters form the foundation of hydrogeological research and are crucial for studying engineering construction and maintenance, climate change, and ecological environment effects in cold regions. However, the soil properties in the permafrost region of the Qinghai–Tibet Plateau (QTP) remain unclear. Hence, in this study, soil temperature (Ts), volumetric specific heat capacity (C), thermal conductivity (K), thermal diffusivity (D), soil water content (SWC), electric conductivity (EC), vertical (Kv) and horizontal (Kh) saturated hydraulic conductivity, bulk density (ρb), and soil texture near the Qinghai-Tibet Railway were measured, and their effects on the freeze-thaw process were evaluated. The results revealed a predominantly sandy loam soil texture, with Kh and Kv showing strong spatial variability, while the other parameters presented moderate spatial variability. Thermokarst lake had a limited influence on D, C, K, and ρb but significantly reduced Kh and Kv. Groundwater affected SWC, Ts, and EC. The model results showed that all parameters indicated small sensitivities to the maximum thawing depth (MTD), with MTD positively responding to all parameters except for Kv and porosity (ρp). Except for Kh and Kv, all parameters showed high sensitivities to the time from starting to complete freezing (TSCF). TSCF responded positively to C, ρp, and density (ρd) and negatively to K and Kh. This study expanded the quantification of soil properties in the QTP, which can help improve the accuracy of cryohydrogeologic models, thus guiding the construction and maintenance of infrastructure engineering.

Applicability of Single-Borehole Dilution Tests in Aquifers with Vertical Flow

A set of experimental field single-borehole dilution tests were completed in the Motril–Salobreña detrital aquifer (Spain) in a sector with coarse material in four different moments under variable hydrological conditions. The comparative study of the tracer washing, and the temperature profile patterns for the tests carried out in two wells located hundreds of m from each other, revealed the presence of ascending vertical flows in one of the wells (not detected by other means) that compromises the reliability of the tracer test. The values of both the apparent horizontal velocity and hydraulic conductivity obtained in the affected well were less than half of those estimated in the well not affected by the upward vertical flows. The repetition of the test eight times during different seasons showed that the hydraulic conductivity calculated from the apparent horizontal velocity can vary; therefore, to approximate to a representative hydraulic conductivity value, using this method is recommended to carry out tests under different hydrological conditions and average the results. The difference generated by the changes in conditions for the specific setting of the study area was 25%. Taking this into account, it was considered that an approximation to the more representative value would be an average under variable hydrological conditions, resulting in a horizontal velocity of 6.7 m/d and hydraulic conductivity of 337 m/d. This information is critical for the management of the aquifer as it has strategic resources against droughts that are becoming more frequent in the Mediterranean area.

Impacts of Topography‐Driven Water Redistribution on Terrestrial Water Storage Change in California Through Ecosystem Responses

AbstractLateral subsurface flow plays an essential role in sustaining the terrestrial ecosystem, but it is not explicitly represented in most Earth System Models. In this study, we implemented an explicit lateral saturated flow model into the E3SM land model (ELM). The model explicitly describes lateral flow in the saturated zone by representing, for each model grid, an idealized hillslope consisting of five hydrologically connected soil columns. We conducted three model experiments driven by 0.125° atmospheric forcing data during 1980–2015 over California using models of the default ELM, a modified version of ELM to enhance infiltration, and the model with the lateral saturated flow model. The simulated runoff, evapotranspiration, and terrestrial water storage anomaly (TWSA) from the three simulations were evaluated against available observations, and the model explicitly representing lateral flow performs best. The new model produces greater gridcell‐averaged evapotranspiration especially over the mountainous regions with moderate relief and seasonally dry climates. Most importantly, it improves the modeled seasonal variations, interannual variabilities, and the recent decadal decline of TWSA. Many of these improvements can be attributed to the enhanced ecosystem resilience to droughts as demonstrated by transpiration increases caused by lateral flow. Model sensitivity experiments suggest that subsurface runoff is most sensitive to the ratio between horizontal and vertical saturated hydraulic conductivity, followed by hillslope planforms (convergent, divergent, and uniform), number of columns, and lower boundary conditions. Future work should effectively characterize hillslopes in global models and explore the long‐term influences of lateral water movement on modeled biogeochemical cycle.

A Large-Sized Permeameter for Studying Suffusion Characteristics of Anisotropic Soils

Abstract Seepage-induced suffusion involves the migration of fine particles within a soil matrix. Seepage flow is affected by the soil permeability anisotropy of anisotropic soil fabric; however, suffusion anisotropy is unclear because of the limited function of existing permeameters. In recent studies, the effect of seepage direction has been investigated under only low hydraulic gradients because the control of seepage direction relies merely on gravity. In this study, a new, large-sized permeameter is developed with which suffusion tests can be conducted along horizontal or vertical seepage directions under high hydraulic gradients. Correspondingly, the permeameter can accommodate a specimen of 540 × 500 × 470 or 540 × 540 × 440 mm3 (length × width × height). The seepage direction is switched by changing the boundary conditions of the specimen with detachable perforated plates that allow pressurized water originating from different inlets to flow along horizontal or vertical directions. Two repeated pairs of tests were performed on a gap-graded clayey gravel to investigate the suffusion anisotropy of saturated clayey gravel. The results show that the maximum relative deviations of measurements for initial hydraulic conductivity, initiation, and failure hydraulic gradients are less than 3.5 %, demonstrating satisfactory reliability. The ratio of the initial horizontal hydraulic conductivity to vertical hydraulic conductivity for the test soil is 13.87, indicating a significantly anisotropic fabric induced by compaction. The ratios of horizontal initiation and failure hydraulic gradients to vertical initiation and failure hydraulic gradients are 0.52 and 0.59, respectively. This implies that suffusion anisotropy should not be neglected for evaluating the internal instability of anisotropic soils.

Heat losses in ATES systems: The impact of processes, storage geometry and temperature

The technical and economic success of an Aquifer Thermal Energy Storage (ATES) system depends strongly on its thermal recovery efficiency, i.e. the ratio of the amount of energy that is recovered to the energy that was injected. Typically, conduction most strongly determines the thermal recovery efficiency of ATES systems at low storage temperatures (<25 °C), while the impact of buoyancy-driven flow can lead to high additional heat losses at high storage temperatures (>50 °C). To date, however, it is unclear how the relative contribution of these processes and mechanical dispersion to heat losses across a broad temperature range is affected by their interaction for the wide range of storage conditions that can be encountered in practice. Since such process-based insights are important to predict ATES performance and support the design phase, numerical thermo-hydraulic ATES simulations were conducted for a wide range of realistic operational storage conditions ([15–90 °C], [50,000–1,000,000 m3/year]) and hydrogeological conditions (aquifer thickness, horizontal hydraulic conductivity, anisotropy). The simulated heat loss fractions of all scenarios were evaluated with respect to analytical solutions to assess the contribution of the individual heat loss processes. Results show that the wide range of heat losses (10–80 % in the 5th year) is the result of varying contributions of conduction, dispersion and buoyancy-driven flow, which are largely determined by the geometry of the storage volume (ratio of screen length / thermal radius, L/Rth) and the potential for buoyancy-driven flow (q0) as affected by the storage temperature and hydraulic conductivity of the aquifer. For ATES systems where conduction dominates the heat losses, a L/Rth ratio of 2 minimizes the thermal area over volume ratio (A/V) and resulting heat losses for a given storage volume. In contrast however, the impact of dispersion decreases with L/Rth and particularly for ATES systems with a high potential for buoyancy-driven flow (q0 > 0.05 m/d), increasingly smaller L/Rth ratios (<1) strongly reduce the heat losses due to tilting. Overall, the results of this study support the assessment of thermal recovery efficiencies for particular aquifer and storage conditions, thereby aiding the optimization of initial ATES designs.

The impact of hydraulic conductivity anisotropy on the effectiveness of subsurface dam

Hydraulic conductivity is a key parameter controlling groundwater flow and solute transport, and anisotropy in hydraulic conductivity is common in aquifers. Previous studies have investigated the effectiveness of subsurface dams in combating seawater intrusion (SWI) and associated environmental concerns. However, the quantitative impact of hydraulic conductivity anisotropy on the performance of subsurface dam has not been explored. This study goes beyond previous research by examining, for the first time, the effects of subsurface dams on SWI prevention in anisotropic settings. Furthermore, the study optimized subsurface dam designs in anisotropic coastal aquifers through numerical simulations that take into account the environmental impact. Our findings reveal the mechanism of hydraulic conductivity anisotropy's influence on the discharging zone and demonstrate that as the anisotropy ratio (rk) decreases, the coastal discharging zone expands landward, reducing SWI and ultimately lowering the minimum effective dam height (MEDH). This process effectively prevents SWI while maximizing fresh groundwater discharge. Increasing the rk values simultaneously expands both the MEDH and the peak fresh groundwater discharge (PFGD). Additionally, increasing the horizontal hydraulic conductivity of the aquifer significantly increases the range of PFGD, while the distance between the dam and shoreline emerges as the main factor influencing the extent of the MEDH.

Influence of landscape position and climatic seasonality on soil water and gas conductivity properties in agricultural soils

Agricultural landscape management and climate seasonality can influence soil structure, hydraulic conductivity, and air permeability within the context of soil water and soil gas mobility. To investigate this, in situ and laboratory-based data were collected from three agricultural landscape positions within a watershed in eastern Ontario, Canada during a growing season. Macropore classification, water infiltration tests, and air permeability measurements were conducted in situ and standard soil characterizations were carried out on soil samples. Hydraulic conductivity of the soil matrix, based on grain size data, indicated that the highest values were consistently measured in the B horizon at each landscape setting. Macropores were found to be more abundant within uncultivated drainage ditch bank soils, compared to the adjacent cropped fields. Macropores in the ditch bank soils were exclusively consisted of circular biopores, while both circular and linear macropores were observed in the cultivated field soils. Air permeability, vertical hydraulic conductivity, and horizontal hydraulic conductivity were also greater in the uncultivated soils, relative to the cultivated soils. Field saturated hydraulic conductivity measurements offered evidence of anisotropy, likely due to the vertical nature of the macropore features. Macropore disposition and extent varied over the growing season, especially in the cultivated field soils where tillage and field trafficking are physically disruptive. Seasonality of macropore development will influence temporal changes in advection-based mass exchange of gas and water in the vadose zone. Modeling of mass exchange in agricultural soils should consider time variability in macroporosity to more realistically characterize infiltration and soil gas emissions.

Controls on Saturated Hydraulic Conductivity in a Degrading Permafrost Peatland Complex

AbstractPermafrost peatlands are vulnerable to rapid structural changes under climatic warming, including vertical collapse. Peatland water budgets, and therefore peat hydraulic properties, are important determinants of vegetation and carbon fluxes. Measurements of hydraulic properties exist for only a limited number of permafrost peatland locations, primarily concentrated in North America. The impacts of thaw‐induced collapse upon properties such as horizontal saturated hydraulic conductivity (Kh), and thus lateral drainage, remain poorly understood. We made laboratory determinations of Kh from 82 peat samples from a degrading Swedish palsa mire. We fitted a linear mixed‐effects model (LMM) to establish the controls on Kh, which declined strongly with increasing depth, humification and dry bulk density. Depth exerted the strongest control on Kh in our LMM, which demonstrated strong predictive performance (r2 = 0.605). Humification and dry bulk density were influential predictors, but the high collinearity of these two variables meant only one could be included reliably in our LMM. Surprisingly, peat Kh did not differ significantly between desiccating and collapsed palsas. We compared our site‐specific LMM to an existing, multi‐site model, fitted primarily to boreal and temperate peatlands. The multi‐site model made less skillful predictions (r2 = 0.528) than our site‐specific model, possibly due to latitudinal differences in peat compaction, floristic composition and climate. Nonetheless, low bias means the multi‐site model may still be useful for estimating peat Kh at high latitudes. Permafrost peatlands remain underrepresented in multi‐site models of peat hydraulic properties, and measurements such as ours could be used to improve future iterations.

Efficient representation of transient tidal overheight in a coastal groundwater flow model using a phase-averaged tidal boundary condition

Ocean tides cause water table overheight near the seaward boundary of coastal aquifers which can have a large impact on groundwater flows and saltwater intrusion. Despite this, regional-scale coastal groundwater flow models often neglect the effects of ocean tides or alternatively assume that the influences of ocean tides and sea level are constant over time. These simplifications are often required because simulation of the phase-resolved tidal signal at a coastal boundary is computationally demanding. Our objective was to derive a phase-averaged tidal boundary condition for application along gently sloping coastlines that enables simulation of real, complex tidal signals combined with sea-level changes due to meteorological effects. The boundary condition extends an existing analytical solution of tidal overheight by including an empirical correction function for conditions where the assumptions of the existing solution are violated. The correction function was developed by conducting a parametric study on an idealized two-dimensional cross-sectional coastal aquifer model and considering the effects of parameters including horizontal hydraulic conductivity, vertical anisotropy, specific yield, aquifer thickness, and beach slope. The performance of the new phase-averaged tidal boundary condition was assessed using a three-dimensional groundwater flow model of the island of Spiekeroog, Northwest Germany, which comprises complex coastal morphology with non-planar beach slopes. Simulations applying the new boundary condition were compared to simulations that adopted a phase-resolved tidal boundary condition and to observed groundwater levels. Accounting for time-varying changes in the tidal signal and sea level was found to be critical to simulate observed data and to adequately reproduce the transient tidal overheight simulated by the phase-resolved model. The performance of the new phase-averaged boundary condition in the regional-scale model varied depending on how the coastal morphology was represented in the boundary condition with local morphological features increasingly important for lower intertidal vertical infiltration capacity (low isotropic hydraulic conductivity or high vertical anisotropy) or specific yield. In conclusion, the new boundary condition presented overcomes current limitations in simulating transient tidal overheight in regional-scale groundwater models.

Parameter identification and range restriction through sensitivity analysis for a high-temperature heat injection test

In order to compensate for the variable mismatch between heat demand and heat production from renewable sources or waste heat, high-temperature aquifer thermal energy storage (HT-ATES) is a promising option. A reliable prediction of the energetic performance as well as thermal and hydraulic impacts of a HT-ATES requires a suitable model parameterization regarding the subsurface properties. In order to identify the subsurface parameters on which investigation efforts should be focused, we carried out an extensive sensitivity analysis of the thermal and hydraulic parameters for a high-temperature heat injection test (HIT) using numerical modeling of the governing coupled thermo-hydraulic processes. The heat injection test was carried out in a quaternary shallow aquifer using injection temperatures of about 75 °C over 5 days, accompanied by an extensive temperature monitoring. The sensitivity analysis is conducted for parameter ranges based on literature values, based on site investigation at the HIT site and based on a model calibrated to the measured temperature distribution following the heat injection. Comparing the parameter ranges thus obtained in this three-step approach allows to identify those parameters, for which model prediction uncertainty decreased most, which are also the parameters, that strongly affect the thermal behavior. The highest sensitivity is found for vertical and horizontal hydraulic conductivity as well as for groundwater flow velocity, indicating that investigation efforts for HT-ATES projects should focus on these parameters. Heat capacity and thermal conductivity have a smaller impact on the temperature distribution. Our work thus yields a consistent approach to identifying the parameters which can be best restricted by field investigations and subsequent model calibration. Focusing on these during field investigations thus enable improved model predictions of both HT-ATES operation and induced impacts.

Two‐region flow caused by pumping at a partial penetration well in a leaky confined aquifer

AbstractAn analytical model for depicting two‐region flow caused by constant‐rate pumping at a partially penetrating well in a leaky confined aquifer is established. The two‐region flow is described by the radial Izbash non‐Darcy flow in the vicinity of the abstraction well and Darcy flow away from the abstraction well in the pumped aquifer. The model considers the effects of aquitard storage, wellbore storage, and wellbore skin. The semi‐analytical solutions of drawdown are developed by means of a linearization procedure combined with Laplace transform and separation of variables. The time‐domain drawdowns are then obtained by using the Stehfest method for numerical Laplace inversion. The solutions encompass previous solutions for one or two‐region flow to a partially penetrating well in a (non‐)leaky confined aquifer. The drawdown response in the abstraction well, non‐Darcy region, and Darcy region is investigated, and sensitivity analysis is made to assess the impact of various controlling parameters. The results demonstrate that the intermediate and late‐stage drawdowns in the abstraction well and non‐Darcy region for the two‐region flow model are larger than the corresponding values for the non‐Darcy flow model. The drawdown in the Darcy region for the two‐region flow model is larger than that for the Darcy flow model throughout the pumping duration. The results of sensitivity analysis show that the drawdowns in the abstraction well, non‐Darcy region, and Darcy region are most sensitive to the non‐Darcy constant n, and is very sensitive to the well configuration, and horizontal hydraulic conductivity of the Darcy region.

Combined Well Multi-Parameter Logs and Low-Flow Purging Data for Soil Permeability Assessment and Related Effects on Groundwater Sampling

Cost-effective remediation is increasingly dependent on high-resolution site characterization (HRSC), which is supposed to be necessary prior to interventions. This paper aims to evaluate the use of low-flow purging and sampling water level data in estimating the horizontal hydraulic conductivity of soils. In a new quali-quantitative view, this procedure can provide much more information and knowledge about the site, reducing time and costs. In case of high heterogeneity along the well screen, the whole procedure, as well as the estimation method, could be less effective and rigorous, with related issues in the purging time. The result showed significant permeability weighted sampling, which could provide different results as the pump position changes along the well screen. The proposed study confirms this phenomenon with field data, demonstrating that the use of multiparameter well logs might be helpful in detecting the behaviour of low-permeability layers and their effects on purging and sampling. A lower correlation between low-flow permeability estimations and LeFranc test results was associated with high heterogeneity along the screen, with a longer purging time. In wells P43, MW08 and MW36, due to the presence of clay layers, results obtained differ for almost one order of magnitude and the purging time increases (by more than 16 min). However, with some precautions prior to the field work, the low-flow purging and sampling procedure could become more representative in a shorter time and provide important hydrogeological parameters such as hydraulic conductivity with many tests and high-resolution related results.

Groundwater flow numerical model to evaluate the water mass balance and flow patterns in Groundwater Circulation Wells (GCW) with varying aquifer parameters

Groundwater Circulation Wells (GCW) can be an effective in-situ remediation option allowing high mass recovery of contaminants in cases where contamination hotspots are located in saturated soil having low hydraulic conductivity. Traditional treatment options such as Pump&amp;Treat, Air Sparging (AS)/Soil Vapor Extraction (SVE) and Multi Phase Extraction (MPE) typically require long operation times and significant costs for long-term plume management. GCWs induce meaningful changes in the groundwater flow introducing vertical flows both downward and upward, generating a “circulation cell”, which facilitates contaminant desorption from the soil. This study aims to understand the effects of a GCW on an aquifer in terms of both groundwater flow directions and water balance. A groundwater numerical model was built using MODFLOW-2005 to simulate the effect of the hydraulic parameters of the aquifer on the hydraulic circulation pattern of the GCW. The use of particle tracking simulated by MODPATH 7 showed the circulation cells and the impact on groundwater directions induced by different configurations of hydraulic parameters. The water flowing into the cell comes from both the injection well and the surrounding aquifer and the model shows how the hydraulic parameters of the aquifer, in particular the horizontal and vertical hydraulic conductivity, have a paramount influence in determining the shape and dimension of the circulation cell. A water mass balance analysis was carried out. It allowed to predict the groundwater flows exchanges between the GCW system and the surrounding aquifer, and to verify the sensitivity of the water budget to specific aquifer parameters. The results of this study are useful for further understanding the hydraulics of a GCW remediation system in order to support the design and to predict its performance.

Spatial variability of leachate tables, leachate composition and hydraulic conductivity in a landfill stabilized by in situ aeration

Within the framework of the Dutch sustainable landfill project iDS, four compartments of the Dutch landfill Braambergen have been treated by in-situ aeration since 2017. The aeration infrastructure comprises 230 wells with a spacing of 15 to 20 m, distributed over an area of around 10 ha, intercepting a waste body of 1.2 × 106 t of contaminated soils, soil treatment residues, bottom ashes and construction and demolition waste. The wells, used in an alternating fashion for air injection and gas extraction, can also be used to monitor water tables within the waste body. In order to describe the spatial variability of waste hydraulics, design a larger scale leachate pumping test and, eventually, support model predictions of the site’s water balance and emission potential, analyses of leachate composition and pumping tests on individual wells have been conducted. The spatial variability of leachate quality and water tables is very high with no geospatial relationship between the sampling points. Each sampling point is representative of itself only. Large differences prevail not only between and across the compartments, but also between directly neighbouring wells. Both the small scale differences in leachate tables as well as in leachate quality indicate a spatial pattern of zones with low horizontal connectivity within the waste body. Recovery rates of drawdown in the wells yielded preliminary estimates of horizontal waste hydraulic conductivity in the order of 1×10-7 to 6×10-4 m/s.

Numerical Investigation of Hydraulic Conductivity Variation on Highway Slopes Made of Expansive Yazoo Clay

Expansive soils cover more than 25% of the total area of the United States and are subjected to shrink-swell behavior with moisture variation. With successive moisture and temperature variations over the seasons, the hydraulic conductivity of the expansive soil is subjected to change because of the development of shrinkage cracks which affect the vertical hydraulic conductivity, whereas the horizontal hydraulic conductivity remains negligibly constant. This affects the percolation behavior of the subgrade soil and, in turn, reduces the soil strength, as one of the major factors of slope failure. However, no study has been done on the change in the hydraulic properties of expansive soil with time and its effect on highway slopes. The current study intends to investigate the hydraulic conductivity and matric suction variation at different wet-dry cycles on highway slopes. An instantaneous profile method to investigate the changes in hydraulic conductivity during 1N to 5N wet-dry cycles was utilized. The finite element method in Plaxis was conducted to evaluate the effect of different frequencies and duration of rainfall on water intrusion, and the corresponding change in the matric suction of the highway slope. The selected rainfall pattern is evaluated at different intensities and durations of rainfall based on 100-years return periods. The flow analysis showed that the suction dropped at the highway slope with the presence of rainfall.

Optimized Pilot Point Emplacement Based Groundwater Flow Calibration Method for Heterogeneous Small-Scale Area

Groundwater flow modeling in a small-scale area requires practical techniques to obtain high accuracy results. The effectiveness of the model calibration is the most challenging for simulating the hydraulic head. In pursuit of this, we proposed an optimized groundwater flow calibration method based on the pilot point emplacement technique for a 3D small-scale area in this work. Subsequently, two emplacement structures were tested during the experimentation, the regular pilot point placement, and the middle head measurement down gradient (MHMDG) placement with two different densities. The parameter estimation (PEST) numerical code applying the kriging interpolation was used to estimate the hydraulic conductivity field by MODFLOW. Moreover, geological SGrid models were chosen for the conceptual model. Thirty-seven observation wells were used for experimental simulations to test the proposed method in a heterogeneous confined aquifer. The result shows that the small-scale modeling was complicated, and the studying area presented a significant heterogeneity in horizontal hydraulic conductivity. The middle head measurement down gradient (MHMDG) pilot point case with the larger density gave the best R-squared 0.901 and minimum residual error of 0.0053 m compared to 0.880 and 0.078 m, respectively, for the regular placement. The calibration accuracy depended on the frequency and the emplacement of the pilot point. Therefore, the initial value should be technically selected to minimize the computation burden. The proposed techniques help to improve the groundwater flow model calibration based on the pilot point methodology for groundwater resources management.

Assessment of Groundwater Flow Dynamics Using MODFLOW in Shallow Aquifer System of Mahanadi Delta (East Coast), India

Despite being a biodiversity hotspot, the Mahanadi delta is facing groundwater salinization as one of the main environmental threats in the recent past. Hence, this study attempts to understand the dynamics of groundwater and its sustainable management options through numerical simulation in the Jagatsinghpur deltaic region. The result shows that groundwater in the study area is extensively abstracted for agricultural activities, which also causes the depletion of groundwater levels. The hydraulic head value varies from 0.7 to 15 m above mean sea level (MSL) with an average head of 6 m in this low-lying coastal region. The horizontal hydraulic conductivity and the specific yield values in the area are found to vary from 40 to 45 m/day and 0.05 to 0.07, respectively. The study area has been calibrated for two years (2004–2005) by using these parameters, followed by the validation of four years (2006–2009). The calibrated numerical model is used to evaluate the net recharge and groundwater balance in this study area. The interaction between the river and coastal unconfined aquifer system responds differently in different seasons. The net groundwater recharge to the coastal aquifer has been estimated and varies from 247.89 to 262.63 million cubic meters (MCM) in the year 2006–2007. The model further indicates a net outflow of 8.92–9.64 MCM of groundwater into the Bay of Bengal. Further, the outflow to the sea is preventing the seawater ingress into the shallow coastal aquifer system.