Research for Investigating and Managing Soil Contamination Caused by Winter Maintenance in Cold Regions

Diseases & disorder

Data assimilation of in situ soil moisture measurements in hydrological models: first annual doctoral progress report, work plan and achievements

Water scarcity and the presence of water of good quality is a serious public concern since it determines the availability of water to society. Water scarcity especially in arid climates and due to extreme droughts related to climate change drive water use technologies such as irrigation to become more efficient and sustainable. Plant root water and nutrient uptake is one of the most important processes in subsurface unsaturated flow and transport modeling, as root uptake controls actual plant evapotranspiration, water recharge and nutrient leaching to the groundwater, and exerts a major influence on predictions of global climate models. To improve irrigation strategies, water flow needs to be accurately described using advanced monitoring and modeling. Our study focuses on the assimilation of hydrological data in hydrological models that predict water flow and solute (pollutants and salts) transport and water redistribution in agricultural soils under irrigation. Field plots of a potato farmer in a sandy region in Belgium were instrumented to continuously monitor soil moisture and water potential before, during and after irrigation in dry summer periods. The aim is to optimize the irrigation process by assimilating online sensor field data into process based models. Over the past year, we demonstrated the calibration and optimization of the Hydrus 1D model for an irrigated grassland on sandy soil. Direct and inverse calibration and optimization for both heterogeneous and homogeneous conceptualizations was applied. Results show that Hydrus 1D closely simulated soil water content at five depths as compared to water content measurements from soil moisture probes, by stepwise calibration and local sensivity analysis and optimization the Ks, n and α value in the calibration and optimization analysis. The errors of the model, expressed by deviations between observed and modeled soil water content were, however, different for each individual depth. The smallest differences between the observed value and soil-water content were attained when using an automated inverse optimization method. The choice of the initial parameter value can be optimized using a stepwise approach. Our results show that statistical evaluation coefficients (R2, Ce and RMSE) are suitable benchmarks to evaluate the performance of the model in reproducing the data. The degree of water stress simulated with Hydrus 1D suggested to increase irrigation at least one time, i.e. at the beginning of the simulation period and further distribute the amount of irrigation during the growing season, instead of using a huge amount of irrigation later in the season. In the next year, we will further look for to the best method (using soft data and methods for instance PTFs, EMI, Penetrometer) to derive and predict the spatial variability of soil hydraulic properties (saturated hydraulic conductivity) of the soil and link to crop yield at the field scale. Linear and non-linear pedotransfer functions (PTFs) have been assessed to predict penetrometer resistance of soils from their water status (matric potential, ψ and degree of saturation, S) and bulk density, ρb, and some other soil properties such as sand content, Ks etc. The geophysical EMI (electromagnetic induction) technique provides a versatile and robust field instrument for determining apparent soil electrical conductivity (ECa). ECa, a quick and reliable measurement, is one of ancillary properties (secondary information) of soil, can improve the spatial and temporal estimation of soil characteristics e.g., salinity, water content, texture, prosity and bulk density at different scales and depths. According to previous literature on penetrometer measurements, we determined the effective stress and used some models to find the relationships between soil properties, especially Ks, and penetrometer resistance as one of the prediction methods for Ks. The initial results obtained in the first yearshowed that a new data set would be necessary to validate the results of this part. In the third year, quasi 3D-modelling of water flow at the field scale will be conducted. In this modeling set -up, the field will be modeled as a collection of 1D-columns representing the different field conditions (combination of soil properties, groundwater depth, root zone depth). The measured soil properties are extrapolated over the entire field by linking them to the available spatially distributed data (such as the EMI-images). The data set of predicted Ks and other soil properties for the whole field constructed in the previous steps will be used for parameterising the model. Sensitivity analysis ‘SA’ is essential to the model optimization or parametrization process. To avoid overparameterization, the use of global sensitivity analysis (SA) will be investigated. In order to include multiple objectives (irrigation management parameters, costs, …) in the parameter optimization strategy, multi-objective techniques such as AMALGAM have been introduced. We will investigate multi-objective strategies in the irrigation optimization

Optimising Agronomic Options At The Farm Scale

Strategic planning and policy development for environmentally sustainable and economically viable management options for the rice based farming systems require the assessment of management options using mathematical models which integrate our understanding of water and salt movement with economic considerations at both the farm and regional scales. This project also had strong links with LWRRDC/MIL/CSIRO project on optimising irrigation intensities in the Murray Valley. During this project a standalone farm scale hydrological economic model SWAGMAN Farm (Salt Water and Groundwater MANagement) was developed and customised for situations in the Coleambally and Murray Irrigation Areas. The model processes were developed and refined by using feed back from irrigation managers, regulators and community groups. The following major achievements have been made: · Collection of crop, soil, irrigation, climatic and economic data sets for fourteen farms in the Murray Irrigation Districts · Rigorous validation of model processes by applying the model to fourteen farms with a range of enterprise, soil and groundwater conditions. · Development of simulation and optimisation modes in SWAGMAN Farm to assess environmental and economic impacts of existing and optimal cropping patterns · Various improvements of water and salt balance processes to suit conditions in the Murray Districts and the Coleambally Irrigation Area · Incorporation of soil water content accounting which provides flexibility in the representation of various starting soil profile water content conditions, water availability to crops and rational computation of recharge and watertable rise during the cropping and fallow periods · Development of a Windows based GAMS independent version of SWAGMAN Farm. GAMS (General Algebraic Modelling System) was an expensive software platform for the previous version with inflexible licence requirements. The new version written in C++ language uses Microsoft Access databases and will be linked with a GIS interface in near future. These sensitivity runs and model developments gained the confidence of members of the steering committee who provided vital inputs throughout this project. While considerable progress was made, they see the need for the work to continue to the stage where it can be applied to assist strategic planning and policy development, taking into account local regional conditions. Parallel to the modelling project an intensive paddock water monitoring project titled “Rigorously determined water balance benchmarks for irrigated crops and pasture’ was also initiated by the steering committee with the assistance of CSIRO, MIL, NSW Agriculture and LWRRDC. The purpose of the monitoring project was to further customise SWAGMAN Farm to local conditions and to validate the model results with the field data. Since monitoring projects take significant time in setting up and calibrating equipment, data analysis has only recently started, however initial comparisons of model results with the field results suggest that the improved SWAGMAN Farm can reasonably simulate field situations. However this work needs to continue to maximise the benefits of the paddock water balance monitoring. However, due to the wide range of groundwater, enterprise and soil conditions in the irrigation areas, SWAGMAN Farm needs to be applied to every farm to develop soundly based policy options. The need for application to individual farms is further driven by the complex regional groundwater interactions causing reversal (downward to upward and local discharge zones) of leakage rates in parts of the irrigation areas e.g. Murray Valley. This project has demonstrated that it is possible to develop methodology which helps assess optimal irrigation intensity within a multitude of biophysical and socio-economic constraints. The methods developed have scientific validity in capturing and representing key processes, and have community acceptance as a way of examining options that are important to them

Recent Developments and Applications of the HYDRUS Computer Software Packages

The HYDRUS-1D and HYDRUS (2D/3D) computer software packages are widely used finite-element models for simulating the one- and two- or three-dimensional movement of water, heat, and multiple solutes in variably saturated media, respectively. In 2008, Šimůnek et al. (2008b) described the entire history of the development of the various HYDRUS programs and related models and tools such as STANMOD, RETC, ROSETTA, UNSODA, UNSATCHEM, HP1, and others. The objective of this manuscript is to review selected capabilities of HYDRUS that have been implemented since 2008. Our review is not limited to listing additional processes that were implemented in the standard computational modules, but also describes many new standard and nonstandard specialized add-on modules that significantly expanded the capabilities of the two software packages. We also review additional capabilities that have been incorporated into the graphical user interface (GUI) that supports the use of HYDRUS (2D/3D). Another objective of this manuscript is to review selected applications of the HYDRUS models such as evaluation of various irrigation schemes, evaluation of the effects of plant water uptake on groundwater recharge, assessing the transport of particle-like substances in the subsurface, and using the models in conjunction with various geophysical methods

QUANTIFYING THE SOIL FREEZING CHARACTERISTIC CURVE IN LABORATORY AND FIELD SOILS

The soil freezing characteristic curve (SFC) controls the hydraulic properties of soils and is especially crucial in understanding snowmelt infiltration and runoff, frost heave formation and thawing settlement in frozen soils. The SFC can be modelled by combining information from the soil moisture characteristic curve of unfrozen soils (SMC) with the Generalized Clapeyron Equation (GCE). While such an approach is straightforward and involves no additional free parameters, the resulting SFC is not always consistent with those observed in the laboratory and field. This study was therefore designed to obtain both laboratory and field data that quantifies the SMC and SFC for different soil textures and salinities and to compare the results with those obtained from the GCE and other alternative relationships. In the laboratory, the SMC of a silica sand was measured using a Hydraulic Property Analyzer (HYPROP). The SFC of the same sand was measured using a series of column experiments with controlled total water content and pore-water salinity. In the field, data were collected from the St Denis National Wildlife Area (SDN), a mixed grassland cropped site in the Canadian prairies in Saskatchewan and the Boreal Ecosystem Research and Monitoring Sites (BERMS) Old Jack Pine (OJP) site in Saskatchewan, Canada. Three alternative models for the SFC were developed (capillary, salt exclusion, and the combined capillary salt models), and compared with observed data from the laboratory and field experiments. The results show that the column experiments were successful in producing well-defined SFCs that matched expectations, where the form of the decrease in liquid water content with temperature was similar to the form of the SMC. Increasing the salinity resulted in enhanced freezing point depression as was expected. The field SFCs followed the same trend as those measured in the laboratory. The modelling results suggest that salinity is a dominant control on the SFC in real soils and that the combined capillary salt model is the most realistic of the three models considered in predicting liquid water content in frozen soils

Effects of Climate Type and Temporal Variability in Meteorological Input Data in Modeling of Salt Transport in Unsaturated Soils

Oilfield produced brine is a major source of salt contamination in soil and groundwater. Salt transport in the upper soil layers is controlled by the atmospheric interactions via infiltration of meteoritic water. In lower layers, it is controlled by fluctuations in groundwater table, which are also linked to atmospheric interactions via groundwater recharge. Therefore, climate is an important factor in the movement of contaminants in the unsaturated zone. A one-dimensional variably saturated flow and transport model with soil atmospheric boundary condition was used to estimate the effect of climate type and soil texture on soil water and salt dynamics in variably saturated soils. Numerical simulations were run with Hydrus-1D, using daily and sub-daily climate. Simulations were run for nine-year climate datasets for ten different ecoclimatic locations in Alberta, Canada. Results show that flow and transport are function of climate type. Results also indicated that higher temporal resolutions of precipitation data resulted in higher net infiltration values. Higher net infiltration values resulted in faster solute displacement, especially, if the precipitation events were assumed to occur outside the evaporation hours. Minimal to no interaction was observed between groundwater table and atmosphere in coarse-grained soil material, especially in wetter climatic conditions. Keywords: Variably saturated soils, climate, soil-atmosphere boundary, water and salt dynamics, groundwater tabl

The hydrosalinity module of ACRU agrohydrological modelling system (ACRUsalinity) : module development and evaluation.

Thesis (M.Sc.)-University of Natal, Pietermaritzburg, 2003.Water is characterised by both its quantity (availability) and its quality. Salinity, which is one of the major water quality parameters limiting use of a wide range of land and water resources, refers to the total dissolved solutes in water. It is influenced by a combination of several soil-water-salt-plant related processes. In order to develop optimum management schemes for environmental control through relevant hydrological modelling techniques, it is important to identify and understand these processes affecting salinity. Therefore, the various sources and processes controlling salt release and transport from the soil surface through the root zone to groundwater and streams as well as reservoirs are extensively reviewed in this project with subsequent exploration of some hydro salinity modelling approaches. The simulation of large and complex hydrological systems, such as these at a catchment scale, requires a flexible and efficient modelling tool to assist in the assessment of the impact of land and water use alternatives on the salt balance. The currently available catchment models offer varying degrees of suitability with respect to modelling hydrological problems, dependent on the model structure and the type of the approach used. The A CR U agrohydrological modelling system, with its physically-conceptually based characteristics as well as being a multi-purpose model that is able to operate both as a lumped and distributed model, was found to be suitable for hydro salinity modelling at a catchment scale through the incorporation of an appropriate hydro salinity module. The main aim of this project was to develop, validate and verify a hydro salinity module for the ACRU model. This module is developed in the object-oriented version of ACRU, viz. ACRU2000, and it inherits the basic structure and objects of the model. The module involves the interaction of the hydrological processes represented in ACRU and salinity related processes. Hence, it is designated as ACRUSalinity. In general, the module is developed through extensive review of ACRU and hydrosalinity models, followed by conceptualisation and design of objects in the module. It is then written in Java object-oriented programming language. The development of ACRUSalinity is based mainly on the interaction between three objects, viz. Components, Data and Processes. Component objects in ACRU2000 represent the physical features in the hydrological system being modelled. Data objects are mainly used to store data or information. The Process objects describe processes that can take place in a conceptual or real world hydrological system. The Process objects in ACRUSalinity are grouped into six packages that conduct: • the initial salt load determination in subsurface components and a reservoir • determination of wet atmospheric deposition and salt input from irrigation water • subsurface salt balance, salt generation and salt movement • surface flow salt balance and salt movement • reservoir salt budgeting and salt routing and • channel-reach salt balancing and, in the case of distributed hydro salinity modelling, salt transfer between sub-catchments. The second aim of the project was the validation and verification of the module. Code validation was undertaken through mass balance computations while verification of the module was through comparison of simulated streamflow salinity against observed values as recorded at gauging weir UIH005 which drains the Upper Mkomazi Catchment in KwaZuluNatal, South Africa. Results from a graphical and statistical analysis of observed and simulated values have shown that the simulated streamflow salinity values mimic the observed values remarkably well. As part of the module development and validation, sensitivity analysis of the major input parameters of ACRUSalinity was also conducted. This is then followed by a case study that demonstrates some potential applications of the module. In general, results from the module evaluation have indicated that ACRUSalinity can be used to provide a reasonable first order approximation in various hydrosalinity studies. Most of the major sources and controlling factors of salinity are accommodated in the ACRUSalinity module which was developed in this project. However, for a more accurate and a better performance of the module in diversified catchments, further research needs to be conducted to account for the impact of salt loading from certain sources and to derive the value of some input parameters to the new module. The research needs include incorporation in the module of the impact of salt loading from fertilizer applications as well as from urban and industrial effluents. Similarly, further research needs to be undertaken to facilitate the module's conducting salt routing at sub-daily time step and to account for the impact of bypass flows in heavy soils on the surface and subsurface salt balances

INVESTIGATION OF SOIL-WATER PROPERTIES FOR RECLAIMED OIL SANDS, FIRE-DISTURBED, AND UNDISTURBED FORESTED SOILS IN NORTHERN ALBERTA, CANADA

Oil Sands mining operations in Northern Alberta, Canada generate large areas that contain marginal soil conditions and must be overlaid with reclamation substrate. In order to expedite revegetation efforts, salvaged peat is often incorporated with mineral subsoil to compose a peat:mineral mix (PMM) to act as a soil cover. However, the soil water characteristics and physical properties of these covers are poorly understood for reclamation. Therefore, the objective of this study was to determine the soil physical properties and soil water characteristics of reclaimed covers compared to naturally disturbed sites (i.e. fire) and undisturbed reference sites. Soil samples were collected in the summer of 2012 and 2013 from three reclaimed PMM soil covers, one recently fire-disturbed natural site and one undisturbed reference site. Of all the nutrients analyzed, soil phosphorous (PO4-) concentrations were significantly lower in the reclaimed soils compared to the disturbed and undisturbed natural sites. Near-saturated hydraulic conductivity (Kns) for water transmission through the soil were measured, along with soil water retention curves developed for describing moisture storage. Topsoil (0-20 cm) Kns measurements revealed no statistical difference between reclaimed and natural sites and extremely high variation was detected at all sites. Three different models for estimating Kns also revealed only minor differences between methods, although high variation within each site prevented conclusions on whether the mini-disc infiltrometer and associated Kns models was an appropriate tool for measuring hydraulic conductivity in peat-dominated reclaimed soils. Soil water retention curves were developed by tension table and pressure plate methods on intact soil cores. Five soil hydraulic models – three unimodal and two bimodal - were fit to the retention curves and parameterized. Bimodal models showed a superior fit compared to the unimodal models at all three reclaimed and one undisturbed sites. Bimodal trends are typically associated with natural soils exhibiting a high degree of soil aggregation and associated heterogeneous pore structure. The fire-burnt site showed a unimodal trend possibly as the result of its sandy texture and lack of aggregation. These model fits suggest that a juvenile PMM have similar soil water storage characteristics to certain highly-structured natural soil as provided by its peat additions. Available water holding capacity was determined by both soil core and Land Capability Classification System methods. No differences were detected between techniques and a mesic soil moisture regime was predicted at all sites. This study found that juvenile PMM soil covers exhibited similar soil-water characteristics to a well-aggregated, undisturbed forested soil after only a few years post-placement. These results establish a comparative baseline for future soil research on reclaimed tailing ponds, as well as provide the necessary soil-water relationships for watershed and/or regional scale hydrological modelling

Modelling the hydraulic behaviour of unsaturated soils and application to the numerical and experimental study of capillary barrier systems

Nowadays, considerable research effort is addressed towards the mitigation of the effects of climate change. The development and application of low-carbon solutions in geotechnical engineering practice is essential for the mitigation of the effects of climate change. Under unsaturated conditions, suction has a beneficial effect on the shear strength of soils but it may easily vanish after intense rainfall. If suction can be maintained in the ground in the long term, its effect can be taken into account in geotechnical design as a natural soil reinforcement, and this can lead to low-carbon designs. Capillary barrier systems can be used to prevent or limit the infiltration of water into the ground, thereby maintaining suction in the long term. Capillary barrier systems are soil covers made of a finer-grained layer overlying a coarser-grained layer. Under unsaturated conditions, the coarser layer is typically at very low degree of saturation and the corresponding unsaturated hydraulic conductivity is so low that it can be considered as impermeable. In these conditions, rainwater is stored in the finer layer and subsequently removed by evapotranspiration or lateral drainage. Accurate modelling of the hydraulic behaviour of unsaturated soils is crucial for the interpretation of the behaviour of capillary barrier systems. The first part of this thesis is focused on the interpretation and modelling of the hydraulic behaviour of unsaturated soils. A critical review of the interpretation of the hydraulic behaviour of unsaturated soils leads to the identification of inaccuracies and inconsistencies in existing conventional hydraulic constitutive models for the soil water retention curve (SWRC) and the soil hydraulic conductivity curve (SHCC). These inaccuracies and inconsistencies relate particularly to the very high degree of saturation range and the very low degree of saturation range. At very high values of degree of saturation, the apparent SWRC measured in a wetting test in the laboratory may differ from the true SWRC, because of the occurrence of air trapping. Analytical and numerical modelling of the phenomenon of gas trapping during wetting shows that, once air trapping occurs, the apparent SWRC depends upon many aspects of the wetting test conditions and is not a fundamental representation of the soil behaviour. The only correct way to represent the occurrence and influence of air trapping during wetting within numerical modelling of boundary value problems is to use the true SWRC in combination with a gas conductivity expression that goes to zero when the gas phase becomes discontinuous. At low values of degree of saturation, conventional models for the SHCC are typically inaccurate. A new predictive hydraulic conductivity model, accurate for the full range of degree of saturation is developed. The hydraulic conductivity is divided into two components: a bulk water component and a liquid film component; each of which varies with degree of saturation or suction. This model is coupled with SWRC models improved at low degree of saturation. Hydraulic hysteresis is subsequently introduced in the SWRC and SHCC by using an original bounding surface approach. The new hydraulic models were validated against experimental data. This set of hydraulic models forms a complete framework of hydraulic constitutive models for unsaturated soil, which was implemented in the numerical finite element software Code_Bright. Finally, these new models are applied to the numerical study of the hydraulic behaviour of capillary barrier systems (CBSs). The new hydraulic conductivity model is able to predict the behaviour of CBSs better than conventional models and the numerical modelling highlights the role of liquid film flow, which is often neglected. Water retention hysteresis is shown to have a significant impact on: i) movement and redistribution of water within the finer layer of a CBS; ii) the phenomenon of water breakthrough across the interface between the finer and coarser layers of a CBS and the subsequent restoration of the CBS after infiltration at the ground surface ceases; iii) the prediction of evaporation from a CBS into the atmosphere. In the second part of this thesis, an original concept of multi-layered capillary barrier systems is presented and analysed. The use of multi-layered CBSs may lead to a substantial increase of the water storage capacity of CBSs, and hence their effectiveness. A simplified method of analysis of multi-layered CBSs is developed and validated against results from numerical finite element analyses and laboratory physical tests. Parametric analyses show the impact of number of layers, materials thickness of the CBS and infiltration rate on the water storage capacity of multi-layered CBS. Laboratory infiltration tests on different multi-layered CBSs are performed demonstrating the efficiency of multi-layered CBSs and clarifying their hydraulic behaviour. In the third part of the thesis, advanced numerical thermo-hydraulic finite element analyses and limit analyses are performed to assess the application of CBSs for suction control and slope stability purposes in the long term. It is demonstrated that sloping CBSs are effective at maintaining suction in the ground and preventing rainfall-induced slope instability for different climatic conditions. In addition, the role of different parameters such as materials, thickness of the CBS and slope height are assessed. In particular, it is shown that CBSs with the finer layer made of a relatively fine material, such as silty sand, are more effective in dry and warm climates due to their ability of storing water, which can subsequently be removed by evaporation, whereas CBSs with a finer layer made of a slightly coarser material, such as fine sand, are more effective in wet and cool climates due to their ability of diverting water laterally down the slope. The effectiveness of solutions aimed to extend the application of CBS to slope of any height, such as the use of multi-layered CBSs and the use of multiple drains, is finally demonstrated

Numerical modelling of unsaturated flow in vertical and inclined waste rock layers using the seep/w model

Conventional disposal of waste rock results in the construction of benches with interbedded fine and coarse layers dipping at the angle of repose. The waste rock benches are typically 20-meters in height and are constructed in a vertical sequence to form waste rock dumps commonly greater than 100-meters high. The interbedded structure influences the flow pathways for infiltration water within the waste rock profile. Preferential flow pathways develop when one material becomes more conductive than the surrounding material. The flow of meteoric waters through the interbedded waste rock structure is difficult to describe since the dumps are constructed above natural topography and are generally unsaturated. Two previous research studies were undertaken at the University of Saskatchewan to study end dumped waste rock piles and the relationship to preferential flow for unsaturated conditions. The first study was conducted during the excavation of a large waste rock pile at Golden Sunlight Mine in Montana (Herasymuik, 1996). Field observations showed that the waste rock pile consisted of steeply dipping fine and coarse-grained layers. The results of further laboratory analysis indicated the potential for preferential flow through the fine-grained material under conditions with negative pore-water pressures and unsaturated flow. The second study investigated the mechanism for preferential flow in vertically layered, unsaturated soil systems (Newman, 1999). The investigation included a vertical two-layer column study and a subsequent numerical modelling program showing that water prefers to flow in the finer-grained material. The preferential flow path was determined to be a function of the applied surface flux rates and the unsaturated hydraulic conductivity of the fine-grained material layer. A numerical modelling program to evaluate preferential flow was conducted for the present study in an inclined four-layer system consisting of alternating fine and coarse-grained waste rock. The numerical modelling program was undertaken using the commercial seepage software package, Seep/W, that is commonly used by geotechnical engineers. The result obtained using Seep/W showed preferential flow to occur in the fine-grained layer. However, difficulties with respect to convergence under low flow conditions with steep hydraulic conductivity functions were encountered. A comprehensive sensitivity analysis was completed to investigate the factors that influence convergence in the Seep/W model including: convergence criteria, mesh design and material properties. It was found that the hydraulic conductivity function used for the coarse-grained material was the most important factor. The problem of the steep slope for the hydraulic conductivity function specified for the coarse-grained material was solved by progressively decreasing the slope of the hydraulic conductivity function at 10-8 m/s (for applied fluxes of 10-7 m/s or less). The sensitivity analysis showed that the manipulation of the hydraulic conductivity function had insignificant changes in the flux distribution between the waste rock layers and great significance for achieving convergence. Based on the discoveries of the sensitivity analysis, a 20-meter high multi-layer waste rock profile inclined at 50º with an applied flux of 7.7e10-9 m/s equal to the annual precipitation at the Golden Sunlight Mine was successfully simulated. A parametric study was subsequently conducted for an applied flux rate of 10-5 m/s for slope heights of 1-meter to 20 meters with slope angles varying between 45º and 90º. The parametric study demonstrated that flow in a multi-layered waste rock dump is a function of inclination, contact length between the layers, and the coarse and fine-grained hydraulic properties for the waste rock. An alternative numerical modelling technique based on a modified Kisch solution was also used to investigate preferential flow. The Kisch method helped to verify and simplify the numerical problem as well as to illustrate the mechanics of preferential flow in a two-layered system. In general, commercial seepage modeling packages are powerful and useful tools that are designed to adequately accommodate a wide range of geotechnical problems. The results of this research study indicate that Seep/W may not be the best-suited tool to analyze unsaturated seepage through sloped waste rock layers. However, numerical modelling is a process and working through the process helps to enhance engineering judgment. The Seep/W model provided an adequate solution for a simplified simulation of unsaturated seepage through waste rock layers. The modified Kisch solution independently verified the solution and provided additional confidence for the results of Seep/W model