Flow In Unsaturated Soils Research Articles

Thermally Induced Moisture Flow in a Silty Sand under a 1-D Thermal Gradient

Thermally induced moisture flow in unsaturated soils involves complex coupled thermal–hydro processes with the moisture flow in both the vapor and liquid phases. The accurate measurement of the moisture flow in unsaturated sands remains a challenging task due to low moisture migration, the temperature effect on moisture sensors, and the gravity effect on moisture flow. This study aims to accurately measure transient moisture flow, heat transfer, and thermal conductivity in a silty sand with 35% non-plastic fines in a closed heat cell with a controlled 1-D temperature gradient. The heat cell consists of two temperature-controlled heat exchanger plates, heat flux sensors, moisture sensors, thermocouples, and thermal conductivity sensors. The soil moisture sensors were calibrated in the test soil at room temperature and then at elevated incremental temperatures. Soil samples compacted at various initial moisture contents were tested under a constant 1-D temperature gradient of 4 °C/cm. Soil moisture redistribution, temperature, and thermal conductivity profiles were determined from the test results. Transient temperature responses indicated that a lower initial moisture content led to a higher temperature drop after reaching the peak, or a more concaved temperature profile in a steady state due to enhanced moisture migration driven by the temperature gradients. Dry soils exhibited uniform thermal properties, while moist soils showed varying thermal conductivity profiles. A critical moisture content was identified when the maximum moisture migration occurred. Thermal conductivity in soils increased with the distance from the heat source due to thermally induced moisture migration. These findings provide valuable insights into coupled moisture–heat flow dynamics in unsaturated sands.

Influence of 3D subsurface flow on slope stability for unsaturated soils

The occurrence of rainfall-induced slope failures has become more frequent due to the effect of climate change. Hence, various studies have been conducted to analyse the effect of rainfall infiltration on slope stability. Physically-based hydrological models have been commonly used with slope stability models such as the infinite slope model to develop slope susceptibility maps. However, a combination of three-dimensional (3D) water balance model with 3D limit equilibrium method (LEM) has not been commonly used. Hence, in this study, a water balance model, GEOtop was used to investigate the influence of subsurface flow in unsaturated soil under extreme rainfall conditions on regional slope stability in 3D directions. The results from the GEOtop model were used as inputs for 3D LEM slope stability analysis performed using the Scoops3D software to obtain the factor of safety (FOS) map for the region. Four slopes within the region were then selected to be modelled in the two-dimensional (2D) seepage and slope stability analyses, SEEP/W and SLOPE/W. Results from the detailed study showed that the pore-water pressures (PWPs) from the 3D water balance analyses were found to be higher than the 2D seepage analyses. Under similar PWP conditions, the FOS from the 2D slope stability analysis was observed to be lower than the 3D analysis for two out of the four slopes. However, the combined 3D water balance and slope stability analyses produced lower FOS compared to the 2D seepage and slope stability analyses due to the higher PWPs in the 3D water balance analyses. Therefore, this study highlights the importance of considering the 3D subsurface flow in unsaturated soil given that it has a significant influence on the FOS of slopes.

Three-Dimensional Model for Bioventing: Mathematical Solution, Calibration and Validation

Bioventing is an established technique extensively employed in the remediation of soil contaminated with petroleum hydrocarbons. In this study, the objective was to develop an improved foundational bioventing model that characterizes gas flow in vadose zones where aqueous and non-aqueous phase liquid (NAPL) are present and immobile, accounting for interphase mass transfer and first order biodegradation kinetics. By incorporating a correlation for the biodegradation rate constant, which is a function of soil properties including initial population of petroleum degrader microorganisms in soil, sand content, clay content, water content, and soil organic matter content, this model offers the ability to integrate a specific biodegradation rate constant tailored to the soil properties for each site. The governing equations were solved using the finite volume method in OpenFOAM employing the “porousMultiphaseFoam v2107” (PMF) toolbox. The equation describing gas flow in unsaturated soil was solved using a mixed pressure-saturation method, where calculated values were employed to solve the component transport equations. Calibration was done against a set of experimental data for a meso-scale reactor considering contaminant volatilization rate as the pre-calibration parameter and the mass transfer coefficient between aqueous and NAPL phase as the main calibration parameter. The calibrated model then was validated by simulating a large-scale reactor. The modelling results showed an error of 2.9% for calibrated case and 4.7% error for validation case which present the fitness to the experimental data, proving that the enhanced bioventing model holds the potential to improve predictions of bioventing and facilitate the development of efficient strategies to remediate soil contaminated with petroleum hydrocarbons.

Two‐Dimensional Analytical Solution for Transient Flow in Unsaturated Soils Considering Hydromechanical Coupling

AbstractThis paper presents a two‐dimensional solution for unsaturated transient seepage flow in a trapezoidal region using analytical solutions for flow in a series of rectangular regions. The coupled formulation considers the interaction among fluid flow due to differences in head and displacement of soil particles. The solution in each rectangular region is derived using Laplace Transform and Discrete Fourier Series for two top boundary conditions: specified pressure head and specified flow rate. The accuracy of the proposed solution is verified by comparing the results against those attained from the finite difference method. The proposed solution is applied to two example problems, demonstrating its efficacy and accuracy. The findings show a significant difference in the coupled and uncoupled results for fine‐grained soils possessing a small Gardner's coefficient. Additionally, the uncoupled pressure heads advanced quicker to a steady state than the coupled ones for soils with a small Gardner's coefficient. The coupling effect becomes less prominent as Gardner's coefficient increases. This study is the first attempt in the literature to provide a solution for unsaturated flow in a trapezoidal or non‐rectangular domain using analytical solution techniques, which can better represent complex real‐world applications (e.g., slopes, embankments, dams).

Modeling water flow in unsaturated soils through physics-informed neural network with principled loss function

Modeling water flow in unsaturated soils is crucial in geotechnical practice. Nowadays, the physics informed neural network (PINN) is gaining popularity in solving the Richardson Richards equation (RRE) thanks to its mesh-free, physics-constrained, and data-driven properties. Despite several successful applications in modelling 1D infiltration problems, its capability and stability to deal with more complicated boundary conditions and multidimensional problems still need to be examined. This paper investigates the impacts of the loss weights and random state on the performance of the RRE-solving PINNs and possible solutions to mitigate such impacts. Two loss-balanced PINNs, GN-PINN and PLF-PINN, were compared to the baseline PINN in modelling three unsaturated groundwater flow problems. The results show that the performance of the baseline PINN severely depends on the loss weight configurations and random states. While GN-PINN’s tendency to ignore the train loss term makes it infeasible for solving RRE, PLF-PINN can strike a good balance between loss terms and hence enhance PINN’s robustness against loss weight initialization and random state greatly.

Effect of Long-Term Semiarid Pasture Management on Soil Hydraulic and Thermal Properties

Semiarid pasture management strategies can affect soil hydraulic and thermal properties that determine water fluxes and storage, and heat flow in unsaturated soils. We evaluated long-term (>10 years) perennial and annual semiarid pasture system effects on saturated hydraulic conductivity (ks), soil water retention curves (SWRCs), soil water thresholds (i.e., volumetric water content (θv) at saturation, field capacity (FC), and permanent wilting point (PWP); plant available water (PAW)), thermal conductivity (λ), and diffusivity (Dt) within the 0-20 cm soil depth. Forage systems included: Old World bluestem (Bothriochloa bladhii) + legumes (predominantly alfalfa (Medicago sativa)) (OWB-legume), native grass-mix (native), alfalfa + tall wheatgrass (Thinopyrum ponticum) (alfalfa-TW), and annual grass-mix (annual) pastures on a clay loam soil; and native, teff (Eragrostis tef), OWB-grazed, and OWB-ungrazed pastures on a sandy clay loam soil. The perennial OWB-legume and native pastures had increased soil organic matter (SOM) and reduced bulk density (ρb), improving ks, soil water thresholds, λ, and Dt, compared to annual teff and alfalfa-TW (P < 0.05). Soil λ, but not Dt, increased with increasing θv. Grazed pastures decreased ks and water retention compared to other treatments (P < 0.05), yet did not affect λ and Dt (P > 0.05), likely due to higher ρb and contact between particles. Greater λ and Dt at saturation and PWP in perennial versus annual pastures may be attributed to differing SOM and ρb, and some a priori differences in soil texture. Overall, our results suggest that perennial pasture systems are more beneficial than annual systems for soil water storage and heat movement in semiarid regions.

Influence of Soil Heterogeneity on Water Flow and Solute Transport Characterized by Dye Tracer Experiments

Soil heterogeneity is a key factor affecting horizontal water flow and solute transport in unsaturated soil, in which particle distribution, pore structure, and pore connectivity in the soil all present fractal characteristics. The initial water content of soil has significant influence in the resulting heterogeneity of the soil structure, which can affect the water flow and solute transport. In this study, through a series of horizontal transport laboratory simulation experiments in soil columns, the initial water content dependency of transport was elucidated using the fractal Richards’ equation (FRE) model. We first observed that water flows faster in soil columns with higher initial water content, but the law is opposite in the initial process of water flow. By analyzing the variation of parameter values in the FRE model, we speculated that the abnormal phenomenon of early diffusion is caused by the heterogeneity of the soil structure. To elucidate the mechanisms of the water content’s dependency of the solute transport process and to identify the circumstance of altering of flow regime, a series of dye tracer experiments were conducted. Results show that in soil columns with low water content, the inflow of external fluid leads to the agglomeration of soil particles. Combined with matric suction, the heterogeneity of the soil structure is enhanced, which affects the formation of water flow and solute transport paths. It even leads to preferential flow in unsaturated soil columns with low water content.

Numerical investigation on three-phase flow in unsaturated soil considering porosity effects on soil hydraulic properties

Ground contamination by mineral oil and hydrocarbons is a serious problem worldwide. These non-aqueous phase liquid (NAPL) represents long-term contamination sources to the soil, groundwater, and ecological environment. In the existing numerical simulation models utilized in most simulation programs, the relation between porosity and the hydraulic properties of unsaturated soils is highly simplified as nonlinear. However, the nonlinear porosity effect on soil permeability and the capillary pressures cannot be well considered in this way. In this study, a new mathematical model has been developed to incorporate porosity effects into the hydraulic properties of soils, including the retention behaviour and permeability function of NAPL and water. This model has been implemented in MATLAB using the finite difference method and verified by a centrifuge test about NAPL infiltration. Then, a series of parametric studies will be carried out to investigate the multi-phase flow under a continuously leaking NAPL source. The influence of porosity magnitude and distribution will be investigated. Special attention will be paid to the influence of porosity distribution by soil consolidation on NAPL flow, which is often ignored by the existing simulations using constant porosity values.

UnSaLuDo: The development of an educational board game on unsaturated soil mechanics

Non-conventional tools of teaching are effective in delivering deep learning of scientific facts as well as skills associated with scientific disciplines. A well-known method to promote student engagement and learning in general is the use of games in classrooms. Games can provide a flexible option that could engage students, create active learning experiences, and enable them to experiment in safe playful environments. This paper presents UnSaLuDo, a board game developed by the GeoFUN group. The goal was to develop a tool that enables students to experience fun and integrational activities in a classroom setting while learning complex scientific targeted threshold concepts related to unsaturated soil mechanics. The topics covered by UnSaLuDo included fundamental concepts of cohesion and adhesion in liquids, surface tension, contact angle and capillary rise; water retention and water flow in unsaturated soils; volume change, deformation, and shear strength of unsaturated soils. This paper provides background information on the motivation for the development of the board game and an overview of the topics covered. The paper also presents all the components of the board game developed and suggests approaches for how it can be incorporated into geotechnics courses.

The Large-Scale Hydraulic Conductivity for Gravitational Fingering Flow in Unsaturated Homogenous Porous Media: A Review and Further Discussion

Gravitational fingering often occurs for water flow in unsaturated porous media. This paper reviews a recent effort in developing a macroscopic theory to describe the gravitational fingering flow of water in homogeneous and unsaturated soils, based on the optimality principle that water flows in unsaturated soils in such a manner that the generated flow patterns correspond to the minimum global flow resistance. The key difference between the new theory and the conventional unsaturated flow theories is that the hydraulic conductivity in the new theory is not only related to water saturation or capillary pressure, but also proportional to a power function of water flux, because the water flux is closely related to the fingering flow patterns and the power function allows for large hydraulic conductivities at locations where water fluxes are large as well to minimize the global flow resistance. The resultant relationship for the fraction of fingering flow zone is compared with that obtained from a parallel effort based on the fractal nature of fingering flow patterns. The relationships from the two efforts are found to be essentially identical for gravity-dominated water flow in unsaturated soils and can both be expressed as a power function of the water saturation. This work also demonstrates that the theoretical values for the exponent of the power function vary in a relatively narrow range between 0.75 and 0.80 for most soils, which is supported by observations from previous field tests. This remarkable finding makes it easy to apply the new theory to field sites where experimental data are not readily available for estimating the exponent value. The potential limitations of the theory and the suggested future research topics in the area are also discussed.

Investigations of Unsaturated Slopes Subjected to Rainfall Infiltration Using Numerical Approaches—A Parametric Study and Comparative Review

In the past 30 years, research on rainfall-induced landslides has grown remarkably. The contribution of matric suction to soil strength and the physics of water flow in unsaturated soils are widely accepted phenomena among researchers. However, the adoption of unsaturated soil mechanics in geotechnical engineering practice has been relatively slow, in part due to the practicality of design solutions available to the engineer. This paper conducts a parametric study on unsaturated silty slopes under a vertical steady flow rate to identify the suitable slope and hydrologic conditions to incorporate unsaturated conditions for preliminary stability analysis. Notably, the contribution of suction is most significant for silt/clay slopes with a water table located below the mid-height of the slope. For slopes with slope height ≥20 m and a fairly high water table, the slope height is a primary controlling factor of slope stability. Two case studies based on distinct failure mechanisms are presented to review the application of common geotechnical software in rainfall seepage and stability analyses of unsaturated slopes. Focus is placed on the pre-failure and failure stages of each case study. The slip surface search method, failure mode, and coupling approach integrated into each computer program caused notable differences in output results.

Development Trends and Research Frontiers of Preferential Flow in Soil Based on CiteSpace

Preferential flow is a non-equilibrium flow in unsaturated soil through which water infiltrates deep into the ground quickly. It has been studied in many fields, such as environment, agriculture, and hydrology. However, researchers from different disciplines have a different understanding of preferential flow, and it is difficult to grasp its development trends and research frontiers through qualitative analysis in a single field, while they can be quantitatively and objectively analyzed through bibliometrics with scientific knowledge map tools. This paper collects 3315 research studies on preferential flow in soil from the Web of Science (WoS) core collection database within 30 years, conducts a statistical analysis on keywords, countries, and research institutions of these studies based on CiteSpace, draws visualized scientific knowledge maps, and presents the development trends and research frontiers of preferential flow. Results showed that preferential flow is a multi-scale coexistence phenomenon, and researchers from different disciplines study preferential water flow movement and pollution at different research scales. New techniques and ideas are research hotspots and directions. Moreover, the difference between bibliometrics methods and review methods is analyzed. This paper is presented to provide a referable knowledge structure and new ideas for research in related fields and to help promote cross-integration between disciplines.

Forward and inverse modeling of water flow in unsaturated soils with discontinuous hydraulic conductivities using physics-informed neural networks with domain decomposition

Abstract. Modeling water flow in unsaturated soils is vital for describing various hydrological and ecological phenomena. Soil water dynamics is described by well-established physical laws (Richardson–Richards equation – RRE). Solving the RRE is difficult due to the inherent nonlinearity of the processes, and various numerical methods have been proposed to solve the issue. However, applying the methods to practical situations is very challenging because they require well-defined initial and boundary conditions. Recent advances in machine learning and the growing availability of soil moisture data provide new opportunities for addressing the lingering challenges. Specifically, physics-informed machine learning allows both the known physics and data-driven modeling to be taken advantage of. Here, we present a physics-informed neural network (PINN) method that approximates the solution to the RRE using neural networks while concurrently matching available soil moisture data. Although the ability of PINNs to solve partial differential equations, including the RRE, has been demonstrated previously, its potential applications and limitations are not fully known. This study conducted a comprehensive analysis of PINNs and carefully tested the accuracy of the solutions by comparing them with analytical solutions and accepted traditional numerical solutions. We demonstrated that the solutions by PINNs with adaptive activation functions are comparable with those by traditional methods. Furthermore, while a single neural network (NN) is adequate to represent a homogeneous soil, we showed that soil moisture dynamics in layered soils with discontinuous hydraulic conductivities are correctly simulated by PINNs with domain decomposition (using separate NNs for each unique layer). A key advantage of PINNs is the absence of the strict requirement for precisely prescribed initial and boundary conditions. In addition, unlike traditional numerical methods, PINNs provide an inverse solution without repeatedly solving the forward problem. We demonstrated the application of these advantages by successfully simulating infiltration and redistribution constrained by sparse soil moisture measurements. As a free by-product, we gain knowledge of the water flux over the entire flow domain, including the unspecified upper and bottom boundary conditions. Nevertheless, there remain challenges that require further development. Chiefly, PINNs are sensitive to the initialization of NNs and are significantly slower than traditional numerical methods.

Hydraulic Issues Concerning Injection of Harvested Rainwater to the Subsurface Through Drywells: Insight From Numerical Simulations of Flow in a Realistic Combined Vadose Zone‐Groundwater Flow System

AbstractThis study focuses on the analyses of field‐scale water flow originating from a drywell, using the 3‐D Richards equation for the local description of the flow in a spatially heterogeneous, combined vadose zone‐groundwater flow system. Realistic features of the flow system, that is, height of the groundwater table, records of the time‐dependent rainfall data, spatial heterogeneity of soil hydraulic properties and flow‐controlled attributes, as well as man‐controlled characteristics of the drywell, were considered in the analyses. The effect of (a) the depth‐dependency of the soil type, (b) the vertical position of the drywell's screen, and (c) the mode of water injection to the drywell (constant or time‐dependent), on the performance of the drywell, were examined. Results, and in particular those related to the importance of the soil type depth‐dependency with regard to the drywell performance, can be explained by the physics of flow in unsaturated soils of differing soil texture. Of specific significance is the transition zone between the two different soil types in the case in which the spatially‐heterogeneous coarse‐textured soil overlies the spatially heterogeneous fine‐textured soil. In this case, when most of the drywell screen is located within this transition zone and when the flow is transient and non‐monotonous, the downward flow from the drywell is maximized. Although this study is site‐specific, we believe that its results are novel and relevant for sandy to sandy‐clay soils associated with managed aquifer recharge technology based on a device whose vertical axis is perpendicular to the soil layering.

Comparison of Seven Weibull Distribution Models for Predicting Relative Hydraulic Conductivity

AbstractModeling water flow in unsaturated soils requires accurate characterization of relative hydraulic conductivity (RHC) and water retention curve (WRC). The overall objective of this study is to investigate the performances of seven Weibull distribution models for predicting RHC using the Assouline et al. (1998), https://doi.org/10.1029/97WR03039 WRC. Specifically, a new RHC model was proposed via the approach of Assouline (2001), https://doi.org/10.1029/2000WR900254 with the assumptions of Burdine (1953), https://doi.org/10.2118/225-G and Kosugi (1999), https://doi.org/10.2136/sssaj1999.03615995006300020003x. The proposed model, together with the other six models, was then compared with data from 40 soils to explore their predictive performances for RHC. The results showed that the proposed model provides the best agreement with measured data and yields a 16.1% improvement in RHC prediction compared to the widely used Assouline et al. (1998), https://doi.org/10.1029/97WR03039‐Mualem (1976), https://doi.org/10.1029/WR012i003p00513 model. The proposed model can be used as RHC parameterization for water flow modeling in the unsaturated zone.

Numerical Solution of Water Flow in Unsaturated Soil with Evapotraspiration

Flow movement in unsaturated soil can be expressed by Richards equation. This equation can be obtained by applying the mass conversation law and the Darcy law. In this work, we solve one-dimensional Kirchhoff transformed Richards equation with loss of water due to the evaporation of unsaturated porous media (soils) and transpiration of plants numerically using Crank-Nicolson method. The result has compared with evapotranspiration function and without it in the governing equation. It has found that an additional work in time and flow movement is needs to reach the given boundary condition for the model without evapotranspiration.

A scaling procedure for straightforward computation of sorptivity

Abstract. Sorptivity is a parameter of primary importance in the study of unsaturated flow in soils. This hydraulic parameter is required to model water infiltration into vertical soil profiles. Sorptivity can be directly estimated from the soil hydraulic functions (water retention and hydraulic conductivity curves), using the integral formulation of Parlange (1975). However, calculating sorptivity in this manner requires the prior determination of the soil hydraulic diffusivity and its numerical integration between initial and final saturation degrees, which may be difficult in some situations (e.g., coarse soil with diffusivity functions that are quasi-infinite close to saturation). In this paper, we present a procedure to compute sorptivity using a scaling parameter, cp, that corresponds to the sorptivity of a unit soil (i.e., unit values for all parameters and zero residual water content) that is utterly dry at the initial state and saturated at the final state. The cp parameter was computed numerically and analytically for five hydraulic models: delta (i.e., Green and Ampt), Brooks and Corey, van Genuchten–Mualem, van Genuchten–Burdine, and Kosugi. Based on the results, we proposed brand new analytical expressions for some of the models and validated previous formulations for the other models. We also tabulated the output values so that they can easily be used to determine the actual sorptivity value for any case. At the same time, our numerical results showed that the relation between cp and the hydraulic shape parameters strongly depends on the chosen model. These results highlight the need for careful selection of the proper model for the description of the water retention and hydraulic conductivity functions when estimating sorptivity.

The potential impact of biochar: Soil hydraulics and responses of maize under soil drying cycles

Biochar (BC) has been shown to positively impact soil hydraulic properties. However, its effect on water flow in unsaturated soil and root access to water have been poorly understood. This study was conducted to investigate the potential impact of BC application on soil water accessibility and plant responses under soil drying cycles.A grapevine wood-based BC was mixed with a sandy loam soil at the rates of 0, 20, and 40 g kg−1 and preincubated in the PVC pots for two months. Then, maize plants were grown in preincubated pots and regularly irrigated during their vegetative phase (64 days) to maintain soil moisture at optimum condition (0.30 cm3 cm−3). Thereafter, plants were subjected to repeated soil drying (via plant transpiration) and wetting cycles (via irrigation from the top) with soil water content varying between 0.18 and 0.30 cm3 cm−3, respectively. Some selected plant growth parameters and plant physiological responses to soil drying cycles were determined. In parallel, soil water retention and hydraulic conductivity curves of different treatments were measured by a combination of the sandbox, pressure plate apparatus, and Hyprop.The results showed that plant dry shoot biomass was slightly increased by the BC application (9% on average). In contrast, the leaf area and root volume did not show any significant difference. As soil dried during a soil drying cycle, the transpiration rate decreased among all treatments. However, the drop in transpiration rate was smaller in the BC-amended soils than in the control. At soil water content of 018 cm3 cm−3, plants grown in BC-amended soils had on average 83% and 164% higher transpiration and photosynthesis rate than plants grown in control soil, respectively. These comparisons suggest that BC improved water accessibility to plants during soil drying, resulting in 76 and 58% increase in grain yield and grain water productivity. The application of BC had little effect on soil water retention in the wet range and had no impacts in the drier range, while the unsaturated hydraulic conductivity (Kh) and calculated matric flux potential (φ) were positively impacted in a wide range of soil water content.The findings of this study revealed that BC mixed with sandy loam soil could prevent a big drop in Kh as soil dries, thereby improving root access to water and transpiration rate under drought stress.

Comparing and Contrasting Travelling Wave Behaviour for Groundwater Flow and Foam Drainage

Liquid drainage within foam is generally described by the foam drainage equation which admits travelling wave solutions. Meanwhile, Richards’ equation has been used to describe liquid flow in unsaturated soil. Travelling wave solutions for Richards equation are also available using soil material property functions which have been developed by Van Genuchten. In order to compare and contrast these solutions, the travelling waves are expressed as dimensionless height, {hat{xi }} , versus moisture content, varTheta . For low moisture content, {{hat{xi }}} exhibits an abrupt change away from the dry state in Richards equation compared to a much more gradual change in foam drainage. When moisture content nears saturation, {hat{xi }} reaches large values (i.e. {hat{xi }} gg 1 ) for both Richards equation and foam drainage, implying a gradual approach of varTheta towards the saturated state. The {hat{xi }} values in Richards equation tend, however, to be larger than those in the foam drainage equation, implying an even more gradual approach towards saturation. The reasons for the difference between foam drainage and Richards equation solutions are traced back to soil material properties and in particular a soil specific parameter “m” which is determined from the soil-water retention curve.

Transition Between Constitutive Equations and the Mechanics of Water Flow in Unsaturated Soil: Numerical Simulations

Richards’ partial differential equation normally governs water flows in soil. It can be utilized to investigate water infiltration in the soil. A case study of the Haverkamp’s water infiltration simulation into Yolo Light Clay was carried out. A common practice to change between the hydraulic functions (from Haverkamp to van Genuchten) could cause a discrepancy in the simulation results. Hence, the first objective is to modify van Genuchten’s equations to reproduce the water infiltration result that was obtained using the Haverkamp constitutive functions. The method used was able to recreate water infiltration by increasing the fitting parameters of the van Genuchten constitutive functions. The second objective is to identify the mechanism governing the flow of water. The soil water diffusivity and the hydraulic conductivity were responsible for the flux of water in the soil. The Richards’ equation was discretized using a finite difference method, and the algebraic solution was coded into Simply Fortran 2008.