Determination of soil parameters via the solution of inverse problems in infiltration (original) (raw)
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Water Resources Research, 2007
Inverse modeling is a powerful technique for identifying the hydraulic properties of unsaturated porous media. However, the selection of an appropriate parameterization of the soil water retention and hydraulic conductivity function remains a challenge. In this article, we present an improved algorithm for estimating these two relationships without assigning an a priori shape to them. The approach uses cubic Hermite interpolation and a global optimization strategy. A multilevel routine identifies the adequate number of degrees of freedom by balancing model performance, the statistical interaction of the estimated model parameters, and their number. A first-order uncertainty analysis provides a quantitative measure of how well the soil hydraulic properties can be identified in different ranges of pressure head. This offers great potential for designing optimal experimental procedures for identifying the hydraulic properties of porous media. We demonstrate the effectiveness of the algorithm for the evaluation of multistep outflow experiments by investigating synthetic data sets and real measurements. The free-form approach yields optimal model parameters that show only moderate correlation, indicating well-posed inverse problems. Since parameterization errors are almost completely avoided, the algorithm is well suited to identifying other error sources in unsaturated flow problems, e.g., limitations in the applicability of the Richards equation or problems caused by spatial heterogeneity.
Estimation of the soil hydraulic properties from field data by solving an inverse problem
Scientific Reports
Estimating unsaturated soil hydraulic properties to predict water dynamics through a vertical soil profile under the effects of irrigation, drainage and evapotranspiration is imperative for managing soils in the arid regions. The aim of this work was to determine the soil water retention curve and the hydraulic permeability function of a bare soil profile in a Tunisian oasis threatened by salinization. The developed model combines a numerical inversion of the unsaturated flow equation with the BOBYQA optimisation algorithm. The direct model solved the Richards equation using a cell-centred finite difference model. Hydraulic properties were described by van Genuchten-Mualem models. Input data for the inverse problem are the infiltration flow, soil water contents and pressure heads measured during ponded infiltration and internal drainage tests. Numerical simulations of these two tests were performed considering a homogeneous single-layer soil profile but a better fitting between meas...
On the solution of some inverse problems in infiltration
2001
In this paper we discuss inverse problems in infiltration. We propose an efficient method for identification of model parameters, eg, soil parameters for unsaturated porous media. Our concept is strongly based on the finite speed of propagation of the wetness front during the infiltration into a dry region. We determine the unknown parameters from the corresponding ODE system arising from the original porous media equation. We use the automatic differentiation implemented in the ODE solver LSODA.
Determination of soil parameters in hydraulic flow model for porous media
2017
Determination of soil parameters (in fundamental flow characteristics) is investigated under new scenario in laboratory experiments with 3D samples. Infiltration into a sample is realized under the gravitation and centrifugal driven forces. Mathematical model for the flow in an unsaturetedsaturated porous media is expressed in terms of Richard’s equation based on the van Genuchten/Mualem experimental capillary-pressure model. Soil parameters characterize the specific porous material and are used as input data in this capillarypressure flow model. Objective of this paper is threefold. The first is to present a direct and inverse efficient solver for governing mathematical model. The second is to apply the inverse solver for parameter estimation using only noninvasive inflow/outflow transient measurements. The third is to avoid resp. significantly reduce the creation of preferred streamlines which shadow reliability in solution of inverse problem. In our setup, a sample of cylindrical...
MATEC Web of Conferences, 2019
Unsaturated zone in the soil generally plays an important role in the transfer of water and pollutants in the underground environment. In this context, the determination of the hydrodynamic parameters constitutes an essential step for any study of transfers of water and solutes in the unsaturated zone. The purpose of this article is the estimation the soil hydrodynamic parameters by the direct method and the inverse method, from the infiltration data by using the disc infiltrometer in the soil the basin Loukkos located in northern Morocco. Our results the numerical modeling reproduced correctly the experimental measurements. These results show that the inverse method remains a robust and accurate method for determining the soil hydrodynamic parameters compared to other conventional methods.
Computers & Geosciences, 2008
We combined an inverse routine for assessing the hydraulic soil parameters of the Campbell/Mualem model with the power series solution developed by Philip for describing one-dimensional vertical infiltration into a homogenous soil. We based the estimation routine on a proposed measurement procedure especially suitable for early-time infiltrometer experiments where the flow can be considered as one-dimensional. The routine requires input of the initial soil water content and cumulative infiltration in two experiments with different pressures at the upper boundary and/or initial conditions. An independent measurement of the soil water content at saturation may reduce the uncertainty of estimated parameters. Response surfaces of the objective function were analysed. Scenarios for various soils and conditions, using numerically generated synthetic cumulative infiltration data with normally distributed errors, show promising results for finding the true values of the optimized parameters. We also investigated the effects of measurement frequency for the cumulative infiltration and errors in water content determinations. r
Estimation of Soil Hydraulic Properties of Basin Loukkos (Morocco) by Inverse Modeling
Ksce Journal of Civil Engineering, 2019
Management of groundwater resources is very important for economic development in arid and semi-arid lands. Unsaturated zone plays an important role in the fate of pollutants in the soil. Modeling of water flow in the vadose zone uses methods and techniques of soil physics. To describe and predict the behavior of water and solutes in unsaturated soil, knowledge of the soil hydraulic parameters is essential. The aim of this work is to evaluate the soil hydraulic parameters by direct and inverse methods from field measurements of cumulative infiltration and water contents. The inverse approach used here combined the numerical solution of the Richards equation two-dimensional with a Levenberg-Marquardt algorithm of optimization. Field experiments, using the disc infiltrometer, were conducted out in the Rmel area, sandy soil, in the Loukkos Basin located in northern Morocco. In this study, numerical and experimental results show that the simulated values are much closer to the measured values with a high correlation (R 2 ≈ 0.92, RMSE ≈ 0.146). Indicating that the model used here is efficient to estimate the soil hydraulic parameters by inverse modeling. Furthermore, the sensitivity analysis showed that the saturated conductivity (K s
Transactions of the ASABE, 2016
In this research, the EISHP (Estimation of Individual Soil Hydraulic Parameters) model was developed for estimation of the individual soil hydraulic parameters of van Genuchten's equation (, n, K s , s , and r). This model was used to predict soil water content and pressure head at different soil depths by implicitly solving the Richards equation, applying the finite difference method. In this model, the objective function (OF) was computed by summation of squared differences between measured and estimated soil water content and pressure head up to ten days after wetting of soil columns. In the EISHP model, each parameter was optimized separately by achieving the minimum value of OF using the Newton-Raphson method and keeping the remaining parameters constant. The optimized parameter value was then used in optimizing the other parameters. Iteration was continued until the difference between the two computational steps of OF was negligibly small and a unique value had been estimated for each parameter. The main contribution of this research is presentation of a methodology for the optimization of individual parameters, which guarantees the uniqueness of parameter values. In contrast, simultaneous optimization of the entire parameter set would not necessarily lead to unique values.
1998
An inverse procedure was used to estimate the soil hydraulic characteristics of a two-layered soil system-soil surface crust and subsoil-from data obtained during a tension-disc infiltration experiment. The inverse procedure combined the Levenberg-Marquardt nonlinear parameter optimization method with a numerical solution of the axisymmetric variably-saturated flow equation. The objective function was defined in terms of the cumulative infiltration curve and the final water content measured directly below the tension-disc infiltrometer at the end of the experiment; this final water content was assumed to correspond to the final supply pressure head. We analyzed two infiltration experiments carried out with a 25-cm diameter tension-disc infiltrometer. One experiment was carried out on a two-layered system, and a second after removal of the surface crust covering the sandy subsoil. Both experiments were performed with six consecutive supply tensions. We first analyzed the infiltration experiment for the subsoil only, thus yielding its hydraulic characteristics. Subsequent analysis of the infiltration experiment for the two-layered system with known hydraulic properties of the subsoil provided estimates of the hydraulic properties of the surface crust. We further compared the estimated hydraulic parameters of the w subsoil with those obtained using Wooding's analytical method Wooding, R.A., 1968. Steady x infiltration from a shallow circular pond. Water Resour. Res. 4, 1259-1273 and predictions based on a neural network model requiring textural input information. All three methods generated roughly the same results. The numerical inversion technique proved to be a convenient tool for
Modelling and understanding water fluxes in the vadose zone are important with regards to water management and require appropriate characterization methods of soil hydraulic properties. The present work studies three common methods for characterization of soil hydraulic properties based on the inverse modelling of water infiltration experiments at zero pressure head at surface (Beerkan method): the CI method for Cumulative Information method and two BEST methods for Beerkan Estimation of soil pedotransfer functions These methods estimate the soil sorptivity and saturated hydraulic conductivity by fitting infiltration data using infiltration models. The CI method directly fits the experimental cumulative infiltration to the usual short time expansion of the complete analytical model proposed by . The BEST methods are based on a specific algorithm that splits the experimental curves into two parts, the first part being fitted to the short time expansion and the second part to the long time expansion. To test the methods, several subsets of infiltration data were generated using the complete analytical model for several radii of the disc infiltrometer source and for times ranging from zero to several truncation times. The methods were then applied and the ratio between their estimations and the target values were evaluated to quantify their related accuracy. The results clearly demonstrated that the CI method must be used only to short time infiltration data. Yet, this method is usually used without any truncation of the experimental data, whereas the truncation should certainly be required. The BEST methods proved efficient and robust, provided the steady state was reached at the end of the infiltration experiment and both short and long time data solutions were used. The gain in accuracy of the BEST methods was all the more important when the disc radius was small.