Parameter estimation for coupled unsaturated flow and transport

This paper deals with the estimation of soil hydraulic and transport parameters from transient unsaturated flow and tracer experiments using a combined simulations-optimization approach. Hydraulic properties are defined by a modified form of van Genuchten's (1980) parametric model for two-phase permeability-saturation-pressure relations, and transport properties are defined by an empirical parametric dispersion model. A nonlinear weighted least squares algorithm is used to estimate unknown model parameters by minimizing deviations between concentrations, water contents, and pressure heads obtained from hypothetical infiltration/redistribution/evaporation experiments, and those predicted by solving a numerical model of coupled unsaturated flow and transport. Simultaneous estimation of hydraulic and transport properties is found to yield smaller estimation errors for model parameters than sequential inversion of hydraulic properties from water content and pressure head data followed by inversion for transport properties from concentration data. Effects of random noise in data measurements, soil layering, and choice of improper parametric model on the parameter estimation process are discussed.

[1]  S. Gorelick,et al.  Optimal groundwater quality management under parameter uncertainty , 1987 .

[2]  Jack C. Parker,et al.  Development and evaluation of closed-form expressions for hysteretic soil hydraulic properties , 1987 .

[3]  William A. Jury,et al.  A field test of the transfer function model for predicting solute transport , 1982 .

[4]  David L. Freyberg,et al.  A natural gradient experiment on solute transport in a sand aquifer: 2. Spatial moments and the advection and dispersion of nonreactive tracers , 1986 .

[5]  W. Yeh.  Review of Parameter Identification Procedures in Groundwater Hydrology: The Inverse Problem , 1986 .

[6]  William A. Jury,et al.  Progress in unsaturated flow and transport modeling , 1987 .

[7]  Robert B. Schnabel,et al.  Computational experience with confidence intervals for nonlinear least squares , 1986 .

[8]  M. Th. van Genuchten,et al.  Parameter estimation for unsaturated flow and transport models — A review , 1987 .

[9]  J. Parker,et al.  Analysis of the inverse problem for transient unsaturated flow , 1988 .

[10]  A. Klute,et al.  The Calibration of the Richards Flow Equation for a Draining Column by Parameter Identification1 , 1981 .

[11]  Van Genuchten,et al.  A closed-form equation for predicting the hydraulic conductivity of unsaturated soils , 1980 .

[12]  J. H. Dane,et al.  In-Situ Determination of Soil Hydraulic Properties during Drainage1 , 1983 .

[13]  S. P. Neuman,et al.  Estimation of Aquifer Parameters Under Transient and Steady State Conditions: 1. Maximum Likelihood Method Incorporating Prior Information , 1986 .

[14]  R. Carsel,et al.  Developing joint probability distributions of soil water retention characteristics , 1988 .

[15]  Lynn W. Gelhar,et al.  Stochastic subsurface hydrology from theory to applications , 1986 .

[16]  M. Th. van Genuchten,et al.  A comparison of numerical solutions of the one-dimensional unsaturated—saturated flow and mass transport equations , 1982 .