Journal of Food, Agriculture and Environment

Evaluation of water retention functions by developing a code for quantifying the hydraulic functions of unsaturated soils

Author(s):

Ali Rasoulzadeh

Recieved Date: 2010-01-19, Accepted Date: 2010-04-09

Abstract:

Agriculture is the highest consumer of water resources in Iran. Soil water models play a vital role in agriculture in terms of estimating water use, water allocation and current water status at a given scale. Modeling water flow and solute transport in vadose zone requires knowledge of soil hydraulic properties, which are soil water retention and unsaturated hydraulic conductivity curves. This study was carried out to evaluate the performance and suitability of some published soil water retention equations (Brooks and Corey, van Genuchten and double-exponential equations). This objective was examined by writing and developing a code based on Levenberg-Marquart optimization algorithm for inverse modeling to estimate parameters of mentioned soil water retention functions using C++ programming language. The code was used to address two specific issues. First, it was used to estimate soil water retention functions parameters (Brooks and Corey, Van Genuchten and double-exponential equations). Second, correlation of parameters, sensitivities and parameter standard error were obtained for evaluation of parameters estimation uncertainty. The results showed that the double-exponential and van Genuchten equations mimic soil water retention curve better than Brooks and Corey equation. The 95% confidence limits (lower and upper values) were in a narrow range and indicated that the estimation was sensitive to all parameters. The correlation matrix for the van Genuchten and Brooks and Corey equations showed that the parameters of these equations were almost completely inter-dependent while the parameters of double-exponential equation were relatively low inter-dependent.

Keywords:

Water retention function, inverse method, double-exponential equation

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Journal: Journal of Food, Agriculture and Environment
Year: 2010
Volume: 8
Issue: 2
Category: Environment
Pages: 1180-1184

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