Improved estimation of soil water retention characteristics from hydrostatic column experiments
Improved estimation of soil water retention characteristics from hydrostatic column experiments
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DOI：
10.1029/2006wr004952
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发表时间：
2006-11-01
影响因子：
5.4
通讯作者：
Durner, W.
中科院分区：
文献类型：
--
作者：
Peters, A.;Durner, W.
土壤持水特性θ（h）是模拟和预测非饱和多孔介质中水分和溶质运移所必需的。通常，通过将压头h与在流体静力平衡条件下的柱实验中测量的平均水含量θ相关联并将参数保留函数拟合到这些数据对来确定θ（h）。该方法隐含的假设是，柱的平均含水量相当于柱中心的点测量值。取决于柱中垂直含水量分布θ（z）的非线性，该假设可能无效并引入系统误差。敏感性分析表明，如果忽略含水量分布的非线性所造成的误差的幅度可能达到百分之几，如果粗材料与低空气入口值和高土柱进行调查。此外，忽略theta（z）会产生平滑的保水特性，因此可能导致关于保水特性的最合适的参数模型的错误结论。如果水力传导率函数K（h）是从这样一个不正确的保留函数预测的，它可能与真实的函数有很大的不同。在本文中，我们建议考虑测得的土壤柱的含水量明确作为一个整体的平衡含水量分布与深度。我们表明，这消除了系统参数估计误差，并导致改善估计的土壤水分保持功能。
The soil water retention characteristic, theta(h), is required for modeling and predicting water and solute transport in unsaturated porous media. Commonly, theta(h) is determined by relating pressure heads, h, to mean water contents, theta, that are measured in column experiments under hydrostatic equilibrium conditions and fitting a parametric retention function to these data pairs. Implicit to this method is the assumption that the mean water content of the column is equivalent to a point measurement in the column center. Dependent on the nonlinearity of the vertical water content distribution, theta(z), in the column, this assumption may be invalid and introduces a systematic error. A sensitivity analysis shows that the magnitude of the error caused by neglecting the nonlinearity of the water content distribution may reach several percent if coarse materials with low air entry values and tall soil columns are investigated. Furthermore, neglecting theta(z) yields a smoothed retention characteristic and thus may lead to wrong conclusions about the most appropriate parametric model for the water retention characteristic. If the hydraulic conductivity function K(h) is predicted from such an incorrect retention function, it can differ greatly from the true function. In this paper, we propose to consider the measured water content of a soil column explicitly as an integral of the equilibrium water content distribution with depth. We show that this eliminates systematic parameter estimation errors and leads to improved estimates of the soil water retention function.