Revisiting the simplified evaporation method: Identification of hydraulic functions considering vapor, film and corner flow
Revisiting the simplified evaporation method: Identification of hydraulic functions considering vapor, film and corner flow
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DOI：
10.1016/j.jhydrol.2015.05.020
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发表时间：
2015-08
影响因子：
6.4
通讯作者：
A. Peters;S. Iden;W. Durner
中科院分区：
文献类型：
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作者：
A. Peters;S. Iden;W. Durner
简化蒸发法（SEM）是一种通过室内蒸发实验确定土壤水力特性的技术，即水分保持曲线和水力传导率曲线。该方法依赖于简化的假设，如压头和水通量的空间线性，这是违反蒸发过程。因此，它的有效性和准确性已检查在过去的数值模拟使用的理查兹方程和随后的评价计算机生成的数据。这些数值试验是使用土壤水力特性的模型进行的，如货车Wischten-Mualem模型，该模型仅考虑完全填充的毛细管中的持水率和电导率，因此对低含水量下的水力特性进行了有偏见的描述。我们重新调查的准确性的SEM的一个广泛的土壤质地从粘土到纯砂的数值模拟研究，使用更现实的功能的土壤水力特性，占水的吸附，在不完全填充的毛细管和等温蒸汽流。我们的结果表明，以前的数值研究低估了裸土蒸发过程中吸力和含水量剖面的非线性，特别是对于桑迪土壤。然而，SEM近似大多数土壤的真正水力功能非常好，平均偏差低于0.1%的体积含水量和低于0.1的log 10的水力传导率。较大的色谱柱或较高的蒸发速率仅略微增加此误差。只有极端的纹理谱，我们发现的偏见估计土壤水力特性。此外，我们研究了不同的策略计算平均吸力，并表明加权组合的算术和几何平均值导致最佳的结果。
The simplified evaporation method (SEM) is a technique to determine soil hydraulic properties, ie the water retention curve and the hydraulic conductivity curve, from evaporation experiments in the laboratory. The method relies on simplifying assumptions like spatial linearity in pressure head and water fluxes, which are violated in the evaporation process. Therefore, its validity and accuracy has been checked in the past by numerical simulation using the Richards equation and subsequent evaluation of the computer-generated data. These numerical tests were conducted using models of the soil hydraulic properties like the van Genuchten–Mualem model, which account only for water retention and conductivity in completely filled capillaries and thus give biased descriptions of the hydraulic properties at low moisture contents. We reinvestigate the accuracy of the SEM by a numerical simulation study for a broad spectrum of soils with textures ranging from clay to pure sand, using more realistic functions of the soil hydraulic properties, which account for water adsorption, flow in incompletely filled capillaries and isothermal vapor flow. Our results show that the previous numerical studies underestimated the non-linearities of suction and water content profiles which occur during bare-soil evaporation, in particular for sandy soils. Nevertheless, the SEM approximates the true hydraulic functions of most soils very well, with mean deviations below 0.1% volumetric water content and below 0.1 for log 10 of hydraulic conductivity. Larger columns or higher evaporation rates increase this error only slightly. Only for the extremes in the texture spectrum, we found bias in the estimated soil hydraulic properties. We furthermore investigate different strategies for calculating a mean suction and show that a weighted combination of the arithmetic and geometric mean leads to the best results.