Extended multistep outflow method for the accurate determination of soil hydraulic properties near water saturation
Extended multistep outflow method for the accurate determination of soil hydraulic properties near water saturation
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DOI：
10.1029/2011wr010632
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发表时间：
2010-05
影响因子：
5.4
通讯作者：
W. Durner;S. Iden
中科院分区：
文献类型：
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作者：
W. Durner;S. Iden
多步流出试验的逆建模是一种成熟、快速的测定土非饱和水力特性的方法。该方法的缺点是相对于饱和时的水力导率函数灵敏度较低，这使得相应的估计非常不确定。因此，通常建议使用独立测量的饱和水力导电性k值。这涉及到缺点，即进行额外实验的努力以及与来自不同实验来源的数据组合相关的一般问题。为了克服这一问题，我们建议在一个实验中结合渗透和流出。这个扩展的多步骤流出实验（XMSO）从一个完全水饱和的土柱开始，在土柱的顶部有少量的水。第一个实验阶段是落水头条件下的饱和渗流。实验结束后，按照非饱和排水过程的标准MSO实验继续进行。利用累积流出量和张力压头数据，通过逆建模对XMSO实验进行了评估。我们对合成数据和实际数据的分析表明，即使对于具有结构化孔隙系统的土壤，XMSO也能非常准确地估计饱和和接近饱和的水力特性。此外，还可以同时准确地确定支撑多孔板和土体的饱和水力系数。我们得出结论，XMSO实验设计解决了土样近饱和水力特性的识别问题，并将k的估计不确定性降低到最小。
Inverse modeling of multistep outflow (MSO) experiments is an established and fast method to determine unsaturated hydraulic properties of soils. A disadvantage of the method is its low sensitivity with respect to the hydraulic conductivity function at saturation, which makes the respective estimation very uncertain. Thus, the use of independently measured values for the saturated hydraulic conductivity, Ks, is generally recommended. This involves disadvantages, namely, the effort to conduct additional experiments and the general problems associated with the combination of data from different experimental sources. To overcome this problem, we propose to combine percolation and outflow in one experiment. This extended multistep outflow experiment (XMSO) starts with a completely water‐saturated soil column, on top of which a small amount of water is ponding. The first experimental phase is a saturated percolation under falling‐head conditions. After ponding ceases, the experiment continues as a standard MSO experiment with an unsaturated drainage process. The XMSO experiment is evaluated by inverse modeling, using measurements of cumulative outflow and tensiometric pressure head data. Our analysis of synthetic and real data demonstrates that XMSO yields very accurate estimates of saturated and near‐saturated hydraulic properties, even for soils with structured pore systems. Furthermore, saturated hydraulic conductivities of the supporting porous plate and the soil can be simultaneously determined with great accuracy. We conclude that the XMSO experimental design solves the problem of the identification of near‐saturated hydraulic properties of soil samples and reduces the estimation uncertainty of Ks to a minimum.