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Extended multistep outflow method for the accurate determination of soil hydraulic properties near water saturation
Author(s) -
Durner W.,
Iden S. C.
Publication year - 2011
Publication title -
water resources research
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.863
H-Index - 217
eISSN - 1944-7973
pISSN - 0043-1397
DOI - 10.1029/2011wr010632
Subject(s) - outflow , hydraulic conductivity , ponding , saturation (graph theory) , soil water , pressure head , hydraulic head , geotechnical engineering , soil science , vadose zone , environmental science , drainage , mechanics , mathematics , geology , thermodynamics , physics , oceanography , combinatorics , ecology , biology
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, K s , 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 K s to a minimum.