Inverse modelling techniques for determining hydraulic properties of coarse-textured porous media by transient outflow methods |
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| Institution: | 1. Institute of Freshwater Ecology and Inland Fisheries, Rudower Chaussee 6a, D-12484 Berlin, Germany;2. Institute of Hydroengineering, Polish Academy of Sciences, Koscierska 7, PL-80953 Gdansk-5, Poland;3. Institute of Water Resources and Hydraulic Engineering, Technical University Berlin, Postfach 100320, D-10623 Berlin, Germany;1. Korea Railroad Research Institute, 176 Cheoldobangmulgwanro Uiwangsi, Gyeonggi-do 16105, South Korea;2. ERS Co., Ltd., 86 Chungjusandan 3ro Chungju-si 27325, South Korea;1. School of Geosciences, China University of Petroleum (East China), Qingdao 266580, China;2. State Key Laboratory of Mining Disaster Prevention and Control, Shandong University of Science and Technology, Qingdao 266590, China;3. College of Mining and Safety Engineering, Shandong University of Science and Technology, Qingdao 266580, China;4. School of Mechanical and Chemical Engineering, University of Western Australia, 35 Stirling Highway, Crawley, WA 6009, Australia;1. 28 Marston Hall, University of Massachusetts, Amherst, MA, USA;2. HyGround Engineering, Williamsburg, MA, USA |
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| Abstract: | A series of multi-step outflow experiments was carried out to identify the unsaturated hydraulic properties of two homogeneous coarse-textured porous media (glass beads and sand). Because of the measured sharp fronts of water content decrease during these experiments the hydraulic functions are assumed to be represented by the complete van Genuchten–Mualem closed-form expressions with variable coefficients α, n, m and θr. The values of θs and Ks were measured directly. A sensitivity analysis with respect to α, n, and m shows that conditions of local identifiability are satisfied if measurements of water content at some inner points inside the column are considered. The inverse modelling technique consists of two steps: first, computation of objective function values based on water content data responses to obtain initial parameter estimations, and second, a more detailed parameter determination using a Levenberg–Marquardt scheme. In both steps a numerical model incorporating the hydraulic functions is utilized to simulate theoretical pressure head and water content distributions along the column. For both porous media unique solutions of the inverse problem could be obtained, and afterwards, the corresponding hydraulic functions were verified from additional drainage experiments.©1998 Elsevier Science Limited. All rights reserved |
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