Inverse modelling techniques for determining hydraulic properties of coarse-textured porous media by transient outflow methods
✍ Scribed by G. Nützmann; M. Thiele; S. Maciejewski; K. Joswig
- Publisher
- Elsevier Science
- Year
- 1998
- Tongue
- English
- Weight
- 439 KB
- Volume
- 22
- Category
- Article
- ISSN
- 0309-1708
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✦ Synopsis
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 a, n, m and v r . The values of v s and K s were measured directly. A sensitivity analysis with respect to a, 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.