HR: 1340h
AN: H53F-1485    [Abstracts]
TI: Drainage Experiments in Heterogeneous Sand Columns With Different Geometric Structures
AU: Vasin, M
EM: milos.vasin@iws.uni-stuttgart.de
AF: University of Stuttgart, Institute of Hydraulic Engineering, Pfaffenwaldring 61, Stuttgart, 70550, Germany
AU: Lehmann, P
EM: peter.lehmann@epfl.ch
AF: Laboratory of Soil and Environmental Physics, Swiss Federal Institute of Technology Lausanne, Station 2 Building GR, Lausanne, 1015, Switzerland
AU: Nowak, W
EM: wolfgang.nowak@iws.uni-stuttgart.de
AF: University of Stuttgart, Institute of Hydraulic Engineering, Pfaffenwaldring 61, Stuttgart, 70550, Germany
AU: Hassanein, R
EM: rene.hassanein@gmx.net
AF: Institute of Terrestial Ecology, Swiss Federal Institute of Technology Zurich, Universitaettsrasse 16, Zurich, 8092, Switzerland
AU: * Neuweiler, I
EM: insa.neuweiler@iws.uni-stuttgart.de
AF: University of Stuttgart, Institute of Hydraulic Engineering, Pfaffenwaldring 61, Stuttgart, 70550, Germany
AB: This poster presents results of multi-step drainage experiments, carried out with two sand columns (10x10x20 cm3) packed with different structures made up from two different sand types. One purpose was to test the influence of the column structure on the movement of the water during drainage. The second purpose was to test upscaled models for the prediction of outflow curves, even when the underlying assumptions on soil structure are not met. The two packing structures used in the experiments can be considered as two opposing extremes. The packing of the columns was made of 1x1x1 cm3 cubes of the two sand types. The first column was packed with a periodic pattern of coarse material inclusions in a fine-material background, having a clearly defined macroscopic representative elementary volume. The second column was packed with a random arrangement of the sand types that has no typical length scale smaller than that one of the column and where fine and coarse materials formed column spanning connected clusters. The depth averaged two-dimensional spatial distribution of the water content in the columns was monitored during the drainage using neutron radiography. A three dimensional tomogram of the water content was measured at steady state after each pressure step. When comparing the results from the two columns, we found that due to trapping effects the different distributions of isolated structures had an effect on the retention of drainage, indicating a significant influence of structure at effective retention curve. In contrast to the retention curve, the effective conductivity of the columns was not significantly influenced by the structure. We compared the experimental results to an upscaled model derived from homogenization theory (for slow flow processes and capillary dominated flow). It has the same form as the Richards equation with an effective retention function and an effective unsaturated hydraulic conductivity function. The hydraulic parameters of the coarse and the fine sand have been defined by least square fitting of to the measured retention curves and by fitting to the outflow curves using a Levenberg Marquardt algorithm. The hydraulic parameters were used as input to the upscaling procedure. We included the effect of structure on retention by using adapted upscaled retention curves, which consider the accessability of inclusion material to air during drainage. The upscaled models predicted the movement of the averaged water content in the two columns well. This can be considered to confirm the applicability of upscaled models even if the underlying requirements are not strictly met.
DE: 1839 Hydrologic scaling
DE: 1866 Soil moisture
DE: 1875 Vadose zone
DE: 1895 Instruments and techniques: monitoring
SC: Hydrology [H]
MN: 2007 Fall Meeting