HR: 0800h
AN: H51C-0655    [Abstracts]
TI: A Linking Test That Explores The Non Uniqueness Of Soil And Vegetation Parameters Of A Unsaturated Flow Model
AU: * Pollacco, J
EM: joseph.pollacco@gmail.com
AF: Univ. Lyon 1, Lab. Ecol. Hydrosyst. Fluv., Villeurbanne, 69622, France
AU: * Pollacco, J
EM: joseph.pollacco@gmail.com
AF: Lab. Sciences Env., ENTPE, Vaulx-en-Velin, 69518, France
AU: Angulo-Jaramillo, R
EM: angulo@hmg.inpg.fr
AF: Lab. Sciences Env., ENTPE, Vaulx-en-Velin, 69518, France
AU: Angulo-Jaramillo, R
EM: angulo@hmg.inpg.fr
AF: Lab. Transf. Hydro. Env., Hydro, Grenoble cedex 9, 38041, France
AU: Soria-Ugalde, J
EM: josesoria@quijote.ugto.mx
AF: Univ. Guanajuato, Dep. Hydro., Guanajuato, 36000, Mexico
AU: Braud, I
EM: isabelle.braud@cemagref.fr
AF: CEMAGREF, Hydro-Hydraulique, Lyon cedex 9, 69336, France
AB: Groundwater recharge can be accurately computed by using models that solves the Richards' equation. A drawback of such models is that they require a considerable number of parameters that need to be determined: Mualem-van Genuchten, interception and crop factor. It is preferable to estimate these parameters indirectly from in situ measurements since values retrieved from sample analysis poorly characterize field conditions. Groundwater recharge can be modelled once the hydraulic and the vegetation parameters have been optimised simultaneously. The optimisation can be achieved by matching solely observed and simulated time series of soil moisture profiles. A good match between simulated and measured soil moisture can be obtained but the parameters are non-unique, leading to the problem of equifinality. We found that a unique groundwater recharge could be obtained only if the vegetation parameters were known. We investigated why the optimum hydraulic parameters were not unique by using the Linking Test. The Linking Test is a simple inverse method developed by the authors that takes into account the non uniqueness of the parameters. The Linking Test shows that very different soils could give similar groundwater recharge. This test also provides all the different combinations of the hydraulic parameters that give similar groundwater recharge. The Linking Test showed that the hydraulic parameters were linked due to "range" and "compensation" equifinalities. We showed that only 2 functional parameters are required to get a satisfactory simulation. It should notably simplify the determination of the hydraulic parameters in a region where various soil types are encountered and thus help in designing upscaling methods for these parameters. Other foreseen applications of knowing how the hydraulic parameters are linked are an improvement (1) of the sensitivity analysis to the hydraulic parameters, (2) the uncertainty analysis of the groundwater recharge by using soil water flow models, (3) the interpretation of the physical meaning of the hydraulic parameters determined by inverse modelling. The Linking Test could be applied to any inverse problem prior to modelling to determine its feasibility and to establish if the non-uniqueness of the parameters is of concern for the problem to be solved.
DE: 1838 Infiltration
DE: 1846 Model calibration (3333)
DE: 1852 Plant uptake
DE: 1865 Soils (0486)
DE: 1866 Soil moisture
SC: Hydrology [H]
MN: 2007 Fall Meeting