Information content of measurements from tracer microlysimeter experiments designed for parameter identification in dual-permeability models

Abstract

Parameters regulating the degree of preferential flow in the dual-permeability water flow and solute transport model MACRO are difficult or impossible to derive from direct measurements. The objectives were (i) to find an improved temporal measurement scheme for identification of these parameters using laboratory microlysimeter experiments and (ii) to evaluate the possibilities of parameter identification in the MACRO model. Artificial data from laboratory microlysimeter experiments consisting of high time-resolution ‘measurements’ of percolation rate, effluent concentration and resident concentrations at six depths were used with PIMLI (parameter identification method using the localisation of information). The data contained enough information to successfully reduce the uncertainty in the parameter governing mass exchange between pore domains, the saturated micropore hydraulic conductivity and the dispersivity for two hypothetical soils representing one typical clay and one loam. Parameters governing water flow in the macropores were shown to be sensitive in a screening analysis with the Morris method and the uncertainty in these parameters was also reduced by PIMLI. However, some of these parameters did not converge towards their true values probably because of parameter interdependence. In all cases, ‘measurements’ with large information content were found early in the experiments where less than 0.2 pore volumes of water had passed through the column. For successful identification of parameters determining the degree of preferential flow, efforts should be made to perform high time-resolution measurements during the first irrigations following solute application.