Sensitivity, estimability and correlation of parameters describing equilibrium and nonequilibrium transports of bromide tracer in the field lysimeter

International audienceModelling of solute transport under transient flow conditions requires many input parameters, especially when using the nonequilibrium model. Most often, these parameters are not accurately measured but estimated by means of the inverse methods. Among different factors causing the nonuniqueness issues of estimated parameters, limited information content and correlations among parameters are the important ones. Therefore, it is necessary to evaluate these factors to better define optimisation approaches. In this study, sensitivity and estimability analysis were performed to evaluate sensitivity, estimability and correlations of parameters describing the equilibrium and nonequilibrium tracer transport in the field lysimeter. Estimability analysis was based on a sequential calculation algorithm of a sensitivity coefficient matrix. The comparison of estimability and sensitivity results indicated that estimability analysis is much more useful than sensitivity analysis. The former allows evaluation of the information content of the tracer breakthrough data and possible correlations among parameters. The estimability results indicated that the tracer breakthrough data contained limited information content for estimating the hydraulic and solute parameters in the nonequilibrium model. Furthermore, the high correlation between the first-order rate solute and water transfer coefficients was found based on those data. This study may be considered as warning for the use of tracer breakthrough data to investigate the nonequilibrium solute transport at the field lysimeter scale. This further suggests that additional data are required to increase the ability of estimating the hydraulic and solute parameters at the given experimental conditions