THE DIFFERENTIAL SYSTEM METHOD FOR THE IDENTIFICATION OF TRANSMISSIVITY AND STORATIVITY

The differential system (DS) method for the identification of transmis sivity and storativity is applied to a confined isotropic aquifer in t ransient conditions. The data that are required for the identification are the piezometric heads and the source terms, together with the val ue of transmissivity at a single point only, which is the only paramet er value needed a priori. In particular, no a priori knowledge of stor ativity is needed and, moreover, the identification of transmissivity does not depend upon storativity. The DS method yields the internode t ransmissivities necessary for the conservative finite differences mode ls in a natural way, because it identifies transmissivities along the internodal segments, so that a well-known formula can be applied that bypasses the difficulty of finding an equivalent cell transmissivity a nd an averaging scheme. In addition, the DS method takes into account several different hows all over the aquifer, so that the identified pa rameters are to a certain degree 'global' and 'flow independent'. More over, the method allows for a piecemeal identification of the paramete rs, thus keeping away from the regions where wells are pumping so that a two-dimensional model can be used throughout. We test the applicabi lity of the DS method with noisy data by means of numerical synthetic examples and compare the identified internode transmissivities with th e reference values. We use the identified parameters to forecast the b ehaviour of the aquifer under different exploitation and boundary cond itions and we compare the forecast piezometric heads, their gradients and the associated fluxes with those computed with the reference param eters.