INVERSE MODELING OF SEAWATER INTRUSION IN THE LLOBREGAT DELTA DEEP AQUIFER

A Row and mass transport mathematical model has been calibrated to sim ulate piezometric head and chloride evolution in the Llobregat delta c onfined aquifer. A twenty-year period (1965 - 1985) is simulated with monthly time steps. Automatic estimation of flow and transport paramet ers are obtained by means of a code that simulates Bow and mass transp ort of constant density fluids, In this case, density differences owin g to groundwater salinity changes by marine intrusion can be neglected because the aquifer thickness is relatively small and because both th e horizontal density gradient and the aquifer dip are small. Calibrati on of the flow problem leads to an excellent fit between measured and computed heads, which, however, can be obtained with different transmi ssivity patterns, When switching to the transport problem, best result s in terms of concentration fits are obtained by associating the seawa ter intrusion plumes with high transmissivity zones that fan be attrib uted to palaeochannels. In short, transient head and concentration dat a have been used jointly for automatic calibration of a regional model , which has proven advantageous both because it facilitates model sele ction and because it has led to a model with an improved conceptual ba sis. (C) 1997 Elsevier Science B.V.