Numerical simulation of groundwater flow in a carbonate aquifer system of central Apennine (Italy)

A conceptual model related to a mountain aquifer that is characterized by a lack of data 15 of hydrogeological parameters and boundary conditions, which were based on a single available 16 observational dataset used for calibration, was studied using numerical models in order to evaluate 17 the associated uncertainties and errors and consequently the goodness of the conceptual model’s 18 assumptions. The analysis was based on four models that were characterized by an increasing 19 degree of complexity using a minimum of two zones and a maximum of five zones, which 20 consequently increased the number of adjustable parameters from a minimum of 10 to a maximum 21 of 22, calibrated using PEST. Statistical index and information criteria were calculated for each 22 model, which showed comparable results; the information criteria indicated that the model with 23 the low number of adjustable parameters was the optimal model. A comparison of the simulated 24 and observed spring hydrographs showed a good shape correspondence but a general 25 overestimation of the discharge, which indicated a good fit with the rainfall time series and a 26 probably incorrect extension of the aquifer structure: the recharge contributes more than half of the 27 total outflow at the springs but is not able to completely feed the springs.