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Modern and effective water management in large alluvial plains that have intensive agricultural activity requires the integrated modeling of soil and groundwater. The models should be complex enough to properly simulate several, often non-linear, processes, but simple enough to be effectively calibrated with the available data. An operative, practical approach to calibration is proposed, based on three main aspects. First, the coupling of two models built on wellvalidated algorithms, to simulate (1) the irrigation system and the soil water balance in the unsaturated zone and (2) the groundwater flow. Second, the solution of the inverse problem of groundwater hydrology with the comparison model method to calibrate the model. Third, the use of appropriate criteria and cross-checks (comparison of the calibration results and of the model outputs with hydraulic and hydrogeological data) to choose the final parameter sets that warrant the physical coherence of the model. The approach has been tested by application to a large and intensively irrigated alluvial basin in northern Italy.

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Water resources represented by coastal aquifers are very important for regions characterized by a relevant request of freshwater, but limited rainfall, lack of surface water bodies and intrusion of the seawater through the sediments which host groundwater. Therefore some coastal areas, like the Salento peninsula (southern Italy), are subjected to the risk of desertification and a proper management of groundwater resources requires tools to analyze and predict the water balance and the evolution of the physical system in response to human activities (e.g., ground water withdrawals) and climatic factors. The Salento peninsula is a typical Mediterranean basin, where the main water resource is the aquifer hosted in Cretaceous carbonatic rocks (Calcare di Altamura, Altamura limestone): this is a fractured and karst aquifer, with a poor recharge and complex relationships with the sea. In order to develop a tool to assess the water balance at regional scale for the considered aquifer system, a groundwater flow model was developed by Giudici et al. (2012a); it is based on a conceptual model obtained from a reconstruction of the hydrostratigraphic architecture of the region, which includes the main aquifer and the overlaying rocks characterized by low permeability which can host local and relatively thin aquifers. In this paper that work is updated, by improving the reconstruction of the hydraulic head and of the conceptual model, above all in those areas that the previous model evidenced as critical for the absence of fresh water along the whole aquifer thickness. Moreover, since the estimate of some model’s input parameters is affected by high uncertainty, a sensitivity analysis is performed to evaluate the effects of this uncertainty on the model’s results.

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Abstract:Modeling flow and transport in porous media requires the management of complexities related both to physical processes and to subsurface heterogeneity. A thorough approach needs a great number of spatially-distributed phenomenological parameters, which are seldom measured in the field. For instance, modeling a phreatic aquifer under high water extraction rates is very challenging, because it requires the simulation of variably-saturated flow. 3D steady groundwater flow is modeled with YAGMod (yet another groundwater flow model), a model based on a finite-difference conservative scheme and implemented in a computer code developed in Fortran90.YAGMod simulates also the presence of partially-saturated or dry cells. The proposed algorithm and other alternative methods developed to manage dry cells in the case of depleted aquifers are analyzed and compared to a simple test. Different approaches yield different solutions, among which, it is not possible to select the best one on the basis of physical arguments. A possible advantage of YAGMod is that no additional non-physical parameter is needed to overcome the numerical difficulties arising to handle drained cells. YAGMod also includes a module that allows one to identify the conductivity field for a phreatic aquifer by solving an inverse problem with the comparison model method.