Abstract
Complex hydrogeological systems require detailed knowledge of aquifer dynamics to ensure appropriate and sustainable management of the groundwater resource. The Riardo Plain aquifer, southern Italy, is a strategic resource for conjunctive uses; nevertheless, the conceptual model still suffers some uncertainties due to the presence of a deep lateral inflow through the carbonate basement. Therefore, the realisation of a 3D numerical model at catchment scale needs preliminary tests to constrain the possible additional inflow rate, which is at the moment only estimated through the results of the groundwater budget calculation. A 2D section of the mixing area was modelled using FEFLOW in order to test the hypothesis of a combined recharge. Seven versions of the same model were calibrated over an increasing number of adjustable parameters according to their sensitivity. The most efficient model version was identified according to the calculated information criteria and the sum of squared-weighted residuals. In the second phase of the work, nine model scenarios characterised by different deep inflow rates were calibrated and validated according to the same procedure of the first model, in order to identify the range of possible acceptable solutions. The most likely deep inflow rate is 34 ± 4% of the total recharge, corresponding to an estimated deep inflow of 415 ± 50 L/s in the Riardo Plain aquifer through the carbonate basement. This methodological approach will be the basis of following numerical 3D numerical models of the Riardo Plain and can be a valuable tool in conceptualising similar mineral water areas.
Highlights
Numerical modelling of aquifers at catchment scale is a fundamental tool for the management of all groundwater resources, especially in strategic aquifers exploited for conjunctive purposes
The covariance matrix values are quite low, even if a few parameters are affected by a high covariance, and the specific storage of the BLT_dx zone (S - blt_dx in the electronic supplemental material (ESM)) presents an extremely high variance
Sometimes the values are close to the autocorrelation (Hill and Tiedeman 2007); a deep analysis of the eigenvectors and the eigenvalues is necessary as suggested by Doherty (2015)
Summary
Numerical modelling of aquifers at catchment scale is a fundamental tool for the management of all groundwater resources, especially in strategic aquifers exploited for conjunctive purposes. The implementation of a regional three-dimensional (3D) numerical model usually suffers many uncertainties depending on the model scale, geometry of the aquifer and reliability of the applied boundary conditions (Bredehoeft 2005; Hill and Tiedeman 2007; Renz et al 2009; Sepúlveda and Doherty 2015; Giacopetti et al 2016; Andrés et al 2017; Lancia et al 2018). Some authors have reduced the amount of information required through the building of two-dimensional (2D) models, where the absence of the third dimension limits the number of adjustable parameters (Sena and Molinero 2009; Pola et al 2015; Lancia et al 2018). 2D numerical investigations can be performed isolating the salient hydrogeological properties, to explain specific dynamics, which cannot be understood otherwise, due to the high number of unknowns at regional scale
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