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• Validating the conceptual model of a hydrothermal system in fractured carbonates. • Parametrization of the units through reinterpreted data and new local measurements. • 2D numerical simulations confuted the available conceptual model. • Revised conceptual model of the system physically validated by simulations. • Applicability of this approach for initial investigations in hydrothermal systems. Carbonate rocks represent the most abundant geothermal aquifers worldwide, excluding active volcanic areas. The most important challenge is to accurately define the conceptual model of a regional hydrothermal system. The focus of modelling is generally on the outflow area of the system and its fluid flow dynamics, while the geological and hydrogeological characterisations of the recharge area and the estimation of the local infiltration rate are rough. Thermal water is usually characterised by long residence time, and classical hydrogeological balance can give misleading results. On the other hand, long-term numerical simulations could represent a useful tool to understand the regional and local fluid flow circulations and to estimate the hydrogeological features of the recharge area. Numerical modelling has to be supported by an accurate characterisation of the regional and local hydraulic and thermal properties of the reservoir. This methodology was applied for the first time in Croatia in the case study of Daruvar hydrothermal system. Its recharge area had been determined decades ago solely by geological mapping, as a wide zone in the mountainous hinterland of natural thermal springs. Mesozoic fractured carbonate rocks represent the geothermal aquifer, and the tectonic juxtaposition of these permeable formations with low permeable Neogene deposits enables the rising of thermal water (38–50 °C) up to the surface. 2D coupled flow and heat transport numerical simulations of the hydrothermal system were performed for the first time in this research using measured data on its temperatures, and hydraulic and thermal conductivities. However, their results did not support the existing conceptual model. Conceptual model of the system was therefore revised decreasing the extent of the possible infiltration area and considering the fracturing induced by local faults in the Daruvar subsurface. A new set of simulations was conducted using the proposed model. The obtained results reproduced the temperature of the Daruvar thermal springs and the regional fluid flow. Despite its limitations, the employed modelling approach was useful to perform a first simulation of the hydrothermal system dynamics, and it could be employed in similar systems to evaluate the consistency of different hypotheses on the available conceptual model and their impact on the temperature distributions. In addition, the modelling demonstrated that the recharge area is smaller than previously considered, which has implications on the protection of the whole hydrothermal system. The greatest danger to the system currently comes from the increasing anthropic impact in the recharge area by multiple active dolomite quarries in the region and the related seismic disturbances, which should be limited in the newly defined recharge area. [ABSTRACT FROM AUTHOR]

The Euganean Geothermal Field (EGF) and its thermal water (temperature from 63 °C to 87 °C) represent an important environmental and economic resource for the Veneto Region (NE Italy). Approximately 14.7 × 10 6 m 3 of hot water were exploited in 2015 through 142 boreholes from rocky aquifers located at different depths. The water is mainly used for balneotherapy feeding approximately 240 pools. Hundreds of thousands of tourists visit the spa facilities of the EGF every year, producing a huge income for the regional economy. The Euganean thermal resource suffered a significant anthropic impact during the 20th century related to the development of the local tourism industry. Hydrogeological data and information about the utilization of the resource spanning the century are analyzed to evaluate this impact with the aim of assessing the sustainable utilization of the thermal resource. In particular, the potentiometric levels of the thermal aquifers are affected by seasonal variations (i.e., decreases during the spring and autumn, recoveries during the winter and summer) induced by the different flow rates related to the tourist seasons. Similarly, the historical reconstruction of the level shows a decrease during the initial and middle parts of the 20th century followed by a gradual recovery up to the present. The reduction of the level was related to the growth of the tourism industry attested by the increase in exploitation, wells, mining claims and tourists. The limitation of the flow rate and its continuous monitoring have produced the observed recovery since the 1990s. The performed reconstruction suggests that the present flow rate (approximately 14 × 10 6 m 3 /y) produces an acceptable drawdown preserving the Euganean thermal resource for future generations and maintaining a constant income for the regional economy. This work attests that thermal resources for balneotherapeutic purposes could be affected by overexploitation and depletion. Therefore, their sustainable utilization has to be achieved through specific management policies, preserving their important environmental and socio-economic values. [ABSTRACT FROM AUTHOR]

The Venetian plain is a densely populated area and one of the most economically competitive regions in Europe. Therefore, a sustainable management of the water resources has to be accomplished to preserve both the social and economic value of this area and the regional environment in accordance with the European water policy directives. This paper presents the analysis of hydrologic and hydrogeological water balances of the high alluvial plain (approximately 790km2) highlighting some important peculiarities that could be crucial for the local water policy. By focusing on the importance of different water budget components, the obtained results indicate in the irrigation the most relevant component of the aquifer recharge. Thus, the irrigation management policy of the Land Reclamation Consortia strongly influences aquifer recharge. Moreover, future scenarios (2071-2100) for the high Venetian plain are performed taking into account the changes of climate and irrigation policy. The inflow of the aquifer suffers a decrease ranging from 18% in the scenario influenced by climate change to 28% in the scenario affected by both the variations. In particular, the irrigation recharge shows the highest reduction due to both an increase in evaporation, owing to an increase in the surface temperature, or the irrigation methods. Therefore, the irrigation management policy adopted by the Land Reclamation Consortia is a fundamental concern. Changes from surface irrigation to spray or drip irrigation could strongly affect the aquifer recharge. The classical technique of surface irrigation is very useful in terms of aquifer recharge in comparison with drip or spray irrigation. However, it also requires a huge volume of water compared with the minimum desirable streamflow of a river and its management policy. Currently in Italy, the transition from conventional irrigation systems to water saving techniques is favored by the Land Reclamation Consortia in response to European and Italian directives. However, the possible reduction of the aquifer recharge could influence the actual social and economic condition of the Venetian plain because the human and industrial water needs are mostly dependent by groundwater exploitation. Therefore, water saving activities should be accompanied by appropriate corrective actions to reduce the environmental and social impact due to the decrease in aquifer recharge. [ABSTRACT FROM AUTHOR]