Climate change can directly influence groundwater systems through modification of recharge. Affecting not only groundwater levels and flow dynamics, climate change can also modify the fragmentation and hierarchy of groundwater flow systems. In this study, the influence of climate change-impacted recharge on groundwater levels and on interconnected groundwater flow patterns is evaluated. Special emphasis is placed on how flow system hierarchy may change, to examine possible consequences on groundwater-related shallow surface water bodies and on groundwater-surface water interaction. As a test site with no significant anthropogenic impacts, the Tihany Peninsula in Hungary was an ideal area for the study. We address the following issues: i) How might a groundwater system, including groundwater-surface water interaction, be modified by predicted climate change?, ii) Given the variable groundwater levels and flow patterns, how will the water levels and fluxes be impacted around surface water bodies?, and iii) How sensitive are groundwater-related wetlands to these changes, and will they be maintained or will they eventually disappear? In order to answer these questions, two-dimensional transient numerical simulations were performed based on site-specific measurements and climatic prediction at the Tihany Peninsula. Results show that future climate trends can cause dynamic evolution and dissipation of transient groundwater flow systems, and the characteristic flow system hierarchy can change from nested flow systems to a set of single flow cells. Preservation of associated groundwaterdependent ecosystems would be challenging under these conditions since long-term climate change could potentially have serious consequences, including wetland disappearance. Understanding these transient processes in two-dimensions can also help to setup three-dimensional site-specific models.
Anthropogenic activity such as damming or diversion of rivers cause extensive disturbance to ecosystems, as well as the interaction between surface water and groundwater.Following the diversion in 1992 of the River Danube (NW Hungary) and the construction of a water barrage system, the level of shallow groundwater dropped and altered the connection between surface water and groundwater. This paper outlines the changes in the interaction of surface water and shallow groundwater and other related environmental consequences caused by an 80% decrease in runoff resulting from this intervention. The time series (1996)(1997)(1998)(1999)(2000)(2001)(2002)(2003)(2004) of 27 water quality variables measured from three surface and three subsurface sampling sites Prerpint of ATHROPOCENE 22, pp. 51-65 doi: https://doi.org/10.1016/j.ancene.2018.05.002 2 were analyzed using periodicity, hierarchical cluster-and principal component analyses. It was found that: (i) the degree of riverbed clogging increased due to diminished runoff; this clogging blocked interaction between surface water and groundwater at certain sampling sites; (ii) extreme floods were capable of resetting this situation and changing the flow currents to differing degrees in the surface/sub-surface waters. These findings enabled a better understanding of the changes in water quality primarily attributable to the diversion of the river (the change in water level, riverbed clogging etc.). The changed hydrological setting of the subject area became very similar to that which might be expected to evolve due to climate change around the world. Thus, the study not only serves as an example for the processes evolving (e.g. riverbed clogging) in similarly modified river sections, but to those as well, which are expected to suffer from aridification.
Hydrogeological processes acting at the margins of confined and unconfined thick carbonate sequences are particularly interesting due to a complex system evolution including partial uplift of fully confined carbonate systems and subsequent erosion of cover layers. We provide insights into this evolution by simulating coupled density-dependent fluid flow and heat transport based on the Buda Thermal Karst (BTK) system (Hungary) in a 2D vertical plane. Applying an equivalent porous medium (EPM) approach using the Heatflow-Smoker finite element model, scenario modelling of three evolutionary steps was carried out between the fully-confined carbonate stage through to partly and completely unconfined conditions over the western ridge. The numerical simulations were used to derive the main evolutionary characteristics of groundwater flow and heat transport patterns for the unconfined and confined parts of the hydrogeologic system. The initial fully-confined state led to the development of thermal convection cells due to the insulating role of the low-permeability confining layer, which facilitates buoyancy-driven flow by restricting the dissipation of heat. Over geological time, these cells were gradually overprinted by gravity-driven flow and thermal advection due to uplift of the west ridge. The limited thickness of the cover allowed sufficient water infiltration into the system, which led to increased cooling. Further uplifting led to a prevalence of gravity-driven groundwater flow. The results highlight the critical role of confining formations on flow patterns, and their effect on heat distribution and dissipation over geological time scales. The results have important implications for heat accumulation as well as for the development of a deep geothermal energy potential in confined carbonates.
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