hydrogeological analysis of thermal water outflow from a carbonate aquifer in the Eastern part of the Julian Alps

Preučevanje dinamike regionalnega sistema toka podzemne vode od napajalnega območja do cone iztoka je zelo učinkovit način iskanja odgovorov na bistvena hidrogeološka vprašanja, kot so: kakšna je geometrija kroženja toka podzemne vode, kje so glavne poti pretakanja, kakšna je naravna porazdelitev temperature v različnih geoloških formacijah in kakšna je intenziteta toplotnega toka. Če so ta vprašanja konceptualno ustrezno postavljena, lahko odgovori pomembno prispevajo k boljšemu razumevanju dinamike podzemne vode in nenazadnje tudi načrtovanju smotrne rabe termalne vode. V doktorski disertaciji preučujemo hidravlične, geokemične in geotermične procese v geotermalnem sistemu s toplimi izviri na območju Bleda, ki ga predstavlja sistem kraško-razpoklinskih vodonosnikov. Tu se z dvema vodnjakoma in izvirom rabi termalna voda s temperaturo med 19 in 23 °C. Geotermalni sistem na Bledu je opredeljen z vrsto robnih pogojev, pri čemer so značilni predvsem: prisotnost vertikalne komponente toka podzemne vode, velike relativne razlike v nadmorski višini med napajalnim območjem in območjem iztoka termalne vode ter vzpostavitev koncentriranega in hitrega iztoka ogrete vode proti površju. Na podlagi terenskih opazovanj v obdobju 2018–2021, laboratorijskih in statističnih metod ter matematičnega modeliranja toka podzemne vode in prenosa toplote smo opredelili značilnosti porazdelitve gladine podzemne vode in tokovnih vzorcev v regionalnem karbonatnem sistemu ter prostorsko opredelili hidrodinamske in geotermične značilnosti iztoka termalne vode. Ugotovili smo, da je iztok termalne vode na Bledu posledica vzpostavitve kompleksnega tokovnega polja, ki ga inducirajo velike višinske razlike med nadmorsko višino napajalnega zaledja in območja iztoka, nanj pa vpliva tudi heterogenost in anizotropnost geoloških formacij ter njihove hidrogeološke značilnosti.Studying the dynamics of the regional groundwater flow system from recharge areas to the discharge zones is probably the most efficient way to answer some fundamental hydrogeological questions, namely: What is the geometry of the groundwater circulation systemwhere are the main flow pathswhat is the natural temperature distribution in the different geologic formationsand what is the magnitude of the heat flow? If properly addressed, these questions can make an important contribution to the study of groundwater dynamics and ultimately to the planning of the sustainable use of thermal water. In this dissertation we study the hydraulic, geochemical, and geothermal processes in the low-temperature geothermal system with warm springs in the Bled area, in a system with karst-fissured aquifers. Here, thermal water with a temperature of 19 to 23 °C is exploited by thermal springs and two pumping wells. The Bled geothermal system is defined by a number of precise boundary conditions, such as a vertical component of groundwater flow, large relative elevation differences between the recharge area, and the discharge of thermal water and concentrated and rapid discharge of warm water to the surface. Based on field observations in period 2018–2020, laboratory and statistical methods, and mathematical modelling of coupled groundwater flow and heat transfer we determined the configuration of the water table and basin-scale flow patterns, and spatially determined the hydrodynamic and geothermal characteristics of the thermal water outflow. We found that the discharge of thermal water in Bled is a consequence of the emergence of complex flow patterns induced by large elevation differences between the recharge area and the discharge zone, and is also influenced by the heterogeneity and anisotropy of the geological formations and their hydrogeological properties