Quantification of groundwater flow in the Molasse basin with respect to density-driven flow

Groundwater flow in the Malm aquifer of the Molasse basin has been the subject of wide-ranging research due to its intense geothermal utilization and regional economic importance. In one such study, a 2D groundwater flow simulation model was developed in 1999 and applied for addressing water management issues including conflicts of use. To ensure consistency between the field-measured and calculated pressure potentials which assumed a uniform density, they defined a mean water density as a correction factor to calibrate the model.While developing the hydrogeological conceptual model, the evaluation and interpretation of data from the geothermal wells in Upper Austria provided the first evidence that, in addition to the pressure potential, the driving force of groundwater flow in the Malm aquifer could also include buoyancy forces caused by density differences. Since the inclined and confined Malm aquifer is exploited for geothermal energy in the Molasse basin, high temperature gradients are induced and thus the buoyancy component of the driving force for flow cannot be neglected.In order to quantify possible deviations from the pressure potentials, the driving-force ratio (DFR) values for selected wells were determined and analysed. The results provide the basis for further development of the flow model with respect to density-driven flow.