Franko Humer

Identification of a karst system’s intrinsic hydrodynamic parameters: upscaling from single springs to the whole aquifer

For water management purposes, information about an entire aquifer system is generally more important than information about a specific spring. Since a karstic aquifer system might drain to several outlets, conclusions derived from a single spring can be misleading for characterization and modeling. In this study we apply a conceptual model to an Alpine dolomite karst system in Austria. The particular challenge was that several small springs with strongly varying hydrological behavior and diffuse flow into surrounding streams drain this system. Instead of applying the model to a single spring, it was calibrated simultaneously to several observations within the system aiming to identify the karst system’s intrinsic hydrodynamic parameters. Parameter identification is supported by modeling the transport of water isotopes (δ18O). The parameters were transferred to the whole system with a simple upscaling procedure and a sensitivity analysis was performed to unfold influence of isotopic information on parameter sensitivity and simulation uncertainty. The results show that it is possible to identify system intrinsic parameters. But the sensitivity analysis revealed that some are hardly identifiable. Only by considering uncertainty reasonable predictions can be provided for the whole system. Including isotopic information increases the sensitivity of some intrinsic parameters, but it goes along with a sensitivity decrease for others. However, a possible reduction of prediction uncertainty by isotopic information is compensated by deficiencies in the transport modeling routines.

Hydrological Modeling of an Alpine Dolomite Karst System

In most cases dolomite karst systems show less karstification than limestone karst systems, especially in terms of the formation of a conduit system. This study site is a dolomite karst system located in the northern part of the Kalkalpen national park, Austria. Preceding water balance investigations and information gained by artificial and environmental tracers provided the base for the development of a conceptual model, which represents the dominant processes of this system. Storages and fluxes are described by a series of reservoirs each representing a particular element of the system, i.e., soil, interflow, preferential flow and flow through the fissures. First, the model predicts only runoff. Then, to check the representation of subsystems and the choice of parameters, it simultaneously simulates δ18O composition and runoff. Regional sensitivity analysis shows that including δ18O information changes parameter identifiability but at the same time reduces model performance.