title: Understanding changes in the hydrological behaviour within a karst aquifer (Lurbach system, Austria).
abstract: A thorough data analysis combined with groundwater modelling was conducted in an Austrian binary karst aquifer to better understand changes in the hydrological behaviour observed at a karst spring. During a period of 4 years after a major flood event the spring hydrograph appears to be more damped with lower peak flow and higher baseflow than in the years before. The analysis of the hydrograph recession suggests that the observed hydrological change is caused by changes within the karst system rather than by varying hydro-meteorological conditions. The functioning of the aquifer and potential causes of the observed changes are further examined using the groundwater flow model MODFLOW. The simulation results suggest that a modification of hydraulic conductivity and storage within the conduit network, e.g. due to the plugging of the drainage conduits with sediments, may be the cause of the different behaviour. MODFLOW was able to reproduce the observed dynamics of spring flow, although it does not account for turbulent flow within karst conduits. Using a simplified model scenario it is demonstrated that the damping of the hydrograph is much stronger if turbulent conduit flow is taken into account. Thus, a turbulent flow model is needed to assess potential changes in the storage properties quantitatively.
authors.affiliation: Institute for Earth Sciences, University of Graz, Heinrichstraße 26, 8010 Graz, Austria.
authors.forename: Cyril
authors.initials: C
authors.lastname: Mayaud
authors.affiliation: Institute for Earth Sciences, University of Graz, Heinrichstraße 26, 8010 Graz, Austria.
authors.forename: Thomas
authors.initials: T
authors.lastname: Wagner
authors.affiliation: Department of Water Resources and Environmental Analytics, Institute for Water, Energy and Sustainability, Joanneum Research Forschungsgesellschaft mbH, Elisabethstraße 18/II, 8010 Graz, Austria.
authors.forename: Ralf
authors.initials: R
authors.lastname: Benischke
authors.affiliation: Institute for Earth Sciences, University of Graz, Heinrichstraße 26, 8010 Graz, Austria.
authors.forename: Steffen
authors.initials: S
authors.lastname: Birk
keywords: Binary karst aquifer; Groundwater modelling; Hydrological behaviour; Laminar/turbulent flow; MODFLOW; Single-continuum model