Hydrogeologic investigations at an overthrusted karst aquifer of the Outer Dinarides ,

Hermann H äusler 1, Philipp Stadler 1 1 University of Vienna , Department for Environmental Geosciences , Althanstrasse 14, A -1090 Vienna /Austria [email protected] , [email protected]

-59,0 250 Research Area -61,0 The research area is located in the , a Geologically the region of the upper Kupa catchments 200 belongs to the Outer Dinarides comprising mainly -63,0 southeast tending green Karst mountain range of the 150

-65,0H 2 D (‰) D Paleozoic to Mesozoic formations. We follow the [l/sec] Q δ Outer Dinarides inin north-western north-western Croatia Croatia with with altitudes altitudes δ 100 between 1000 and 1500 metres. It is well known for big tectonic concept of Herak (1980), who identified -67,0 End Jurassic formations as karst aquifers below 50 -69,0 End Karst springs such as Kupa, Kupica and Zeleni Vir, Start overthrusted and confining Permotriassic Start Biondi ć et al., 1998 overthrusted and confining Permotriassic 0 -71,0 belonging to the upper catchments of Kupa river. East of 15.06.2010 12:00 16.06.2010 00:00 16.06.2010 12:00 17. 06.2010 00:00 17.06.2010 12:00 18.06.2010 00:00 -10,45 -10,25 -10,05 -9,85 -9,65 -9,45 -9,25 δ18Oδ18 (‰)O formations (Biondi ć et al., 2006). Q Karst Spring Precipitation Signal Q Creek Precipitation Signal Delnice the karst spring Zeleni Vir is located below the Karst Spring Precipitation Signal Reference Sample Karst Creek Precipitation Signal Reference Sample Creek LMWL

village . Spring zone Fig 1 (left): Course of isotope ratio during short termed monitoring at Zeleni Vir. Appreciable karst springs discharge Precipitation signal (marked red) shows the arrival of rainwater at the sample spot. The discharge of Zeleni Vir from Jurassic carbonate rocks. This The best fitting LMWL was taken from Vreca et al., 2006 aquifer lithology is highly karstified, [δ2H = (7.6 ± 0.4) δ18 O + (10.5 ± 4.0)]. spring ranges between big caves are bound to this area. April2011 3 -1 Karst springs and caves are related Fig 2 (right): Discharge graph with precipitation signal. April2011 0.3 and 65 m sec to fold- and fault structures of the red marking the arrival of rainwater at the sample spot. (Biondi ć et al., 2006) and Outer Dinarides. An event monitoring for stable isotopes was done in is collected in a An event monitoring for stable isotopes was done in Vienna Zeleni Vir (June 2010). A thundershower followed a Vienna , powerplant´s pressure Thrust fault , Impermeable Permotriassic clastica are overthrusted over Jurassic formations. Clastica, rainless period. A sample spot was chosen that allowed a pipe line. appearing as an aquiclude are separating the hydrogeological catchment from the spring zone and leading to specific discharge and storage dynamics of the local karst springs. parallel sampling of a karst spring and a surface

Hydrogeological catchment runoff dominated creek. The sample campaign lasted 48 Assembly Triassic and Jurassic formations are Assembly highly fractured and karstifed. hours. Speleothemes and palaeo soil fillings were observed. Environmental isotopes of samples were measured using a Picarro Inc. Isotopic Water Analyzer combined with a CTC HTC-Pal autosampler (LEAP Technologies).

The karst spring shows a parallel but massively damped Union, General Union, General Union, General Union, General reaction on the event (Fig. 1). No decisive precipitation influence (event water) during Detail from the Hydrogeological Map of Croatia, after Croatian Geological Survey 48 hours of monitoring was measured. This fits the general hydrogeological model (see profile Geological profil (left) from the 1:100 000 sheet „Delnice“ (HGI 1985, Geosciences sketch on the left) of a recharge area approximately 10 Geosciences Savic & Dozet) showing impermeable Paleozoic clastics with a kilometres to the south. persistent thickness up to 1000 meter. This older stratigraphic The estimated linear velocity inin thethe locallocal karstkarst aquifer aquifer isis interpretationinterpretation is is contrary contrary to to the the modern modern hydrogeolo hydrogeological map (HGI lessless thanthan 5cm/sec.5cm/sec. Hydrogeological map of Croatia) where Paleozoic clastics are European References: European overthrusted over carbonate rocks (karstified), allowing a karst water BIONDI Ć,, B.,B., BIONDIBIONDI Ć,, R.,R., DUKARIDUKARI Ć F. (1998): Protection of karst aquifers in the Dinarides in Croatia,Croatia, EnvironmentalEnvironmental Geology,Geology, 34,34, 44 Schematic profile-sketch BIONDI Ć,, B., B., BIONDIBIONDI Ć,, R., R., KAPELJKAPELJ S.S. (2006):(2006): KarstKarst groundwater groundwater protectionprotection inin thethe KupaKupa River River catchmentcatchment area area andand sustainablesustainable flow below the impermeable formations (right). development, Environmental Geology, 49, 828-839 Showing the local hydrogeologic model of a Jurassic karst aquifer which is HERAK, M. (1980): The nappe system between and Delnice in Gorski Kotar (Croatia), Acta Geologica (Prirodoslovanalovana overthrusted by Paleozoic confining formations. Istrazivanja),Istrazivanja), 10/2,10/2, 35-51,35-51, ZagrebZagreb VRE ĆA, P., BRONI Ć,, I.I. K.,K., HORVATINHORVATIN ĆIC,IC, N.,N., BARESIBARESI Ć J.J. (2006):(2006): IsotopicIsotopic characteristicscharacteristics ofof precipitationprecipitation HS 8.26 A310 inin SloveniaSlovenia andand Croatia:Croatia: ComparisonComparison ofof continentalcontinental andand marine stations, Journal of Hydrology, 330, 457-469