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Integral approach for the protection of the Jadro and Žrnovnica springs catchment - Dalmatia, Croatia

The catchment of the Jadro and Žrnovnica springs has a crucial importance as a water resouces for Split and neighboring coastal and inland inhabited areas. According to different hydrology and hydrogeology estimations, the Jadro and Žrnovnica recharge area stretches between 250 and 500 km2. The whole region is composed of carbonate rocks, mainly well permeable Mesozoic, Eocene and Perms limestones, dolomites and impermeable lower Triassic clastic deposits and Eocene flysch. Jadro spring outflows below the Mosor Mountain (1300 m) and Kozjak (600 m) on the elevation of 32 m (34, 6 m), and bellow the Mosor Mountain, Žrnovnica spring on 90 m above sea level. Both springs appear on the contact between well permeable limestones and impermeable flysch deposits.The minimum measured discharge of the Jadro spring was 0, 22 m3/s (16.11.1985.), maximum was 78, 1 m3/s (13.11.1997.), and an annual average discharge was 9, 7 m3/s. Zrnovnica spring has a relative smaller discharge with minimum of 0, 250 m3/s (09.09.1993.), a maximum discharge of 19, 1 m3/s (18.12.2004.) and an annual average discharge of 1, 5 m3/s. Previous, very valuable studies mainly were focused on regional hydrologic or hydrogeologic evaluations or some particular issues within the catchments related to environmental or groundwater protection. Despite being a major source of fresh potable water area for over 300.000 inhabitants, until today the monitoring of groundwater quantity and quality were performed only on outflow points - on springs. Knowledge about a water level and its fluctuations within the whole study underground were always only presumed in comparison with previous measurements in boreholes constructed for monitoring a few artificial accumulations in the karst of Dinarides. Also, recent anthropogenic pressures in inland part of recharge area and increasing trends of some contaminant content in spring waters initiated a comprehensive study which included detailed geological, morphological, structural, hydrogeological, hydro geochemical and environmental isotope research. The main aim of this study is to prepare baselines for managing the quantity and a quality of groundwater resources. Basic previous knowledge about the study area was analyzed, summarized and interrelated with incorporation of new obtained data of geological, morphological, structural, hydrological, and hydrogeological part of study especially new tracing tests and hydrogeochemical results. Structural and morphological analyses contribute to design a layer for further assessment of groundwater risk (density of dolines map, map of relief slopes, map of dominant runoff direction etc.). All data are prepared and presented using GIS tools. According to European Framework Water Directives and added appendixes, one part of project was focused on establishing a monitoring system which should include monitoring of groundwater quantity and quality within the large recharge area. For this purpose four monitoring bore-holes were design in different part of catchment. Locations of monitoring bore-holes are connected with estimated groundwater direction towards to Jadro and Žrnovnica springs on following karst poljes Dugopolje, Konjsko polje, Gizdavac and Bisko polje. First monitoring borehole located on the Dugopolje is now ready for further installation of monitoring equipment. During the last two years continuous monitoring of hydrogeochemical and environmental isotope where performed on both mentioned springs as well as on 9 additional springs from surrounding catchments. This will provide additional data for delineation of recharge area. The use of obtained hydrogeochemical and environmental isotope data enabled new knowledge of groundwater origin and flow and recharge mechanism within the study catchment. Obtained results confirmed some previous hypothesis about the origin of the Jadro and Žrnovnica spring water as well as the size of recharge area along the eastern hydrogeological border. There are quite serious indicators that few karst springs of the Cetina River catchment share the same recharge area of Jadro and Žrnovnica springs. Consequently, for the future study the Jadro and Žrnovnica recharge area should be considered as a transboundary aquifer. Groundwater resources in karst areas are one of the most fragile environments of the world. Continuously increasing natural influences, caused by world wide climate changes especially in Mediterranean region, and recent anthropogenic impact, obligate an intensive consideration of all influences connected with such a valuable water resource. For this purpose, the recharge area of the springs, Jadro and Žrnovnica, will be the first in the Croatian karst region with hydrogeological guidelines and designed quantity and quality monitoring system suitable for further groundwater management.

karst ; monitoring design ; water management

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