Extreme hydrological events in karst areas of Slovenia, the case of the Unica River basin

Abstract

The study presents natural hazards in Slovenia's karst, focusing on flooding in karst poljes. A specific study was done on the flood dynamics of two typical and connected karst poljes (Cerknica and Planina) of the Classical Karst region. In the case of particularly extreme hydrological conditions in the autumn of 2008, detailed analyses of the recharge-discharge regime and the interrelationship of flooding on the two poljes were done. Daily precipitation, discharge, and water level values from several monitoring sites were analyzed and cross-correlated, and additional hydrological analyses were done using a digital elevation model in order to acquire water level increase and decrease intensity, flood water volumes, and the extent of flooding and to understand the conditions controlling karst flooding. The results reveal that the hydrological functioning of the studied karst poljes is influenced by the hydrogeological and temporary hydrological conditions in the catchment area. The response of the binary karst system (i.e., the influence of autogenic and allogenic recharge) is especially distinct. The study shows that during extremely intense recharge, the reactions of karst aquifer systems to precipitation are as rapid as the response of surface waters (the water level of Cerknica Lake increased with an intensity of 38-63 cm/day or 55 m 3 /s respectively) while retention capacities are negligible. In contrast to flash floods, floods in karst areas may last from several weeks to several months. For the observed period a three-dimensional simulation of the flooding was made. At the maximum recorded water level, the volume of water on the Cerknica polje was 51 million m 3 , and 26 million m 3 on the Planina polje. The maximum extent of flooding on the Cerknica polje was 23 km 2 and on the Planina polje 9.5 km 2 . On the basis of the study, information was provided regarding future hazard mitigation. However, the study demonstrated that a sufficiently dense monitoring network is necessary to predict the occurrence and duration of floods with greater certainty.

Sedimentary evolution and persistence of open forests between the south-eastern Alpine fringe and the Northern Dinarides during the Last Glacial Maximum

“…While Alpine rivers have wide catchments, with seasonal regime related both to snow-meltdown and abundant rainfall (Janža, 2013), those coming from the Northern Dinarides are strongly influenced by karst hydrology (Kovačič and Ravbar, 2010), thus showing underground reaches and enhanced sensitivity to heavy precipitations. The two hydrologic systems had different responses to climate changes during the Late Pleistocene.…”

Correlating Alpine glaciation with Adriatic sea‐level changes through lake and alluvial stratigraphy

“…6). Lake episodes were ephemeral and likely controlled by seasonal or decadal flooding, common in poljes of the Slovenian Karst (Kovačič and Ravbar, 2010).…”

Recent advances in karst research: from theory to fieldwork and applications

“…There is an urgent need to understand how human activities directly affect the recharge and flow of groundwater in karst because there are important consequences if karst lands are inundated during heavy and torrential rainstorms. This potentially leads to flash floods, which, in addition to sinkholes, represent the most common and dangerous hazard in karst (López-Chicano et al 2002;Parise 2003;Bonacci et al 2006;Jourde et al 2007Jourde et al , 2014Najib et al 2008;Kovacǐč& Ravbar 2010). There is a great need to improve our understanding of flood dynamics in karst terrains to contribute to the assessment and management of flood risks (European Council 2007).…”