Abstract. Flash floods constitute one of the deadliest and costliest natural disasters worldwide. This paper explains the karst flash flood phenomenon, which represents a special kind of flash flood. As the majority of flash floods karst flash floods are caused by intensive short-term precipitation in an area whose surface rarely exceeds a few square kilometres. The characteristics of all flash floods are their short duration, small areal extent, high flood peaks and rapid flows, and heavy loss of life and property. Karst flash floods have specific characteristics due to special conditions for water circulation, which exist in karst terrains. During karst flash floods a sudden rise of groundwater levels occurs, which causes the appearance of numerous, unexpected, abundant and temporary karst springs. This paper presents in detail an example of a karst flash flood in the Marina bay (Dinaric karst region of Croatia), which occurred in December 2004.

The study area consists of the spring zones of the Krčić, Krka and Cetina river catchments located in the Dinaric karst, Croatia. Classical hydrological approaches and some newer time and frequency domain methods are used in order to validate the existing hypotheses both qualitatively and quantitatively, and these contribute to factual information about the hydrological behaviour of the catchments. The groundwater recharge rates are calculated by a mathematical model based on Palmer's soil-moisture balance method. The values of parameters of the groundwater recharge model are estimated by the spectral method. The calculated monthly and annual groundwater recharge rates form the basis for estimating the hydrological catchment areas of the spring zones and also for the determination of quantitative relationships between the catchments.Key words catchment area; Croatia; effective rainfall; groundwater recharge; karst hydrology; karst spring Définition de l'aire d'un bassin versant karstique: cas des rivières Krčić et Krka (Croatie)Résumé La zone d'étude correspond aux zones de sources des bassins versants des rivières Krčić, Krka et Cetina dans le karst des Dinarides. Les méthodes hydrologiques classiques, ainsi que certaines nouvelles méthodes dans les domaines temporel et fréquentiel, sont utilisées afin de valider qualitativement et quantitativement les hypothèses existantes, et de contribuer à la caractérisation factuelle du fonctionnement de ces bassins versants. Les taux de recharge hydrogéologique sont calculés au moyen d'un modèle mathématique basé sur la méthode du bilan de l'humidité du sol de Palmer. Les valeurs des paramètres du modèle de recharge hydrogéologique sont estimées par méthode spectrale. Les taux de recharge mensuels et annuels calculés sont à la base de l'estimation des aires des bassins versants des zones de sources, ainsi que de la détermination de relations quantitatives entre les bassins.Mots clefs aire de bassin versant; Croatie; pluie efficace; recharge hydrogéologique; hydrologie karstique; source karstique

No abstract

No abstract

Abstract:The Jadro River with total length of 4.3 km and average annual discharge of 7.9 m 3 s -1 is a relatively small river on the east coast of the Adriatic Sea, close to Split. Field campaign measurements were made to estimate salt intrusion in the Jadro estuary in July 2012. This measurement confirmed the stratified character of the estuary where fresh water flows in a thin layer over denser sea water. Furthermore, a numerical model was set up for simulating unsteady stratified flow without mixing between the layers. The model is applied for the Jadro River and field measurements are used for calibration. In addition, the steady state of stratification within the estuary is analyzed by a box model which assumes mixing between layers. Results of the numerical and the box models were compared. The flushing time estimated with the box model is approximately 1.5 day for summer steady conditions. Numerical analysis however shows that the residence time is much larger owing to flow unsteadiness.