This paper shows the results of the hydraulic-hydrologic calculations of karst spring discharges and the groundwater level in the aquifer of spring catchment. The calculations were performed for the Golubinka spring in Zadar area for the 4-year period. The chosen approach was a model using relatively scarce data set, including limnigraphic data on the difference between the sea water level and the freshwater level on the spring itself and the precipitation data from the meteorological station Zadar. The determination of discharge hydrographs, based on inherent assumptions and available data, yields the proportionality coefficients between the discharge and the limnigraphic data on the Golubinka spring itself. Further, based on the discharge hydrograph, groundwater level oscillation was determined. The resulting spring discharge hydrograph and groundwater levels, along with the assumption of Golubinka spring as the only spring on the catchment, were used in creating turbulent seepage model of the fractured system within the aquifer, which evidently extends along the axis of the Golubinka spring catchment. The model yielded suitable turbulent seepage coefficients of the fracture system. By using the numerical model KarstMod it was estimated that, on average, concentrated fracture flow drains around 85% of infiltrated volumes and the remaining 15% accounts for diffuse matrix flow. Finally, the Modflow model was used in order to get insight into the flow field and the distribution of equipotentials in the aquifer of the Golubinka catchment.

This paper presents the methodology for determining the die-off coefficient of faecal indicator bacteria (enterococci) when transported in a karst environment. The main problem in exploring karst environments, which this methodology strives to cope with, is lack of field measurements, poor data on karst rock formation, fractures and channels within it, and groundwater level dynamics. The analysed karst catchment (Bokanjac–Poličnik) is situated in the hinterland of the city of Zadar (Republic of Croatia) and covers an area of 235.07 km². In the water supply wells within the analysed catchment, a frequent occurrence of enterococci was observed. The proposed methodology consists of two basic steps. Preliminary analyses as the initial step were used in the accumulation of certain assumptions related to the detection of increased concentrations of enterococci as well as in determination of the potential source of pollution. In the second step, the analytical model was constructed with the aim of resolving processes of sorption and die-off and determining the dominant factor in the process of natural removal of enterococci when transported in karst environment. Within the model, two parts of the pollutant transport are integrated: vertical percolation and horizontal seepage flow and transport. The mean value of the total die-off coefficient by transport through the unsaturated zone in the analysed case is $k_{tot}$ = 8.25. Within the saturated zone the total die-off coefficient $k_{tot}$ is within the limits of 0.1 and 0.5.

The primary processing of high-resolution precipitation records (5 min and shorter) is crucial for constructing dimensionless design hyetographs and identifying design-critical precipitation scenarios for urban drainage systems. A key step in this process is separating continuous precipitation records into individual precipitation events, typically based on minimum inter-event time (MIT) and precipitation amount thresholds. This separation directly influences the subsequent analysis steps and the accuracy of the design hyetographs. Building upon this foundation, this study systematically analyses how different MIT determination methods influence the construction of dimensionless Huff hyetographs in a moderately humid continental climate. Three approaches for defining MIT were examined: a fixed MIT method (1–12 h), an autocorrelation-based method (AC), and a kernel density estimation approach (KDE). The analysis also considers the effects of minimum precipitation thresholds (P = 1, 3, and 5 mm) and precipitation duration classes (all durations and short-duration events with $T\le 2$ h), utilising a continuous 10-year series of 5 min precipitation data. The results demonstrate that the choice of MIT substantially affects the identified precipitation events, duration, total amount, and the median Huff curve’s shape, especially for precipitation types with early and late maximum intensity. Specifically, increasing MIT values produces longer and deeper events with steeper Huff curves, while precipitation thresholds mainly filter weaker events rather than impacting peak intensities. The AC method yields results similar to larger fixed MIT values (≈6–9 h), whereas the KDE method corresponds to shorter separations (≈1–3 h). To unify the assessment of design relevance, a composite design index combining Huff curve slope and short-term peak intensities was introduced. Analysis shows that short-duration convective precipitation with an early maximum is the most critical design scenario. However, late-maximum events (events in which peak intensity occurs in the fourth quartile of storm duration, Type 4) can become equally critical when longer MIT values or autocorrelation-based separation are applied. These findings underscore the importance of a transparent and methodologically consistent definition of precipitation event separation criteria when using dimensionless hyetographs in urban drainage design.

U ovom radu izvršeno je dimenzioniranje visoke masivne armiranobetonske brane prema uvjetima opće stabilnosti konstrukcije. Analitičkim postupkom su proračunate vrijednosti normalnih naprezanja u tijelu brane. Provedena je usporedba s rezultatima vrijednosti naprezanja dobivenih numeričkom analizom u programu SAP2000. Provjerene su tri kombinacije opterećenja za dva tipa temeljne stijene. Bolje poklapanje rezultata analitičkog i numeričkog proračuna uočeno je u slučaju temeljenja brane na krućoj stijeni.

Aim of the study: The aim of the study is to analyze the occurrence of drought in Požega, its temporal evolution, and its influence on daily discharges of the Orljava River, which flows through Požega, with an additional discussion on possible implications for hydropower potential. Material and methods: In this paper, the analysis of drought for the period from 1961 to 2024 is based on the Standardized Precipitation Evapotranspiration Index (SPEI), which is calculated for Požega, a city in the continental part of Croatia. Results obtained with SPEI were compared with those from another drought index, the New Drought Index (NDI). Further analysis of both indices across all time scales is provided using the RAPS (Rescaled Adjusted Partial Sums) method, and, based on the obtained sub-periods, daily discharges of the Orljava River are analyzed, and an index representing hydrological drought, Standardized Streamflow Index (SSI), for the Orljava River (station Požega) is also calculated. Results and conclusions: The results showed that there are two statistically different subperiods regarding drought occurrence: from 1961 to 1999 and from 2000 to 2024. The second subperiod is characterized by lower SPEI and NDI values, indicating more severe drought conditions. Based on daily discharges from the Orljava River, discharges are calculated for the entire period and for two subperiods identified through drought analysis, corresponding to 50% and 70% probability of occurrence. The lowest discharges are observed during the second subperiod, which is also characterized by more intense drought conditions. These results underscore the significance of drought and indicate possible constraints for hydropower development.

Design hyetographs derived with the Method of average variability (MAV) depend on two decisions usually made subjectively: the boundaries of the duration classes used to average rainfall events and the number of blocks into which the events are divided. This study proposes an objective framework for both decisions and applies it to 259 events lasting 10–120 minutes from 10 years of 5-minute rainfall data in Osijek, Croatia. The stability of each candidate MAV hyetograph was quantified by bootstrap subsampling. Admissibility required a sufficient number of rainfall events, stable peak characteristics and compliance with the prescribed discretisation constraints. Among admissible combinations, the partition of the duration range was found by exact dynamic programming (DP), implicitly considering approximately 2.1 million possible partitions. As peak dispersion increased with block count, stability was treated as a constraint, while the deviation of block durations from the recording interval was minimised. The data supported four to five classes; the selected partition, [10, 25], (25, 45], (45, 70] and (70, 120] min with 3, 7, 12 and 16 blocks, satisfied all criteria. Two subjectively defined partitions had almost three times poorer resolution and at least twice the peak dispersion, and only one of their nine classes was admissible.