Discharge regimes of the Bregana and Breganica rivers in Croatia

Abstract

The Bregana River is the 16.5 km long main right tributary of the Sava River on the border of Croatia and Slovenia. There are two hydrological stations on the Bregana River and one more on its main tributary, the Breganica River. The Bregana River drainage basin is mostly hilly and mountainous, sparsely populated, wooded, and humid, with a relatively developed stream network. The annual discharge change and the characteristics of the discharge regimes were analysed on the three hydrological stations between 1981 and 2020. No trend was recognised in mean annual discharges, but all three stations recorded a slight increase in annual minima discharges and a more pronounced increase in annual maxima discharges in the last twenty-year period (2001–2020) compared to the previous twenty-year period (1981–2000). Moreover, in the last twenty-year period, some changes occurred in the discharge regime in the research area. For all three stations in the Bregana catchment an increase in the share of annual discharge was recorded in February and March and a decrease in the share of annual discharge in December and January. Bregana River stations recorded a decreased share of annual discharge from May to July (especially in June). At all three stations, in the last twenty-year period compared to the previous twenty period, the primary maximum in March is a bit more pronounced, and the secondary maximum in December (November at Koretići station) is less pronounced. Also, for all three stations in the last twenty-year period, the primary minimum shifted from August to July and the secondary minimum shifted from February to January.