Post-flood field investigation of the June 2020 flash flood in the upper Muráň River basin and the catastrophic flash flood scenario

After a dry spring, in June 2020 several intense storms occurred at the headwaters of the small basins of the Muráň and Zdychava rivers in the territory of the Muránska planina National Park (Slaná River basin, Slovakia). In the first part of the study– according to a hydrological survey made by the authors after the flash flood – the peak discharge was reconstructed at several Muráň River profiles. Next, the flash flood waves were reconstructed by the rainfall-runoff model NLC (non-linear cascade). The results of modelling based on field investigations show that, despite the extreme precipitation event (108 mm per 1 hour at the precipitation gauging station at Predná Hora), the peak flow rates were not exceptional in selected profiles on the Muráň River. The fact that extreme precipitation above 120 mm fell in a relatively very small area at the division of the Muráň and Zdychava rivers’ water contributed to this result. In the second part, a catastrophic 1000-year rainfall event scenario on the Zdychava River basin has been prepared. In analysing time series and identifying T-year daily rainfall depths, daily data was used from six precipitation stations in the vicinity of Muránska planina. Then, the 1000-year discharge of the Zdychava at Revúca was simulated by the calibrated NLC model. In such an extreme precipitation scenario, the peak flow rate would reach 105.15 m³ s⁻¹, i.e. with a specific runoff of 1.78 m³ s⁻¹ km–2. The total runoff in an 18-hour period would be 1.119 million m³, representing 21.11% of the rainfall (5.301 million m³).