The reconstruction of the great 2020 torrential flood in Western Serbia

Abstract

The Ljubovida watershed in Western Serbia with an area of 158 km(2) is frequently affected by torrential floods, which have devastating effects. The soil characteristics, land use patterns and rugged topography ensure the rapid generation of surface runoff during extreme rainfall events. The main focus of this work is to reconstruct the extreme torrential flood event of Ljubovida on 22 June 2020, by applying three flood estimation methods suitable for ungauged watersheds-the hydraulic method of flood traces, the rational method and the combined method of Soil Conservation Service and synthetic unit hydrograph theory (SCS-SUH). In all three methods, there are the most sensitive and critical parameters, so the derivation of their values was carefully carried out. These parameters are the Manning roughness coefficient, n in the method of flood traces, the runoff coefficient, C in the rational method and the curve number, CN in the SCS-SUH method. Therefore, in the case of a watershed with no hydrological record, we propose the employment of multiple methods to minimize the uncertainties in the analysis of torrential floods. The approach with three implemented methods in this work allowed to compare the obtained results, i.e. estimated peak discharges: (a) Q(maxFT) = 176.8 m(3) s(-1) by applying the hydraulic method of flood traces; (b) Q(maxRM) = 152.7 m(3) s(-1) by applying the rational method; and (c) Q(maxSCS) = 186.7 m(3) s(-1) by applying the SCS-SUH method. Taking into account the variability of the results, the mean peak discharge of the June 2020 Ljubovida flood of 172.07 m(3) s(-1) is adopted, so the specific maximal discharge is 1.09 m(3) s(-1) km(-2). According to the SCS-SUH method, we concluded that the flood event of Ljubovida on 22 June 2020, was a flood with a 100-year return period. The main results and findings could serve as a solid basis for designing future studies on flood risk management in response to the growing hazards of torrential floods.