FLOOD CONDITIONS in the Bolsk River catchment area

A hydrological study of high water events was carried out for the Bolsk River catchment area, determining the ‘actual’ maximum discharges and high-water waves with return periods of 10, 20, 50, 100 and 500 years at certain cross-sections of the Bolsk River and its tributaries. For the purposes of hydraulic modelling, input hydrographs are provided up to the confluence of the Bolsk and Konjšica rivers.

For the purposes of the analysis, meteorological and hydrological data were obtained from and analysed by the Slovenian Environment Agency (hereinafter ARSO). The analysis of precipitation (maximum daily precipitation, maximum precipitation over various durations ranging from 5 minutes to 24 hours) covered 18 precipitation stations, including 2 ombrographs.

A hydrological model of surface runoff was developed for each catchment area using version 4.0 of the HEC–HMS programme. Flood waves were evaluated using the synthetic unit hydrograph method according to the SCS method. The Muskingum–Cunge method was used to model the transformation of the high-water wave.

The assumption was made that rainfall with a return period of N causes runoff with a return period of N.