The paper presents the results of applying the deterministic model "Hydrograph" for calculating the water flow hydrographs of the mountain catchment of the river Derekoyka-Yalta (49.7 km2, elevation difference of 14-1398 m). Runoff modeling was performed with a daily time step for the periods 1967-1988 and 2016-2017 using data from the AI-Petri and Yalta meteorological stations. The average and median Nash-Sutcliffe efficiency values were 0.28 and 0.33, exceeding the 0.60 value in more than a third of cases. The quality of the calculated hydrographs largely depends on the representativeness of the input precipitation data. Comparison of the calculated and observed curves of maximum water flow security allowed us to evaluate the simulation results as satisfactory. The maximum water consumption of the rain flood that occurred in Yalta on September 6, 2018 was calculated. According to calculations, the maximum daily discharge was 14.9 m3/s and exceeded the previous maximum value observed in
