The flow rate is one of the most important elements of the river’s water regime. Establishing patterns in river flow rates’ changes within a year and by season is of great importance for the hydrological forecasts for spring floods, rain floods and hydrological calculations. By now, there are few publications on this area, both in Russia and abroad. The initial data were divided into 5 hydrological seasons – winter and summer low water, rise and fall of spring floods and autumn rain floods. For each season, an analysis of river flow rate over a period (1936-2013) was done. The average flow rate in rivers varied greatly depending on the water regime’ phase and the type of terrain in which the river flows. For all seasons, the amplitude of fluctuations in the flow rate on the plain rivers is less than on the mountain ones. So, in mountain rivers, flow rates vary from 0.04 to 2.42 m/s, and on flat rivers from 0.02 to 1.43 m/s. As well the pairwise and multiple correlation coefficients of flow rates for each morphometric and catchment characteristics were calculated. The highest correlation coefficients were obtained for the dependency between the average flow rate and the watershed elevation (0.30-0.75) and the watershed slope (0.42-0.76). The multiple correlation coefficients between the average flow rate and all catchment’s morphometric characteristics varied from 0.97 to 0.99. Results verification on an independent data demonstrated that the relative error was on average 2%.