Using the Horyn River Basin rivers as an example the hydrograph separation algorithm was defined. The results of calculating different river feeding types values were given in the paper. Also, were analyzed their long-term dynamics. Ukrainian rivers are characterized by snow, rain, and ground (soil and underground) types of rivers feeding. The amount of snow and rain rivers feeding is determined by taking into account the characteristics of atmospheric precipitation and their correlation with water runoff characteristics. In the paper, the ground rivers feeding amount, in particular underground feeding, was established using an analytical (calculation) method. The key principles for river feeding amount determination such as graphic and geometric components of the hydrograph separation method application were described. Examples of using computer software for elementary figures areas calculating were considered. The total amount of separated hydrographs was 480. Daily observation data from 8 hydrological stations (water discharges) and 15 meteorological stations (air temperature, precipitation and snow cover height) were used for the research. Meteorological characteristics were correlated to the corresponding watersheds by determining the weight coefficient. The GIS system tools – ArcGIS were used for the catchment areas construction and their further division into separate areas of each weather station influence (Thiessen polygons). The resulting contours of the catchments were further refined on maps with a scale of 1: 50000. In general, for the period 1961-2020, it was established that the Horyn River Basin ground feeding values were from 31.6% to 68.4%; the share of snow feeding ranged from 19.7% (Horyn – Ozhenyn) to 41.6% (Smilka – Susly), and the average long-term values of the rain feeding share were ranged from 11% (Horyn – Derazhne) to 26.8% (Smilka – Susly). For Horyn River Basin rivers feeding types changes were assessed for two representative periods – 1961-1990 and 1991-2020. In general, for the Horyn River Basin in the present period (1991-2020) it was revealed a decrease in the relative values of the snow and rain feeding share by 8.4% and 1.6%, respectively, and an increase in the underground and soil feeding share by 5.7% and 4.3%, respectively.