This work presents the impact of land cover on water relations in the catchment of the Bogdanka watercourse which is 51.9 km². The research and analysis of available cartographic materials have shown a significant increase in the anthropogenically transformed areas due to urbanization from almost 8% in 1940 to over 42% in 2012. Urbanized areas (buildings and communication routes) have contributed to sealing the area and thus reduced retention capacity by 0.25 million m³. Therefore, the effective rainfall P_10% and P_1% have increased respectively by 0.4 mm and 0.8 mm. As a result the maximum flow of exceedance probability of 10% and 1% have reached over 20% in the Bogdanka watercourse.