Flash floods occurred repeatedly in different places on earth. We are a big threat in the cities situated in the foreland of the mountains. Flowing down from the mountains causes flood wave passing through the city of large material losses. High risk the occurrence of a flood prevails in Bogatynia located in the Sudeten. In August 2010, in the Miedzianka catchment (89.2 k^{2}), located at Bogatynia town has occurred a flash flood. The maximum flow was 190 m^{3}s^{-1} and the maximum outflow unit reached 4.3 m^{3}s^{-1}km^{-2} (one of the highest ever recorded in the Sudety catchments). Result of this flooding in Bogatynia were huge material losses (sume 225 million zł). In Bogatynia in the history of repeated floods, and several of them caused huge material losses. The largest of them occurred: 29 July 1609, 31 July 1703, 2 May 1804, 29 July 1897 and 7 August 2010.