WATERCOURSE (EN: channel, water course, stream, water flow; DE: Wasserstrom, Wasserlauf; FR: cours d'eau; ES: curso de agua, corriente de agua; RU: водоток) is the natural (or artificial) water flow, which is moving along the direction of the slope. They distinguish the permanent or temporary watercourses, and the superficial and underground watercourses. They categorize as the superficial watercourses the rivers, brooks, canals, and so on, which can serve as the sources of the supply for the aquifers, and for the water flooding of the mine workings; and they categorize as the underground watercourses the flows of the karstic canals and caves within the massif of the rock, and also the flows of the water diversion ditches within the underground mine workings. In case of the undermining of the watercourse, there are observed the sudden breakthroughs of the water from this watercourse into the mine workings, sometimes with the carrying of the loose sandy-clayish, gravel, and pebble rocks (especially during the freshet periods) on the account of the erosion of these rocks by the water.