Rivers

Rivers flow in channeled watercourses and merge in confluences to form drainage basins, areas where surface water eventually flows to a common outlet. Drainage divides keep rivers separated from other courses of water and causes upstream water within the confines of the divide to fall into the downhill stream. Rivers have a great effect on the landscape around them. They may regularly overflow their banks and floodthe surrounding area, spreading nutrients to it. Sediment or alluvium carried by rivers shapes the landscape around it, forming deltas and islands where the flow slows down. Rivers seldom run a straight course, but instead meander (bend); the locations of a river's banks can change frequently. Rivers take up their alluvium by erosion of their beds, which carves rock and soil into canyons and valleys.