A river valley is a low-lying area of land that is formed by the erosion of a river over time. The term can refer to a variety of different types of valleys, including dales, wadis, and straths. A DALE is a valley that is typically found in Northern England and is characterized by its steep sides and flat bottom. A WADI is a dry riverbed that is found in desert regions and is usually filled with water only during times of heavy rain. A strath is a wide, flat valley that is typically found in Scotland and is often bordered by mountains.