river in Shanxi (Shansi) and Hebei provinces, part of the Hai River system, northwestern China. The Sanggan River is formed from source streams that rise close to Ningwu, near the Great Wall of China, and flows across the dry plateau of northern Shanxi. After running northeast in a trough parallel to the Heng Mountains, just south of Xuanhua (in Hebei), it turns east and flows into the Guanting Reservoir. Its main tributaries in Shanxi are the Yuanzi, Hun, and Yu rivers; in Hebei they are the Huliu and Yang rivers. During the Sui and Tang periods (AD 589–907), the name Sanggan was also applied to what since the late 17th century have been called the Yongding River, which flows from the Guanting Reservoir to Tianjin, and the Hai River, which flows from Tianjin to the Bo Hai (Gulf of Chihli). The Sanggan itself has a total length of about 180 miles (290 km) and a drainage area of approximately 18,500 square miles (48,000 square km).