Yan River

The Yan River's source is Zhou Mountain (Chinese: 周山), in the town of Tianciwan Jingbian County, Yulin.[1][4] The river then flows to the south into Yan'an, entering by passing through Ansai District.[5]

The Yan River continues its flow south to Baota District,[6] the urban center of Yan'an. In Baota District, the river passes through Hezhuangping, Qiaogou Subdistrict, Chuankou, Liqu, Yaodian, and finally, Ganguyi.[4] The portion of the river which flows through Baota District totals 62 kilometres (39 mi), and has a basin area of 2,203.68 square kilometres (850.85 sq mi).[4]

From Baota District, the river flows east through Yanchang County, where it merges into the larger Yellow River.[3]

The Yan River is highly seasonal, due to the large disparities in the region's wet season and dry season.[4] There is little year-round water flow contributing to the river.[4]

The Yan River's basin follows a gradient of higher elevations in the northwest, and lower elevations in the southeast, resulting in the river's flow in that direction.[4] Due to the geology of the Loess Plateau, the Yan River often follows a highly curvy path, and has a high sand content.[4] Landslides are common in the Yan River's basin.[4] 34% of the basin is covered in forest.[4]

The normal flow of the Yan River is about 4 cubic metres (140 cu ft) per second, and the annual average runoff is 220,000,000 cubic metres (290,000,000 cu yd).[4] The average sediment transport volume is 16 million tons.[4]

Throughout China's long history, the Yan River has been called a number of different names. During the Warring States period, the river was known as the Qushui (Chinese: 区水; pinyin: Qūshuǐ).[4] Later, during the Western Han, the river was called the Weishui (Chinese: 洧水; pinyin: Wěishuǐ).[4] Afterwards, in the Northern and Southern dynasties, and during the Western Wei, the river was known as the Qingshui (Chinese: 清水; pinyin: Qīngshuǐ).[4] During various points after the Western Wei, the river was called a number of other names, including the Jinshui (Chinese: 筋水; pinyin: Jīnshuǐ) and the Zhuojinshui (Chinese: 濯筋水; pinyin: Zhuójīnshuǐ).[4] The current name, the Yan River (Chinese: 延河; pinyin: Yán Hé), is only a more recent name for the river.[4]

The total length of the Yan River's tributaries total 10 kilometres (6.2 mi), and 11 of them have a basin area of over 100 square kilometres (39 sq mi).[4]

Tributaries along the Yan River's left bank include the Fengfu River (Chinese: 丰富川; pinyin: Fēngfù Chuān), the Panlong River (Chinese: 蟠龙川; pinyin: Pánlóng Chuān), and the Wuyang River (Chinese: 五阳川; pinyin: Wǔyáng Chuān).[4] Tributaries along the river's right bank include the Xi River (Chinese: 西川; pinyin: Xī Chuān), the Nan River (Chinese: 南川; pinyin: Nán Chuān), and the Masi River (Chinese: 马四川; pinyin: Mǎsì Chuān).[4]