Ao River (Zhejiang)

The Ao River (Chinese: ), also known as the Aojiang River, is a river in Wenzhou, Zhejiang, China. One of the eight major river systems in Zhejiang, the Ao is traditionally divided into three sections: the upper reaches known as Shunxi, the middle reaches called Beigang, and the lower reaches referred to as Aojiang. The largest tributary is Nangang, also known as the Hengyang Branch River. The main stream extends for 90 kilometres (56 mi). The Ao River basin covers Wencheng County, Taishun County, Pingyang County, Cangnan County, and Longgang City in Wenzhou, with a total drainage area of 1,521.49 square kilometres (587.45 sq mi). The Ao River is one of the few rivers in China, apart from the Qiantang River and the Min River, that exhibits a tidal bore phenomenon, and it has long been associated with the traditional practice of tide watching.

The Ao River was historically known as the Shiyang River, a name derived from Shiyang County, which was established in 283 CE. When Shiyang County was later renamed Hengyang County, the river accordingly became known as the Hengyang River. By the Song dynasty, the river had become known as the Qiancang River, due to the town of Qiancang on the river, while the section downstream of Xindu was called the Ao River. In modern usage, "Ao River" has become the standard name for the entire river. The name "Ao" is associated with the tidal bore at its estuary. In local tradition, the surging tide was likened to a giant mythical turtle bearing a mountain on its back, hence the name Ao River. The town of Aojiang on the northern bank of the estuary also takes its name from this feature. The people from Jiangnan Plain on the southern bank traditionally referred to the river as the Qinglong River, and the name of Longgang City derives from this name.

The Ao River basin covers four counties and one county level city in southwestern Wenzhou, namely Wencheng, Taishun, Pingyang, Cangnan, and Longgang. Its main stream is commonly divided into three sections: Shun Creek , Beigang , and the Ao River proper. The river is 90 kilometres (56 mi) long, including an estuarine reach of about 10 kilometres (6.2 mi), and drains a total catchment area of 1,521.49 square kilometres (587.45 sq mi). A chain of small islands lies offshore from the estuary, which facilitates the formation of tidal flats. According to long term statistics from the water resources authorities, the Ao River estuary, shaped by tidal motion and upstream sediment deposition, is currently prograding seaward by about 10–20 metres (33–66 ft) per year. Major tributaries on the left bank include Mei Creek , Tengjiao Creek , Fengwo Creek , Huai Creek , Yue Creek , and Shizhu Creek . On the right bank, the main tributaries are Nangang , Qingjie Creek , and Aoxia Creek , with Nangang being the largest.

The headwaters of the Ao Riverlie in the border area where four counties meet: Wencheng, Pingyang, Cangnan, and Taishun. In June 1987, the Ao River Water Conservancy Command organised an upstream field survey and ultimately identified the river's source as Wudi Mountain , a branch of the South Yandang Mountains, located at the southern foot of Guiku Village , Guishan Township, Wencheng County. The main peak of Wudi Mountain reaches 1,124 metres (3,688 ft) metres above sea level, while the Ao River rises from its southern slope at an elevation of 835 metres (2,740 ft). From its source to Dongmen Village in Nanyan Town, Pingyang, the Ao River's upper course is known as Shunxi , or the Shun Creek. This reach is about 30 kilometres (19 mi) long, has an average channel gradient of 2.7%, and drains a catchment area of 215 square kilometres (83 sq mi). Within it, the section from the river source to Shunxi is about 19.1 kilometres (11.9 mi) long and drains 112 sq

Flows through: People's Republic of China.

River data from Wikidata (CC0); lengths normalised to a common unit.