The Yongding River has two branches of headstreams— the Xinghe County in inner Mongolia in the north and Guancen Mountain(in the north of Shanxi Province) in the south. The River was named Wuding River in ancient times. It runs past Shanxi, Inner Mongolia and Hebei Provinces, 650 kilometers long. Its section in Beijing is 170 kilometers long. Yongding River flows out of the mountain in Sanjiadian of Mentougou District, where its river way is even 40 meters higher than the Tian’anmen Square. Throughout history, the river had been relentlessly overflowing many times on the Beijing Plateau. During the stretch from the founding of Jin Dynasty in 1115 through 1949, there han been 83 dam bursts — one in every five years. Historical record said that during rhe Ming and Qing Dynasties, the flood swept across the city, passing the five water gates to Tongzhou County, bringing a high death toll. The uncontrolled torrent flooded the Zhengyang, Chongwen, Xuanwu and Qihua Gates and an corner of the Wu Gate was soaked and collapsed. The water in Chang’an street was one meter deep. The city walls within the Donghua Gate and Desheng Gate were all ruined. The flooding hadn’t been controlled until the year1854 when the Guanting Reservoir was built in Huailai County, Hebei Province, which also left Yongding River dried up since then.
The sand and mud carried by the River from the Loess Plateau formed a vast piece of alluvial fan with soft soil. The undercurrent of the alluvial fan combined into springs, lakes, and age-old waterways, which had created a fertile land for Beijing.