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永定河斜贯北京市的西南,是北京地区最大的河流。其上源分南北两支:北支洋河,源自内蒙古兴和县以北的山麓;南支以桑干河为主干,源于山西宁武的管涔山。桑干河在东流至河北省朱官屯附近,与北来的洋河会合以后,始称永定河。永定河切穿北京西山,形成了一条长达108公里长的峡谷,即官厅山峡,尔后在三家店附近出山,泄于平原之上,又东南流经天津市海河流入渤海,全长680多公里。流域面积4.7万平方公里。永
Yongding River obliquely through the southwest of Beijing, is the largest river in Beijing. Its source points north and south two branches: North Branch Yang River, from the foothills north of Xinghe County, Inner Mongolia; South branch to Sanggan River as the backbone, stems from the Shanxi Nunnery Guan Yu Shan. The Sanggan River flows eastward to Zhu Guantun in Hebei Province and joins the Yangyang River in the north to the Yongding River. The Yongding River cuts through the Xishan Mountain in Beijing and forms a canyon of 108 kilometers long, the Guanting Mountain Gorge. Later, it flows out of the Sanjiadian near the plain and flows southward through the Haihe River in Tianjin into the Bohai Sea. It is over 680 kilometers long . The basin area of 47,000 square kilometers. Wing