北京石景山、八角山、老山与古永定河的走向

Discussion on the Trending of Shijing Hill, Bajiao Hill, Lao Hill and Ancient Yongding River in Beijing

永定河是北京的过境河流,其上游称桑干河,发源于山西省宁武县管涔山天池。在河北省怀来县会合洋河妫水河以后,水量大增,然后转向南流,穿过北京西山进入北京平原。永定河挟带大量石沙奔腾而下,在平原地区石沙沉积于河底,使下游洪水多发,为害北京、河北二地。康熙皇帝更其名为永定河,祈求河水安澜。永定河古河道的走向与现在有所不同,现在是向东南流,古代是向东北流。古永定河河道为什么向东北流?前人缺乏研究探索。笔者根据实地考察所见河相沉积的分布,指出古永定河的走向,是从庞村转向东北流,这种流向与八角山、老山的阻挡直接相关。

Yongding River is a passing river through Beijing,its upstream called Sanggan River originated from sky pond of Guancen Mountain in Ningwu,Shanxi.Its capacity increases abundantly after it joins Weishui River and Yang River from Hebei Province.Then it flows to the south,passing by the West Mountain to Beijing Plain.Yongding River brings a mass of sediments to the plain,while the large sediments under the river often floods to the downstream where Beijing and Tianjin suffered a lot.Therefore,Emperor Kangxi changed the river's name as Yongding for optimistic blessings.The ancient Yongding River's riverway is to the northeast,different from nowadays to the southeastern.The reason for its change is induced by the distribution of the sediment and the natural barriers as Shijing Hill,Bajiao Hill,and Lao Hill