历史时期北京平原上湖泊众多,地表泉数以百计。历史时期由于永定河冲积扇的地下潜水水位较高,在潜水溢出带周围出露数以百计的下降泉,成为平原上众多湖泊的主要水源补给,并满足城市规划、园林设计、运河漕运、游憩休闲的需要。随着现代化城市的迅速发展,永定河冲积扇的地下潜水水位迅速下降,原来分布在潜水溢出带周围的数以百计的下降泉已经全部枯竭,位于其下游许多湖泊也随之干涸消亡,北京平原地表水系被彻底改造,城市生态环境发生巨大变化。

The origin and development of the old Beijing City is closely related with its local surface water system of the alluvial plain.The surface water within or around the city not only was the part of local ecological system,but also provided the needs for the everyday life in the old city,such as the cannel transportation,the landscape garden design,even the city planning.According to the historical documents,more than one-hundred seepage springs and many small lakes were distributed on the Beijing Plain that was mainly consisted of the Yongding River’s alluvial fans.During the historical time,the underground water table was much higher than today,and a plenty of phreatic water discharged along the hyporheic zone of the toes of alluvial fans as the seepage springs.These seepage springs not only provided the water for the nearby small lakes,but also acted as the sources of rivers that originated on the fans.Based on their locations,the seepage springs can be grouped into two sets.The northern group of springs,which were distributed on the Yongding River’s old fan, included the Wanquan springs,the Diaoyutai springs,the Lianhua springs,and the Baixi springs.The southern group of springs,which were located on the Yongding River’s new fan,included the Caoqiao springs,the Yimuquan springs,and the Tuanpo springs.Generally,the phreatic water table had been fluctuating with the changes of rainfall and underground hydraulic condition,which might cause the changes of the seepage springs.From a long time scale,the seepage springs had been keeping stable,and some of them have existed for over one-thousand years.In the past 100 years,especially in the past 50 years,all the seepage springs once distributed on the alluvial fans vanished,and many lakes that formed upon the Yongding River’s abandoned meanders or ox-bow lakes dried up.This human’s irrational activities led to the rapidly dropping of the water table.Comparing to the historical time,the surface water system of the Beijing Plain has been thoroughly transformed by human.