中文摘要：

南四湖是华北地区最大的淡水湖，通过对南四湖近50年来降水量、湖泊水位和蓄泄水量等水文要素分析，结果显示南四湖水位和蓄水量有较大变化，水位和蓄水量的变化除与年降水量的大小等自然因素有关系外，还与湖区工农业用水量的变化及水利工程建设等人类活动有关系。对南四湖水量蓄、泄变化关系分析可看出，在丰水年和平水年它表现出相似于天然湖泊的性质；而枯水年则体现出人工控制型湖泊特点，整年过程中湖泊处于以蓄为主的状态，对径流起显著调节作用。南水北调东线工程实施后，下级湖在输蓄水期间将长期维持33．0m的高水位，结果会使南四湖的水位变化保持一个相对稳定的高水位状态。

英文摘要：

Nansihu Lake located in the southwest part of Shangdong Province is of great value in environment ecology and economy. It is the largest lake in North China. The hydrographic features of Nansihu Lake, such as rainfall,water level, water storage and discharge amount are investigated. Results show that the water level and water storage in the lake has changed tremendously in recent 50 years, and the magnitude of water level and storage change is related to human activities, such as water consumption of industry and agriculture, and hydraulic engineering building, besides annual precipitation of drainage basin. The characteristics of water storage and discharge amount in Nansihu Lake exhibit similarity to those of the crude lake in high-flow year and mediu-flow year, and to those of manual-control lake in low-flow year that in all year the state of lake is in water accumulation, and the lake has controled of runoff of the basin. Since the plan of south-north water transfer was put into practice, the water level of the lake will keep lasting high water level over a long period of time.