维持东洞庭湖湖泊功能的河湖格局研究

River-lake patterns to support lake functions of East Dongting Lake

洞庭湖为我国第二大淡水湖,湖泊功能丰富。近年来,受气候变化、三峡工程运用和社会经济发展共同影响,洞庭湖水位偏低,湖泊功能面临挑战。湖泊功能的发挥需要以一定的水文条件为基础,本文以城陵矶七里山水位表征东洞庭湖河湖格局,将河湖格局分为河相（水位小于22 m）、河相主导（水位介于22～24 m）、湖相主导（水位介于24～26 m）、湖相（水位大于26 m）共四个阶段,对应的湖相指数分别为小于1.0、1.0～1.7、1.7～4.3、大于4.3。1950—2012年观测资料表明,这四个阶段多年平均在年内所占比例分别为45%、13%、16%、26%,其中湖相主导和湖相天数均呈下降趋势。基于湿周法,总结维持东洞庭湖湖泊功能的适宜水位范围为24～26 m,年内天数应在60天以上为宜。

Dongting Lake, the second largest freshwater lake in China, is facing various challenges coming from relatively low water levels due to climate changes, the operation of the Three Gorges project, and the development of social economies. The lake functions are supported by certain hydrological conditions. This paper analyzes the river-lake patterns of this lake with different water stages at the Chenglingji hydrological station. These patterns are divided into four phases, i.e. river-like patterns at the water stages below 22 m, river-dominated patterns at the stages of 22-24 m, lake-dominated patterns at the stages of 24-26 m, and lake-like patterns at the stages above 26 m, corresponding to lake-river indexes smaller than 1.0, 1.0-1.7, 1.7-4.3 and larger than 4.3 respectively. In-situ observations during 1950-2012 show that the annual mean percentage time periods during which the four phases occurred within a year, were 45%, 13%, 16% and 26% respectively. And the periods of both lake-dominated and lake-like patterns were presenting a decreasing trend. We have applied a wetted perimeter method to examine the relationship of lake functions versus water stage, and come to the conclusion： To maintain the functions of East Dongting Lake, the Chenglingji water stage should be in the range of 24-26 m and its annual occurrence longer than 60 days.