洞庭湖环境系统变化对水文情势的响应

The Response of Environment System Changes of Dongting Lake to Hydrological Situation

为全面揭示洞庭湖近数十年的水情异常与成因,将湖区视作一个大系统来研究.经水位～流量关系等多种方法研究表明:(1)入湖四水尾闾同水位流量减少1 200～2 800 m3/s,同流量水位抬高0.49～1.28 m;(2)荆江三口分水比减少19.2%,分沙比减少25.1%;(3)澧水、松滋、南洞庭湖等主洪道的水位流量关系均发生了较大变化;(4)天然调蓄能力下降40%,湖口同流量水位抬高1.80～2.50 m;(5)7～8月湖垸关系常处于危急状态.其主要原因是泥沙淤积恶性循环,导致了湖泊环境系统功能的变化,而由下荆江3处裁弯所引起的江湖水沙调整则加速了其变化过程.这些变化过程对水情的复合响应是:入湖水沙呈逐渐减少趋势变化,洪水位普遍抬高1.50～1.80 m,湖口有时出现江水倒流,洪水涨率增大,高洪水位持续时间长等异常水文现象,且给湖区造成了巨大的洪水压力.

To fu1ly reveal the water abnormity and its formative causes in Dongting Lake during recent decades, this paper takes Dongting Lake as a big system. Researches through a variety of methods such as the relation between water-level and runoff show: (1) The runoff on the same water-level reduces 1200 m3/s-2800 m3/s in the lower reaches of the four rivers flowing into the lake, the water-level with the same runoff runs up 0.49 m-1.28 m; (2) The dividing-water ratios of the three bayous of the Jingjiang River reduces by 19.2%, and the dividing-sand ratios 25.1%; (3) Great changes have taken place in the relation between water-level and runoff in the main flooding roads such as Li River, Songzi and southern Dongting Lake etc.; (4) The natural regulation and storage capacity fall off by 40%, the water-level with the same runoff at the bayous drives up 1.80 m-2.50 m; (5) The relation between lake and protective embankment is often at hazard during the period of July and August. The main reason is that the filling-up of mud-sand arises a vicious circle which leads to environmental function changes of the lake system, and the water-sand adjustment from the three curve-cuttings on the lower reaches of Jingjiang River accelerates the change process.