洞庭湖环境系统变化对水文情势的响应

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。

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

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.