洞庭湖演变趋势探讨

洞庭湖的演变主要受构造沉降、泥沙淤积和人类活动影响三大因素的控制。目前 ,洞庭湖盆的构造沉降速率虽然较低 (3～ 10mm/a) ,但构造沉降量仍抵消了部分泥沙淤积量 ,在一定程度上抑制了洞庭湖日益萎缩的趋势。由于湖盆中泥沙淤积速率大于构造沉降速率 ,洲滩会继续发育和扩展 ,洞庭湖仍保持淤高的趋势。在“4 35 0工程”完成和三峡建坝后 80年内 ,湖盆泥沙淤积速率将降低到 1 79mm/a ,洞庭湖不断淤高的趋势将得到减缓。

Discussion on the evolutionary trend of Lake Dongting

The evolution of Lake Dongting is determined by three main factors, which are tectonic subsidence, siltation and human impacts. "The Dongting Basin" and "the basin of Lake Dongting" are two different spatial concepts. "The basin of Lake Dongting" is only one of the components of "the Dongting Basin". The basin of Lake Dongting, the levees and the farmlands synchronously keep subsiding and relatively actionless due to the tectonic subsidence of the whole Dongting Basin. At present, the mean sedimentation rate of Lake East Dongting,Lake South Dongting and Lake Muping is 9.43, 19.11, 12.46mm/a, respectively. The rate of tectonic subsidence of the lake is low (3～10mm/a), but the capacity of tectonic subsidence still counteract a certain capacity of siltation, which restrains the shrinkage of Lake Dongting. The sedimentation rate is bigger than the rate of tectonic subsidence in Lake Dongting. Sandbars will continue to grow and expand, and Lake Dongting will still keep the trend of siltation and shrinkage. At present, the whole Dongting Basin is subsiding and expanding due to tectonic subsidence, which has no influence on the change of the capacity of storing flood of Lake Dongting, and siltation is playing a main role. The capacity of storing flood of Lake Dongting will continue to decrease as siltation goes on. During the 80 years after the Three Gorge Dam is completed with the completion of "the 4350 Project", the sedimentation rate of Lake Dongting will reduce to 1.79 mm/a. Then, the trend of siltation of Lake Dongting will be restrained.