洞庭湖的演变及其整治

本文指出洞庭湖发育的地质构造基础是新第三纪以来洞庭盆地的拗陷沉降。晚更新世末期,洞庭湖区为河网切割的波状平原。全新世以来,先是顺左河槽谷地发育河川型“沉溺湖”。近几百年来,主要由于四口分流携入大量泥沙在湖区北部淤填,形成宽广的漫滩平原,并导致西部入湖的水流在湖区绕行及在湖区南部出现湖面的扩张。根据目前情况,作者认为解决水流在湖区的绕行问题是洞庭湖实施整治的关键。

ON THE EVOLUTION OF THE DONGTING LAKE DURING HOLOCENE AND THE WAY OF MANAGEMENT

The Dongting Lake, which really consists of many Jakes, is situated at the northern Hunan Province and lies to the south of Middle Changjiaang River.It gathers the water from the Xiangjiang, Zishui, Yuanjiang and Lishui River (four rivers) and the distributaries coming from the Chanjiang River and then it flows into the Changjiang River again.In the end of the late Pleistocene and early Holocene, there was a wide eroded plain with several valleys, of which the tail of the Paleo-Yuanjiang valley was situated at the northern part of the Dongting region and its bottom reached a depth of about -12m above sea-level.Then, these incised valleys gradually became some "drowned-lakes" in consequence of the rising of world sea level and then the rising of the water level in the Mid-Lower Chang-Jiang Valley since post-glacial period.The main body of the Dongting Lake was situated at the northern part of the Dongting region hundreds or more than one hundred years ago.The marked change in geomorphology has been taking place from that time to the present. These changes include.(1) The drowned-lake situated originally at the northern part of the Dongting region has been quickly reducing and basically disappearing, and new lakes have been developing and gradually enlarging.But the total area of the lakes in the Dongting region has been unceasingly and rapidly reducing in this time.(2) After the flow of the Yuanjiang River into the Dongting region it changed its direction southeastwardly and round to the lake outlet The position of the Zishui's debouch has been migrating to the east.(3) The extent of the change of the water level has been gradually increasing in the Dongting region.These changes were the result of the increasing of sediments into the Dong-ting region, of which the distributaries coming from the Changjiang River have taken important part. Of late period, the amount of sediments from the distributaries into the Dongting region has been reduced and the coarse sand coming from the four rivers has been increased more and more.As far the management of the Dongting region for the future, the author proposes that we should reduce the amount of sediments into the Dongting region and change the flow system in the Dongting region for decreasing flow course, and raise the flood plain and "Yuan" surface situated at the debouchs of the four rivers by increasing the amount of mud and necok sediment for enlarging the ground gradient toward the lake outlet in the Dongting region.