长江中游荆江高洪水位形成的地质环境分析

GEOLOGICAL ENVIRONMENT OF THE FORMATION OF HIGH FLOOD STAGE ALONG THE JINGJIANG SEGMENT OF THE MIDDLE YANGTZE REACH

万里长江,险在荆江。其高堤防高洪水位(高出堤内地面大于13m)危险态势的形成,是由于一方面在地质构造控制下堤内地面沉降,另一方面大堤不断加高,荆江洲滩不断淤积抬高和洞庭湖出流顶托,造成同流量水位不断升高,结果是洪水位与堤内地面势差不断加大,形成恶性循环。三峡水库建成后,具有调蓄长江上游洪水的巨大空间和能力,但没有改变形成荆江高洪水位的地质作用及过程。在高堤防高洪水位形势下,加上大堤管涌、岸崩、地震等致灾地质因素的作用,荆江有向北溃决,自然分流的趋势,其中尤以沙市湾迎流顶冲的盐卡段更具有危险性。为避免发生区域性重大地质环境灾害,协调人、地、水关系,给水沙以出路和洪水资源化已迫切地摆在人们面前。

For hydrological regime,Jingjiang segment is the most dangerous part of the Yangtze River.Due to elevation of Jingjiang beach,warping of Dongting Lake,heightening of water level at same discharge and thus the silting of Jingjiang on one hand,and structurally controlled subsidence of basin on the other hand,the potential difference between flood level and basin ground keeps increasing continuously,and high embankments and high flood stage（more than 13mabove the embank ground）along Jingjiang Segment is formed.Although establishment of the Three Gorges Reservoir has brought about great regulation and storage capacity against the flood in the Upper Yangtze River,it has not changed the geological process.This leads to the formation of high flood stage in Jingjiang Segment.Heightening of the levee and the flood stage are accompanied with disaster-causing geological processes such as embankment piping,shore collapse,earthquake etc..The Jingbei Plain is severely threatened because Jingjiang river segment has a natural streaming tendency to burst from the Yangtze River,and the Yanka section at the Shashi-bay is more dangerous.To avoid great geological and environmental disasters and to harmonize the relationship of human,land and water,strategies for giving way to river water and sand as well as for utilization of flood resources are urgently needed.