摘要:
长江上游剥蚀沉积物通量是影响长江流域河湖体系平衡的最重要因素。近几十年来,不适人为的地质作用已严重影响并打破了原有的长江流域河湖体系的沉积一搬运平衡系统,主要表现在:①上游自然环境的破坏,使河湖沉积体系沉积物通量大量增加;②中下游围湖造田和不适当的人为河湖治理工程(如裁弯取直、送沙出湖等),改变了长江流域洪沙的自然分配平衡。研究表明,洞庭湖及鄱阳湖为现代构造沉降型补偿平衡盆地,沉降速率等于或略大于目前盆地范围内的沉积物平均淤积速率,具备为长江分洪滞淤的潜在沉积可容空间。长江流域河湖体系沉积平衡的恢复治理,应包括以下几个方面的措施:①整治上游,减少水土流失,减少或抑制整个河湖体系沉积物通量,减缓河湖淤积压力;②顺应长江流域河湖自然分洪分沙规律,开辟荆江南北二岸分洪分沙河道,同时开垸扩湖或湖垸置换;③疏通河道与加固垸堤并举;④上游(主、支流)建坝分洪分沙。
Abstract:
The denuded sediment flux in the upper reaches of the Yangtze River is the most im-portant factor which exerts the influence on the evolution and equilibrium of the fluvial-la-custrine systems in the Yangtze River drainage area.The wanton and artificial geological processes are responsible for the disruption of the pre-existing deposition-transport equi-librium of the fluvial-lacustrine systems in the Yangtze River drainage area over the last decades,and mainly manifested in:(1)the significant increase in the sediment flux in the fluvial-lacustrine systems due to the destruction of the natural environments in the upper reaches of the Yangtze River,and (2)the changes of the natural distribution and equilibri-um of flood deposits along the Yangtze River due to the reclamation of land from the lakes and wanton and artificial control (e.g.cutoff) in the lower and middle reaches of the Yangtze River.The results of research in this study have revealed that the subsidence rates are equal to or slightly greater than the average silting rates in the present-day Dongting and Poyang Lakes as modern tectonic subsidence-type compensation-equilibrium basins;therefore they may provide the potential accommodation spaces for flood diversion of the Yangtze River.Finally the authors have suggested several measures for the recon-struction and management of sediment equilibrium in the fluvial-lacustrine systems along the Yangtze River.It is imperative that we should:(1) strengthen the management of the upper reaches of the Yangtze River,and reduce the soil erosion and sediment flux through-out the fluvial-lacustrine systems so as to reduce the loading of river and lake silting;(2) open up the flood channels on both the northern and southern banks of the Jingjiang River in Hubei,and open the protective embankments and expand the areas of lakes;(3)dredge the channels and reinforce the embankments,dykes and dams,and (4)build more dams in the upper reaches of the Yangtze River and its tributaries aiming at flood diversion.
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