The evolution of the fluvial-lacustrine systems and protection and control of catastrophic floods along the Yangtze River

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.