THE EVOLUTION OF GEO ENVIRONMENTAL SYSTEM OF MIDDLE REACHES BASIN OF YANGTZE RIVER AND THE STRATEGIES FOR FLOOD PREVENTION

As a result of interaction of tectonic subsidence, silt sedimentation and embankment, the geo environmental system of Middle Reaches Basin of Yangtze River has been separated into two parts with different evolution tendencies:(1)the outside of embankment is an artificial over fed basin; (2)the inside of embankment is an artificial starved basin. Therefore, the flood levels become higher and higher in some parts of the Yangtze River and the Dongting Lake,and the elevations of the embanked lowlands increasingly decline. Flood and waterlogging disasters aggravate year by year. On the basis of systems analysis, the idea of reconstructing a new human nature composite geo environmental system is developed and the strategies for flood prevention are advanced.