EVALUATION ON THE FLOOD DISASTERS AND EFFECT OF HUMAN ACTIVITIES IN TAIHU PLAIN IN 1991

Abstract

1991年6、7月间,太湖地区遭受特大洪涝灾害,受灾面积达3309km²,直接经济损失达106亿元。梅雨暴雨是造成这次洪灾的直接原因,短时间内,降雨量达899mm,为100—200年一遇,超过该地区的承受能力。人类活动对加重灾情亦有着重要影响,包括:围垦与泥沙淤积,使河湖调蓄功能下降;太湖出口河道74.6%被封淤堵死,致使太湖水位达4.79m,超过历史最高记录;圩外面积减少及城市化发展等。治理对策包括充分发挥河湖调蓄功能;合理安排圩外调蓄流量,打通骨干排水河道及城市防洪系统建设等。;The heavy storm rain from May 21 to July 13,1991 caused huge torrents and hit this area. About 3309km² in Taihu Plain were submerged by the flood water with total economic losses of US $ 2×10⁹.According to the investigation and statistics it is showed that about 45.0% of the area was below 4.5m and 52.2% of the area below 3.5m,but the water stage during the flood time reached 4.79m,so that about 62.5% of the area below 4.5m was inundated by the flood water. About 95% of the flooded area belongs to the paddy field and vegetable land. About 4 million people were affected by the calamities.On the basis of distribution of the flooded area,it can be divided into five catastrophic regions:the western part of the Plain affected by the waterlogging;the sorrounding area of Taihu Lake hit by high-level of flood water;the east plain flooded regions as a result of blockage of the drainage river,and urban areas such as Suzhou,Wuxi and Changzhou and their suburbs due to the development of the urbanization.The huge rainfall in Taihu Plain reached 899mm with its frequency years of one time in 100-200 years, excessing its whole capacity. So the lake level rose to the historical height. Human activities,in other hand,are playing an important role in aggravating the seriousness of disasters. (1) The storage and regulation function in lakes and rivers were decreased in past fourty years as a result of siltation and reclamation. (2) The drainage channels were blocked up by siltation,for example 70 streams among 84 streams of outlets in Taihu Lake were blocked up. (3) The area protected by embankments surrounding the low-lying paddy fields has been increased and led to the loss of 633km² of drainage and storage area. (4) In the urbanized areas the drainage systems were unsuitable to the prevention of flood disasters.The countermeasures include the rational arrangement of reclamation and storage, regulation of lakes and rivers, drawing up a plan of urban and regional development coordinating with flood prevention, enhancing the nonstructural programms such as establishing a monitoring system,disaster data base and flood insurance.