长江中游西部地区洪水灾害的历史演变——人文因素与当前趋势

探讨了近3000年来长江中游西部洪水灾害发展的人文因素。古代（3000—700aBP）人口较少,多择地势高的岗地居住,只有少数沿江城市需要堤防保护;长江干流洪水可多处分道散流,所携带泥沙导致云梦泽解体消亡。自宋代开始,低地筑垸围湖,与水争地,但九穴十三口畅通,洪水灾害不严重。明代（700—450a B P）几乎完全堵塞了荆江北流的穴口,荆北大堤联成一体,但堤防薄弱,出现过30次决口成灾。清代以来,随着人口激增,与水争地矛盾加剧,堤防加高培厚,使荆江河道洪水位大幅度上升,溃堤和溃坝洪水灾害较明代成倍出现。同时,历代的“舍南保北”政策迫使长江干流大洪水中过半水量与泥沙向南泄入洞庭湖,曾使洞庭湖面积扩至6000km^2,以后洞庭湖迅速淤积萎缩。1949至1985年间,人口又一次迅速增长,进一步加强围湖垦殖,大量通江湖泊面积萎缩。除1954和1998年那样人所共知的严重洪水灾害外,内涝渍水灾害也非常严重,人类与洪水的矛盾达到了顶点。改革开放后,尤其是三峡大坝的修建,极大地改变了长江中游的水文情势,工业化与城市化的迅猛发展,农村人口压力减轻,而21世纪初期降水相对较少,因此当前相当一段时间长江中游洪水灾害大为缓和。应抓住时机,总结经验,在人地和谐的现代水科学技术理念指导下,制定21世纪前半期,特别是2020年前的长江水利和水资源发展规划,促使人与洪水和谐共处。

Historic evolution of flood hazard in western middle reaches of the Yangtze River: human impact and current flood situation

The impact of human activity on historical evolution of flood hazards in the last three thousand years in the western parts of the middle Yangtze River basin is analyzed.During 3000-700a B P,scarcely distributed resident tend to live in highland areas not affected by floods.The Yangtze River is in a free-flowing condition after coming off the Three Gorges with limited flood hazards.Since Song dynasty,lots of the islet beaches made by the river sand had been cultivated and embankment appeared in the lowland and lake area along the river.But thanks to the existence of the outlets,flood hazards are not serious at the time.In Ming dynasty,embankment of the north bank was integrated,but not strong enough to resist the floods and there occurred 30 times dam breaking events.With the rapid increase of the population in Qing dynasty,the embankment along the river was heightened and thickened without preventing the farmland from being submerged by the flood,which in turn,raises the water level of Jingjiang section evidently and increases the flood hazards.Simultaneously,under the "guarding the north at the expense of the south" strategy,lots of water and sands were input to the Dongting Lake and make it enlarged at first, and shrink quickly later.After liberation,with rapid increase of the population and the cultivated lands,lake area in Jianghan plains reduced sharply from 8 730 km~(2)in 1950s to 2 730 km~(2) nowdays.The aggravation of flood disasters and waterlogging hazards give us a clue that the contradiction of the mankind and floods is further deepened.Due to the changing of hydrological regime of the Yangtze River after construction of the Three Gorge Projects and the reducing of population pressure in countryside with the development of industrialization and urbanization,flood disaster will be alleviated largely in the first half time of 21st century.It is time to enact a scientific plan to induce the harmonious development of the mankind and floods.