历史时期长江中游河道演变与洪灾发展的规律

Evaluation of the channels in the middle reach of the Yangtze River and intensification of floods in its historical period

历史时期,长江中游的河道在科氏力、掀斜构造活动的影响下,长期南移。在主泓南移、气候由湿变干、分汊淤浅的背景下,大量人口由北方迁入,促使沿长江主泓的围堤迅速发展。原先多汊分流的河道,演变为被围堤约束的狭窄河道。水沙集中于狭窄的堤围河道,洪峰难以调节,泥沙淤高河床,形成水涨堤高、堤高水涨的恶性循环。宋末至明代,是长江中游围堤基本成型与完善,也是洪水位不断抬升,洪灾不断加剧的时期,说明洪灾加剧与围堤密不可分。现有的防洪方针,延续了历史上"抗拒洪水"的思路,没有体现"与洪水共处"的原则,需要进行反思。建议采取"疏导为本"的防洪方针,恢复与增加长江中游分流汊道,扩大江河行洪能力,分散泥沙淤积,以达到可持续治洪的目的。

During the historical period, the interaction of Carioles force and unequal tectonic movement, the channels of the middle reach of the Yangtze River continuously moved toward south. With the main channels moving southward and the climate becoming drier, the northern branches have been silted and become shallow. The embankment along the main channel has quickly developed as a result of population moving from the North China to this area. Therefore, the original broad channel with diffluent outlets has become a narrow embanked one without outlets. Water and soil concentrated in the narrow channel and the flood peaks were hardly regulated. The riverbed rose as a result of silting. Then a vicious circle of alternately rising of dyke and flood water level developed. From the facts that the embankment and intensification of flood had developed during the same period, from the later Song Dynasty to Ming Dynasty, it is concluded that embankment is the main reason for the flood intensification. The present strategy for flood control continues the historical one and it reflects the antiquated ideas'keep flood away'. It is necessary to rethink of it and transform it into the contemporary ideas'coexist with flood'. For the purpose of sustainable floodcontrol, recovering and increasing diffluent outlets for regulating the flood peak and silting in the riverbed are suggested.