On the Catastrophabilities of Urban Geomorphic Environment of Shanghai
DAI Xue-Rong~1,SHI Yu-Xin~1,YU Li-Zhong~2,LI Liang-Jie~1,HE Xiao-Qin~1 (1.Department of Geography,East China Normal University,Shanghai 200062;2.State Key Laboratory of Estuary and Coastal Research,East China Normal University,Shanghai 200062)
With the rapid development of urbanization and re-urbanization, the urban geomorphic environment(UGE) of Shanghai has ever been featured with obvious catastrophabilities.The latest disastrous and representative case is the water-seeping incident happened on July 1st 2003 in constructing the No.4 metro line(underground),which has caused a huge economic loss of 150×10~6 Yuan(RMB).In deed,this incident includes three continuous catastrophic stages—water seeping,land collapse and local flooding.It implies that the Shanghai's UGE has become sensitive,fragile,and therefore catastrophic under conditions of high pressure of human activities.Viewing from the geomorphic materials,geomorphic forms and geomorphic processes respectively,this paper discusses the catastrophabilities of UGE in Shanghai proper in relation to man-land interaction. From the geomorphic materials,the most catastrophic factor is the wide spread water-bearing sand-to-silt layers formed in different ages in Quaternary,which may cause water-seeping incidents under conditions of frequent engineering activities.They are well developed in this area and exist in different depths within the extent of the activities.From the geomorphic forms,Shanghai is an extremely flat land with low elevation as just emerged from the sea(the Yangtze delta).Since 1921 the central city has experienced strong land subsidence and formed a huge depression covering an area of 850 km~2.Flood,therefore,has become the biggest threatening to the city both at present and in the future.And from the geomorphic processes,the high pressure of human activities has caused not only the tremendous changes of character,feature and dimensions of the physical landform,but also the deformation of the land surface due to land subsidence. The former,as we known,has given rise to changes in many aspects of urban climate and hydrology.The latter has led to a more serious sedimentary accumulation in the water channels(e.g.the Suzhou Creek and the Huangpu River etc.).The fragile and catastrophic UGE(especially the irreversible land deformation) will exert influences on the future urbanization and re-urbanization of Shanghai.Facts tell us that the Shanghai's UGE must be protected effectively and used rationally to keep us on the way of healthy,sustainable urban development.