关键词: 城市地貌, 城市安全, 地貌形变, 防汛墙, 城市可持续发展, 上海

Abstract:

From an interdisciplinary point of view of urban geomorphology,this paper discusses the land deformation process（LDP） of the urban area of central Shanghai,the controlling role to the sedimentation of river system,and relations to the flood prevention wall as well as the problems faced and countermeasures at present time.Conclusions can been drawn as follows: （1） The LDP has been characterized by obvious stages in relation to human activities during industrialization and urbanization since 1843.Five stages divided:（a） embryonic deformation stage from 1843¹920 AD;（b） relatively strong deformation stage from 1921¹956 AD;（c） strong deformation stage from 1957¹965AD;（d） slow deformation stage from 1966¹989 AD;and（e） accelerate deformation stage from 1990 to the present.Each stage has different extents of land subsidence and ranges of depression. （2） The LDP here is considered as a catastrophic process.It has given rise to many negative environmental effects and even calamities.The most serious one of them is the threatening of flood to the city safety.The LDP has become a controller of the sedimentation of rivers and creeks within the area of depression.Here the authors put forward a conceptual model of land deformation controlling sedimentation.If land deformation develops continuously,it can be foreseen that the drown valley system at the estuary of the Yangtze River will advance toward land area of Shanghai,and the depression will enlarge toward the lowland（or marshland） in the west of Shanghai.Land deformation has caused a loss of 260 billion Yuan（RMB）.In fact,the ultimate economic loss is difficult to calculate as known as an irreversible process. （3） The flood prevention wall standing along banks of Huangpu River and Suzhou Creek,the fourth flood-defending line in Shanghai,has close relation to the land deformation.So it is considered as a passive countermeasure to the catastrophic urban geomorphic environment.Further study shows that this countermeasure at present time is effective,but not in the future as a result of the ongoing land deformation.The flood prevention wall 5.72m（Wusong Elevation System） tidal table of "one time over one thousand year" recorded by Huangpu Park Station will be probably broken through soon.So a new flood-defending countermeasure for Shanghai is to be urgently needed. （4） The flood prevention wall,as a product of urban geomorphologic evolution,still has safety problems,e.g.uneven land subsidence,water erosion,artificial impacts,piles of heavy materials,and even purposely removal of it.An urgent response to the flood prevention wall system is still not established.So it should be strengthened both in design and management.Furthermore,its importance of eco-environmental effect must be recognized in the future development along Huangpu and Suzhou river banks. （5） Finally,the authors recognize that the urban geomorphic environmental problems should be solved completely only on a level of city planning.The pressure of human activities to the physical geographical system in central urban area must be reduced during re-urbanization,aiming to realize the sustainable development and avoid more economic loss.

Key words: urban geomorphology, city safety, land deformation process(LDP), flood prevention wall, urban sustainable development, Shanghai