上海城市地貌环境的致灾性

随着城市化和再城市化的快速发展,上海城市地貌环境呈现出明显的致灾性。通过从地貌物质、地貌过程和地貌形态三方面进行了剖析,认为地貌物质中含水沙层广泛发育和层数多是地貌灾害发生的重要因素,其横向上的不连续性、成因和形成时间的差异性更为地貌灾害的发生埋下阴影;地势低平及中心城区碟形洼地的存在使得洪水构成对上海城市安全的最大威胁;高强度人类活动不仅改变城市自然地貌面(下垫面)的性质、特征和规模,而且直接导致它的沉降变形,从而使城市地貌环境更为脆弱和致灾机制的复杂化。特别是地貌形变过程的不可逆性,已引起城市自然地理其它要素(如水文、气候等)的一系列变化和造成城市生态环境的恶化,对城市规划建设起到明显的制约作用。上海只有重视城市地貌资源的合理利用和城市地貌环境的有效保护才能走上健康、持续的发展道路。

On the Catastrophabilities of Urban Geomorphic Environment of Shanghai

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 150×10⁶ 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 km². 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.