Waterlogging Vulnerability Study Of Underground Metro In Shanghai Urban Areas

With the rapid development of social economy, the urban land resources become increasingly scarce; people began to develop the underground space. But the underground space is vulnerable to storms and floods because it often below a ground elevation. How to enhance the flood management and eliminate flood hazards of underground space effectively has become an urgent problem to study and solve.Founded by National Natural Science Foundation project "Coastal Cities Natural Disasters Emergency Plan Scenario Analysis" (NO.40730526), the present study started from the underground space waterlogging vulnerability analysis, reviewed the theories and methods of vulnerability analysis at home and abroad, defined the concept of underground space waterlogging vulnerability and the content of this study, established the index system of vulnerability analysis, and analyzed the waterlogging vulnerability of underground Metro in central urban areas of Shanghai. Finally, according to the characters of Shanghai, the waterlogging conditions of underground space was simulated through the combination of both a simplified model of urban storm water logging and the underground space waterlogging model with the consideration of GIS spatial analysis techniques. The resules provided the scientific basis for flood disaster control and reduction of the urban underground space and the government policy-making and management.Several main conclusions of this research are as follows:(1) The trend of the storm's frequency and strength is significantly increased due to climate change, urbanization effect, global warming and land subsidence. Rainfall is concentrated in July and August, the frequency of which was occurred in August accounted for 52%; From the spatial distribution, the number of rainfall events in Xuhui District is the largest, Yangpu District, Luwan District, Hongkou District and Putuo District ranked secondly, and the number of rainfall events in Huangpu District is relatively small.Since the foundation of the People's Republic of China in 1949, the occurrence number of once in five hundred and a thousand years of rainfall, once in fifty years and a hundred years of rainfall was 4 and 10, respectively,. (2) The waterlogging vulnerability of underground metro is a characteristic which show vulnerable to the degree of disturbance and lack of resilience when the system disturbanced by storm. There are two factors:one is the vulnerable to the degree of disturbance of their own physical characteristics, that is sensitivity; second is the response capabilities which related to socio-economic and cultural background, that is resilience.(3) The results of sensitivity analysis showed that the waterlogging sensitivity of underground metro in Shanghai central urban areas is low overall. The ratio of lower sensitivity, medium sensitivity and higher sensitivity is 84.8%,6.2% and 9.1%, respectively. The results of resilience analysis shows that:the resilience of central urban areas of Shanghai are strong, the resilience of Hongkou and Huangpu District are strongest, the resilience of Xuhui,Zhabei District, Jing'an and Putuo District are weak. The comparative analysis of the indicators of the resilience shows that the density of pumping stations in Hongkou and Huangpu District is the highest; the standard-reaching rate of pipeline in Xuhui District is the highest; the paying ability of Jing'an goverment is the strongest, but the drainage capacity of rain drainage system is lower due to lower denisity of pumping station; the standard-reaching rate of rain drainage system in Putuo District is the lowest.(4) From the prospective of the sensitivity and resilience, the results of the vulnerability analysis shows that the waterlogging vulnerability of underground metro in shanghai urban areas is low from the whole aspect. The ratio of lower vulnerability and medium vulnerability is 81.5% and 13.8%, respectively. And only three entrances have higher vulnerablity rank. The common character of entrances which have higher vulnerability rank is that they are the open-style entrance. And the height of the steps at these entrances is less than 30cm.(5) The results of the waterlogging simulation in underground metro shows, Under realistic conditiond, all underground station entrances could not be exposured to the waterlogging disasters in the condition of once in 50 years of rainfall; when the rainfall return period is 100 years, there are only two entrances'inundated water depth was less than 10cm. And in this condition, there is no influence on the passengers and subway operations. When the rainfall return period is 500 years, there are 14 entrance's inundated water depth was less than 10cm, five entrances' inundated water depth was between 10-30cm. When the rainfall return period is one thousand years, there are 11 entrances'inundated water depth was less than 10cm,16 entrances' inundated water depth was between 10-30cm, and 2 entrances' inundated water depth was more than 30cm. When the drainage capacity improved in the central urban area of Shanghai, there is 46% reduction in the total entrances which had inundated water, when the rainfall return period is 50 years and 100 years, all underground station entrances could not be exposured to the waterlogging disasters. When the rainfall return period is 500 years, there are 5 entrances'inundated water depth was less than 10cm,1 entrance's inundated water depth was between 10-30cm. When the rainfall return period is 1000 years, there are 15 entrances'inundated water depth was less than 10cm,6 entrance's inundated water depth was between 10-30cm.(6) According to the waterlogging vulnerability analysis in shanghai central urban areas, the present study proposed countermeasures on the flood management of underground spaces:â‘ rasing the design standard of the height of steps which are in front of entrances to reduce the vulnerability of metro entrances;â‘¡improve the design of metro entrances to reduce their sensitivity;â‘¢transformation of the backward Sewerage System to improve the capacity of urban rain drainage system;â‘£dredge the river and sewer regularly to improve the regulation and storage capacity of urban rivers.