Study On The Impact Of Urbanization On Stream Structure, River Network Connectivity And Storage Capacity In Pudong New Area, Shanghai

Yangtze River Delta is a typical place of plain water system areas, scattered with lakes and rivers crisscrossing the region. The city of Shanghai, Suzhou, Wuxi and Changzhou are located in this area. They have a high urbanization level with rapid economic development. Among them, Pudong New Area is a typical case of rapid urbanization in china. However, due to the high intensity of human activities, the stream system is interfered along with the extended urbanization. Lots of rivers have been replaced with the urban construction lands. The stream morphology and structure has been changed and the river connectivity was weakened. The river storage capacity, one of the key factors to control floods, is directly decided by the stream structure and river connectivity. Therefore, to study on stream structure, river connectivity and storage capacity of river network in Yangtze River Delta is of great significance in improving the ability of controlling flood, constructing sponge and ecological city.This paper is supported by commonweal project of ministry of water resources, entitled "Study on the Improvement of Stream Structure and Lake Connectivity in Yangtze River Delta" (No:201201072), cooperated with NJU. Based on the GIS grid technology and remote sensing interpretation, comprehensively applying time series analysis, GIS spatial analysis and spatial auto-regressive model and other methods, taking Pudong New Area in Shanghai without Nanhui district as the research object, this paper studied on variations of stream structure, river network connectivity and storage capacity in the process of urbanization, explored the main driving factors causing stream structure change and the indexes of urban landscape pattern that affected river network connectivity, compared the regional flood storage capacity with rainstorm runoff, provided the basis of the argument to protect the river system and improve the regional flood control and drainage capability.The main contents and conclusions were as follows:(1) The changes of river system from 1989 to 2010 were summarized by calculating quantitative index and structure index, and the main driving factors causing stream structure to change were analyzed. The results showed that:① Affected by human activities, not only the length, number and area of river in study area were significantly decreased, but also the five parameters, including drainage density, water surface rate of river and village-level river development coefficient and so on. There were differences among changes of river of different levels. During the study period, village-level river was continued to disappear, but the number, length and area of municipal river and district-level river had a certain degree of growth. This showed a phenomenon of attaching great importance to the main rivers but less to the tributaries was existed in the process of urbanization. ② During the study period, waters were mainly replaced by urban construction lands, such as industrial, residential and traffic land. From the spatial perspective, waters area in southeastern region was obviously less than western region, but the changes of water area was the opposite. Between 2006 and 2010, while the study area basically achieved water area’s dynamic balance, broadening the original river channels was much more used than other compensation measures. It showed a phenomenon of more attention to the water surface rate but less attention to stream structure in the protection of river system was existed.(2) More detailed spatial and temporal variations of river network connectivity were analyzed by applying GIS gridding technology to divide the study area into 100 cells, the size of which was 2700*2700m. The indexes of urban landscape pattern that affected river network connectivity were detected by using spatial auto-regression model. The results showed that: ① The average values of β and y both had a certain degree of decline. The value ofβ in 73% cells and the value of γ in 75% cells were decreased. The network structure of water system was badly affected. ② From the spatial perspective, the condition of river network connectivity in southeastern region was obviously better than western region, but river network connectivity in southeastern region changed much more than western region. This phenomenon is related to the urbanization process from west to east in Pudong New Area. ③ The model showed that number of patches (NP) for public building land and mean of patches area (AREA_MN) for water area are the most significant factors which influence river network connectivity. Besides, mean of patches area (AREA_MN) for road and traffic land, largest patch index (LPI) for industrial land, and interspersion juxtaposition index (IJI) of industrial land, residential land and water area also affect the change of river network connectivity. Pudong New Area should be considered the above landscape pattern factors in the new round of development planning to recover and protect the river system.(3) Four parameters were chosen to analyze the temporal changes in river storage capacity, which was then compared with the rainfall runoff estimated by modified SCS model. The results showed that:① The overall storage capacity represented a continued downward trend. There were differences in river storage capacity changes of different levels. The river storage capacity of village and town level was declined sharply, meanwhile the municipal and district level was increased. It reflected disappearance of the river of lower level resulted in overall regional storage capacity decline. ② The runoff increased by years, but storage capacity continued to fall. The contradiction between the two was more prominent. Based on the above, suggestions to raise flood storage capacity were put forward.