Surgery of City Wall-Canal System from Urban Segregator to Green Archival Linkage - Rejuvenation of Historic Eastern Water Gate Area of Nanjing

Abstract

As the capital of China for 10 dynasties, Nanjing has experienced urban development in parallel to the construction of city wall-canal system for thousand years. However, the historic city wall- canal system which used to be the protective border of the city is now subject to the erosion of public space along it. Thus it leads to many problems, such as culture recession, river pollution, urban flooding due to the malfunction of sewage infrastructure, community segregation on two sides of the city wall-canal system. Accordingly, on urban level, five types of green belts as the green infrastructure are proposed in this paper to re-stitch the city wall-canal system for retarding urban sprawl and restoring historic context. Additionally, eastern water gate area of the city wall-canal system is an important waterway transportation junction and the facility center for water exchange and flood control. On local level, urban surgery is conducted in “ cut-removal-suture-growth” sequence. This paper also probes into the hydrological and urban issues of this area specifically regarding storm water and flood management, rain-water harvesting system as well as urban renewal, thus proposing 3 strategies: the extension of Fuzi Temple shopping center, facilitation of water exchange in eastern water gate area and improvement of community rain-water harvesting. In detail, the community adjacent to city wall is converted into a green public center integrated with shopping malls, community amenities, rainwater harvesting facilities and urban landscape; and the nearby communities are connected to the city wall-canal system by community canal system, green space, walkways, visual channels through the design of softened river bank, pervasive road surface, biotopes, eco-islands, water purification systems and various community activities, which as a whole form the holistic green infrastructure of the storm water and flood management. The key of above strategies lies in the regenerative design of eastern water gate park which constitutes the monitor and adjustor of Qinhuai river in 4 different phases: low water period, high water period, potential flood period, potential heavy rainfall period. On the one hand, the city wall walkways are integrated with water processing facilities including purification pipes, silt sieves, sedimentation ponds, wetland cells, infiltration ponds, oxygen basins, siphon pumps which as a whole control and manage flood and storm water. On the other hand, the archaic beauty and the historic scenes are presented just like the outdoor museum as people are walking down the walkways on top of the city walls. This green archival linkage further connects the communities on double sides to each other in every sense. Based on that, there form nine water processing systems in this area in total by which water confluences into the flood detention area in the nearby wetland park for further sedimentation, bio-purification and supplement to underground water storage.