Sustainable Drainage and Surface Water Management in Xiamen, China
Sammanfattning: Sustainable urban drainage systems (SUDS) is a relatively new way of handling stormwater in urban environments. Originating in the late 1980’s, the concept has developed as an alternative to the traditional way of removing the urban water as quick as possible in pipes, buried underneath the ground. Sustainable urban drainage systems are open solutions, designed to regenerate nature’s way of stormwater management, reducing peak flows and providing treatment of the water on its way to the recipients. Instead of only focusing on quantity, quality and amenity are of equal importance. Situated in Southern China, Xiamen enjoys a subtropical climate with a yearly average temperature of 20.8 degrees, and an average yearly rainfall of 1347mm. The city has a population of around 2.5 million people. Being one of six special economic zones in China, Xiamen has seen an enormous development in economy and infrastructure during the last decades. This rapid development has however often come to the price of the environment. Stormwater management has had a low priority, with water seen as a burden conducted as quickly as possible in pipes to the recipients. Flooding and high levels of contaminants in the water are common issues in the city. The main focus with this thesis is to evaluate the possibility of implementing sustainable urban drainage solutions in the central parts of Xiamen to achieve a better qualitative and quantitative control of the stormwater. Current situation in the city, concerning administration and legislations is investigated, followed by an evaluation of feasible solutions of implementation. A chapter is dedicated to the conditions in Sweden, a country which has developed the concept of SUDS during several decades. This chapter is meant to give readers the possibility of comparing differences between the two countries. The stormwater administration in Xiamen involves a large number of departments, which often complicates and delays important decision making. Chinese national quality standards for pollution control are used as guidelines in the recipients in Xiamen. The main recipients of Xiamen Island are either the sea, or Yuan Dang Lake. Formerly an open harbor, Yuan Dang Lake has been created through a series of land-reclamation projects, and has today the size of 1.5 km2. The lake is under constant observation, and the condition of the lake has improved significantly during the last decades. The area investigated in this report is a heavily urbanized district of central Xiamen, and a part of the Yuan Dang Lake catchment. The area evaluated should be considered a typical urbanized district of central Xiamen, and the solutions evaluated are meant to be applicable for other, similar areas of the city. Since all the land in central Xiamen is already developed, the implementation of stormwater solutions will be through retrofitting. Area-demanding solutions like wetlands and green filter strips are therefore difficult to realize in Xiamen. The same applies to swales, which also due to lack of space will be hard to implement. Evaluations in this report show that green roofs will be the most feasible solution to implement on rooftops. Recreational ponds and open recreational areas like football fields located in central Xiamen may be converted to better detain stormwater, releasing it with an even flow, to mitigate downstream stress at the event of a storm. Green areas in central Xiamen are relatively abundant, and have the potential be redesigned to bioretention areas. Though often small in size, the multitude of installations will add up to a significant improvement in the total stormwater control. Other Infiltration devices such as permeable paving, soakaways and infiltration basins may be installed where space is available. Because of the risk of groundwater contamination, infiltration devices should be installed with an underdrain. The stormwater is conducted downstream through the investigated area in concrete canals. Though not the optimal sustainable urban stormwater solution, a pragmatic approach has been used in the evaluation, eliminating other non-feasible alternatives. In the area of investigation, water from storms will be conducted to Yuan Dang Lake, which is regarded as the final downstream recipient, before released in the sea. This evaluation shows that if the suggested solutions are implemented, the stormwater will be intercepted by several stormwater management solutions on its way downstream, which will contribute to notable improvements in Xiamen’s urban drainage situation. Evaluations show that the maximum runoff during a 24-hour flow is reduced to less than half of the flow quantity before the improvements were implemented. A management train is favorable, in order to achieve highest potential level of qualitative and quantitative improvement.
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