Soil bioengineering and the ecological restoration of riverbanks at the Airport Town, Shanghai, China
Introduction
The Shanghai metropolitan region is located on the eastern coast of China and covers approximately 6340 km2, with the Yangtse Estuary to the north, the East China Sea to the east and Hangzhou Bay to the south, between 30°23′–31°37′N and 120°50′–121°45′E (Fig. 1). Historically, the city of Shanghai was established in the Yuan Dynasty (1292 AD). The late 1800s marked a major turning point in the history of Shanghai with its development as an industrial and trading port. Since then, Shanghai has become the largest city in China. Shanghai is now the fastest growing area among all major Chinese cities with the population increasing from 5.2 million in1949 to 16 million in 2004 and the urban area from 91.5 km2 in 1947 to more than 800 km2 in 2000. Since the beginning of the 1990s, Shanghai has experienced a very rapid land transformation from an agricultural to urban area and the urban fringe has advanced steadily outward into the surrounding agricultural land (Zhang et al., 2004).
Riparian ecosystems are important in terms of their ecological, social, economic and aesthetic value (Li and Eddleman, 2002). As a consequence of rapid urbanization, more and more rivers in the Shanghai metropolitan region are also now being channelized with concrete which has threatened the integrity of semi-natural riparian ecosystems (Li and Zhang, 2005). The evolution of methods for ecological rehabilitation of degraded riparian ecosystems has seen explosive growth in the recent years and most Chinese municipal governments and urban planners have now attempted to conserve and recreate riparian ecosystems in response to rapid urbanization, and to protect the natural environment, improve quality of life for the residents and to moderate urban microclimates (Yu et al., in press).
Ecological engineering has been defined as “the design of sustainable ecosystems that integrate human society with its natural environment for the benefit of both” (Mitsch, 1998). Schiechtl (1980) presented, for the first time in English, the works of many important European soil bioengineers, and made restoration technologies and history of their development as well as their applications accessible to the English-speaking world. Soil bioengineering uses sound engineering practices in conjunction with integrated ecological principles, using living vegetation and other materials to construct slopes (hillslopes, riverbanks, and lake/shorelines), to stabilize slopes, control erosion, protect wildlife habitats and enhance the functioning of ecosystems (Donald and Robbin, 1996, Gray and Sotir, 1996). Successes of ecological engineering make it an increasingly attractive alternative to traditional engineering approaches, which are often much more expensive to construct and sustain (Li and Eddleman, 2002, Mitsch et al., 2002).
It has been shown that soil bioengineering is an important means of restoring damaged ecosystems and follows ecological principles, investigating, designing and recreating vegetation-soil systems, enhancing soil shear strength and limiting soil particle movements on slopes by utilizing the effects of root systems on soil structure. However, methods do not just assist with slope stabilization and erosion control, but also involve the recreation of horizontal and vertical structures of riparian vegetation together with their seasonal changes in species composition and increase aesthetic value. Compared with traditional methods, soil bioengineering is most successful when used in combination with conventional technology maximizing both engineering and ecological benefit of vegetation (Li and Eddleman, 2002).
In 2003, the Pudong Water Authority, Shanghai asked the Shanghai Academy of Environmental Sciences and the State Key Laboratory of Estuarine and Coastal Research, East China Normal University to investigate the potential of soil bioengineering for riverbank ecological restoration. In 2004, a demonstration project was conducted at Airport Town, Pudong New District, Shanghai, which represented the first example of soil bioengineering in China. In this project, a new engineering system for riverbank ecological restoration was implemented for approximately 16 km of riverbank, involving slope stabilization and ecosystem recovery and protection. The project required slope stabilization measures where slopes were steep or soil was loose and the introduction of native vegetation. The finished work had to provide an environmentally safe, ecologically healthy, aesthetically pleasing, and low cost alternative that served the needs of the public.
Section snippets
Background
Shanghai has a northern subtropical monsoon climate, with an average annual temperature of 16 °C, average summer temperatures of 28 °C and cold winters, with an average temperature of 4 °C. Average annual precipitation is approximately 1200 mm, with 60% of rainfall occurring during May to September. The native vegetation is characterized by subtropical evergreen broadleaved forests dominated by Castanopsis sclerophylla, Cyclobalanopsis glauca, Machilus thunbergii, Schima superba and Cinnamomum
Project objectives
Goals of a typical biotechnical project include preventing erosion, stabilizing slopes, protecting stream channels, and enhancing aesthetics and wildlife habitat. The primary goal of this study was to implement soil bioengineering approaches to protect riverbanks at the Airport Town, and to restore the riparian ecosystems ecologically.
The specific objectives were to:
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Design and implement ecological engineering approaches to stabilize the riverbank with an aesthetically pleasing, ecologically
Project design
The demonstration project was designed and implemented on several segments of the five main rivers, Changtang River, Shajiao River, Bayi River, Chawang River and Liqing River (Fig. 2). To be compatible to the local conditions, five main techniques of soil bioengineering were adopted (Salix Applied Earthcare, 2002), which were live staking, live fascines, use of a brush layer, vegetated geo-grids and geo-gabions. The total length of vegetated reinforced riverbank was over 16 km, of which 2437 m2
Analysis and evaluation
The actual success of ecological restoration of riverbanks needed to be assessed after the implementation of the project. Site analysis and post-project evaluation were performed by measuring parameters such as the length and biomass of new roots of the planted cuttings, plant diversity, habitat improvement and other environmental factors.
Conclusions
A demonstration project to design a structurally sound, ecologically sustainable and socio-economically beneficial method for restoring the riverbanks using techniques of ecological engineering was developed and implemented at the Airport Town, Shanghai. The project design incorporated live stakes, live fascines, use of a brush layer, vegetated geo-grids and geo-gabions as an alternative to conventional river restoration using concrete channelization.
Geo-technical parameters, including soil
Acknowledgements
The authors would like to acknowledge the support of the Pudong Water Authority, Shanghai, and Mr. Zhengming Yu, Mr. Bo Wang and Mrs. Hui Zhou. This project could not have been accomplished without the dedication and support and efforts of these agencies and people. We also thank Professor Martin Kent, University of Plymouth, UK, for valuable comments and linguistic checking. We appreciate two anonymous reviewers for many helpful suggestions on an earlier version of this paper. This research
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