Multiscale watershed landscape infrastructure: Integrated system design for sponge city development

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Abstract

Conventional centralized drainage systems are not only expensive, but their mono-function to discharge surface runoff also imposes a negative effect on the local environment while compounding regional watershed dysfunction. Sponge city initiative promoted by the Chinese government is a broader sustainable stormwater management concept that aims to use more nature-based solutions, reduce urban flooding and runoff pollution, and increase rainwater resource usage. As part of decentralized and cost-effective solutions, green infrastructure (GI) is considered in the Sponge City development across China. Although GI has been successfully implemented through a range of small-scale projects, the GI approach has not been adopted widely, which is because the GI approach is micro-scale techniques and the local government is skeptical about the efficiency of GI to mitigate stormwater on a large scale. Although some researchers have explored the effectiveness of GI to reduce stormwater in small catchments, only a limited number of studies have examined the efficacy of GI at the watershed scale. Moreover, there is lack of a system and cross-scale approach in sponge city practices. To understand the effect of GI on the watershed scale, this paper proposed a comprehensive approach using ArcGIS and SWMM platforms to study the spatial configuration and implementation of multi-scale stormwater management. The approach is to apply a three-step sequence of catchments, sub-catchments, and micro-catchments for the urban watershed through designing interconnected network of landscape infrastructure (LI) systems. The design scenarios and performance of LI system-based approach with different combinations and sizes of the sponge facilities were analyzed based on the Old Town district of Hefei City, China. This study demonstrated that the inherent capacity of the landscape can act as the conduit for multifunctional, flexible, localized, and synergistic infrastructural systems, in which cross watershed holds promise to decrease both runoff volumes and peak flows while providing ecosystem services, such as enhancing neighborhood aesthetics and cultural/health benefits through shared public green spaces. Thus, Sponge City Development here as green concepts and techniques for nature-based solutions enhances the function and value of green infrastructure with benefits of ecological, economic and social significances, which presents a new approach for sustainable city making.

Introduction

In the past 40 years, China’s urban population has grown by 58.5 %, and the urbanized area was increased from 7438 km2 in 1981 to 56,225.4 km2 in 2017. Rapid urbanization and climate change have put tremendous pressures on development, which cause urban flooding to become a major issue in China (Jia et al., 2013; Chen et al., 2013). The conventional engineered measures, which are widely used in the urban piped drainage systems, are expensive and do not meet the climate characteristics of uneven rainfall distribution patterns in China. Additionally, their mono-function of discharging surface runoff imposes a negative impact on the local ecosystem, consequently compounding regional watershed dysfunction. Meanwhile, cities worldwide are facing great planning challenges (Jacobs, 1961): to develop an urban infrastructure that solves for eco-based water management and facilitates the city’s functioning and growth (UACDC, 2016). A transition towards more sustainable stormwater management (SSM) is identified as necessary and contributes to increasing urban resilience to environmental problems and the overall sustainability of urban centers (Mguni et al., 2015; Habtemariama et al., 2019).

The Sponge City Initiative was introduced by the Chinese central government in 2014 to deal with stormwater challenges (MOHURD, 2014). Sponge City is similar to the approaches of Sustainable Drainage Systems (SuDS) and Low Impact Developments (LID) (Li et al., 2020). Still, it has different regional characteristics for rapid and intensified urbanization, which has caused severe flooding problems and environmental pollution issues. Sponge City aims to implement nature-based

stormwater management and takes multi-functional objectives: to reduce urban flood risk, to capture, purify and store more rainwater for use, and to provide additional amenity values (such as ecological and cultural/health benefits) through shared green spaces (Chan et al., 2018). The traditional stormwater management of grey infrastructures (such as detention basins, pipes, storm sewers) cannot effectively deal with the risks of stormwater flooding and pollution (Zhang et al., 2021).

However, Green Infrastructure (GI), technically used in the context of low impact development (LID), enables the system adaptable to the evolving multiple social and ecological requirements for stormwater management (Nguyen et al., 2019). With increasing threats at multiple scales from climate change and continuing rapid urbanization, it is urgent to consider the research question about how to use an adaptive Green Infrastructure (GI) approach to deal with local and regional stormwater risk issues to benefit climate adaptation and to contribute social well-being.

As part of decentralized solutions, small scale GI units are often designed to mimic the natural hydrological response. It aims to absorb urban stormwater runoff through soil infiltration, bioretention, grassed swale, and vegetated buffers, recharging groundwater and improving the runoff's water quality (UNEP, 2014; Colemana et al., 2018). GI approach has been widely experimented to tackle stormwater-related issues, such as Sponge City initiative. However, many challenges remain. For example, how to intelligently utilize and synthesize GI units to develop spatial strategies that simultaneously increase cultural/health benefits, enhance biodiversity, and integrate with larger nested systems of the territory, including, for instance, the logics of watershed management (Shannon, 2018).

Although GI units have been deployed successfully through a range of small-scale pilot projects in Chinese cities (Dai et al., 2017; Qiao et al., 2019), waterlogging occurred in 19 of the 30 nationwide pilot sponge cities which were selected by the Chinese central government (Wang, 2016). The Sponge City concept with cross-scale GI deployment has not yet been implemented at the city or territory scale.

There are several reasons why GI has not been widely adopted on a large scale (Garcia-Cuerva et al., 2018): (1) Local governments are not convinced about the efficiency of GI to mitigate stormwater (The Sponge Cities Initiative was made by the central government and implementation is currently up to local governments), because most of these local guidelines for the selection of GI techniques are mainly at the micro-level or limited to the site-scale without considerations and interactions with the urban watershed (Dai et al., 2017). (2) Although some research has demonstrated the effectiveness of GI projects to reduce stormwater in small catchments (Shuster and Rhea, 2013; Jarden et al., 2016; Garcia-Cuerva et al., 2018), only a limited small studies has explored the overall planning and cross-scale coordination of the micro, meso, and macro scale of urban catchment area (Romnée et al., 2015; Bacchin et al., 2014; Lee et al., 2012). However, small-scale projects that are not replicated throughout a watershed will have limited effects on runoff and flood reduction (Garcia-Cuerva et al., 2018). (3) Site selection for GI implementation in a dense urban environment is limited, especially in highly urbanized cities where the pace of urbanization rapidly reduces the availability of natural areas. In this context, integrative and synergistic approaches are needed in both theory and practices of urban planning and design.

The innovative approach should consider the entire urban watershed for stormwater management and provide both ecological and social benefits through integration among GI and other types of infrastructures in a multi-scale system. Robustness can be achieved only when infrastructure is consolidated, working in synergy with spatial patterns, natural characteristics, and socioeconomic aspects (Bacchin et al., 2014).

To understand the effect of GI on the watershed scale, this paper proposed a comprehensive approach using ArcGIS and SWMM platforms to study the spatial configuration and implementation of multi-scale stormwater management. The approach is to apply a three-step sequence of catchments, sub-catchments, and micro-catchments for the urban watershed through designing an interconnected network of landscape infrastructure (LI) systems. The design scenarios and performance of LI system-based approach with different combinations and sizes of the sponge facilities were analyzed based on the Old Town district of Hefei City, China (SGRIUC, 2013).

Section snippets

Landscape (Eco) system and landscape infrastructure

“A landscape is at the same time a unit and a system, depending on the role and the scale in which we wish to examine it”(Farina, 2010). The internal organization of a landscape ecosystem comprises distinctive sub-systems that perform both single and collective ecosystem processes. Landscape ecology approach can manage and conserve landscape elements at different spatial scales (Turner and Gardner, 2015). Although it is vital to maintain the system as a whole, the balanced interaction among the

Method

After the above theoretical discussion, the representative Old Town of Hefei was selected as a case study to explore the adaptability of the proposed system metioned above. Hefei, rich in scientific research resources, is an essential scientific city of China (SGRIUC, 2013). The Old Town of Hefei, located in the center of the city, is severely affected by the rainstorm. Therefore, it is of great practical significance to select the Old Town of Hefei as the case study site. The case study

Deployment of LI system-based approaches

Conventional centralized drainage systems are generally designed in a top-down manner, which often results in high runoff volumes and peak flows. This study explored LI system-based strategies that adopt a bottom-up, decentralized, and close to the source on-site treatment approach, which is carried out from the micro-catchment. When the rainfall is intensified and the runoff volume exceeds the self-absorption capacity of a single micro-catchment, the clustering and jointed response of

Discussion

The LI system-based approach has shown the physical limitations of GI implementation in a dense urban environment, particularly in developing cities. The rapid urbanization significantly reduces the availability of natural areas, thus limiting site selection for GI implementation, which mainly depends on scattered sponge units for stormwater mitigation.

To further assess the effectiveness of the LI system-based approach on flood control, the results obtained by SWMM were used to evaluate the

Conclusions

This study indicates that the inherent capacity of the landscape can act as the conduit for multifunctional, flexible, localized, and synergistic infrastructural systems. The proposed system can improve hydrological performance while increasing ecosystem function and biodiversity, enhancing neighborhood aesthetics, and providing cultural and health benefits through shared public spaces. The following points can be drawn:

  • (1)

    For a high-density urban environment, the LI system-based approach that

Declaration of Competing Interest

The authors declare no conflict of interest.

Acknowledgements

The authors wish to thank two anonymous reviewers for their constructive comments and rational suggestions, which helped us to significantly improve this manuscript. Author Yixin Zhang’s research is partially supported by the grant (p113800618) of Soochow University - Suzhou Yuanke (SU-SY) Collaborative Innovation Center of Architecture and Urban Environment. He thanks the SU-SY Collaborative Innovation Center.

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