How Does Water Sensitive Urban Design Ameliorate Flood Hazards in China

Highlights

•The stormwater management system can mitigate the frequency, length, and volume of stormwater runoff and control post-development flows to waterways,which can reduce the danger of nuisance floods •WSUD utilizes Natural Biodegradation treat stormwater pollution, thereby reducing the hazard of flooding and enhancing the urban environment’s aesthetics. Not only does this reduce the runoff volume and peak flow through infiltration and evaporation, but it also improves stormwater quality.

Introduction

Water sensitive urban design (WSUD) is a land planning method that incorporates the urban water cycle, such as stormwater, groundwater, wastewater management, and water supply, into urban design to enhance the amenity and ‘naturalness’ of the urban environment.China Urban flooding has detrimental effects on cities’ economies, ecology, and citizens’ health and quality of life, in addition to risking their safety and comfort.

To solve this issue, the concept of water-sensitive urban design is recommended to reduce urban flooding hazard. As strategies of USWD, the stormwater management system and natural biodegradation are high efficiency methods for controlling sewer overflows and removing rainfall pollution.

Stormwater Manages System

Urban flooding in China is prevalent during rainstorms, resulting in enormous direct economic damages (Figure 1). In traditional stormwater infrastructure， the drainage of untreated rainwater into a nearby water source. (Bellet al., 2016).The stormwater management system through infiltration, reuse, and evapotranspiration forms the cornerstone of Water Sensitive Urban Design as a sustainable urban strategy (Figure 1). It works on preventing sewage system overflow. It includes sustainable urban drainage solutions to limit the quantity of stormwater entering combined sewers and, consequently, the frequency and size of combined sewer overflows. (EPA, 2011).

More specifically, evapotranspiration explains the process of trees and plants, such as green roofs and the street tree, utilizing water. Infiltration refers to the water soaking into the ground, and includes flow reduction practices, for example, permeable pavements, grass filters, and swales. In addition, according to the EPA (2011), The catch and reuse approach stores collected rainwater in a rain barrel or cistern for subsequent use in landscape irrigation or flushing toilets. In accordance with US WSUD rainfall figures, a 60,567 L rainwater cistern is employed to manage the majority of stormwater. In conjunction with efficient low-flow fixtures, this rainwater reuse strategy can save up to 461,820 L of potable water each year (Sharma, A, Gardner, T & Begbie, D 2018).

Natural Biodegradation

During the downpour, the considerable accumulation of pollutants is washed into urban receiving waters, damaging the water quality (Jacobson, 2011; Miller et al., 2014). The chief sources of contaminants in stormwater include automotive traffic, human and animal faeces, and industrial operations (Quigley, M., Brown, B., 2014). Consequently, this can en-danger human and ecological health. In order to improve urban livability, preventing sewage system overflow and reducing stormwater pollution are crucial components of urban water management (Bellet al., 2016).

During the downpour, the considerable accumulation of pollutants is washed into urban receiving waters, damaging the water quality (Jacobson, 2011; Miller et al., 2014). The chief sources of contaminants in stormwater include automotive traffic, human and animal faeces, and industrial operations (Quigley, M., Brown, B., 2014). Consequently, this can en-danger human and ecological health. In order to improve urban livability, preventing sewage system overflow and reducing stormwater pollution are crucial components of urban water management (Bellet al., 2016). WSUD treats sewage on-site with a set of biological processes, which respectively regulate stormwater runoff from streets and runoff from Ecological landscapes in a sustainable manner As strategies of USWD, the natural biodegradation are high efficiency methods for removing rainfall pollution. Biological processes are extremely efficient because they rely solely on natural biodegradation and do not require a significant amount of electrical input (Blecken et al., 2010a,b; Hatt et al., 2008). Numerous conventional methods require substantially more electrical inputs and generate more sludge that must be cleaned off-site. Comparatively, biological systems produce less sludge, but they are typically slower and require a larger footprint.

Specifically, in the WSUD project in Haikou (Figure 3), China, pervious pavements and tree pits are used to sustainably manage street stormwater runoff (kadurupokune, N & Jayasuriya, N 2007). Pervious pavements through a coarse subbase into the soil to filtrate underlying drainage system to divert captured stormwater runoff to various treatment devices, such as sedimentation ponds, for the removal of traffic-related pollutants (Hvitved-Jacobsen, T., Vollertsen, J., Nielsen, A.H., 2010). As stormwater management includes filtration, detention, and biological uptake, tree pits are also known as bioretention systems. Connecting to additional WSUD devices, such as pervious pavements, can improve the treatment’s performance.

Secondary, according to NRMMC, the constructed wetlands (Figure 6) and biofilters have the ability to address risk management-related contaminants which are include pathogens, nutrients, and suspended solids. Although the efficacy of pollutant removal can be highly variable, built wetlands remove nutrients, suspended particles, and metals effectively (Hvitved-Jacobsen, T., Vollertsen, J., Nielsen, A.H., 2010). In addition to improving stormwater quality, the created wetlands and sedimentation ponds (Figure 2)lower runoff volume and peak flow through infiltration and evaporation as water is kept in the wetland. However, the volume of runoff is gradually decreasing. Sedimentation ponds are utilized to reduce sediment deposition in downstream treatment devices, avoiding direct access artificial wetlands (Quigley, M., Brown, B., 2014).

Discussion

This study of the strategies for WSUD was placed firmly within the China urban flood context, and the lack of a sample of WSUD from other countries has led to the information limitations of this study. However, some universal guidelines on the implementation of WSUD for support of urban livability can be drawn from this review which is that rather than just about managing stormwater at source, it has a high focus on the use of natural processes and vegetation to provide stormwater treatment, reduction and attenuation, as well as enhance the amenity and ‘naturalness’ of the urban environment. Thus，These landscape types should connect each other to maximize environmental performances. For the study process，because of the high construction costs of WSUD and experimental difficulties in monitoring these options, much of the “validation” has been undertaken using computer models. Indeed, few experimental studies have quantified the behavior of these systems at urban catchments scales.

Conclusion

Water sensitive urban design utilizes the stormwater management system and natural Biodegradation to improved stormwater capture and beneficial use. It provides a means to reduce combined sewer overflows and stormwater pollution discharges .

Reference

Bell, C.D., McMillan, S.K., Clinton, S.M., Jefferson, A.J., 2016. Hydrologic response to stormwater control measures in urban watersheds. Journal of Hydrology 541 (Part B), 1488e1500.

Blecken, G.-T., Zinger, Y., Deleti c, A., Fletcher, T.D., Hedström, A., Viklander, M., 2010a. Laboratory study on stormwater biofiltration: nutrient and sediment removal in cold temperatures. Journal of Hydrology 394 (3), 507e514.

Blecken, G.-T., Zinger, Y., Deleti c, A., Fletcher, T.D., Viklander, M., 2010b. Laboratory studies on metal treatment efficiency of stormwater biofilters. In: International Short Course: Advances in Knowledge of Urban Drainage from the Catchment to the Recieving Water. University of Calabria, Italy, 15/06/2010-15/06/2010.

Coutts, AM, Tapper, NJ, Beringer, J, Loughnan, M & Demuzere, M 2013, ‘Watering our cities: The capacity for Water Sensitive Urban Design to support urban cooling and improve human thermal comfort in the Australian context’, Progress in Physical Geography, vol. 37, no. 1, pp. 2–28.

EPA, 2001. Achieving Water Quality through Integrated Municipal Stormwater and Wastewater Plans. Memo from N. Stoner and C. Giles to EPA Regional Administrators and OW and OECA Directors. Washington, DC, October 27, 2011. 3 p. Hvitved-Jacobsen, T., Vollertsen, J., Nielsen, A.H., 2010. Urban and Highway Stormwater Pollution: Concepts and Engineering. CRC Press, Taylor and Francis Group.

Kadurupokune, N & Jayasuriya, N 2007, ‘Field testing the effectiveness of pervious pavements as a water sensitive urban design initiative’, in Rainwater and Urban Design 2007, Engineers Australia, Barton, A.C.T., pp. 468–475.

NRMMC, EPHC, NHMRC, 2009a. Australian Guidelines for Water Recycling: Managing Health and Environmental Risks (Phase 2) – Stormwater Harvesting and Reuse, National Resource Management Ministerial Council (NRMMC), Environmental Protection and Heritage Council (EPHC) & National Health and Medical Research Council (NHMRC). National Water Quality Management Strategy, Canberra, ACT, Australia.

Quigley, M., Brown, B., 2014. Transforming Our Cities: High-Performance Green Infrastructures: 978-1-78040-673-2/178040-673-8. Water Environment Research Foundation, Alexandria, VA, 96 p.

Sharma, A, Gardner, T & Begbie, D 2018, Approaches to water sensitive urban design: potential, design, ecological health, economics, policies and community perceptions, Woodhead Publishing.