Nguyen, Cuong Ngoc ORCID: 0000-0003-3791-1628 (2024) Developing innovative green roof strategies for improving runoff retention and water quality. PhD thesis, Victoria University.

Abstract

A significant consequence of rapid urbanization is the conversion of green spaces into impervious surfaces, such as concrete pavements and roads. This has led to an increase in flash flooding, more intense Urban Heat Island (UHI) effects, and higher levels of water and air pollution. In response, numerous innovative solutions have been explored and implemented. Among these, green roofs (GRs) stand out for their potential to address a range of environmental and social challenges. Despite several efforts in GR research over the past few decades, the widespread implementation of GRs remains limited due to an incomplete understanding of their performance and influencing factors, insufficient local research, lack of supportive legislation, and uncertain economic benefits. This PhD thesis aims to deepen the understanding of GR performance within the Australian climate, with a particular focus on runoff quantity and quality. The findings in this study are intended to support the widespread adoption of GRs by highlighting their substantial benefits to both the community and decision-makers. This thesis is organized into three main sections. The first section provides foundational knowledge for the subsequent chapters, derived from two comprehensive review papers. The first review paper identifies research gaps in general GR studies, while the second focuses on biochar and its application in GR research. The second section involves the development of a stormwater model to assess the hydrological performance of GRs on a catchment scale. The third section evaluates the effects of biochar on GRs through field experiments that analyze runoff quantity, runoff quality, and plant performance. Based on the findings from this PhD study, the following conclusions can be drawn: Section 1 The first review identifies knowledge gaps and generate future research directions. These gaps include identifying factors that affect GR performance, developing innovative GR materials and technologies, assessing GR performance on a larger scale, and obtaining local research data. The second review pointed out an overall trend of positive impacts of biochar on GR performance. However, the understanding of the effects of biochar on GRs is still in the preliminary stages. Future studies with long-term observations are required, particularly on the environmental impacts of biochar, its economic feasibility, and optimal biochar-related parameters. Section 2 A stormwater model based on eWater’s MUSICX software was developed to simulate the hydrological performance of GRs applied on each building at Victoria University’s Footscray Park campus. The results showed that large-scale GRs positively impacted annual runoff volume and loads of Total Phosphorus (TP), Total Nitrogen (TN), and Total Suspended Solids (TSS). However, a treatment train including GRs and other treatment devices was required to achieve local stormwater objectives. Section 3 Field experiments were carried out to examine the effects of biochar on GR runoff retention. Data was collected from the six newly established 1m2 biochar-amended GR test beds under different artificial rainfall intensities. The results illustrated that biochar successfully enhanced GR benefits by reducing runoff volume and delaying runoff outflows. The optimal biochar-GR setup was the GR modified by 7.5% v/v medium biochar particles applied at the bottom of the GR substrate. The impacts of biochar on the quality of GR runoff were also assessed using the same GR test beds. GR runoff was analyzed for pH, Electrical Conductivity (EC), and concentrations of Total Phosphorus (TP) and Total Nitrogen (TN). Mixed results were observed among different biochar-GR setups and water quality parameters. However, biochar retained significant potential to improve runoff quality by significantly increasing water retention. One-year observational data on plant performance was obtained from the same GR test beds. Biochar was found to improve performance of wallaby grass, common everlasting, and billy buttons. The most pronounced impact of biochar was observed in the GR substrate mixed with 15% v/v medium biochar particles. The enhanced plant performance plays a major role in maintaining GR performance during its life cycle while improving the economic value of GRs.

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