Author(s): Sai Shing Chim; King Ho Wong; Selina Wai Man Fong; Ching Man Lee; Chuen King Kwok; Chun Yee Joey Tang; Yang Liu And Kai Wu

Linked Author(s):

Keywords: Rain Gardens; Sustainable Drainage; Urban Flooding; Hydrologic Performance; Bioretention; Underdrain; Stormwater Management; Water Quality Improvement

Abstract: To address the escalating threats of flooding due to urbanization, extreme weather events, and aging drainage infrastructure, combined with the unique climatic and urban conditions in Hong Kong, the Drainage Services Department (DSD) of the Government of the Hong Kong Special Administrative Region initiated a pilot project employing rain gardens as a sustainable drainage solution, utilizing local plant species. This initiative was implemented in three roadside areas in Hong Kong: Chai Wan (CW), Tai Po (TPO), and the Shatin Sewage Treatment Works (ST). In collaboration with the Hong Kong Productivity Council, the DSD conducted a comprehensive study to evaluate the hydraulic performance of these rain gardens from 2021 to 2023. The study aimed to assess their effectiveness in reducing runoff, improving water quality, evaluate plant species suitability, identify maintenance issues, and recommend potential enhancements. The study revealed that bioretention-type rain gardens in TPO and ST are effective in areas with pervious soil and moderate runoff loads, while the underdrain system in CW is advantageous in urban settings due to its rapid drainage capabilities. Without rain gardens, peak runoff occurs immediately during heavy rainfall, which can overwhelm drainage systems. However, our study shows that rain gardens can significantly delay peak runoff, reducing the immediate load on drainage systems and helping to prevent flooding. Specifically, the CW garden demonstrated a peak delay of 41 minutes and a peak shaving rate of 22%. It effectively removed 67% of total nitrogen (TN) and achieved an average total phosphorus (TP) removal rate of 74%, both surpassing the target removal rate of 45%. However, the CW garden struggled with total suspended solids (TSS) removal, achieving only a 3% average reduction, which is significantly below the target minimum of 80%. The ST garden exhibited a peak delay of 45 minutes and an impressive peak shaving rate of 92%. It achieved moderate pollutant removal rates, with 49% for TN and 34% for TP. Additionally, TSS levels increased, which is counterproductive. The TPO garden achieved complete stormwater retention and effective pollutant removal, with up to 73% TN removal and over 90% TP removal. It also achieved a 60% reduction in TSS concentration, which, although substantial, still falls short of the target minimum removal rate. Regular maintenance, including debris cleaning and plant health monitoring, was essential for optimal performance. However, challenges such as waterlogging, clogging, and maintenance difficulties were identified. Overall, the rain gardens proved effective for stormwater management and water quality improvement, providing valuable insights for future implementation in Hong Kong.

DOI: https://doi.org/10.64697/978-90-835589-7-4_41WC-P2138-cd

Year: 2025