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): Chuen King Kwok
Keywords: Rain gardens Sustainable drainage Urban flooding Hydrologic performance Bioretention Underdrain Stormwater management Water quality improvement
Abstract: To explore sustainable drainage solutions addressing the increasing threats of flooding due to urbanization, extreme weather, and aging infrastructure, the Drainage Services Department (DSD) of the Government of the Hong Kong Special Administrative Region of the People’s Republic of China implemented a pilot project using rain gardens at three roadside areas: Chai Wan, Tai Po, and the Shatin Sewage Treatment Works. Rain gardens, featuring planted depressions, collect and filter surface runoff. The pilot project included an underdrain-type rain garden in Chai Wan and bioretention-type rain gardens in Shatin and Tai Po. The DSD, in collaboration with the Hong Kong Productivity Council, conducted an in-depth review of these rain gardens' hydrologic and treatment performance. The objectives of this study were to evaluate the effectiveness of rain gardens in slowing down and reducing runoff entering the drainage system, assess the performance of rain gardens in improving water quality and minimizing pollutants of low flow and first flush from discharging to public drains, review the suitability of plant species for the rain gardens, identify operational and maintenance issues of rain gardens, and recommend enhancement measures for improving rain garden performance. Results indicated that the underdrain-type rain garden in Chai Wan demonstrated a peak delay time of 41 minutes and a peak shaving rate of 22%, effectively removing total nitrogen (TN) and total phosphorus (TP) but not total suspended solids (TSS). In Shatin, the bioretention-type garden achieved a peak delay time of 45 minutes and a peak shaving rate of 92%, with moderate pollutant removal performance. The Tai Po garden achieved complete retention of stormwater and effective pollutant removal, with up to 73% TN and over 90% TP removal. The study highlighted the advantages of underdrain systems in urbanized areas and the cost-effectiveness of bioretention systems, while also noting issues like waterlogging and nutrient leaching. Regular cleaning of debris and addressing plant health issues were essential for maintaining performance. Overall, the rain gardens proved effective for stormwater management and water quality improvement, providing valuable insights for future adoption in Hong Kong.
Year: 2025