Degradation and biodiversity of rain gardens in the tropics

Rain gardens are commonly applied as a nature-based stormwater management method in urban areas, yet the long-term impacts, possible degradation, and effects on biodiversity as a type of green infrastructure remain underexplored. By comparing two rain gardens in Singapore– one of the earlier prototypes in a neighbourhood managed by a local town council in Central Singapore at Potong Pasir, and a more recent one managed by the National Parks in the West at Jurong Lake Gardens, the ecological and aesthetic functions are investigated. Thus, the rain gardens are explored through the lenses of both functional and aesthetic degradation. Quantitative methods, including the Shannon Biodiversity Index, Green View Index, Colourfulness Index, and surface heat mapping, are applied. Observational methods, including spatial configurations of the rain gardens, plant health, and soil conditions, were also explored to understand the extent of degradation. Common challenges encountered in rain gardens included poor or improper maintenance, poor aesthetic and visual engagement, as well as improper design. Through the findings, comprehensive design and maintenance suggestions are provided for designers and planners to improve existing rain gardens and extend the lifespan and function of future gardens. Rain garden lifespans can be lengthened to reap long-term benefits like effective stormwater management and habitat creation for local biodiversity. Maintenance suggestions build upon existing grey infrastructure and nature-based solutions routine maintenance protocols, tackling the four key functions of a rain garden: sedimentation, filtration, infiltration, and bioretention. Design suggestions are drawn from the data analysed, including potential tree planting configurations and the use of groundcover to reduce surface temperature.