article · Water Science & Technology
Rapid urbanisation and climate change place growing pressure on urban drainage networks. Blue-Green Infrastructure, which includes rainwater harvesting systems, infiltration trenches, bioretention cells, and detention ponds, offers an approach to enhance drainage resilience against pluvial flooding. Using coupled one-dimensional and two-dimensional modelling, the performance of these interventions was evaluated across two drainage systems in Kampala that experience catastrophic flooding from extreme rainfall. Flooding impacts were assessed under both failed and non-failed initial drainage states, tracking changes in total flood volume and average flood duration. Spatially distributed rainwater harvesting systems alone reduced total flood volume by 16 to 45 per cent and cut average flood duration by 18 to 24 per cent. Blue-Green Infrastructure was found to be most effective during moderate rainfall events with return periods under ten years, supporting recommendations for city-scale implementation.
Severe rainfall and expanding urbanisation increasingly overwhelm conventional city drainage networks, causing destructive surface water flooding. By demonstrating how nature-based solutions such as rainwater harvesting reduce flood volumes and duration, this research provides quantitative evidence for municipal authorities and civil engineers seeking practical methods to protect vulnerable urban centres during heavy rainfall.
This work can inform civil engineering projects, municipal drainage design, and stormwater management products. Likely users include municipal authorities, urban planning agencies, and infrastructure engineering consultancies seeking to deploy rainwater harvesting solutions at scale. Because the findings are based on computerised one-dimensional and two-dimensional modelling of Kampala drainage networks, the work sits at an applied research stage that requires real-world physical pilots before commercialisation or broad municipal deployment.
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The need to enhance the resilience of urban drainage systems (UDSs) in view of emerging global climate change and urbanisation threats is well recognised. Blue-Green Infrastructure (BGI) provides a suitable strategy for building the resilience of existing UDSs. However, there are limited quantitative studies that provide evidence of their effectiveness for increased uptake in cities. In this research, coupled one-dimensional-two-dimensional (1D-2D) modelling is applied to assess the effectiveness of BGI that include rainwater harvesting systems, infiltration trenches, bioretention cells, and detention ponds using two case study UDSs located in Kampala that experience catastrophic pluvial flooding caused by extreme rainfall. The resulting flooding impacts are quantified considering 'failed' and 'non-failed' UDS initial states, using total flood volume and average flood duration as system performance indicators. The study results suggest that spatially distributed rainwater harvesting systems singularly lead to a reduction in total flood volume and average flood duration of 16-45% and 18-24% in the case study UDSs, respectively. Furthermore, the study results suggest that BGIs are more effective during moderate rainfall (T < 10 years). Based on the study findings, city scale implementation of multifunctional rainwater harvesting systems is recommended as a suitable strategy for enhancing UDSs' resilience.
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DOI: 10.2166/wst.2024.032
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