Assessment of Partial Blockage in Urban Drains for Flood Risk Reduction 

Partial blockage in open channels and urban drainage systems is a common issue arising from debris accumulation, sediment deposition, and inadequate maintenance, often resulting in reduced flow capacity and increased flood risk. Despite its practical relevance, the hydraulic effects of partial blockage on flow behaviour are not well quantified through controlled experimental studies. This work aims to investigate the influence of partial blockage on flow characteristics in open channels and explore its implications for urban stormwater drainage systems.Laboratory experiments are carried out in a rectangular open-channel flume under steady flow conditions. Velocity measurements are obtained at multiple depths for unblocked conditions and for different partial blockage configurations. Blockages of varying size and location are introduced manually to represent realistic obstructions commonly observed in urban drains. The changes in velocity distribution, water depth, and flow-carrying capacity due to partial blockage are analysed to understand the hydraulic response of the system.Based on these observations, relationships between blockage extent and hydraulic performance are developed to identify critical blockage conditions.The study framework is applied to urban stormwater drainage networks using SWMM modelling to extend the experimental findings to real-world applications. Blockage scenarios are simulated in selected channels to assess their impact on system performance and flooding behaviour.The outcomes of this study provide experimental insight into blockage-induced hydraulic effects and highlight the importance of considering partial blockage in urban drainage analysis. The combined experimental and modelling approach offers a practical basis for improving flood risk assessment and maintenance planning in urban stormwater systems.