Abstract
Urban drainage systems, often designed for outdated rainfall assumptions, are increasingly unable to cope with extreme rainfall events. This leads to flooding, infrastructure damage, and economic losses, necessitating effective diagnostic and improvement strategies. In current practice, conventional analysis platforms built on hydrological-hydraulic models provide only limited analytical support, making it difficult to pinpoint defects, inspect causal mechanisms, or evaluate alternative design options in an integrated manner. In this paper, we develop DrainScope, to our knowledge, the first visual analytics approach for comprehensive diagnosis and iterative improvement of urban drainage systems. Defects are initially observed in the map view, after which DrainScope extracts the critical sub-systems associated with them using a rule-based search strategy, enabling focused analysis. It introduces a novel drainage-oriented Sankey diagram to visualize internal flow dynamics within the focused, static drainage system, revealing the causes of identified system defects. Furthermore, it enables flexible modification of drainage components corresponding to identified defects, coupled with a comparison view for rapid, iterative evaluation of improvement plans. We evaluate DrainScope through a real-world case study and positive feedback collected from domain experts.