This study evaluated the effectiveness of blue–green infrastructure (BGI) for flood mitigation in riverine communities of Rivers State, Nigeria, focusing on hydrological performance, spatial optimisation, and socio-economic outcomes. The investigation was prompted by recurring urban flooding associated with high-intensity rainfall, insufficient drainage capacity, accelerated urbanisation, and weak institutional coordination within the Port Harcourt metropolitan region. A mixed-methods framework was employed, integrating hydrological modelling, geospatial analysis, cost–benefit assessment, and stakeholder consultations across selected flood-prone communities—Rumuokwurushi, Rumuola, and Obio-Akpor. Simulation results comparing baseline conditions with both standalone and integrated BGI configurations (retention ponds, bioswales, permeable pavements, and green corridors) demonstrate clear performance advantages for networked systems. The integrated scenario achieved a 54.5% reduction in peak flow, 54.3% decrease in runoff volume, 58.3% shortening of flood duration, and 55.3% contraction of inundation extent, alongside a 73.3% improvement in water quality indicators. Spatial optimisation further showed that positioning retention ponds within natural depressions and hydraulically linking them to bioswales and permeable surfaces significantly improves system efficiency and ecological continuity. Multi-criteria evaluation confirmed that integrated BGI consistently delivered superior outcomes across flood attenuation, climate resilience, ecological enhancement, and social acceptance metrics. Economic appraisal indicates strong financial feasibility, with a benefit–cost ratio of 5.87:1, reflecting substantial avoided flood losses, property value appreciation, and employment opportunities. The study therefore establishes that context-sensitive, interconnected BGI systems constitute a technically robust and economically justified pathway for climate-resilient flood management in Rivers State’s riverine settlements. Nevertheless, large-scale implementation will depend on enabling policy frameworks, strengthened institutional coordination, and active community participation. The research expands the empirical evidence base on BGI within Nigeria and offers a practical decision-support reference for planners and policymakers pursuing sustainable flood risk reduction in rapidly urbanising coastal environments.
Johnbull et al. (Wed,) studied this question.