SCENARIO-BASED OPTIMIZATION AND CLIMATE RESILIENCE OF URBAN STORMWATER DRAINAGE SYSTEMS IN ASABA, NIGERIA

Summary

Urban drainage systems in growing cities tend to experience capacity deficiencies and intensified runoff in the face of a changing climate. The resilience of urban drainage corridors in Asaba, Delta State, Nigeria, was investigated through scenario-based hydrologic and hydraulic modelling of five drainage corridors: Okpanam Road, DLA Road, Summit Road, Nnebisi Road, and Cable Point. Each corridor was assessed using EPA SWMM, GIS-based spatial analysis, the Rational Method, and Manning's equation under four intervention scenarios—increased rainfall, low-impact development (LID), smart operational improvement, and drainage upsizing—in addition to a baseline scenario. The study found that the existing drainage systems have deficient conveyance capacity, with FoS values ranging from 0.20 to 0.59 across the five corridors under baseline conditions. Under a 1.5× rainfall scenario, a 50% increase in rainfall produced an approximately 50% increase in peak runoff, reducing hydraulic adequacy. LID measures reduced peak runoff by approximately 20%, while smart operational improvements produced a modest increase in full-flow capacity. Drainage upsizing provided the largest individual increase in reported capacity, reaching approximately 62.6% at the best-performing corridor under the assessed scenario. No single intervention achieved uniformly adequate outcomes across all corridors. The combined 40% LID and 40% channel-upsizing scenario reported zero hydraulic shortfall at all five corridors. The study therefore demonstrates a scenario-based approach for assessing urban drainage resilience and comparing alternative runoff-reduction and conveyance-improvement measures in Asaba.

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