Assessment of Flood Vulnerability and Drainage Capacity in Port Harcourt Municipality, Rivers State

This study assesses flood vulnerability and storm drain capacity adequacy in Port Harcourt Municipality, Rivers State, South South Nigeria. Port Harcourt experiences frequent and damaging urban flooding attributable to its low-lying coastal topography, high seasonal rainfall, inadequate storm drainage infrastructure, and rapid unplanned urban expansion that has reduced pervious land cover. The study combined hydraulic field surveys of primary and secondary drainage channels, remote sensing land cover analysis, and household flood impact surveys. Channel cross-section measurements and flow velocity data were used to compute drainage capacity using Manning's equation. Rainfall frequency analysis using forty years of rainfall records determined peak design storms for the five-year, ten-year, and twenty-five-year return periods. Survey interviews were conducted with 240 households in eight flood-prone communities to document flood frequency, depth, duration, and economic losses. Results indicate that the majority of surveyed channels have hydraulic capacities insufficient to convey the five-year design storm discharge without surcharging, with conveyance deficits most severe in Rumuola, Diobu, and Trans-Amadi areas. Sedimentation and blockage by solid waste reduce effective channel capacity by an estimated 35 percent from design dimensions. Household surveys record annual flood damages averaging 180,000 naira per affected household. The study identifies a combination of infrastructure underinvestment and inadequate drainage maintenance as the primary cause of chronic urban flooding. Keywords: urban flooding, drainage capacity, flood vulnerability, Port Harcourt, storm drainage.