EFFECTIVENESS OF INTEGRATED GRAY–GREEN INFRASTRUCTURE FOR URBAN STORMWATER RUNOFF MANAGEMENT IN ABA METROPOLIS, NIGERIA.

Rapid urbanisation, increasing impervious surfaces and inadequate drainage infrastructure have intensified stormwater flooding in Aba Metropolis, Abia State, Nigeria. This study assessed the perceived effectiveness of integrated gray–green infrastructure for stormwater-runoff management in the metropolis. A descriptive survey research design supported by field observations was adopted. The study population comprised adult residents of Aba North and Aba South Local Government Areas and built-environment professionals involved in infrastructure and environmental management. Through a multistage sampling procedure, 400 adult residents were selected, while relevant professionals were purposively engaged. Data were collected using a validated structured questionnaire and analysed using frequencies, percentages, weighted means, ranks and multiple linear regression at a 0.05 significance level. The findings showed that respondents agreed that integrated gray–green infrastructure could reduce urban flooding (mean = 3.89), reduce runoff volume (mean = 3.85), improve stormwater-drainage efficiency (mean = 3.84), improve urban environmental quality (mean = 3.77) and enhance groundwater recharge (mean = 3.72). The grand mean of 3.68 demonstrated a positive perception of the effectiveness of infrastructure integration. The regression result revealed a strong and statistically significant positive association between integrated gray–green infrastructure and stormwater-management outcomes (R = 0.782, R² = 0.611, adjusted R² = 0.606, F = 118.64, p < 0.001). The study concluded that combining rehabilitated drains and culverts with permeable pavements, bioswales, rain gardens, retention ponds, wetlands and riparian vegetation could strengthen stormwater management in Aba Metropolis. It recommended the adoption of an integrated infrastructure policy, rehabilitation of existing existing drainage facilities and implementation of pilot gray–green projects in flood-prone areas.