Integrating Nature-Based Solutions and Hydraulic Modelling for Coastal Urban Drainage Resilience in Ghana: A Case Study

"background": "Coastal urban centres in West Africa face escalating flood risks due to climate-induced sea-level rise and intensified rainfall, compounded by conventional drainage systems that are often inadequate. This creates an urgent need for resilient infrastructure designs that synergise grey and green engineering approaches. ", "purpose and objectives": "This case study aimed to develop and evaluate a climate-resilient urban drainage design for a coastal municipality, integrating nature-based solutions (NBS) with detailed hydraulic modelling to mitigate compound flooding from pluvial and tidal sources. ", "methodology": "A coupled 1D-2D hydrodynamic model was built and calibrated using local topographical, rainfall, and tidal data. The performance of the existing drainage network was simulated under projected climate scenarios. Subsequently, a hybrid design incorporating bioswales, retention basins, and upgraded conduit capacity was modelled. A generalised linear model, \ (E (Y) ) = \0 + \1 X{ + \2 X + \3 X, was used to quantify the impact of predictors on flood extent (Y). Uncertainty was addressed through Monte Carlo simulation, with results reported with 95% confidence intervals. ", "findings": "The hybrid NBS-grey infrastructure design reduced the extent of combined flooding by approximately 40% under a 10-year storm surge coincident with a 1-in-10-year rainfall event, compared to the baseline conventional system. Model inference indicated that the NBS component significantly reduced flood volume (\3 = -0. 28, CI: -0. 35 to -0. 21). ", "conclusion": "The integrated approach demonstrably enhances drainage resilience in the coastal urban context. The study confirms that strategically engineered NBS can substantially augment the capacity of hydraulic networks to manage compound waterlogging. ", "recommendations": "Municipal engineers should adopt coupled hydraulic modelling as a standard planning tool for coastal drainage. Design guidelines should