Numerical Simulation of Tidal Flooding Dynamics in the Lekki Lagoon System, Lagos State

Tidal flooding in the complex lagoonal systems of Lagos State is an escalating hazard that interacts with storm drainage deficits and sea level rise to produce compound flood events of growing severity and extent. This study develops a calibrated two-dimensional hydrodynamic model of the Lekki Lagoon system using Delft3D-FM to simulate tidal flooding dynamics, overland flow propagation, and the sensitivity of flood extent to sea level rise and rainfall scenarios. Model bathymetry is constructed from a combination of echo sounding surveys and digital elevation model data from drone photogrammetry at 20-centimetre resolution for the intertidal and low-lying coastal land areas adjacent to the lagoon. The model domain encompasses the Lagos Lagoon, Lekki Lagoon, Ologe Lagoon, and Badagry Creek connected system, with tidal forcing applied at the Lagos Harbour entrance and calibrated against water level records from five tide gauges installed for this study. Mesh refinement to five-metre resolution is applied in urban areas of Ajah, Ikota, and Chevron residential zones identified as highest exposure zones. Validation uses independent flood extent observations from Sentinel-1 SAR imagery during the October 2024 flood event. Scenarios simulate compound flooding from a one-in-25-year storm surge combined with 0.5-metre and one-metre sea level rise additions. Findings are expected to demonstrate that one-metre sea level rise extends the 25-year flood return period event inundation area by 65 percent, affecting critical infrastructure including the Lekki-Ajah Expressway. Keywords: tidal flooding, hydrodynamic modelling, Delft3D, Lekki Lagoon, Lagos sea level rise