High-resolution wave modeling of the Southwestern Nigerian coastal shelf: Implications on geomorphic contrasts between barrier-lagoon and mud coasts

Abstract

This study characterizes the spatio-temporal wave variability along Southwestern Nigerian coastal and shelf areas in the Gulf of Guinea. This is to provide further insight into the hydrodynamic factors that influence geomorphologic changes on the low-lying coast. Reanalysis wind-field datasets are employed to generate hourly wind forcing for an unstructured WAVEWATCH III model to simulate some bulk wave parameters. The model is validated against data from offshore buoys and satellite altimetry at selected locations near the coast. Results show that the waves have an annual average of significant wave height (Hs), peak period (Tp), and wind speed (u) of ∼0.5 m, 4.1 s, and 3.9 m/s, respectively. They exhibit seasonal spatial variability that is highest in the peak rainy season from July to September (Av. Hs: 0.56–0.79 m; Av. Tp: 4.68–5.18 s; Av. u: 4.30–5.22 m/s) and lowest in the early dry season from November to January (Av. Hs: 0.26–0.34 m; Av. Tp: 3.37–3.80 s; Av. u: 3.25–3.50 m/s). Also, the monthly averaged wave power varies from 0.2 to 2.8 kW/m annually. However, a maximum Hs of 2.2 m that generated power of 9.4 kW/m for 11.1 s was recorded during the peak of the rainy season in August. Overall, waves with relatively low intensity, which can be classified as smooth to moderate, propagate from the southwest direction and decrease towards the coast. The higher Hs and Tp recorded during the peak of rainy and end of dry seasons are attributed to the influence of far-away swells. A comparative assessment indicates that the Barrier-Lagoon coast is highly controlled by waves, while the Mahin mud coast, which witnesses frequent flooding events that degrade its shoreline, has little wave influence. Thus, local subsidence that increases the relative sea level is suggested to be taking place at sections of the muddy coast. This information is crucial for the sustainable engineering design and management of low-lying coasts.