Internal Wave Dynamics on the Nigerian Continental Slope and Their Interaction with Deepwater Infrastructure

Internal gravity waves generated at the continental shelf break of the Gulf of Guinea propagate onto the Nigerian continental slope as high-amplitude nonlinear wave trains that exert poorly characterised dynamic loads on deepwater infrastructure, including mooring systems, risers, and subsea pipelines. This dissertation advances understanding of internal wave dynamics on the Nigerian slope through an integrated observational and theoretical research programme. A two-year moored array programme deploys six acoustic Doppler current profiler and thermistor chain moorings along the 400 to 2000-metre isobath off the Niger Delta, recording sub-inertial and internal wave-band current and temperature fluctuations at hourly resolution from 2023 to 2024. Analysis quantifies internal wave amplitude, energy flux, propagation direction, and shoaling behaviour using rotary spectral analysis and wavelet-based mode decomposition. Synthetic aperture radar imagery from Sentinel-1 is used to map the surface expression of internal wave trains across the Nigerian shelf, providing spatial context for the moored observations. A high-resolution three-dimensional numerical simulation using the Massachusetts Institute of Technology ocean model (MITgcm) with tidal forcing at the shelf break reproduces the observed internal wave generation and propagation characteristics. Morison equation modelling translates simulated current velocity fields into dynamic force time series on idealised deepwater riser geometries, quantifying fatigue loading from internal wave forcing. The dissertation provides the first comprehensive characterisation of internal wave climatology on the Nigerian slope and delivers engineering-relevant loading statistics essential for improved deepwater infrastructure design standards in Nigerian waters. Keywords: internal waves, Nigerian continental slope, deepwater infrastructure, nonlinear wave trains, mooring dynamics