Wave Power Assessment in the Presence of Currents: an Overview of Analytical Versus Complex Numerical Approaches

Resource characterization studies at wave energy sites generally ignore the effect of tidal currents, due to the difficulties associated with running coupled wave-tide models. Further, there is a need to estimate the significance of wave-tide interaction effects on the wave power using simplified methods, before investing in time consuming and costly numerical models. Additionally, many wave buoy measurements are collected in deep waters, where wave-current interaction effects may not be significant; this makes validation of coupled models more challenging. Here, we give an overview of the application of simplified analytical methods as well as fully coupled wave-tide models to address this problem. Firstly, we present and validate a simplified analytical method, based on linear wave theory, to estimate the influence of tidal currents on the wave power resource. The method estimates the resulting increase (or decrease) in wave height and wavelength for opposing (or following) currents, as well as quantifying the change in wave power. Results demonstrate a high level of accuracy for the simplified analytical approach, which can thus be used as an efficient tool for making rapid estimates of likely tidal effects on the wave power resource. Secondly, we discuss the application of a coupled modelling system, COAWST (Coupled-Ocean-Atmosphere-Wave-Sediment Transport), and present issues such as computational cost, as well as the success of this approach in characterizing wave power in the presence of currents.