Episodic density-induced current velocities at the Gemini offshore wind park

Abstract

This thesis investigates the origin of observed current velocities at the Gemini offshore wind farm in 2015. Currents have been measured of 1.2 m/s while, based upon tidal and storm predictions, currents of only 0.7 m/s were expected. The aim of this research is to gain insight into the origin of these higher currents, taking into account the physical oceanography at this location. We find that these high currents measured in August are forced by baroclinic currents. Stratification was present at a measurement ship, 32 km northeast from Gemini. In addition, satellite imagery shows Gemini to be located in a region with fronts, between warm water from the Wadden Sea and colder water from the North Sea. In fact, a tidal mixing front is formed on top of the already established saline stratification [Van Aken, 1986]. The origin of fresh water is found to be from sluices discharging onto the Wadden Sea. Prior to the period with high currents a pulse of fresh water is discharged onto the Wadden Sea. Followed by the lowest winds recorded in 2015, an optimal climate is formed in which fronts can travel offshore. This is supported by the satellite imagery. In addition, density-induced currents are calculated based upon the mathematical model of Heaps [1972]. The analysis if the data suggests that density driven currents of 0.4 m/s are generated in August, which combined with the tide can give 1.2 m/s currents.