Current conditions in the northern North Sea

In order to acquire sufficient simultaneous data to establish joint distributions of waves and currents for design, an extensive measurement programme of simultaneous waves and current profiles has been performed for approximately 5 years at several locations in the northern North Sea. The measured current data have been found to be more inaccurate than the specified accuracy of the instruments. However, the measured current data still give a good over-all description of the main features of the current conditions in the northern North Sea. Variations in current conditions are seen between the different measurement locations. At the southernmost locations, wind-driven currents, i.e. inertial oscillations, are the governing current conditions and contribute to larger current speeds during summer than in the spring and fall, both operational and extreme. At all locations, year-to-year variation in estimated extreme current speeds based on different individual years are larger than expected, indicating that current measurements for considerably more than one year is required for reliable estimates of extreme current conditions for design of offshore structures. These results highlight the need for a better understanding of the current conditions in order to account for the uncertainties associated with these in design of offshore structures.