7.5.5 Currents 159. Current speeds and directions are largely dictated by an astronomically-driven tidal signal, but can also be affected (strengthened, weakened or realigned) by meteorological influences or surge effects.
7.5.5.1 Tidal Currents 160. Figure 7.4 depicts the tidal ellipses across the East Anglia Zone.
161. Current data measured within the East Anglia THREE site (described in Appendix 7.2) show that the majority of the currents flow along a north of northeast to south of southwest aligned axis.
162. The near-surface current speeds are generally below 1m/s, except at the peak of spring tides or during surges when they can exceed this value. During neap tides, peak currents range between 0.5 - 0.6m/s.
7.5.5.2 Non-tidal Currents 163. In addition to astronomical tidal influences, current patterns can become modified for short durations due to other processes, such as meteorological conditions and stratification in the water column.
164. Storm surges can elevate currents by up to 0.4m/s during a 1 in 50 year return period event, typically orientated in a south of southwesterly direction (GL Noble Denton 2011).
7.5.6 Wind and Wave Regimes 165. The wind regime is important in generating local wind waves. The dominant wind direction is from the southwest.
166. Wave data measured within the East Anglia THREE site (described in Appendix 7.2) show that a high percentage of the waves arrive from the southwest, in keeping with the predominant wind direction. A significant grouping of waves also arrive from the northeast, as a result of swell waves generated further afield in the North Sea. Waves can, however, approach from all directions.
167. During the East Anglia THREE metocean survey, the minimumsignificant wave height recorded was 0.18m, with a maximum significant wave height of 6.03m. The mean significant wave height was 1.27m.
168. Extreme return period wave data within the East Anglia THREE site show a 1 in 1 year return period significant wave height of 6.0m with an associated peak wave period of 11.1s. Under a 1 in 50 year return period, the corresponding values increase to 7.5m and 12.5s, respectively.
Preliminary Environmental Information May 2014
East Anglia THREE Offshore Windfarm Chapter 7 Marine Geology, Oceanography and Physical Processes Page 35
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