2004, RPS Hydrosearch, Gunfleet Sands Offshore Wind Farm, Summary and Collation of Oceanographic Data Acquired Between January 2002 and February 2003

Description

This project involved the collection of observations from two Valeport 730D oceanographic moorings on Gunfleet Sands from January 2002 to February 2003 by RPS Hydrosearch with wind data collected from an anemometer mast deployed at the southern end of Gunfleet Sand. The moorings recorded water level, current, wave and turbidity data, while the met mast collected wind speed and direction at six heights. However, during the initial deployments the water depth was too great to collect reliable wave data, even though the conditions were within the specifications of the instrument. The moorings were therefore moved higher up the bank. Furthermore, the project collates the observations from two Valeport 730D oceanographic moorings deployed on Gunfleet Sand from January 2002 to February 2003, with wind data collected from an anemometer (meteorological or met) mast deployed at the southern end of Gunfleet Sand.  Observations at the northern (west) site and the southern (east) site have highlighted certain aspects regarding the oceanographic regime around Gunfleet Sand.  There are higher currents at the northern mooring, suggesting stronger flow on the western side of the bank.  The maximum speed at 0.5 m above bed was 0.94 m/s at the northern site. The maximum speed at the surface, derived from the observation using the 7th power law, gives an estimate of 1.4 m/s (2.7 knots).  The ebb tide is stronger at the northern site, and the flood stronger at the southern site indicating a clockwise circulation around the bank.  In general, the flood tide is towards the south, and the ebb tide towards the north. However, local conditions at the moorings meant that the tidal axis was closer to an east/west direction.  Local cross currents occur at specific locations, probably due to the local bathymetry.  The temperature varies with the tidal variation. The semi-diurnal range can reach
1.5°C.  Wave direction closely follows the wind direction, particularly at the offshore site (south).  The maximum wave height observed was 2.14 m in November 2002, although higher waves may have occurred during January and February 2002 and not been recorded.  Waves, and wind speeds, are lower during the summer months, but Hs may still exceed 1 m in July.  Turbidity is greater on the ebb on the western side of the bank, and on the flood on the eastern side of the bank, producing a clockwise movement of material.