Currents and near-bottom suspended matter dynamics in the central north sea during stormy weather — Results of the PIPE’98 field experiment —Strömungen und bodennahe Schwebstoffdynamik in der zentralen Nordsee bei stürmischem Wetter — Ergebnisse des PIPE ’98 Feldexperiments —

In order to investigate near-bottom suspended participate matter (SPM) dynamics and near-bottom currents, between January 18 and 25,1998, a small array of optical backscatter meters and current meters was deployed in the central North Sea close to the pipelines NORFRA and ZEEPIPE I. The data were supplemented by local wave measurements (WAVEC buoy) and shipborne measurements as CTD profiles, water samples for the determination of the SPM concentration, and meteorological data. At the position of the PIPE site previous Side Scan surveys indicated scouring processes at the ZEEPIPE I. Therefore, possible interactions between the pipe and SPM dynamics and currents should be investigated. A special challenge was the positioning of the instruments at a water depth of 60 metres. In the North Sea, January is known for rough weather and as intended two heavy storms hit the area. Due to rough sea during the first days of the experiment, we did not succeed to place the instruments directly beside the pipes. Unfortunately, two near-bottom current meters failed. However, the interaction between wind, waves, currents, and SPM concentration during periods with wind speeds up to 43 kn and peak waves of 11 m was observed and will be discussed. For the interpretation of the field data we used also the results of the European Shelf Wave Model which proved to be very reliable. High swell, generated by remote wind fields, proved to be the key mechanism for sediment mobilization. The vertical range which is influenced by wind, wind waves, and swell and its temporal variation was estimated.