Local Currents at a shoreface-connected Ridge in the German Bight. 
¡Measurements during moderate and stormy winds off Norderney 
Holger Klein and Ekkehard Pvl i it el slaed t 
UDC 551.465..553 :551.465.78; German Bight 
Summary 
Current data at a shoreface-connected ridge in the German Bight have been sampled 
in January 1990 and January 1991. During the 1991 experiment a violent southwest stonn 
hit the area so that the storm-induced currents can be compared to those under moderate 
periods. The stonn significantly changed the tide dominated spatial and temporal current 
regime. Estimates suggest, that all sediment grain sizes which occur in the ridge area 
(0.1 to 0.5 mm) can be resuspended clue to the stonn-induced intensification of the 
bottom currents. 
Lokale Strömungen an einem ZungenriiT in der Deutschen Bucht 
(Zusam in eu fassu ng) 
Im Januar 199t) und 1991 wurden Slrömungsmessungen an einem Zungenriff in 
der Deutschen Bucht durchgeführl. Im Januar 1991 zog ein schwerer Siidweslstunn mit 
Orkanslärke durch das Untersuclumgsgebiet. so daß die lokale Stömung unter extremen 
Winclbedingungen milder während ruhigerer Phasen verglichen werden kann. Der Sturm 
veränderte das vorwiegend gc/eitenbeherrschle Strömungsregime grundlegend. Abschät 
zungen ergeben, daß die infolge des Sturms intensivierte Bodenströmung alle örtlich 
vorhandenen Sandfraktionen (0,1 bis 0,5 mm) resuspendicren kann. 
L Introduction 
Shoreface-connected sand ridges, about 5 metres in height and some kilometres long are 
common features of the East Frisian coast (southern North Sea). The location of these ridges 
can vary from year to year while their morphological structure remains mainly conserved. Axial 
displacements of the order of 200 metres within 2 years have been observed, but without a 
preferred sea or landward direction. Although these ridges arc exposed to strong tidal currents, 
morphological changes can only be explained by the effects of strong storms, i. e., the morpholo 
gical forces can be effective for only a feu days within a year (F1 e m m i n g [ 1991 j). 
Two current-measurement campaigns, TOPEX-I and -II (Topographical Experiment) were 
carried out at a shoreface-conneetcd ridge northwards off the island of Norderney in January 
1990 and January 1991 (fig. 1). The ridge is about 5 m high, 15 km long and I to 2 km wide. 
Its axis runs nearly straight-lined from 295° to 115°. The water depths above the ridge amounts 
to 20 m and about 25 m in the troughs. According to (S w i f t et al. [ 1977]) the landward flank 
of the ridge near the junction to the shore face is steeper than the seaward flank while further 
seawards the ridge is nearly symmetrical or steeper al the seaward flank. The mean bottom 
slope amounts to about I : 300.