Concerning the current conditions and transport of sand in the shallow water areas off the coast of the south-eastern [Translation from: Hamburger Kustenforschung 29 [pages 41-43 only], 1974]

Item Type monograph

Authors Gohren, I.H.

Publisher Freshwater Biological Association

Download date 27/09/2021 03:09:20

Link to Item http://hdl.handle.net/1834/22529 Freshwater Biological Association FBA Translation (New Series) No. 147

Title: Concerning the current conditions and transport of sand in the shallow water areas off the coast of the south-eastern North Sea. (pages 41-43 only).

Author(s) Gohren, I.H.

Reference: Hamburger Kustenforschung, 29, (pages 41-43 only).

Original language: German

Date of publication of original:1974

Translator: J.V.Bird

Date of publication of translation: 1981

Number of pages of translation: pages 2

FBA Translations are to be considered as "provisional". As a rule they have not been prepared by expert translators nor have they been edited by the original authors. They are available from The Librarian, Freshwater Biological Association, The Ferry House, Far Sawrey, AMBLESIDE Westmorland. England, at the current rare for xerox copying. FBA Translation (New Series), No. 147 Concerning the current conditions and transport of sand in the shallow water areas off the coast of the south-eastern North Sea. [Page 41-43 only]. Gohren, I.H. Hamburger Kustenforschung , 29, 41-43 (1974) Translated by J.V. Bird.

Summary With the aid of the German Research Association in the central programme 'Sand movements in the German coastal region', an investigation into the current conditions in the shallow water areas of the coasts of the south-eastern North Sea between and the Weser estuary was carried out by the author. Foundations of the work are 19 continuous current recordings in five profiles normal to the coast from years 1971 to 1973. As well as these a few older current observations were made use of. Off the coasts of the south-eastern North Sea varying tidal currents impinge; they are currents whose directions may vary periodically through all points of the compass. They are caused by the circulating tides in the North Sea (Amphidromien). The turning flow movement experiences a deformation in the very shallow coastal waters, and as it happens the flow turning movement in the case of high tide continues right up onto the outer flats, while here and in the fore-lying shallow water areas around the time of low water (on account of the small depths of waters), there prevails a more variable current. A result of this hydrodynamical procedure is the development of counter currents. This special effect which is shown schematically in Fig. 27. is to be investigated within the framework of the research programme and confirmed by flow observations.

Recordings with continuous current meters on the flat (a recording height of 1m above the bed) were taken from the shallow water areas in front of , Suderoogsand , Eiderstedt, Trischen,and Knechtsand. Comparative current flow observations were already available for the Scharhamsandbank. The records were prepared with an electronic calculator using existing programmes and are set out together in Figs. 9 to 13 in the form of lines, showing movement directions and in Figs 15 and 20 in a polar vector diagram. From these a succession of polar vector diagrams can' be drawn (Figs 28-34) which leave the afore- mentioned deformation of the turning currents well clarified. From the. scheme given in Fig. 27 the characteristic circulating or loop-shaped flowpath can be seen. The investigations have confirmed essentially, that the deforming effect of the turning currents spreads onto the region between the outer Weser and the island of Sylt. In front of the flats between the Weser and estuary and in any case in the region in. front of Eiderstedt it is evident in particularly striking form in the remaining recording profiles. Linked up with it are the remaining counter-currents as set out in Fig. 45. The orientation direction of the remaining counter-currents is associated with the knowledge of the circulating flow off the coast - agreeing with theoretical considerations. This is a left hand turning movement (anticlockwise) north of the Elbe estuary and a clockwise movement in the region between Elbe and Jade.

With three profile recordings the strong depositional effect due to the wind with wind at a strength of 6 to 7 Bft from the north west can be appreciated. A special investigation of the wind influence shows that in all cases at the affected stations the drift currents were impinging in the direction of the effective force of wind (primary drift currents) with a residual intensity of between 2 and 8 Km/tide. (Fig.47) From the preceding results a few indications of the direction of prevailing transport of sand can be gained. They are valid however only with the reservation that an investigation of the process of movement of the floor materials must be enclosed within a broader parameter, especially in the case of the shallow water areas regarded here, with the influence of sea swells, surf and drift currents.

In front of the mudflat areas between the Elbe and Weser there exists in normal tide conditions an easily achieved movement of material, with one of the systems of counter currents. (Fig. 49). This is upheld by earlier investigations. In the shallow water zones in front of Amrum, Suderoogsand, and Eiderstedt observations on one of the coastwards moving sand movements are being concluded. It is to be presumed that this material is agitated more widely parallel to the coast in front of the islands and lens shaped deposits (where it also comes under the influence of the surf currents), and.-is taken away seawards again in the channels of the large flats, so that a circulation develops.

Notice

Please note that these translations were produced to assist the scientific staff of the FBA (Freshwater Biological Association) in their research. These translations were done by scientific staff with relevant language skills and not by professional translators.