scholarly journals STABILITY OF TIDAL CHANNELS DEPENDENT ON RIVER IMPROVEMENT

1976 ◽  
Vol 1 (15) ◽  
pp. 102 ◽  
Author(s):  
Volker Barthel

Many authors have dealt with the migration of sand in front of the German coast of the North Sea. Especially the movement of sand-banks and deep channels in the Weser-estuary was subject matter of several investigations with different results. Thorough investigations of selected cross-sections point out, that the movement goes on in some regions. The important shipping channel however has obtained a certain stability during the last 3o - 4o years, because the migration of sand occurs otherwise than in former days. This phenomenon coincides with the extensive and decisive river improvement measures in the inner part of the Weser-estuary. Current measurements in the investigation area demonstrate, that concentrated tidal currents in the deep channels guarantee a sufficient clearance for shipping purpose. It seems to be sure, that for the present no essential shifting of the main channel calls for important measures in the field of shipping, dredging and building of sea-marks.

1974 ◽  
Vol 1 (14) ◽  
pp. 59
Author(s):  
Horst Pasenau ◽  
Johannes Ulrich

In a lot of regions the bottom of the North Sea is covered with large ripple fields, especially in the estuaries and in the tidal channels. A great number of echo sounding profiles (29.500 n.m.) were evaluated to determine the boundaries of these areas and to describe the dimension of patterns. Special investigations of the hydrographic situation, the distribution of deposits and the migration of ripples under the influence of tidal currents only, were carried out in a testing area in the Lister Tief on 11 cruises since 1971.


Author(s):  
C. Luczak ◽  
J.-M. Dewarumez ◽  
K. Essink

Ensis directus (Bivalvia: Solenidae) was noted for the first time along the French coast of the North Sea in June 1991. High numbers of post larvae after a period of northerly winds indicate that settled larvae originated from adult populations in Belgian or Dutch coastal waters. Future dispersal of Ensis directus could be used as a biological tracer of coastal water movements between the Southern Bight of the North Sea and the English Channel.The American jack knife clam, Ensis directus (Conrad, 1843), synonym Ensis americanus (Binney, 1870)sensu van Urk (1964,1972), was discovered in Europe in the German Bight for the first time in June 1979 (Von Cosel et al., 1982). This species is assumed to have been transported in its larval stage by a ship containing ballast water. Considering the dimensions of the specimens, this probably happened in the first half of 1978 (Von Cosel et al., 1982; Mühlenhardt-Siegel et al., 1983). Since then this species has spread rapidly in the North Sea in subtidal and intertidal areas. Dense populations were found along the German coast within a few years (Von Cosel et al., 1982; Mühlenhardt-Siegel et al., 1983; Swennen et al., 1985). In 1986 Ensis directus was reported from the north and east Danish coasts as far as the Belgian coast (Kerkhof & Dumoulin, 1987) (Figure 1). Since then no new records have been reported.


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