A preliminary investigation into the possibility of erosion in the area of the Flemish banks

Abstract

A knowledge of the distribution of sediment in terms of bed and suspended load is essential for a good working description, both qualitative and quantitative, of a coastal sea. A variety of physical, chemical and biological processes in coastal waters are directly connected to, or influenced by, the sediment regime present there. Physical processes may be affected by erosion, transport and sedimentation phenomena, all of which have a direct bearing on beach and harbor stability, the formation of coastal deltas, navigability of shipping lanes, etc. The importance of chemical processes may be inferred from environmental problems arising from the transport and build-up of heavy metal concentrations and their relation to suspended sediment transport. The role of biological processes is typified by the underwater light regime in association with primary production and is eventually coupled to fisheries capacity. These are particularly important considerations in the case of the North Sea. As a result, many investigations of phenomena relating to the distribution of bottom and suspended sediment have been carried out over a long period. An area of major importance for investigators is the southern bight of the North Sea, bounded by the coasts of England, France, Belgium and the Netherlands and separated from the northern North Sea by the Humber Spur and the Texel Spur. The present study is based on a preliminary investigation into the possibility of bottom erosion in a relatively small region of the North Sea along the French-Belgian coast, the northern extremity of the Flemish banks. The possibility of such erosion taking place is a question of especial interest with regard to sediment transport along the Dutch coast. Depending on the results of this study, future investigation on a considerably larger scale will be carried out. CONCLUSION Using the technique of point-for-point correlation of sounding data, hydrographic charts from 1894-1895 and 1970-1971 were compared for the northern extremity of the Flemish banks. The study was intended as a preliminary investigation of bottom changes in a relatively small area and over a relatively short period of time. Neither absolute accuracy nor completeness are pretended in this first study, the point behind the study being to arrive at order-of-magnitude figures for the bed sediment balance and to test the usefulness of the method used in arriving at these results. In the light of this, there can be no definite conclusions made concerning the present results except to note that they indicate that future study of a large part of the banks region, using the technique developed here, is warranted. A tentative conclusion might be drawn from the good agreement found between the data of Morra and Haring (see Morra et al, 1961) and the present results. This agreement seems to imply that an extrapolation from 27 to 76 years is reliable and, therefore, that a stable erosion process has been taking place for at least this period of time. The total amount of erosion is relatively small however and consequently difficult to determine accurately.