Seabed Mapping

For more information on the allocation of sand and gravel extraction licences and the provision of much statistical data on volumes and transport, visit one of the Licensing Authorities

BELGIUM

In 1998, the Ministry of Economic Affairs decided to sponsor the acquisition of a multibeam system which has been installed on board of the Belgica, the Belgian oceanographic vessel managed by the MUMM (Management Unit of the North Sea Mathematical Models).

Furthermore, the Ministry of Economic Affairs hired in 1998 the services of 5 scientists (2 geologists, 1 geographer, 1 chemist and 1 biologist) for monitoring the environmental impact of marine aggregate extraction on the natural environment. As secondary task the geologists and the geographer will also work on a series of maps. The first maps will be detailed maps of the extraction areas and will cover the aspects of geomorphology and sedimentology. Next, a general seabed mapping of the nature of the Belgian continental shelf will be undertaken.

Published maps:

Maps made by the Management Unit of the North Sea Mathematical Models (1987):

DENMARK

Mapping of the seabed is an integrated part of the systematic reconnaissance resource-mapping program in Danish Waters.

The mapping program continues and is concentrated in The North Sea, Kattegat and The Baltic. Since 1991 mapping programs have been carried out on Jutland Bank and Horns Reef in The North Sea and in Femer Baelt, Adler Ground, Rønne Banke and Kriegers Flak in The Baltic. Maps in scale 1:100.000 of surface sediments, Quaternary geology and sand and gravel resources have been prepared. At present, between 80 % and 90 % of potential resource areas in the Inner Danish Waters have been mapped.

In 1997 and 1998 reconnaissance mapping has been carried out on greater water depths in the central part of Kattegat and in the North Sea. The preliminary results indicate the presence of interesting resources in the deeper parts of the area.

Mapping program in Danish Waters. Dark shaded areas indicate where surface sediment maps have been prepared during the reconnaissance-mapping program (unpublished and published data).

Detailed resource mapping programmes have been carried out in some regional extraction areas with materials of high quality and in areas licensed for bridge and tunnel projects. In 1997 detailed seabed mapping has been carried out for a possible fixed link between Germany and Denmark in the Femer Belt between Putgarten and Roedby.

Small scale seabed mapping programs has been carried out in relation to applications for dredging permits, e.g. in the Bay of Århus, Kattegat and North Sea, and surface sediment map from Jytland Bank, North Sea will be published in 1999.

Some of the most important stone reefs in Danish waters have been mapped 1990-1996 using shallow seismic equipment, side scan sonar, SCUBA-diving and sampling. The project is a co-operation between The National Forest and Nature Agency, The Geological Survey of Denmark and University of Copenhagen. Two reports have been published to date. The reports include surface sediment maps, gravel and stone concentration maps and descriptions of the biology in the areas.

There are three organizations in France working on national seabed sediment mapping, namely;

IFREMER
IFREMER is mapping surface sediments in the West Indies (completed in Guadeloupe and on-going in Martinique) and in the southern part of the Atlantic coast in the Bayonne area near the Spanish border.

BRGM
BRGM (French Geological Survey) is mapping the whole of the French territory at 1:50,000 scale. The amount of sediment logical information available for different coastal and marine areas differs.

There will be a total of 107 maps covering the French coast. Of these 45 have complete sedimentological information (mainly Brittany, Mediterranean Sea, Southern Atlantic coast), eight are partially complete, and 35 have no sedimentological information (mainly Corsica, eastern English Channel, Atlantic coast).

Nearly 50 % of the littoral maps still need to be processed. The objective is to digitise the maps to enable the linking with other data sets within G.I.S.

More recently, BRGM realised several studies dealing with marine aggregate prospecting taking into account other marine activities, particularly fishing. Three main areas have been studied (Baie de Seine, Loire River mouth, Charente Maritime) with the production of a numerical atlas and identification of new areas of potential interest for dredging activity.

SHOM
SHOM is also editing maps at 1:50,000 scale, in collaboration with the French universities. Nine have already been published (South Brittany, Baie de Seine, Charente-Maritime and Gironde mouth) and four others are being developed.

GERMANY

The Federal Maritime and Hydrographic Agency (BSH) has finished a seabed mapping project in December 1998. The objective was to map and quantify movable sands along the German North Sea coast between the waterline and 20 m water depth. Results will be published in the near future.

THE NETHERLANDS

Resource mapping within the Netherlands is the responsibility of the National Geological Survey. In 1997, the survey has become a component body of the national applied science and technology conglomerate TNO named ‘Netherlands Institute of Applied Geoscience TNO, national geological survey’.

A review of the progress in the field of seabed resource mapping in 1998/9 is presented below.

1:250,000 Geological Reconnaissance Map Series

This map series consists, inter alia, a surface geology (sea bed sediments) sheet, which includes a main map in UTM on scale 1:250,000 showing the uppermost 10 cm of the seabed following the Folk classification system and various subsidiary maps. These maps on scale 1:100,000 include the seismic line grid, thickness of Holocene sediments, depth to the base of the Holocene sediments, distribution of (older) Holocene formations, mean grain size, biogenic and lithic gravel content and/or carbonate content of sand fraction, geochemistry of surface sediments (Oyster Grounds map), a key to colours and symbols and a short description. Each mapped area covers 1° latitude and 2° longitude.

All the sheets of the 6 mapped areas are now available in digital format. The seabed sediment map of Terschelling Bank (53 ° -54ºN, 4 ° -6ºE) is in preparation.

1:100,000 Geology and Resource Map Series

This map series consist of map sheets with both geological information and resource information.

The geological component includes a fence diagram with the geological structure of the younger layers (1:100,000), a bathymetric map on 1:150,000, 1:250,000 maps on geomorphology, on the occurrence of Holocene formations, on thickness of Holocene and of Pleistocene deposits, a fence diagram of older sediments, nature and depth of the top Pleistocene and of the top Tertiary and a short description of the stratigraphic units.

The resource component includes a map of the mean grain size and mud content of the uppermost metre on 1:100,000, a similar map of the metre below on scale 1:150,000 and 1:250,000 maps on the carbonate content in the first and the second metre, on lithic and biogenic gravel contents in the first and second metre, and on interfering (clayey) layers in the first and in the second metre and a short note on methodology, sediment classification and on the availability of further information.

The map sheets Rabsbank (51 ° 20’-51 ° 40’N, 3 ° -3 ° 40’E) and Buitenbanken (51º 40’-52ºN, 3 ° -3º 40’E) are also available in printed form. Schouwenbank (51º 40’-52ºN, 3º 40’-4º 30’E) was the first sheet to become available in digital form only. The Indusbank (52 ° -52º 20’N, 3º 50’-4º 30’E) and IJmuiden Ground (52º 20’-52º 40’N, 4 ° -4º 40’E) sheets are in various states of completion. Data acquisition programmes on two sheets more to the north are currently under way.

Applied and other Geological Investigations in 1998/1999

As in previous years various beach nourishment and other extraction schemes has resulted in dedicated site surveys (see reports cited below). The yearly demand for beach recharge materials remains about 15x106.m3.

Several studies have been carried out in recent years to evaluate extraction sites for Rotterdam harbour extension schemes (Maasvlakte 2 project) and other major infrastructure plans. No new studies have been completed during the last year.

The department is at present engaged in an image analysis study on sand grains. Aim is to set up and validate parameters for grain shape and grain roundness analysis. Potential applications include provenance and sediment transport studies and normalisation of sand grain properties.

Geochemical Investigations

Geochemical distribution graphs of surface sediments, as outlined in an earlier ICES progress report, are being prepared for the 1:250,000 Terschelling Bank sheet and now also for the southern half of the Dutch sector. Aim is to have reliable information on natural background values and their variation and so on human-induced changes. Occasionally longer cores are being investigated as well. In doing so, the thickness of the mobile layer (mobile since the start of the industrial revolution) might be estimated as well.

Reports

Zonneveld, P.C., 1998. Onderzoek in het zandwingebied M9D ten Noorden van Ameland in de Noordzee, (survey in the North Sea sand extraction area M9D, north of Ameland), Rept. NITG 98-65-B (in Dutch).

Zwanenburg-Nederlof, H.P., 1999. Onderzoek in het zandwingebied Q16D nabij Scheveningen, (survey in extraction area Q16D near Scheveningen), Rept. NITG 99-75-B (in Dutch).

Zwanenburg-Nederlof, H.P., 1999. Onderzoek in het zandwingebied Q16C nabij Scheveningen, (survey in extraction area Q16C near Scheveningen), Rept. NITG 99-96-B (in Dutch).

NORWAY

A seabed sediment map covering the area off south western Norway has been published. The map covers both the Norwegian Channel and the eastern North Sea Plateau, delimited by 3 ° E and the Norwegian coast, and between 57 ° 30´N and 59 ° N (Scale 1: 250 000).

The mapping of seabed sediments will continue on the Mid-Norwegian Shelf between 62 ° N and 68 ° N as a co-operative project with the Norwegian Hydro graphic Service and the Institute of Marine Research. The focus of this work will be on habitat mapping, especially deep-water corals (Lophelia reefs) and recent sedimentary processes.

UNITED KINGDOM

The mapping programs indicated in 1998 have yet to be fully reported with the exception of the inshore seabed characterisation study of selected sectors of the English Coast which was published in 1998 (Evans, et al., 1998).

The aim of this project was to provide a computerised overview of the geosciences within sectors of the English coast, which would assist with offshore aggregate related planning issues. This was provided as a set of digital files using Microstation Review software. A separate report was provided to complement the data held on the digital files, and to provide a description of the geology of the designated sectors.

Report

Evans, C D R, Crosby, A., Wingfield, J W C., James, J W C., Slater, M P., and Newsham, R. (1988).

Inshore seabed characterisation of selected sectors of the English coast. British Geological Survey Technical Report WB 98/45.

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