Hydrographic Society Benelux

News
Successful Workshop Hydro-Archaeology
The workshop held on the subject of hydrography and archaeology on April 11th was very successful.
Underwater archeology is a very popular item. A lot of documentaries about this subject have been shown lately on Discovery channel and National Geographic. It turns out that it is very difficult to find archaeologically interesting sites and to maintain them.
The workshop started with an introduction of the IMAGO-project (Dutch acronym for Innovative Measurements of Sunken Objects). The goal of this project is to investigate whether techniques exist which can detect manmade or uncommon (particularly wooden) objects in the water bottom. These objects include e.g. (wooden) shipwrecks, ammunition, aeroplane wrecks and prehistoric forests. Secondly, the care for archaeological objects plays an important role. N. Kinneging the project manager of the IMAGO project, explained about the difficulties related to finding a wooden wreck and how different disciplines have to be combined for the best results.
The next speaker, S. v. d. Brenk, told the meeting about two archaeological projects in the Yssel lake (IJsselmeer) and what problems they had encountered in identifying the objects without disturbing them. One object was a wooden wreck from 1460. All kinds of surveys were carried out to identify it: multibeam survey, magnetometer survey, side scan sonar survey and a parametric echosounder survey. To better define the shape a seismic horizontal tomography survey was conducted. Finally, core samples and Cone Penetration Tests were taken to identify the different layers on top of the object. This survey clearly showed how difficult it is to identify objects under the seabed and that knowledge of several disciplines, such as hydrography, geology and knowledge of history have to be combined to interpret the data.
J. Bolle explained the different types of equipment and the best way to operate them to find (iron) wrecks. Such wrecks have to be eliminated to ensure a safe passage for shipping-traffic. Objects could be found using mulitbeam, side scan sonar and differential magnetometer equipment. The most difficult part of these kinds of surveys involved shallow water depth (only 1-20m) and wrecks under the seabed. In particular, positioning the side scan sonar fish and the magnetometer is quite difficult under these circumstances.
All these speakers had a hydrographic or geological background. The next speaker, P. Stassen, was a marine archaeologist specialised in wood and rope. He works in the Maas area in Limburg. For us as hydrographers it was very interesting to hear and see the methods used by archaeologists. Until recently, a lot of the investigations were carried out with divers and land measurers. The divers are still necessary but land measurers are replaced by the multibeam echosounders and side scan sonars.
The last speaker, N. v. Woerkom, had performed a high resolution multibeam survey at a Roman city in Baia, Italy and a Roman harbour in Porto Guilio, Italy. Both areas had slowly sunk in the sea. Pictures of earlier surveys were compared with the 3D results of the multibeam data and it was remarkable how well the different objects could be seen. This survey showed the area that divers and land measurers had investigated over years being recovered in a couple of days with the multibeam equipment.
Several conclusions could be drawn from the workshop. First of all, the several disciplines have to work together to preserve and maintain the archaeological background of the country.
The workshop also showed that with today's equipment objects located on the seabed could be detected quite easily. But to detect objects under the seabed is a completely different story requiring further research. But that lay far beyond the scope of this workshop!

Next workshop will be June 11th. For details look at the web-site www.hydrographicsociety.nl

Contact
Hydrographic Society Benelux
T.H. Heringa
Postbus 175
1970 AD IJmuiden
The Netherlands
Tel: +31 255 545 622
Fax: +31 255 545 645