Page 97 - Manual for Activities directed at the Underwater Cultural Heritage

• depth contours according to recent and older navigation maps;
• the substrate and the type of seabed also with respect to shifting sands, scouring (erosion) or silting (deposition of seabed materials);
• the sedimentary make-up of the area;
• data on local sea-level change in relation to
submerged land-surfaces;
• seawater composition;
• weather conditions and sea-state, dominant
winds and fetch;
• tides, currents and underwater visibility;
• information on historical use of the area,
including the presence of historical ports and
navigation channels;
• information on shipwrecks in the area;
• previous archaeological observations in the area
and its wider surroundings, including both loose finds and sites.
It is wise to back-up the assessment through inter- views with people with thorough local knowledge, such as fishermen or pilots. The data combined in a deskbased assessment may have to come from very different archives, institutions and informants. Project archives of previous construction or clea- rance projects may be highly informative.
Consequences of potential
intrusion for long-term stability
Rule 15 requires that an assessment should be made of the consequences of any potential intrusion for the long-term stability of the un- derwater cultural heritage affected by the activities. Such an impact assessment evaluates whether and to what extent a project is likely to cause changes for a site or its environment. Here, the modelling of site stability is crucial for an assessment of a site’s future.
 © Syddansk Universitet.
Diver exploring the wrecksite of Skjernøsund, Norway. Environmental factors such as sand movements, longshore drift and geomorphology need to be considered in surveys as they greatly impact what has been preserved, in what way it can be surveyed and in what way it can be managed.
A shallow wrecksite in Skjernøsund in southern Norway was discovered due to anomalous vegetation on the seabottom.The salinity is high in these waters and all uncovered timber is quickly infested by the common ship- worm Teredo Navalis. Long term preservation in situ does not seem to be an option.The competent authority therefore instigated full documentation and research.
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Preliminary work