Limiting impact (Rules 3 and 4)


Activities directed at underwater cultural heritage fall within the wider context of heritage protection and its management. Within this context, there can be plenty of reasons to undertake, fully endorse and authorize activities. While the ANNEX regulates activities directed at underwater cultural heritage, it is important to stress that there are reasons for not disturbing a heritage site at all, clearly including the principle to not disturb sites for the purpose of retrieving finds and selling them.

Unavoidably, any activities directed at a site have an impact. Rules 3, 4, 5 and 6 specify the general principles in view of qualifying impact and regulating activities accordingly.

In activities directed at underwater cultural heritage with the objective of contributing to protection, knowledge or enhancement:

  • impact shall be proportional to the objective,
  • impact shall not be greater than necessary, and
  • impact and observations shall be documented.


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No more impact than necessary


Rule 3 is a specific reiteration of the principle addressed under Rule 1. In situ preservation is the first option. Heritage should not be disturbed in the absence of good reason. In addition, Rule 3 emphasizes the relative impact of activities and specifies that a site should not be disturbed beyond what is strictly necessary to attain the objectives of a project. Rule 3 thus calls for proportionality, both in terms of how much research, archaeological observation and intervention is needed in order to gain the expected knowledge or protection, and how much impact inflicted by these activities the site can bear. 

The determination of just what impact is proportionate lies with the competent authority, but will be informed by the proposals of the initiator of the project, if that is not the authority itself. The quality and comprehensiveness of the project plan will obviously be an important factor in negotiating urgency and limits.

The reasons for disturbing a site can be diverse. There can be external factors that determine that in situ preservation is not an option, implying that the site presents itself as an opportunity for the pursuit of knowledge through archaeological excavation. The project design for such an activity needs to be embedded in the wider context of research questions and expertise, as is discussed in Chapters II and VII. This wider context is equally important if it is not external factors, but the pursuit of knowledge, protection or enhancement that provoke the planning of such activity. Whether it is protection, consolidation, contribution to knowledge, enhancement or improved site accessibility that are cause to action, Rule 3 will apply, as no activity shall adversely affect the site more than necessary.

Protective measures and measures facilitating access will by their nature tend to remain as limited as possible. Different technical alternatives may exist. In deciding between them, relative pricing will be a factor, as well as the expected durability.

With regard to activities that are motivated by research, Rule 3 calls for a clear focus on the research objectives, in function of research priorities. Some research questions can be answered by limited interventions, while others cannot be isolated without compromising the whole site. This calls for careful consideration of the following questions:

  • How does the proposed research fit, not just in the management of the site in question, but in a wider context of research and heritage management?
  • Is this the right site for these objectives?
  • Or, can equally valuable scientific information better be gathered elsewhere?
  • Perhaps on a site with little potential significance other than for and through research, or little potential for long-term preservation?

This issue is taken up again in Chapter III, where the assessment of significance is discussed.

On the basis of the site’s characteristics and conditions, it needs to be determined which research questions need addressing first and which research questions are proportionate to their impact, given the present knowledge of the site. A cautious step-by-step approach and phased decision-making may be the best way to avoid disproportional impact.

Due to the constraints of proportionality of impact, archaeological research is continually caught between sampling strategies and total excavation. In order for science to progress, a combination of both strategies is needed. Sampling and excavation are complementary. One is not necessarily less radical than the other. Sampling the construction of a ship’s hull for example, is extremely radical. It is perhaps more radical than a total excavation in which a hull is left intact, because that is deemed more ‘consistent with protection’. Such sampling is not necessarily less proportionate or responsible, however, as it also yields other information.

In order to facilitate decisions on what is urgent, responsible and proportionate, it is helpful to formulate a research agenda for a region or for a certain type of site. Scrupulous preparation and scrupulous competent authorization can then indeed ensure that the impact of activities that are primarily undertaken for research is proportionate to their objectives.

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Preference for non-destructive techniques


Rule 4 further reiterates the principle of Rule 1. Just like Rule 3 it stresses that activities should not affect a site more than necessary, and that the overarching aim is to preserve and protect a site as much and as best as possible. In Rule 4 the emphasis is on the methodology and on the techniques to be deployed. Every initiator of an activity directed at a site is encouraged to consider whether the objectives defined cannot be achieved with the deployment of non-destructive techniques and survey methods rather than by traditional digging and the recovery of objects and samples.

Many non-destructive techniques exist and many others are likely to be created or to be adapted to the specific needs of archaeological research. Hydrographical and geophysical survey methods can be applied to underwater cultural heritage and in the interpretation of submerged landscapes or sea-bottom conditions. The development of such methods and the techniques involved went hand in hand with the development of underwater archaeology. Archaeological sites have often been the showcase for what new devices are capable of.

In Chapter III on preliminary work, the most relevant present-day techniques, such as sonar and swath-bathymetry, are discussed in a  sidebar on the process of inventory. These techniques are used to visualise the bottom surface of a body of water.

In relation to underwater cultural heritage, such survey methods, as well as magnetometers were at first solely applied to find, retrace and position individual sites. The integration of data generated by geophysical techniques, with accurate positioning data generated by global or local positioning systems (such as GPS), allowed for the application of these tools to precisely map large or smaller areas at great resolution. That in itself is of great help both in research and management.

Developments continue, however, and the integration of various techniques of surface mapping and sub-bottom imaging means that non-destructive techniques can now provide an understanding of thus far unknown and invisible structures. Certainly there is no end to development. In many fields, probing by means of sound, light, magnetism and radiation find application, leading to the development of ever more sensitive devices, and using ever more different ranges of the various physical spectra. Equally important, software to process, filter and distil two- and three- dimensional scale images from data is being developed for a wide range of applications. The development of techniques that may be useful in archaeology is thus definitely not isolated from innovation in astronomy, engineering or the medical sciences. 

It is unlikely that all these non-destructive techniques will ever completely replace coring and excavation in archaeological research under water or on land. Intrusive approaches will continue to be important, but they will be much more effectively deployed if they are informed by preliminary non-destructive work. Acquaintance with the possibilities of such techniques is therefore fundamental.

In recommending the consideration of non-destructive techniques, Rule 4 has considerable meaning for the management of individual sites, for management questions relating to spatial planning and development, for fundamental archaeological research and for the planning of intrusive research interventions. As Rule 4 suggests, one should always consider whether non-destructive techniques are sufficient to achieve specific objectives that traditionally would have been dependent on intrusive approaches.

It is important to take into account that:

  • All research and management depends on data;
  • Data gathering by non-destructive techniques is essential;
  • In all activities non-destructive techniques come first; and
  • Non-destructive techniques are to be preferred to intrusive methods, whenever intrusion can be avoided.
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