When do you need an Archaeological Desk-Based Assessment (DBA) and what will it tell you?

In the planning process a desk-based assessment will be needed where a site is judged to have an elevated risk of impact to archaeology because of its proximity to known archaeological sites, its location within areas of known archaeological potential (such as historic settlement boundaries) or due to the scale of the development. It is by no means a hard and fast rule, but as a general guide most Major Planning Applications will need a level of consideration of archaeological potential. Initial consultation with an archaeological consultant and/or seeking pre-application advice from the LPA can help to clarify this.

The DBA will set out the known archaeological resource within a set study area around the site. This will be based on a range of sources but usually relies heavily on the County Historic Environment Record for the bulk of the information. In addition, topography, LiDAR data, historic mapping, geological information, consultation with the local authority archaeologist and examining previous archaeological work on or in the near vicinity of the site can all provide important information on the nature and survival of archaeology.

It is important to set this assessment of the archaeological resource against the possibility that it has been disturbed by more recent activity on the site. Modern buildings (especially those with basements), landscaping, terracing of sloping land amongst other things can remove below ground archaeology. A site visit is usually essential to understand this.

Having outlined the known archaeology in the area it is then necessary to draw some inferences regarding what this means in terms of three things:

• Is there sufficient evidence to draw confident conclusions?
• How likely it is that archaeology survives on the site?
• How important is any archaeology likely to be?

Regarding the first point, it is important not to over interpret a lack of known archaeology around the site as a lack of potential. It can be the case that the reason for the lack of evidence is that little previous archaeological work in the area has been done.

A good deal of judgement and experience needs to be exercised in making inferences from the available baseline information and it is entirely possible that the potential of the site will remain uncertain following a purely desk-based study.

Most DBAs are to inform a planning decision and their results will feed into one of three outcomes. If it can be shown convincingly that there is very low potential for any archaeology on the site, there may be no further work needed. If there is potential that there may be archaeology, but that it is not of the highest importance then it may be recommended that the impacts of development are offset through further work as a condition of planning consent. If potential remains uncertain, or it looks as though there are very important remains on the site which need a greater level of clarity, it may be that a field investigation is required before a planning decision is made.

An archaeology DBA should meet the Standard set by the Chartered Institute for Archaeologists. This Standard covers the assessment of the historic environment in its entirety and requires the assessment to ‘establish the impact of the proposed development on the significance of the historic environment’. Its text captures the three outcomes described above as the need to ‘identify the need for further evaluation …[or] enable reasoned proposals and decisions to be made on whether to mitigate, offset or accept [the results] without further intervention’

In practice, impacts to potential below ground archaeology can often only be outlined in very general terms by a desk-based assessment. This is because of both the inherent uncertainty over the location, extent and survival of archaeological remains and because at application stage the below ground impacts of a development are not usually clearly defined in detailed engineering drawings.

In a development context the DBA will usually be submitted as part of a planning application and its audience is principally the Local Authority. I find it helpful therefore to also provide a candid client advice note to summarise the potential outcomes and what they could mean for the project.

Ultimately you can never know what’s below the ground without digging it up and archaeological development management is about risk management. Through a staged approach, the risks of harm to important archaeology and the risk of unexpected discoveries which disrupt development can be reduced significantly.