Setting the study area in an archaeological DBA

The archaeological desk-based assessment study area is the first methodological decision in the report and the one that most often gets made by accident. A consultant orders a Historic Environment Record search at whatever radius the county charges least for, the data arrives, and the baseline is then written around whatever turned up. Officers and county archaeologists read the report the other way round. They look at the study area, ask whether it is justified for this site and this proposal, and treat everything downstream as only as good as that decision.

Define the radius in the method section, give the reason, and say what you would have included had the site been different.

Why the search radius decides the report

Everything the assessment can say about archaeological potential comes from what sits inside the boundary you drew. Draw it at 250 metres on a site where the relevant evidence is a cropmark complex 700 metres upslope and the report will conclude low potential, entirely honestly and entirely wrongly.

The radius is doing two separate jobs, and confusing them causes most of the trouble. It defines the area within which recorded assets inform the site's potential, which is an archaeological question about landscape and deposit survival. It also defines the area within which designated assets whose setting might be affected are identified, which is a heritage question about visibility, experience and appreciation. Those two areas are rarely the same shape, and a report that uses one circle for both should say why.

State the coordinates, the area of the application site, and the radius. Then show the study area on a figure with the site outline, because a reviewer who cannot see the boundary cannot check the conclusion.

Radii in common use and when to justify a wider one

Common practice in England runs roughly like this. A small urban infill site with heavy modern truncation is often searched at 250 metres. A standard site of up to a hectare or so is usually searched at 500 metres. Sites in open countryside, larger allocations and anything on a river terrace or a chalk ridge are more often searched at 1 kilometre.

None of that is a rule. It is convention, and conventions are negotiable in both directions.

Push the radius outward where any of the following applies:

• A scheduled monument, registered park or grade I or II* listed building sits close enough that setting could be affected.
• The site lies in an Archaeological Priority Area or a locally designated zone of potential.
• The geology or topography means the relevant activity is likely to be dispersed, such as a prehistoric landscape on gravel terraces.
• Recorded finds nearby are stray or antiquarian, so the pattern only becomes legible at a wider scale.
• The scheme is large, deep, or involves off-site infrastructure such as a drainage outfall or an access road.

Where the county archaeologist has issued pre-application advice specifying a radius, use it and say so. Where they have not, propose one at pre-application stage and get it agreed in writing. A study area agreed in advance almost never becomes a reason for a holding objection later, which is the whole point.

Ordering the Historic Environment Record data

The Historic Environment Record is maintained by the county council or the unitary authority, and in two-tier areas that is a different organisation from the one determining your application. Most charge for a commercial search, and turnaround varies from a few days to several weeks. Order it at the start of the commission, not the week the archaeological desk-based assessment is due.

Ask for monument records, event records and find spots, and ask explicitly for the grey literature reports behind the event records. The event data is the more useful half. Knowing that a watching brief in 2009 on the adjacent plot recorded a ditch at 0.8 metres below ground level tells you more about deposit survival than a dozen undated monument entries.

Supplement the record search with the National Heritage List for England, historic Ordnance Survey mapping, tithe and enclosure maps where they exist, aerial photographic and lidar coverage, geotechnical logs from the site investigation, and any published excavation reports for the parish. The baseline section of the assessment then has something to work with beyond a list of grid references.

Scheduled monuments and setting inside the study area

A scheduled monument inside the study area changes the report's structure. Works affecting a scheduled monument need scheduled monument consent under the Ancient Monuments and Archaeological Areas Act 1979, which is a separate consent from planning permission and is decided nationally. Even where no consent is needed, harm to the setting of a scheduled monument attracts the statutory and policy weight given to designated heritage assets.

Assess setting with the staged approach in the Historic England guidance: identify the assets, assess whether and how the setting contributes to significance, assess the effect of the proposal on that contribution, and consider mitigation. Do it on site, in the conditions a visitor would experience, and record the viewpoints. Where the effect is more than negligible, the analysis belongs in a heritage statement alongside the archaeological work rather than buried in an appendix.

Recording negative evidence properly

An empty stretch of the record is data. It might mean nothing is there, or that nobody has ever looked, or that a 1960s basement removed everything above the natural. Those three conclusions carry completely different weight, and a report that presents them as one is doing the reader a disservice.

Say which parts of the study area have seen archaeological intervention and which have not. Where interventions found nothing, give the method and the depth reached, because a 30-metre trial trench to natural is evidence and a set of window samples is not. Where modern development has truncated deposits, evidence it from basement plans, site levels or borehole logs rather than assuming it.

Then draw the conclusion in plain terms: potential by period, with a confidence statement. Low potential for Roman activity based on eight negative interventions within 300 metres is a defensible position. Low potential because nothing appeared in the search is not.

When the study area points to field evaluation

The assessment's job is to say whether the archaeological resource can be characterised from existing information or whether it cannot. Where the answer is that it cannot, recommend the intervention rather than hedging.

Geophysical survey suits large open sites on suitable geology. Trial trenching gives the direct evidence a county archaeologist will usually want before determination on a sensitive site, and an archaeological field evaluation done pre-determination often costs less than the risk of a mitigation condition of unknown scope. On smaller schemes with moderate potential, a written scheme of investigation secured by condition is the proportionate answer.

The honest uncertainty here is that county archaeologists differ in where they draw the pre-determination line, and the same evidence base can produce different advice in neighbouring authorities. Ask, in writing, before you commit a programme.

What the CIfA standard expects of scope

The Chartered Institute for Archaeologists standard and guidance for historic environment desk-based assessment requires the study area to be defined and appropriate to the site, and expects the assessment to be proportionate to the significance of the heritage assets and the scale of the proposal. It also expects the sources consulted to be listed and the limitations stated.

That last point is the one to take seriously. A short paragraph naming what you could not obtain, whether that is unindexed aerial photography or a delayed record search, protects the report and tells the reviewer exactly how much weight the conclusions can carry.

This is general guidance, not legal advice. Check the position with your local planning authority or a qualified professional before relying on it.

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