Blue Willow Heritage is an independent leading provider of archaeological and heritage planning documents submitted within the supporting information of planning applications. Whilst many readers may be familiar with Heritage Impact Assessments, the 'cousin' document known as a Desk Based Assessment is often lesser known, especially within the realm of small-scale householder developments.
In general terms, the former (HIA) involves the analysis of built heritage and may even specifically exclude the assessment of archaeological impact, whilst the latter is more often associated with determining the extent and nature of buried archaeological remains within a development site (DBA).
What is a Desk Based Assessment?
The Chartered Institute for Archaeologists (CIfA) defines a Desk-Based Assessment as the following:
Desk-based assessment is a programme of study of the historic environment within a specified area or site on land, in the inter-tidal zone or underwater that addresses agreed research and/or conservation objectives. It consists of an analysis of existing written, graphic, photographic and electronic information in order to identify the likely heritage assets, their interests and significance; the character of the study area, including appropriate consideration of the settings of heritage assets; and, in England, the nature, extent and quality of the known or potential archaeological, historic, architectural and artistic interest. Significance is to be judged in a local, regional, national or international context as appropriate.
When is a Desk-Based Assessment Required?
Historic England Advice Note 17 has usefully described the role of archaeology in the English planning system according to the requirements set out by the National Planning Policy Framework. Paragraph 200 of the NPPF (2023) states that:
In determining applications, local planning authorities should require an applicant to describe the significance of any heritage assets affected, including any contribution made by their setting. The level of detail should be proportionate to the assets’ importance and no more than is sufficient to understand the potential impact of the proposal on their significance. As a minimum the relevant historic environment record should have been consulted and the heritage assets assessed using appropriate expertise where necessary. Where a site on which development is proposed includes, or has the potential to include, heritage assets with archaeological interest, local planning authorities should require developers to submit an appropriate desk-based assessment and, where necessary, a field evaluation.
Some Desk-Based Assessments are commissioned from the outset of a development project during the feasibility study and design stage as a way to ensure that any proposals involving groundworks which are situated within known historic environments are 'heritage-led'. This is particularly concerning large plots of land considered for new-build developments which are expected to contain, by virtue of their size, at least some form of archaeological potential. Other sites of any size may also contain known archaeological features within their boundaries which necessitate the production of a DBA. This includes Scheduled Monuments and non-designated heritage assets alike.
In addition, Local Plans may provide specific guidance regarding known regions of high archaeological potential and significance, whilst also specifying in which circumstances DBAs will likely be required. Such information can therefore be taken into account from an early stage in the planning process. On the other hand, Desk Based Assessments may be commissioned as part of the consultation period of a planning application. For instance, it may be requested by the planning archaeologist consulted on behalf of the local council prior to the determination of the application.
What is Involved in a Desk-Based Assessment?
The Chartered Institute for Archaeologists (CIfA) sets the following aims for Desk-Based Assessments:
An assessment of the potential for heritage assets to survive within the area of study
An assessment of the significance of the known or predicted heritage assets considering, in England, their archaeological, historic, architectural and artistic interest.
Strategies for further evaluation whether or not intrusive, where the nature, extent or significance of the resource is not sufficiently well defined.
An assessment of the impact of proposed development or other land-use changes on the significance of the heritage assets and their settings
Strategies to conserve the significance of heritage assets, and their settings
What Sources are Consulted?
Aerial Photos: Photographs captured from the air within manned aircraft, usually limited to a select number of years.
Satellite Imagery: Imagery captured from airborne satellites usually containing a large quantity of data spanning throughout the 21st century - including known years of drought which bore favourable conditions for the production of cropmarks pertaining to buried archaeological features.
LiDAR: Remote sensing data captured using lasers to map the earth's surface.
Cartographic Sources: Archival maps, Tithe maps, Ordnance Survey.
Documentary Sources: Britain's newspaper archive, mortgage documents, writings of historians, census records etc.
National Heritage List for England (NHLE): National database which maps designated sites, cropmarks, and other archaeological priority areas.
Historic Environment Records (HER): Local databases including a record of non-designated heritage assets and regional Historic Landscape Characterisation (HLC) data.
Archaeological Data Service (ADS): Digital repository containing project archives and fieldwork reports.
Our Work here at Blue Willow Heritage
Due to extensive external and in-house training, our team is able to incorporate rapid desk-based assessments of archaeological potential and impact into various different kinds of projects. Our work has also involved producing further research for sites which have already been subject to some form of archaeological investigation - such as a geophysical survey. For various reasons, such surveys are not always able to yield clear results for the entirety of a development site.
For example, where magnetometry is deployed close to metal objects, dipolar anomalies obscure readings of the ground below. Methods deployed to assess such sites further, in addition to their surrounding contexts, have included the production of hillshades using publicly-available LiDAR data. Such analyses of the earth's surface allows various different types of archaeological features to be rapidly identified, such as ridge and furrow, medieval field boundaries, housing platforms, mounds, ditches, and various other kinds of evidence pertaining to past human activity.
In other instances, our reports have managed to demonstrate that no expected archaeological potential is considered to be present within a development site. Such conclusions are based on the ability to identify modern disturbances within a site, some of which can often resemble archaeological features. As such, it is clear that a thorough understanding of the site's context can prevent archaeological conditions being imposed unnecessarily upon a development site - saving our clients time and money.
The Outcome
Through the production of Desk-Based Assessments - or else, 'Heritage Impact Assessments' specifically including the assessment of archaeological impact - our reports aim to present a clear impression of the archaeological potential of a given site to both landowners, developers, and the local planning archaeologist alike. Assessments commissioned from the outset of a project can also enable a developer to determine the viability of the site for a proposed development, including a prediction of any planning conditions likely to be required as part of the scheme. The production of thorough, well-researched reports can make it easier for the local council to determine planning applications and apply proportionate mitigation measures, in order to save costs and time.
A variety of mitigation measures may be considered for a development site which holds some archaeological potential. This depends on the nature of the groundworks, how much is known about the archaeological resource within the development site, its condition, extent, and significance. Whilst Archaeological Watching Briefs are often imposed to allow a suitably-qualified archaeologist to monitor development works as they progress, more extensive schemes of mitigation include Evaluation Trenching as well as Strip, Map, and Record exercises. Such measures aim to advance our understandings of the archaeological resource, in addition to securing a permanent record of any identified features.
Blue Willow Heritage can help developers make informed planning decisions based on a thorough understanding of a site's heritage constraints. Through rapid consultations of open source data informed by rigorous training in line with current academic standards, our team strives to adopt cost-effective and non-invasive approaches proportionate to the scale of the proposed development, and the expected archaeological significance of the site.
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