Chartered Institute for Archaeologists 2023

P R O F E S S I O N A L A R C H A E O L O G Y | A G U I D E F O R C L I E N T S 2 0 2 3 2 3 CASE STUDIES | MANAGING ARCHAEOLOGY: Evaluation techniques that reduce uncertainty Targeted trial trenching as part of the HS2 historic environment works ©HS2 indicated that there may be high potential for unknown archaeology to be present. Known archaeological and heritage assets were not deemed high risk in this model, as they could be factored into programmes of mitigation. This assessment of risk was undertaken prior to any field evaluation and fed into the design of initial evaluation work in the form of a geophysical survey and evaluation trenching. The field evaluation programme primarily utilised a combination of LiDAR data, geophysical survey, trial trenching and borehole data to assess the presence of archaeological deposits. In addition, detailed and extensive route-wide desk-based assessments for specific themes, such as geoarchaeology or palaeoenvironmental archaeology, sought to indicate areas of higher or lower potential. A variation on standard approaches to evaluation was undertaken for a section of the scheme in areas where geophysical surveys returned limited results (in regions and on geologies where the technique otherwise worked well). Here, a bespoke approach was employed across what appeared to be ‘blank’ areas. A predictive model was devised in order to determine locations where, for example, earlier prehistoric activity may be more likely. These remains are often present as flint scatters in topsoil or insubstantial sub-surface features, which are arguably less easily identified through geophysical survey. This model formed the basis for extensive test pit work and the sampling of topsoil. Novel approaches such as geochemical survey were also trialled, where anomalies in the data helped determine follow-up intrusive work. The predictive model and intrusive fieldwork successfully identified earlier prehistoric archaeology in a number of locations, with other areas indicating a genuine lack of past human activity. In conclusion, the historic environment works for HS2 Phase One demonstrate that having a robust and well-considered understanding, both of known heritage assets and an assessment of the potential for unknown archaeology, can help determine a suitable evaluation strategy that will help to identify and define any archaeological deposits on a site and reduce the risk of unexpected discoveries. The approach can be tailored to the type of archaeology that the preceding assessment and non-intrusive work has considered most likely to be present or which specific research objectives have been highlighted as a priority for investigation. This approach to evaluation can help to define targeted mitigation strategies which are suited to the archaeological aims of the investigation.