Philpotstown Neolithic House, Co. Meath, Ireland

This document reviews Legacy Data generated from 10 years’ worth of road scheme activity in Ireland to determine how archaeological geophysical surveys could be carried out on national roads in the future. The geophysical surveys were carried out by several different contractors across a range of challenging field conditions, geologies, weather and seasons. The research is based upon the results of linear schemes but also has validity for wider approaches. The findings of this research are based upon the compilation of all terrestrial archaeological geophysical surveys carried out on behalf of the National Roads Authority (the NRA, now Transport Infrastructure Ireland), a review of the success or otherwise of those surveys in comparison with ground-observed excavations and in combination with experimental surveys that tested previously held assumptions or knowledge to determine best practice methods for the future. The use and success of geophysical surveys in Ireland differ quite significantly from those in the UK, from where many of the methods of assessment were derived or adapted. Many of these differences can be attributed to geology. Ireland has a very high percentage of Carboniferous limestone geology, overlain mostly by tills and frequent occurrences of peat. These soils can reduce, to some extent, the effectiveness of magnetometer surveys; the most frequently used geophysical technique in Ireland. However, magnetometer data can be maximised in these cases by increasing the spatial resolution to produce effective results. An increase in spatial resolution is also effective generally, for enhancing the chances of identifying archaeological features by discriminating between archaeological and geological anomalies as well as increasing anomaly definition and visualisation of small and subtle archaeological features. Seasonal tests have determined that Irish soils are generally suitable for year round earth resistance assessments although some counties in the southeast of the country may experience very dry soils at the surface during some periods of the year. A variety of sampling strategies were used in the past, however it is now apparent that detailed assessments across the full length and width of a proposed road corridor are the most appropriate form of geophysical investigation. Magnetometer surveys are generally suitable for most Irish soils and geologies, although exceptions apply in areas of near-surface igneous deposits, deep peat and alluvial soils; however magnetometer surveys are not capable of identifying all types of archaeological features and other methods will be required for a full evaluation. Analysis of the Legacy Data has determined that in general the NRA archaeological geophysical surveys were historically used in a very positive way on road schemes. The range of features assessed or identified account for most types of archaeological sites in Ireland. These have provided a significant archive of case studies that will be of benefit to future archaeological geophysical research and will help to protect the globally dwindling archaeological resource that is threatened by development-led or commercially driven projects.

2017

Geophysical survey and national road schemes Intuition, experience and observation are among the ingredients in a successful field investigation. At the outset of a big development project, the field archaeologist uses all three in trying to predict what might be found on the development site. The sources of evidence include historic maps, aerial photographs, museum records, published local histories and anecdotal information from landowners. The archaeologist's own observations, from site inspections, are very important, but even the keen eyes of an experienced fieldworker cannot penetrate the soil. Ultimately, groundbreaking test excavations, by hand or machine (Illus. 1), are the most effective means of finding new archaeological sites, and such excavations are performed on the routes of all new national road schemes in advance of construction. (For more information on the archaeological assessment of road schemes see O'Sullivan 2007a.) There is one non-intrusive method, however, that has been described as 'seeing beneath the soil' (Clark 1990). This method employs geophysical survey equipment (Illus. 2) and has been widely used in Environmental Impact Assessments (EIAs) on road schemes in Galway and adjoining counties in recent years. 29 4. Geophysics, tillage and the ghost ridges of County Galway, c. 1700-1850 Jerry O'Sullivan Illus. 1-Archaeologist Ronan Jones recording features observed in machine-cut test excavations at Rahally on the N6 Galway to Ballinasloe scheme (Galway County Council). Scheme details Area of road scheme 588 ha Length of road scheme (centreline) 56 km Number of fully excavated archaeological sites 37 Methods of discovery of significant excavation sites Test excavation 16 Desk study 8 Geophysical survey 8 Field inspection 4 Construction monitoring 1 Geophysical survey Combined areas of geophysical survey 163 ha (27.7%) Criteria for selected survey areas Good land Adjacent monuments Adjacent historic population centres Survey method Recorded magnetometry Survey results 202 geophysical anomalies of all sorts 63 possible archaeological sites 49 sites identified by anomalies alone 8 significant excavated sites = net result

This is the eighth instalment of the 'Archaeology and the National Roads Authority Monograph Series' and presents the results of nine papers given at a public seminar held at the Gresham Hotel, Dublin, in 2010. Despite such opulent surroundings, the theme for the seminar was more in keeping with current economic concerns of the vicissitudes of life and wealth -never let it be said that archaeologists are disconnected from the modern world around us! As I noted in my review of the preceding monograph, Creative Minds, the focus is less on individual sites and more towards the creation of syntheses based on a broad range of data from various road schemes.

2009

Futures and Pasts: archaeological science on Irish road schemes (eds. Kelly, B., Roycroft, N. & Stanley, M.), 2013

Cite as: Bonsall, J., Gaffney, C. and Armit, I. 2013. Back and forth: paving the way forward by assessing 10 years of geophysical surveys on Irish road schemes. In Futures and Pasts: archaeological science on Irish road schemes (eds. Kelly, B., Roycroft, N. & Stanley, M.). NRA Monograph. Geophysical surveys have played an important role in the discovery of archaeological sites on Irish national road schemes. The National Roads Authority has recently funded a Research Fellowship to critically review all of the archaeological geophysical surveys conducted on such schemes between 2001 and 2010. The review, which is being carried out by the University of Bradford and its industrial partner Earthsound Archaeological Geophysics, has reappraised the success or otherwise of these geophysical assessments and has suggested ways to enhance the effectiveness of future surveys on NRA-funded roads.

Creative Minds is the result of a 2009 public seminar on archaeological results from National Road Authority schemes in the Republic of Ireland. The volume is also the seventh in the 'Archaeology and the National Roads Authority Monograph Series' publications of conference papers. To anyone involved in Irish archaeology over the last decade, these volumes have become a staple source for the dissemination of the latest results and ideas on some of the major excavations of our times. It is inevitable that, with the completion of many road schemes, coupled with the general downturn in the economy, this volume should present more thematic overviews of entire road schemes, rather than the results of individual excavations. The volume is dedicated to the late Dáire O'Rourke, Head of Archaeology at the NRA from