An investigation as to the suitability and effectiveness of geophysical survey techniques as a tool to aid archaeological interpretation of upland sites within the area of south east Wales

Abstract

Geophysical survey as a tool to aid archaeological interpretation has been shown to be of varied usefulness across the differing site morphology and underlying geology of Wales. Its uptake has also varied greatly between regions with bias often existing towards certain types of site or particular periods of interests. Consequently, a need exists to establish baseline data covering all regions before definitive conclusions with respect to its suitability can be reached. This study applies geophysical analysis to selected Iron Age hillfort sites in southeast Wales in an attempt to ascertain the suitability and effectiveness of the techniques for more widespread application throughout the region. The primary
site chosen for investigation was Llanmelin hillfort located approximately 14.5km east of the city of Newport. The well documented prior excavation of the site (Nash-Williams 1933), albeit using pre-war techniques, allowed the interpretation of the geophysical surveys to be tested against the results of the excavation where they coincided. This site was also particularly suitable as its underlying Carboniferous limestone geology is known to produce good responses for the two main geophysical techniques of resistivity and
fluxgate gradiometer survey (English Heritage 1995, 15). Both the fluxgate gradiometer and resistivity surveys undertaken proved highly successful surpassing all initial expectations and fulfilling all of the stated aims set at the outset.
Having proved the usefulness of geophysical survey on such sites two supplementary sites at Coed y Caerau and Gaer Fawr were selected to test the response of geophysical survey to specific sets of conditions. The underlying geology of both sites is the Old Red Sandstone series, on which much of southeast Wales lies, so resistivity surveys were carried out as these soils are best suited to this technique (English Heritage 1995, 15). The former site is located to the west of Llanmelin and overlooks the Gwent Levels to the south and also the lower reaches of the Usk river valley to the west. It consists of a series of three overlapping earthworks, two circular and one square and was chosen to assess how successful geophysics survey would be in detecting possible internal features on such soils. This survey, on a site that had seen little disturbance, also proved highly successful leading to the selection of the latter site. Gaer Fawr hillfort is situated to the north of the other two on the edge of a spur overlooking the confluence of two valleys and has seen extensive disturbance at various times from the medieval period up to the
present day. Despite this the line of the earthworks could still be detected, where they were no longer visible on the ground today, and it was also possible to suggest internal Iron Age features. The success of these surveys suggests that the geophysical techniques applied in this study are appropriate for more widespread use throughout the region and could become an effective tool to inform future excavation.

Date of Award	2014
Original language	English