ARCHEOLOGY APPLICATIONS Geophysics Helps Developers Avoid Temple Of Doom (Published in Geomatics World June 2004)
Geophysical techniques not only play a prominent role in archaeological investigations, they also help developers achieve planning consent and avoid the costly implications of an 'unexpected find'. Since the introduction of Planning Policy Guidance 16 (PPG 16) in 1991, archaeology has played an increasingly prominent role in planning consent for developments. Most county councils and unitary authorities now employ Development Control Archaeologists to advise the planning department on the archaeological implications of proposed developments, and on the basis of that advice may place a constraint order until the presence or absence of archaeological features has been determined.
If remains are found they must either be left undisturbed or, more commonly, be excavated and recorded to a standard set out by the planning authority. Archaeological constraints are rarely imposed until a planning application has been submitted, at which point it is often too late to amend design solutions to avoid the remains and so excavation and recording usually have to be undertaken - with major financial and time implications for developers. Costs can vary from several thousand pounds for excavating a small trial trench to in excess of £100000 for an archaeological site of regional importance which can take several months to excavate and record. The best way to avoid unexpected delays late in the design process is to assess a site as early as possible. In archaeological terms this can be achieved by a geophysical survey. It may not totally negate the need for excavation but it will give an accurate indication of archaeological potential and hence can be used to determine likely cost and time implications if archaeology is found. Subterranean surveying technology was recently successfully employed by a Met Surveys for a local authority in the East of England to investigate a brownfield site for evidence of a mediaeval building ahead of redevelopment.
	A non-intrusive ground penetrating radar (GPR) survey was used to help pinpoint the precise location of a 12th century manor house and moat buried several metres beneath industrial landfill, which itself dated back almost a hundred years. The survey was able to reveal the profile and dimensions of a moat as well as a potential structural or foundation features associated with the manor house, and also provided information on the minimum depth of the infill material.
As a result the moat and any structural remains associated with the manor house were able to be preserved in situ, after archaeological excavation revealed their extent and preservation. If undertaken early enough the results of a geophysical survey can also be used to amend the proposed design such that the impact on archaeological remains, and hence the cost of excavating them, can be reduced. Conversely, if it is known that an archaeological geophysical survey has to be executed anyway, carrying it out at an early stage in the project design may provide geotechnical information that can be used in the design, such as identifying areas of made ground, or subsurface structures, or other features. An good example of this was illustrated by the results of a geophysical survey project conducted for Alfred McAlpine at Swindon railway station prior to re-development which not only saved construction costs, but helped recover a piece of local industrial heritage. The brief given to the geophysics team was to investigate for anomalies that might hinder the construction process or compromise operational safety. McAlpine were about to construct a new platform and subway, so prior knowledge of voids or poorly consolidated subsurface beneath the station would be essential. An initial investigation using GPR and Microgravity techniques provided an accurate picture of local subterranean features, and also identified the presence of a large unknown void directly beneath the planned subway location. Further excavation revealed the void to be a lift shaft dating back to the late nineteenth century. Forewarned of the previously unknown structure, McAlpine were able to amend their design solution to incorporate two of the walls of the lift shaft, which not only reduced construction costs but also helped restore part of the local industrial heritage to public view.