Evaluation of Archaeological Decisionmaking Processes and Sampling Strategies

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Evaluation of Archaeological Decisionmaking Processes and Sampling Strategies

Text of Evaluation of Archaeological Decisionmaking Processes and Sampling Strategies

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EVALUATION OF ARCHAEOLOGICAL DECISION-MAKING PROCESSES AND SAMPLING STRATEGIES GILL HEY & MARK LACEY

Evaluation of Archaeological Decision-making Processes and Sampling Strategies

Gill Hey & Mark Laceywith N Linford, A David & N Shepherd

Kent County Council 2001

OAU

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EVALUATION OF ARCHAEOLOGICAL DECISION-MAKING PROCESSES AND SAMPLING STRATEGIESEuropean Regional Development Fund Interreg IIC - Planarch Project

by Gill Hey and Mark Laceywith contributions by Neil Linford, Andrew David and Nick Shepherd

OXFORD ARCHAEOLOGICAL UNIT

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Kent County Council 2001 Printed in Oxford, England by Alden Group Limited ISBN 0904 220 265

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Preface The introduction of PPG 16 in 1990 has resulted in a considerable increase in archaeological evaluation, as archaeology is more and more integrated within the planning system. How can effective mitigation strategies be devised and in particular how can approaches to sampling be applied to evaluation, which both pass the test of planning reasonableness in respect of cost and other constraints and yet can be relied on for accurate prediction in relation to archaeological realities on and under the ground? A variety of approaches has been developed over the years, including desk-based survey, fieldwalking, geophysical survey, boreholing and, of course, the ubiquitous trial-trenching in its various forms. Many of these techniques go back way before PPG 16 and time has seen their refinement. There has, however, been little systematic appraisal of the suitability of these tools for the job in hand and, in spite of notable progress in some areas, in others, either through inertia or tradition, there has perhaps been a tendency for past practices to be uncritically reinforced in the present. Thus, for example, 2% trial-trenching has perhaps become an industry norm in some areas, with archaeological practitioners failing to realise that such a scheme was devised with the specific objective of finding ring ditches in Berkshire: the approach was mathematically based and carefully thought through to give a high probability of locating ring ditches 40 m in diameter within a specific landscape context. There is a clear warning to us all not to become archaeological lemmings. Alongside the integration of archaeology in planning, recent years have seen increasing cooperation between European archaeologists with the establishment of European Association of Archaeologists and the European Archaeological Council, which brings together the various state archaeological services across Europe. It is appropriate, therefore, that approaches to archaeological evaluation are reviewed within the framework of the Interreg IIC programme for the North West Metropolitan Area (NWMA) which is very much concerned with spatial planning issues and is supported by the European Regional Development Fund. For its part, English Heritage has been pleased to support a project which is making a significant contribution to taking forward best practice in archaeological evaluation and to the further integration of archaeology within the planning process. David Miles John Williams Chief Archaeologist, English Heritage Head of Heritage Conservation, Kent County Council and Chairman of the Planarch Project

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CONTENTS List of figures List of tables Summary Acknowledgements 1 Introduction 1.1 Background and previous work 1.2 The key issues and circumstances of the project 1.3 The sites selected for examination 1.4 Aim and objectives of the project Method 2.1 Assessing evaluation strategies and decision-making processes 2.2 Analysis of geophysical results 2.3 Assessing alternative strategies 2.4 Assessing Best Value Results: assessment of evaluation techniques employed 3.1 The sites 3.2 Success of techniques in relation to physical characteristics of sites 3.3 The success of different techniques 3.4 Assessing different aspects of the archaeological remains Results: computer simulations 4.1 Comparison between the trench arrays 4.2 Comparison between the different sample fractions 4.3 Assessing variability 4.4 Summary of results 4.5 Independently evaluating simulations Cost-effectiveness 5.1 The cost of evaluation 5.2 Strip, map and sample Conclusions 6.1 Evaluation methods in relation to physical circumstances 6.2 Non-intrusive evaluation methods 6.3 Intrusive methods of evaluation and the results of computer simulations 6.4 Evaluation in relation to different periods and types of archaeological remains 6.5 Implications for the decision-making process 6.6 The way forward Bibliography Site questionnaire Study of geophysical surveys, by Neil Linford and Andrew David Detailed methodology of the computer simulations, and their results iv v vii xv 1 1 1 2 5 6 6 10 10 12 14 14 15 21 32 34 34 43 45 48 49 52 52 55 58 58 58 58 59 61 63 64 67 76 90

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Appendix 1 Appendix 2 Appendix 3

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List of Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9 Figure 10 Figure 11 Figure 12 Figure 13 Figure 14 Figure 15 Figure 16 Figure 17 Figure 18 Figure 19 Figure 20 Figure 21 Figure 22 Figure 23 Figure 24 Figure 25 Figure 26 Figure 27 Figure 28 Figure 29 Figure 30 Figure 31 Figure 32 Figure 33 Figure 34 Figure 35 Location of the sites in the study area Geophysics and machine trenching at Yarnton, Site 7 Form used to assess success of evaluation techniques Success of techniques in relation to size of project, A All periods, B Roman period, and C Iron Age period Success of techniques in relation to shape of project Success of techniques in relation to geology Success of techniques in relation to colluvium/alluvium Success of techniques in relation to depth of overburden Success of techniques in relation to recent land use Success of desk-based assessment by period Success of fieldwalking by period Fieldwalking at Thurnham Villa, Roman pottery Fieldwalking at Stansted, Prehistoric pottery Success of geophysical surveys by period Magnetometer survey at Yarnton Site 5 Excavated features at Westhawk Farm Geophysical survey results overlain on excavated features at Westhawk Farm Success of machine trenching by period Thurnham Villa, actual trenching (3%) The simulated trench arrays Thurnham Villa with 5% standard grid array White Horse Stone with 10% parallel trenches Comparison of success of standard grid and parallel trenches (Arrays 1 and 4) White Horse Stone with grid array of wide trenches The Ramsgate Harbour Array Comparative success of different trench arrays Improvement of success as sample size increases: grid and parallel trenching Improvement in success rate as sample size increases for different periods Westhawk Farm with 3% trenching Westhawk Farm: archaeological features exposed in 3% trenches Relative cost of evaluation techniques Success of techniques for all periods Increase in cost in relation to increased trenching Success of techniques for Neolithic/Bronze Age period Success of techniques for Iron Age period 44 46 47 53 53 55 60 60 3 4 8 17 19 19 20 20 21 22 24 25 25 26 27 28 29 30 31 34 38 39 40 40 41 42 43

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Figure 36 Figure 37 Figure 38 Figure 39

Success of techniques for Roman period Success of techniques for early medieval (Anglo-Saxon) period Success of techniques for medieval period Westhawk Farm: archaeological features superimposed over a false colour image illustrating spatial analysis of the geophysical survey interpretation

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Yarnton Cresswell Field: archaeological features superimposed over a false colour image illustrating spatial analysis of the geophysical survey interpretation 84 Yarnton Site 5: archaeological features superimposed over a false colour image illustrating spatial analysis of the geophysical survey interpretation Thurnham Roman Villa: archaeological features superimposed over a false colour image illustrating spatial analysis of the geophysical survey interpretation Thanet Way: archaeological features superimposed over a false colour image illustrating spatial analysis of the geophysical survey interpretation

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List of Tables Table 1 Table 2 Table 3 Table 4 Table 5 Table 6 Table 7 Table 8 Table 9 Table A1.1 Table A1.2 Table A1.3 Table A1.4 Table A1.5 Table A1.6 Table A1.7 Table A1.8 Table A1.9 Table A2.1 Table A2.2 The scoring system Physical attributes of the sites Evaluation techniques employed Periods present on projects studied Simulations undertaken Simulation results for different arrays for all archaeology and by period Results of quantification calculations, showing archaeology discovered The results of best- and worst-trench positions Results of moving trenches a regular distance Questionnaire: initial information Questionnaire: desk-based assessment Questionnaire: fieldwalking Questionnaire: geophysical survey Questionnaire: test pits and boreholes Questionnaire: trench evaluation Questionnaire: excavation Questionnaire: watching brief Questionnaire: other information The sites and surveys Results of analysis of geophysical surveys 9 14 15 16 35 37 45 48 49 67 68 69 70 71 72 73