Client: Various (including Bristol and Region Archaeological Services (BaRAS),
Cotswold Archaeology, Pre-Construct Archaeology, and English Heritage)

The Environment Agency

Background: Over the last decade, ARCA have worked extensively in central Bristol gaining considerable experience of sampling, assessing, and modelling the stratigraphy formed by the rivers Avon and Frome and archaeological deposits associated with development of the historic city. The projects carried out by ARCA have focused on investigating and understanding changes in the landscape of central Bristol over the last seven millennia, the nature of prehistoric human activity in the area, and response of medieval and later communities to environmental change as the city was founded and grew.

Major projects undertaken by ARCA include a series of borehole investigations in the
Harbourside and Canon’s Marsh area of the city, the Cabot Circus development, and
a recent English Heritage funded project modelling the presence of waterlogged deposits
throughout the city.

Geoarchaeological Investigations
central Bristol (2004 – present)

Case study 1


The projects: In recent years many areas of central Bristol have undergone significant
redevelopment as buildings constructed in the 1960-1980s came to the end of their useful lives. These developments have provided a number of opportunities to record and sample stratigraphy for the early origins of human activity in Bristol, with ARCA working alongside other archaeological contractors, engineers, and construction firms.

Most projects undertaken by ARCA in Bristol have involved at least some fieldwork element – i.e. drilling boreholes. Depending on the ground conditions, ARCA have either utilised their own mechanical drilling kit, or where boreholes were to be drilled through thick deposits of rubble, concrete and tarmac, the services of one of
ARCA’s geotechnical partners was utilised.

ARCA’s mechanical borehole kit has allowed the collection of virtually undisturbed cores of softer sediments with minimal compression and sample loss, making such samples highly suitable for detailed laboratory description and assessment. Larger, more powerful equipment such as the Pioneer drilling rig, on the other hand, allows coarser and deeper sediments to be sampled.

Geoarchaeological boreholes in central Bristol were mostly positioned to investigate
intertidal and alluvial (river) sediments deposited in the Avon and Frome valleys.
These sediments accumulated from the Mesolithic period until the Medieval period, and in places preserved records of changing environments and early human activity in the area.

Laboratory assessment of samples from organic sediments, especially the extensive peat layers discovered around Canon’s Marsh, have most frequently involved pollen analysis. Analysis of pollen grains preserved in these sediments allow the reconstruction of past vegetation in the area, reflecting changes in the natural environment (including changing sea-levels and climate) as well as showing evidence
for human activity (clearance of woodland, burning etc).

Having worked so extensively in the area, ARCA have built up a significant database of borehole records from central Bristol. This has allowed the sediments (and past landscapes) of the area to be modelled using specialist computer software.
ARCA were therefore involved in a major English Heritage funded project
(lead by Cotswold Archaeology) aimed at modelling the extent, depth and thickness of waterlogged deposits in central Bristol. Such deposits can be very important, since they often allow a fantastic level of archaeological preservation rarely seen on dry land.

Results: During much of the last 10,000 years the Avon and Frome valleys in the area
of central Bristol were subject to intertidal conditions – i.e. the area was covered with estuarine mudflats and marshes and subject to flooding at high tide. Under many parts of central Bristol by the banks of the Avon, thick deposits of intertidal sediments (mostly clays, silts and sands) occur, overlying Pleistocene (last 2 million years) river gravels.

Investigations at a series of sites in Canon’s Marsh, situated between Bristol cathedral and the floating harbour, revealed extensive layers of peat and organic muds which developed at the margins of the estuary. At Deanery Road, and at the Harbour-side development, these peat layers were dated using 14C, which showed that peat began forming in the Early Neolithic period and into the Bronze Age. Analysis of microscopic charcoal and pollen preserved in these layers showed evidence for ancient human activity including both burning on the marsh itself and clearance of the forests on
the surrounding dry land, potentially for early farming.

Deposit modelling in central Bristol has shown that the thickest waterlogged layers, mostly associated with Medieval and later revetments and other waterside structures, occur in the Redcliffe and Temple areas of Bristol, in a meander of the Avon.
The highest, and possibly latest, waterlogged deposits appear to occur in the
Canon’s Marsh area.

ARCA’s geoarchaeological investigations in Bristol have provided both rare glimpses
of prehistoric human activity and environmental conditions in the area, as well as producing detailed models which can be used to predict the likely distribution of deposits likely to have excellent archaeological preservation. These projects highlight the value of geoarchaeology to not only provide environmental context and archaeological data for the very earliest periods of Bristol’s history, but also have the potential to inform future archaeological investigations and development in the city.

Further reading: ARCA’s work in Bristol over the years has been incorporated into a
number of publications including:

Cox et al (2006) The Archaeology and History of the Former Bryan Brothers’ Garage Site,
Deanery Road, Bristol: the evolution of an urban landscape.
Transactions of the Bristol & Gloucestershire Archaeological Society 124, 55-71.
The University of Winchester, Winchester SO22 4NR, UK
Registered Organisation, Institute for Archaeologists (IfA)