Thames Holocene A Geoarchaeological Approach to the Investigation of the River Floodplain for High Speed 1, 1994–2003 Oxford Wessex Archaeology 2013

The archaeological investigation of the route of High
Speed 1 (HS1) (formerly known as the Channel Tunnel
Rail Link), through the Thames Marshes, is not a
conventional one, and this report is neither intended to
be a complete landscape history of the Lower Thames,
nor an exhaustive archaeological narrative of human
occupation of the region. Rather, this work is primarily
intended to present the methodological approach that
was adopted for the investigation of approximately 18km
(17%) of the HS1 route across an area of thick alluvium.
By comparison with the remainder of the route, where
conventional archaeological approaches to site location,
assessment and, in some cases, excavation has been
reported elsewhere (Booth et al 2011), the alluvial
corridor of the Thames required a different approach.
From an early stage in the construction project
(1994) it was determined that a geoarchaeological
approach to the investigation of the alluvial corridor
would be necessary because of the depth of sequences (in
excess of 10m in many locations), and the relative
invisibility of the archaeological resource in both the
Historic Environment Record and to conventional
survey. The project commenced with a thorough
consideration of existing geotechnical and geomorphological
records. This allowed the construction of
a geoarchaeological model for the alluvial corridor
whereby different parts of the route were categorised as
of low, medium and high potential based on a
combination of archaeological and geomorphological
inferences. Careful integration of the results of the
geoarchaeological investigation were subsequently
matched against engineering and route construction
parameters in order to determine a cost-effective and
logical approach to archaeological mitigation.
The field survey that was developed, following model
construction, included geophysical investigation of
buried sediment bodies, the use of boreholes, cone
penetration testing and conventional test-pitting and
trenching. These were deployed in key areas such as the
Thames Tunnel portal in Swanscombe Marsh and the
Ebbsfleet Valley. The project was successful in predicting
the location of buried archaeological remains in a
number of locations. Key amongst these are extensive
remains excavated in the Ebbsfleet Valley (Andrews et al
2011a–b; Barnett et al 2011; Biddulph et al 2011;
Wenban-Smith et al forthcoming), Mesolithic flint
scatters at Tank Hill Road, Aveley (Leivers et al 2007)
and Late Upper Palaeolithic and Neolithic scatters on
Swanscombe Marsh (this volume). Other sites described
here include an in situ Early Neolithic flint scatter on
Rainham Marsh, close to the Neolithic site at Brookway
Allotments (Meddens 1996), and evidence of seasonal
Roman and medieval activity, including concentrations
of pottery, animal bone and marine shell. The medieval
activity, dated to the 11th to 13th centuries AD, may be
associated with a phase of marshland reclamation and
the building of sea-banks in the area of the former
Wennington Creek.
Overall the investigation also confirmed, where
fieldwork took place, that those areas of the route
corridor considered of low archaeological potential did
not contain significant evidence for human activity. The
success of the project can therefore be measured not
only in the prediction of zones of different
archaeological potential but also in the fact that the
project delivered a robust and well-structured
archaeological response to specific construction impact,
and in the process caused no major delays to the
completion of HS1. This report makes the case for
adopting a geoarchaeological approach to mitigating the
impacts caused by future major construction projects in
alluvial environments.