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Prehistoric wetland-dryland interactions on a buried island, Walpole, Somerset, UKCharles Hollinrake, Nancy Hollinrake, Arthur Hollinrake and Matt Law.

C&N Hollinrake Ltd., 12 Bove Town, Glastonbury, Somerset BA6 8JE. http://www.hollinrake.org.uk.

matt.law@hollinrake.org.uk

Before the neolithic

After the Late Glacial Maximum (end of MIS 2), the river Severn flowed along its current path through a deep rocky gorge, out

to a sea which was much farther west than the present day Bristol Channel (Allen and Rae 1987). As temperatures warmed,

however, land to the north of the river which had been covered by ice during MIS 2 began to rise relative to sea level, while

the land to the south began to sink. Gradually, the sea began to move further up the path of the river, creating the Severn

Estuary and burying the gorge in estuarine mud. At this time Walpole would have been an inland site, with a hill at the east

where there is an outcrop of Lias bedrock extending more than 400 m WNW-ESE and approximately 200m N-S. Most of the

archaeological evidence for this period off the outcrop is too deeply buried for the excavations to find, but some patches of

the original soil survive on the former hilltop, where they contain shells of snails such as Discus rotundatus, Pomatias elegans

and Clausilia bidentatathat would have lived in a woodland environment. A peat deposit discovered during the excavations in

2000 approximately 600m north of the outcrop has been radiocarbon dated to the middle of the 5 thmillennium BC and

formed under marshland conditions, with pollen dominated by grasses and goosefoot.

IntroductionWalpole landfill site is owned and operated by Viridor Ltd, and lies between Bridgwater and Highbridge in Somerset, on a stretch of land known as Pawlett

Level, part of the low-lying Somerset Levels to the south of the Severn Estuary. The landscape is monotonously flat, rarely rising above 7 metres a.O.D

(Since 2000, C & N Hollinrake Ltd have been carrying out investigations at the site, working in advance of landfill cell construction. Landfill cells are

massiveat Walpole each cell is 600m long, 30m wide and 5m deep. This has allowed an unparalleled chance to look at the sequence of clays and peats

that have been laid down by the estuary over the last eight millennia and the archaeological remains they preserve.

Later Prehistory: from outcrop to islandAs sea level continued to rise, the island surface became gradually smaller. Finds of bronze age and iron age pottery suggest that the site continued to be visited,

most likely as a base from which to hunt animals on the neighbouring tidal flats. A deep storage pit for grain was dug through the bedrock. At the south west of

the island, a wooden stake was found thought to be a mooring post. Most mysteriously, a sub-circular ditch with an exterior diameter of 8m was dug. The ditch

has no entrance, and no sign of a structure was found in the enclosed area, so as yet its function is not understood. The ditch was gradually infilled by an alluvial

clay which contained sherds of Beaker pottery and charcoal. Suggestions are welcomed!

Sedimentation was especially rapid during the iron age, with up to 1.5 metres of estuarine alluvium being deposited across the site, although there appear to

have been two distinct periods of stasis during which there was possible incipient reed growth with burning. A network of ditches was dug across the Lias

outcrop to mitigate sea level rise, the fills of which contain snails suggesting they carried brackish water. These ditches were recut and maintained through the

Romano-British period.

The neolithic: wooden structures and the advancing

seaLate in the 5thmillennium BC, nearly a metre of clay was

deposited across the low-lying part of the site by a rapid rise in

sea level. By the 4thMillennium BC, the low-lying land at

Walpole had become marshland, crossed by a series of river

channels draining the Polden hills. Evidence from seeds

suggests that this was a complex environment, with areas of

dry ground and channels carrying freshwater from the local

watershed, but also subject to periodic tidal inundations.

Between two of the river channels, a roughly N-S aligned

wooden structure (Structure 3) was built using split oak planks

and ash, oak, hawthorn, hazel, maple and lime roundwood.

Dendrochronological analysis by Nigel Nayling of University of

Wales, Trinity St David, revealed that the oak did not contain

any sapwood so could not be dated precisely, but was felledsometime after 3861 BC. A larger wooden structure was found

in the eastern of the two channels (Structure 2), consisting of

driven stakes or posts, including a large plank over 2m long

which appeared to have been washed away from its original

position. Wood from this structure was radiocarbon dated to

the early 4thmillennium BC. The channel silts underneath the

plank suggest that the wider environment was subject to some

marine influence, with seeds of annual sea-blite being present.

In the mid 4thmillennium, a trackway (found at different times

as Structures 4, 6, and 7) comprising double rows of posts was

built, with Structure 4 crossing a palaeochannel. Bones of perch

(Perca fluviatilis), a freshwater fish that is not tolerant of

salinity, were found in the palaeochannel. The largest section,

Structure 7, was over 40m in length. Over the ensuing

millennium, numerous other wooden structures were built at

Walpole: during watching briefs between 2005 and 2009, a

total of 16 wooden structures were recorded. The largest of

these was Structure 16, found towards the eastern edge of theeastern palaeochannel, which contained a large number of

pointed stakessome up to 2m long laid horizontally across

the channel. Structures 5, 13 and 14 were also part of this

structure, although 13 and 14 had been washed along a

palaeochannel. In the western channel, bones of an aurochs

were found washed up on Structure 1. These have been

radiocarbon dated to late within the 4thmillennium BC. Other

animal bone finds from the channel include mute swan, wild

boar, eel and stickleback; along with a small number of fresh

and brackish water snails.

Further to the east, the Lias outcrop gradually became an island

as the low lying land became progressively wetter saltmarsh. A

series of burnt areas across part of the island suggest that trees

were deliberately cleared. Analysis of molluscs, bryozoans,

foraminifera and insects suggest that a reedy brackish water

lagoon formed on the south and west of the island early in the

bronze age, providing a rich environment for large herbivores

whose hoof prints have been found preserved by tidal silts.

Finds of flint arrowheads and smaller flakes suggest that

hunting took place during the neolithic and bronze age.

AcknowledgementsThe work at Walpole has benefitted from the input of a number of specialists over the years. These include Richard Brunning (worked wood), Dana Challinor (wood), Rowena Gale (charcoal and wood), Sheila Hamilton-Dyer (fish), Hayley Ellis (beetles), Jen Heathcote (geoarchaeology), Lorrain Higbee

(animal bones), Julie Jones (plant macrofossils), Toby Jones (3D laser scanning), David Jordan ( geoarchaeology), Annette Kreiser (foraminifera), Matt Law (molluscs, bryozoans and foraminifera), Elaine Morris (prehistoric ceramics), Nigel Nayling (dendrochronology), Dave Norcott (geoarchaeology),

Lauren Shotter (beetles), Ellen Simmons (plant macrofossils), David S mith (beetles), and Heather Tinsley (pollen). Radiocarbon assays were c arried out at University of Waikato. Invaluable guidance and advice has been provided by Martin Bell, Richard Brunning and Vanessa Straker. The archaeological

project has been managed by Charles and Nancy Hollinrake, the fieldwork directed by Charles Hollinrake, Arthur Hollinrake, John Davey , Matt Law, Dawn Powell Roberts and Dave Roberts, and the entire project generously supported by Viridor Ltd.

Reference

Allen, J.R.L., and Rae, J.E., 1987, Late Flandrian Shoreline Oscillations in the Severn Estuary: A Geomorphological and Stratigraphical Reconnaissance, Philosophical Transactions of the Royal Society of London B , 315, pp. 185-230.

Above: The sub-circular ditch on

the Lias outcrop, looking west

Above left: plan showing location of the

wooden structures and Lias outcrop or island;Top centre: Structure 16;

Top right: Structure 1;

Above centre: Structure 2

Above right: sequence of ditch cuts and fill at

the north of the Lias outcrop

Right: hoofprints in south end of the buried

surface of the Lias outcrop

Below right: excavation of the south end of the

Lias outcrop

Below left: part of the double post alignment

Structure 7