Cookham Fish Pass Project, Cookham Sashes, Berkshire

The Environment Agency commissioned Oxford Archaeology (OA) in March/April 2009 to undertake a geoarchaeological borehole survey to examine the archaeological resource at land at Cookham Sashes in Berkshire. Sashes Island is located to the north east of the town of Cookham
in Berkshire, and is encircled by the River Thames. It is centred on NGR SU 900 865, and is within the administrative area of the Royal Borough of Windsor and Maidenhead.
The Environment Agency propose to create a fish and wildlife channel across Sashes Island to alleviate the environmental consequences of the existing weir. To achieve this a channel will need to be dug along one of
three potential routes, and cut to below the water-table. This survey was commissioned to assess which of the route options would cause least damageto any surviving archaeological resource.
Sashes Island is believed to have been the site of a Saxon burgh, and the probable location of a Roman road and bridge. There is also a possible Roman cemetery within the south east of the island, and although this may
not affect the route options to the west, associated settlement evidence may be present. Therefore any work on the island carries a high risk of discovering archaeological remains. The desk-based assessment identified
the need to undertake archaeological works in order to further assess the archaeological potential for each of the proposed routes.
A total of 30 boreholes spaced on a 20 m grid were used to create a sedimentary deposit model for the site. It was hoped that this information would provide baseline data on the underlying buried sequence. The survey revealed a sequence of thick made-ground deposits overlying a
buried alluvial and organic sequence. There is the potential for early prehistoric archaeology to be preserved at this level, associated with a buried dry land surface. It is possible that this surface was transformed by
rising ground water-levels from the late prehistoric period. This was followed by widespread alluviation in the Middle Thames during the late Roman Period.
The site appears to have been prone to flooding from the late prehistoric period onwards, making it less suitable for settlement activity. No evidence for either the Roman settlement or the Saxon burgh was identified within the
site. Only the high gravel elevations to the east and two islands toward the centre of site may have remained dryer for longer in the Mid Holocene before eventually being submerged.
In terms of the preferred options for the fish passes, the survey was able to assess the potential impacts of the three proposed routes. Based on the findings of the survey, options 1 is considered to have the least impact on
any potential archaeological deposits, being the shortest and most fluvial active area. This is followed by option 2 that crosses the main low-lying area of the site which may have been submerged by the late prehistoric period.
Option 3 is considered to have the highest archaeological potential of all the routes, crossing the higher ground to the south east.