| Abstract: |
Wessex Archaeology was commissioned to undertake purposive geoarchaeological boreholes, grab-sampling of geophysical anomalies and monitoring during SI works prior to bed lowering activities as part of the River Thames Scheme, in a section of the River Thames just east of Desborough Island, Surrey. The work was undertaken to provide further information on the archaeological and geoarchaeological resource that may be impacted by the proposed bed lowering, anticipated to reach a maximum of 0.75m below river bed level, and facilitate an informed decision with regard to the requirement for, and methods of, any further archaeological and geoarchaeological investigations. The Shepperton Gravel, comprising sand and gravel deposited within a high energy braided channel during the Late Devensian (c. 17-11.7 Ka), was widespread across the Study Area, present in thicknesses of up to 2.7m at elevations between c. 6.5 and 8.8m OD. No fine-grained or organic-rich units were identified within the Shepperton Gravel in any of the boreholes across the Study Area, and it is considered to be of low geoarchaeological potential. Holocene alluvium was rare, recorded in only two sequences (BH10 and BH25), and no organic-rich or peat deposits were recorded within the alluvium. The sequence was capped by modern riverbed sediments comprising reworked gravel or fine-grained alluvium with modern inclusions. No finds of archaeological relevance were recovered or identified during the grab sampling of geophysical anomalies; however there remains the possibility that previously identified material has been moved by water flow either deeper into the channel, or away from its recorded position, or that the geophysics targets are deeper in the riverbed than the grab could reach and may therefore still be in-situ. On the basis of the anticipated depth of the bed lowering (0.75m below riverbed level), the proposed development is likely to impact on deposits of both Holocene alluvium and Late Devensian Shepperton Gravel. However, no organic-rich or peat deposits were recorded within the alluvium, and similarly, no fine-grained or organic-rich units were identified within the Shepperton Gravel. On this basis, the geoarchaeological potential of these deposits is considered to be low, and no further geoarchaeological investigations are recommended. In line with methodology set out within the WSI (Wessex Archaeology 2022), it is recommended that the Protocol for Archaeological Discoveries is fully implemented via a watching brief during the bed lowering phase of the project, in order to mitigate against chance finds. |
