Site Event/Activity record ECH6784 - Mersey Gateway Bridge Project: Archaeological Investigation Report

An archaeological watching brief was undertaken between 2014 and 2017 during onshore and offshore groundworks associated with the construction of the Mersey Gateway bridge. The new bridge over the River Mersey is located to the east of the existing Silver Jubilee Bridge, and extends between Widnes and Runcorn. The project was subdivided into a series of 6 areas called 'sections'; the watching briefs occurred in sections 2, 3 and the northern extent of section 4 on the northern bank of the Mersey. The archaeological monitoring recorded the presence of preserved organic remains beneath the estuary sediments. In P9, at a depth of between -4 to -6m OD, red deer bone and antler was retrieved from an organic-rich layer directly overlying natural glacial till, also containing unworked oak timbers C- 14 dated to between 5450 to 5650 BP. This late Mesolithic date broadly correlates with the estimated date of formation of the Mersey estuary during post-glacial seal level rise, reaching present levels by c. 5000 BP. Further timbers were reported at the base of excavations in P10 and the northern bridge pylon, suggesting that the same deposit may extend beneath the northern side of the river. In P10, at a depth of -3m OD, a further oak timber was retrieved and C-14 dated to 4100 BP (the late Neolithic period). The timber’s horizontal position within coarse alluvial sediment indicates that this timber almost certainly washed downstream from another location. Animal bones recovered from the same deposit sequence in P9 were all identified as red deer, potentially deriving from the same individual. Red deer bone was also recovered between -3 to - 6m OD in P10, beneath the silts bearing a Neolithic oak tree trunk. None of the bones exhibited any kind of anthropogenic modification, and the antler displayed evidence of having been shed naturally, and therefore whilst providing evidence of the late Mesolithic environment, are not archaeologically-significant. Seven samples from oak timbers were recovered from coffer dams along the alignment of the new Mersey Gateway bridge between Widnes and Runcorn. Three of the samples were suitable for dendrochronological analysis although none were successfully dated. These timbers were found at depths of -6m to -4m OD in the Mersey estuary and are thought to date from some point after 5000 BP. Post medieval activity within the saltmarsh/river environment observed during the watching brief was confined to evidence for sunken vessels. All of the wrecks identified during the course of the Project lie outside the impact area of the Project and remain preserved in situ in the estuary. During the course of the archaeological monitoring works various structural remains were observed which clearly relate to the later industrial heritage of the area: to the north of the river, structural remains have been interpreted as relating to the later phase of activity associated with chemical works (in areas later used as a scrapyard and the Catalyst business park), railway sidings, the St Helens Canal and associated culverting of former water courses; to the south of the river, scant remains correlating to the location of a tannery shown on historic mapping were exposed and recorded. In general, however, the intermittent nature of the watching brief was not conducive to creating a full record of the structures encountered or processes they may have represented, and it has not been possible to confidently associate fragments of structures identified with structures shown on historic mapping. (1)