SDO21055 - Knapp Mill, Christchurch: Archaeological and Geoarchaeological Evaluation

‘Wessex Archaeology was commissioned by Terence O'Rourke Limited to undertake a Archaeological and Geoarchaeological Evaluation in advance of proposed development within the existing Water Treatment Works (WTW) at Knapp Mill, in Christchurch, Dorset. These works follow on from the results of a geoarchaeological desk-based assessment (GDBA) prepared by Wessex Archaeology. Palaeolithic archaeological and geoarchaeological test pitting evaluation was carried out alongside an archaeological trial trenching. Two archaeological trial trenches measuring 50 m by 1.8 m were excavated on the 26th April 2022, within which two of the geoarchaeological test pits were dug. No archaeological features or deposits were exposed, modern quarrying activity and associated recurrent dumped deposits were observed within both trenches. This quarrying activity appears to have heavily disturbed and truncated the soil sequence and natural geology, and therefore also the archaeological horizon. Four Palaeolithic archaeological and geoarchaeological test pits were undertaken at the Site on the 26th and 27th April 2022, the data from which was combined with that of previous GI works reviewed in the GDBA in order to develop a more detailed and targeted assessment of the location, nature, extent and archaeological and geoarchaeological significance of superficial geological deposits likely to be impacted by the proposed development. The evaluation has successfully assessed the character and distribution of Quaternary deposits at the Site, and has demonstrated that across much of the area of investigation these deposits are entirely truncated by previous gravel extraction. In these areas, quarry backfill, comprised of reworked sands and gravels and overlain by Made Ground, is recorded to the surface of the bedrock at levels of between c. 2.2 and 4.0m below ground level (bgl), and there is very low potential for Palaeolithic and post-Palaeolithic archaeology within these areas of the Site. However, the work has demonstrated that in parts of the Site, outside of these areas of quarrying, intact Quaternary deposits, including Pleistocene Fluvial Sands and Gravels of high Palaeolithic archaeological and geoarchaeological potential, are present. These deposits were identified, along with the cut of the former quarry, to the northwest of the Site, and are likely to be present towards the south, north and west of the Site in areas not previously impacted by quarrying, and which have not been archaeologically evaluated. Such a conclusion is consistent with the extent of former quarrying at the Site shown in historic mapping. The western area of the Site, where these intact deposits are likely to be present, was not accessible during evaluation. However, the edge of a former railway cutting was identified in this area; although the section exposed by this cutting could not be investigated in detail, several post-Palaeolithic prehistoric lithics were recovered from the topsoil in this exposed section, potentially derived from colluvial deposits or Head overlying Fluvial Sands and Gravels. Where development impacts are expected on areas of intact Quaternary deposits (i.e the western area of the Site), further investigations to evaluate these deposits recommended. The aims of the mitigative work should be to investigate in detail whether intact Pleistocene and/or Holocene sediments are preserved within these areas, and to establish whether Palaeolithic and/or later archaeology and sediments suitable for scientific dating/palaeoenvironmental are present. The most appropriate and effective method for achieving these aims is through a program of targeted trenching and test pitting to investigate and sample these deposits.’