SDO21646 - Blacknoll Reservoir Decommisioning, Winfrith, Dorset. Heritage Impact Assessment

‘This Baseline Heritage Impact Assessment (HIA) has been prepared by Roy King BA MCIfA and Kim Watkins BA ACIfA and updated by Diana King BA MCIfA. The illustrations for the report were prepared by Diana King and Santiago Erimo. The project was undertaken on behalf of Magnox Ltd. This proportionate HIA has been prepared to accompany a Planning Application in relation to the Blacknoll Reservoir Decommissioning Scheme, on Winfrith Heath in Dorset (NGR: 380608 86332). The proposal is for the main structure of the reservoir, which is built into the side of the Blacknoll Hill, to be part-demolished and removed. This will involve excavation of areas which have been previously disturbed on the north side of the reservoir and within the structure itself. The proposals also include the removal of topsoil from within the Extent of Works area and the removal/infilling of a series of manholes along the line of the pipe which runs to the north of the site. This HIA has considered the potential for the proposed development to affect known and potential heritage assets, as required by National Planning Policy Framework 2023 and Local Planning Policy. There are six designated heritage assets present adjacent to the site in the form of Bronze Age Bowl Barrows on Blacknoll Hill, which are Scheduled as a group (SM 1015334) and lie just to the southwest of the reservoir structure. There are a further four Scheduled Monuments, all comprising Bronze Age barrows located to the west and southwest within the wider study area. There are ten Grade II Listed buildings located to the south of Blacknoll Hill, all within the study area. The report has also considered the potential for unknown heritage assets with an archaeological interest to be present on the site, based on the known archaeological remains that are presently recorded in the vicinity. The potential has been assessed as very high for the Prehistoric period, and negligible for the Roman, early Medieval and Medieval periods, with the recognition that if features were present they would be of moderate to high significance, given their rarity in the area. The potential for Post-medieval features to be present is assessed as low, although there are landscape features such as land boundaries and quarries in the immediate area. The proposed decommissioning works have the potential to impact the adjacent Scheduled bowl barrow group on Blacknoll Hill. A Heritage Management Plan has therefore been designed and approved by Historic England which would reduce the impact of the works on the scheduled monument to neutral. The Extent of Works will not encroach into the Scheduled area and Scheduled Monument Consent will not be required. The original cut for the reservoir is shown on historic photographs to extend south beyond the proposed worksite and therefore no buried features are anticipated to survive within the proposed demolition area. The topsoil strip is not anticipated to penetrate deeply enough to have the potential to disturb archaeological remains and will be located predominantly within areas already heavily truncated as part of the reservoir installation. A neutral impact on buried remains of archaeological significance is therefore anticipated. The proposed decommissioning works will return the site to its existing profile and reinstate the heathland through infilling to void left by the demolition and removal of part of the reservoir structure. Infill soil will come from the Magnox main site and topsoil stripped from the Extent of Works area and stockpiled on the site will be reinstated. As such the proposed works will have a neutral impact on the setting of the Scheduled Monument and all other heritage assets. No recorded archaeological features are believed to be impacted upon by the proposed infilling of manholes along the pipe, with the possible exception of post-medieval quarrying to the east/northeast (HER MDO30337). Adherence to the Heritage Management Plan will remove any requirement for decommissioning works to be archaeologically monitored.’