As a general guide the DVMWHS Partnership encourages local planning authorities to insist on applicants submitting a HIA in accordance with ICOMOS guidance for all proposals that are over 10 dwellings and/or over ½ hectare. There will be cases where smaller development proposals will also necessitate a HIA in accordance with ICOMOS guidance. Hopefully these can be identified through early engagement between the local planning authorities and the DVMWHS Coordination Team.
The International Council on Monuments and Sites (ICOMOS) Guidance on Heritage Impact Assessments for Cultural World Heritage Properties (2011) sets out an approach to judge the scale or severity of impacts or changes taking into account their direct and indirect effects and whether they are temporary or permanent, reversible or irreversible. The cumulative effect of separate impacts should also be considered.
The UNESCO World Heritage Committee favours this methodology, which can be found at https://www.iccrom.org/sites/default/files/2018-07/icomos_guidance_on_heritage_impact_assessments_for_cultural_world_heritage_properties.pdf. This is the methodology for which Heritage Impact Assessments should be undertaken within the Derwent Valley Mills World Heritage Site, and included in the list of validatory documents for any development of the scale identified in 3.2.1.