Combined effects refer to multiple local environmental impacts that act in combination over a wider area, such as the depletion of a habitat. They also refer to multiple different local impacts that act in combination to exacerbate an experience, such as general disturbance from construction activity. The following environmental topics will be where combined effects are most likely to prevail.
Ecology and biodiversity
For ecology, combined impacts will take account of impacts on habitats and species within a regional, national or international context. For example, the findings of the Habitats Regulation Assessment or HRA (required under the Conservation of Habitats and Species Regulations 2017), will address the protection of certain species and habitats that form part of a network of internationally protected sites across the UK (referred to as Habitats Sites).
Combined effects will also take account of the accumulation of other species or habitat impacts (not addressed by HRA) across different route sections in order to frame these impacts within a wider geographical context.
Although not part of the EIA, the biodiversity net gain (BNG) assessment will take a route-wide approach, presenting the loss of habitat units across the project as a whole, as the basis for identifying areas of new or enhanced habitats to achieve 10% BNG. The government is due to publish a statutory BNG metric for Nationally Significant Infrastructure Projects (NSIP) shortly and the BNG assessment will align with this.
Community
Combined community impacts will consider the combination of different impacts in one location; for example, where impacts from construction noise, public rights of way (PRoW) diversions and closures, traffic and visual impact act together to result in an overall diminution of health or wellbeing for people living within a particular area.
Historic environment
Combined impacts on historic assets can result both from the accumulation of multiple local impacts over a wider area, and from the occurrence of several different impacts at one place. An example of the latter includes potential impacts on the setting of an historic asset (such as a listed building or historic landscape) resulting from a combination of noise impact and visual intrusion, as well as from wider landscape impacts. Another example would be where physical impacts from vibration and changes in groundwater levels result in structural changes to an asset that undermines its heritage value.
An example of a combined impact resulting from local impacts over a wider area would be where the collective understanding of the heritage value of a related group of assets is undermined by respective changes in their integrity and/or setting.
Land and soil resources
As well as a focus on the impacts of the project on viability and ease of farming within specific land holdings or for specific businesses, the EIA will consider the impact on the agricultural land resource in the round. In particular, it will consider the impact on the most productive land, referred to as the BMV land (best and most versatile). BMV land comprises land that is classified under the Agricultural Land Classification system as being Grade 1, 2 or 3a by policy guidance (see Annex 2 of the National Planning Policy Framework (NPPF)). This is the land which is most flexible, productive and efficient in response to inputs and which can best deliver future crops for food and non-food uses such as biomass, fibres and pharmaceuticals.
