An objective approach to human population impact assessment

9th March 2015

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Robert Lockwood

Andrew Burwood from Black and Veatch considers how the Northwich flood risk management scheme assesses impacts on the human population.

“Population” is the first aspect of the environment listed in Schedule 4, Part 1(3) of the 2011 EIA regulations. However, the human population chapter of environmental statements can often be limited to a summary of other impacts that also relate to humans, such as visual amenity, traffic and transport, but without a clear approach to assessing the significance of the development on human beings in their own right.

A lack of clarity over what is being assessed can lead to confusion about the difference between, for example, assessing effects on the operation of the transport network and assessing effects on human beings who live or work near affected roads. It can also result in repetition and apparent inconsistency between ES chapters.

More importantly, a lack of clarity over how the assessment is carried out can mean that a key component of an EIA, to identify which effects could be significant and therefore need mitigating, is not carried out effectively. This means the significance of effects may either be exaggerated or down-played if the assessment is not based on a clear, objective approach.

This means the significance of effects may either be exaggerated or down-played if the assessment is not based on a clear, objective approach.

This article uses the Environment Agency’s Northwich town centre flood risk management scheme as a case study of how a clear and objective human population assessment can be carried out.

Flood risk management schemes (FRMS) are designed to provide a benefit to the local population. However, FRMS are often within urban areas where construction work and the presence of flood defences can be intrusive. In addition, a river corridor through an urban area can provide an important community resource.

Defining receptors is an important stage in being able to identify potentially significant effects. A balance is needed between defining receptors as single points such as single properties which can lead to underestimation of total effects, and grouping too many together, which can lead to individual sensitivities being missed.

For the Northwich town centre FRMS, receptors were grouped into four categories: residential areas; commercial areas; community facilities such as a medical centre; and informal recreation areas such as open space and paths. Individual receptors were identified, assigned a category, and marked on a map. This allowed effects on key elements of the human environment to be considered at the whole scheme level, while allowing the characteristics of individual receptors to be taken into account.

Although all human beings can be considered sensitive, an objective approach is needed for EIA to identify members of a population, and facilities used by a community, that are particularly sensitive. As an example, for the Northwich FRMS the sensitivity of residential areas was defined based on census data, specifically the index of multiple deprivation (IMD) and the proportion of vulnerable residents, for example, elderly residents and residents with long-term health problems. Residential areas within the 10% most deprived in England, according to the IMD, were considered to be of high sensitivity. Residential areas among the 10-20% most deprived in England or within an area where more than 20% of residents are vulnerable, were considered as having moderate sensitivity.

This approach assumes that communities that are among the 20% most deprived in England are more sensitive to temporary and permanent changes than other communities. Residents may be more susceptible to the effects of noise, dust, visual disturbance and changes to access during construction as they are more likely to be at home during the day. They are also more likely to have access, mobility or resource limitations that could affect their ability to cope with the stress of disturbance.

Quantitative definitions of magnitude were also made. These were based on the number of properties, or the proportion of a particular type of amenity that could be affected by the scheme. This meant that for the Northwich FRMS, the assessment of significance, which is a combination of sensitivity and magnitude, was based on a clear and objective method, and that the findings of the assessment are auditable and can be readily justified. It also allows mitigation at the detailed design and construction stages to focus on the most vulnerable communities and most important facilities in order to minimise the impacts of delivering the scheme.


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