The Norfolk Nutrient Budget Calculator and updated Catchment Maps: One step closer to a solution?

Key Changes to the Calculator include:

• Reduction in occupancy rates for dwellings from 2.4 to 1.89;
• Reduction in assumed water usage from 120 l/p/d to 110 l/p/d;
• Use of more up to date rainfall figures;
• Ability to distinguish between different types of overnight accommodation – hotels/guest houses and HMOs have their own category;
• Wider and more relevant list of existing and proposed land use options;
• Ability to differentiate between a scheme that discharges to a Water Recycling Centre (WRC) and one that seeks to deal with sewage on site via a Package Treatment Plant (PTP) or Septic Tank (ST);
• Indication of potential mitigation options, on- or off-site, to achieve Nutrient Neutrality, including consideration of post-2025 and post-2030 Anglian Water permits;
• ‘Zero-value’ calculator allows calculation of the number of dwellings that can be built without any mitigation, as a result of taking the whole site out of agricultural use.

Catchment Maps

The Catchment Maps, which are more detailed than those issued by Natural England, have been updated to show both the Surface Water Catchments, and the Waste Water Treatment Works that drain into the Catchment and those which do not.  For those which do not, such as North Walsham, the guidance suggests that no further work is required, even if the site is within the Surface Water Catchment.

One step closer to a solution?

The use of local household occupancy rates and water consumption rates that reflect local policy is clearly a major advantage of the Norfolk Calculator; the occupancy rates are more than 20% lower than the National Calculator, meaning a similarly reduced nutrient budget and therefore significantly less mitigation.

As well as providing a more tailored and localised approach, the Norfolk Calculator also provides clarity on a number of the key questions that practitioners and developers have been asking since March.  For instance, confirmation that sites located within the Surface Water Catchment, but where the foul drainage discharges to a Water Recycling Centre (WRC) that discharges outside of the Catchment require no assessment is welcomed.  Similarly, the guidance makes it clear that for any development proposals that would be located outside of the defined surface water catchment area, but would discharge effluent to a WRC within the surface water catchment, stages 2 and 3 of the calculator, which relate to surface water runoff considerations, do not apply.  

The refinement of options for both existing and proposed land-use also appears to be a notable improvement – the ability to differentiate between different types of overnight accommodation, and the option to distinguish between low-, medium- and high-density residential development means this should be a far less blunt tool.

But perhaps the most significant feature of the Calculator is the inclusion of a function to calculate the area of land required for different types of mitigation, such as constructed wetland, urban open space or woodland,  both on- and off-site.  This represents a significant step forward, and will help to reduce some of the uncertainties that developers have been facing when trying to understand the extent of the burden of achieving Nutrient Neutrality.  The ability to consider phasing of developments, by including post-2025 and post-2030 permit allowances, is also a really useful feature, particularly for larger scale developments.  Similarly, the ‘zero-value’ calculator, which allows calculation of the number of dwellings that can be built without any mitigation, simply by taking the whole site out of agricultural use, is another very helpful feature.

However, the fact remains that in order to deliver the County’s planned housing growth, there will still be significant requirements for Nutrient Pollution mitigation, and the big questions about where and how this will be delivered remain unanswered.  Furthermore, whilst we understand that the Norfolk Calculator has been devised in discussion with Natural England, securing their formal endorsement would provide a significant degree of comfort to the development industry

So, whilst the release of the Calculator and updated Maps certainly represent a step in the right direction, providing increased clarity on the level of the mitigation required, as well as substantially reducing the extent of mitigation, the next step is to identify a mitigation strategy that can be used by both Councils and developers to unlock development.