Nutrient neutral development

Development in areas with nutrient-rich water must mitigate its effects and provide a nutrient-neutral environment.  

Evidence has shown that residential development contributes to high levels of nutrients in the water environment, specifically nitrates in Solent catchments and phosphates in the Avon catchment. Adverse effects on international nature conservation sites in the Avon and Test river catchments cannot be ruled out. The full list of affected European Sites can be found in Policy ENV1 of the Local Plan.

The extent of nutrient enrichment causes an excessive growth of plants and algae, known as eutrophication, which reduces the oxygen content in water. This process makes it more difficult for aquatic insects or fish to survive, in turn removing a food source from the food cycle for protected species such as wading birds and salmon.

Following recent case law, residential and other development providing overnight accommodation will need to mitigate its effects to become nutrient-neutral, to avoid making the current situation worse. Adverse effects arise from increased sewerage treatment, and from surface water run-off from both urban and greenspace areas.

A nutrient avoidance and mitigation package will be needed to achieve nutrient neutral development before a planning permission can lawfully be issued in accordance with The Conservation of Habitats and Species Regulations 2017.

On this page:

Affected areas

The Nutrient Mitigation map shows the areas within New Forest District Council that are required to achieve nutrient neutrality. If your development is within this area, it is important you follow the requirements.

You can download a map below showing the nutrient mitigation areas.

Icon for pdf Nutrient Mitigation Areas Map [3.11MB]

Nutrient Mitigation Areas
AreaDrainage catchmentSuitable mitigation locationsPossible credit providers
Totton and the WatersideSlowhill Copse WwTW (Southern Water)Rivers Test, Ritchen and Bartley WaterEastleigh BC Bishopstoke, Roke Manor
Totton and the WatersideAshlett Creek WwTW (Southern Water)Rivers Test, Itchen, Meon and Eastern New ForestEastleigh BC Bishopstoke and Botley, Roke Manor, Warnford Park, Whitewool
Totton and the WatersideAreas not on sewer network* (Southern Water area)River Test, Itchen and Bartley WaterEastleigh BC Bishopstoke, Roke Manor
South Coastal TownsPennington WwTW (Southern Water) S. coast New Forest, Western Yar, and Newtown HarbourHeaton's Farm, Kings Farm
South Coastal TownsAreas not on sewer network* (Southern Water area)S. coast New Forest, Western Yar, and Newtown HarbourHeaton's Farm, Kings Farm
South Coastal TownsMudeford Catchment**To be confirmed whether requiredTo be confirmed whether required
Avon Valley and DownlandsFordingbridge or Ringwood WwTW (Wessex Water)Areas at, or upstream of, where waste water from the development enters the River AvonCredits not currently available
Avon Valley and DownlandsChristchurch WwTW (Wessex Water)*** Areas at, or upstream of, where waste water from the development enters the River AvonCredits not currently available
Avon Valley and DownlandsAreas not on sewer network* (Wessex Water area)Areas at, or upstream of, where waste water from the development enters the River AvonCredits not currently available


* Check with the water company and Environment Agency whether a mains sewer connection is available or practicable.  If not, mitgation requirement calculations should be based on a septic tank/packet treatment plant system.

** As this  catchment does not drain to the River Avon or to the Solent, NFDC is checking whether any nutrient mitigation is necessary.

*** As this WwTW does not drain to the River Avon, phosphate neutrality is required for surface water runoff from the development only.

Nutrient avoidance, mitigation and offsetting

The Mitigation Hierarchy is the accepted national approach to managing harmful impacts on biodiversity.  Avoidance of any impacts should be the first consideration.  The next step is on-site mitigation of any impacts that cannot be avoided.  The last step is compensation measures in an off-site location to offset any unavoidable remaining impacts.

The avoidance and mitigation package for nutrients should start at development master planning stage with avoidance and mitigation measures to manage surface water run-off.  The aim should be to achieve run-off neutrality wherever possible (and a credit where practicable), to minimise the extent of offsetting required for the main source of additional nutrients, foul drainage.  

Nutrient offsetting credits

In most cases on-site mitigation will not be enough and additional off-site offsetting measures will also be required. Off-site measures may include:

  • The purchase of nutrient offset 'credits' from an appropriate body (such as but not limited to the Council, the Hampshire and Isle of Wight Wildlife Trust or in due course from the Solent nutrient trading platform currently being set up by DEFRA).   Credits are made available in return for a financial contribution paid by the developer to implement the approved mitigation scheme.  
  • Bespoke mitigation projects prepared by the developer.   Projects should be discussed with the Council at pre-application stage, following which use of Natural England's Developer Advice Service should also be considered.

The Council is working with partners to identify appropriate schemes to provide offsetting credits.  Some nitrate schemes are available and you are advised to check the PUSH website to identify a relevant scheme depending on the waste water treatment plant your development is served by.

  • Avon phosphates: The Council is working in partnership with other local authorities, Wessex Water and EnTrade to identify suitable mitigation projects.  
  • Solent Nitrates, NFDC South Coast: A Hampshire and Isle of Wight Wildlife Trust offsetting credit scheme is at an advanced stage.
  • Solent Nitrates, NFDC East Coast: a potentially significant wetland project is being explored after encouraging initial feasibility assessment and landowner interest.

Planning application requirements

As part of the information needed to determine relevant planning applications, a European Site avoidance and mitigation checklist will be required. You can download this document below.

Icon for pdf European site avoidance and mitigation checklist [211.38KB]

This web page contains the latest information currently, but our adopted 2019 Position Statement on nutrient neutral development can be seen below.   Whilst the position statement refers to nitrates in the Solent, the same principles apply to phosphates in the River Avon. The Position Statement will be updated when there are specific mitigation programmes available.

Icon for pdf Position statement on nutrient neutral development [277.73KB]

Achieving nutrient neutrality

Links to the latest documents on nitrate neutrality in the Solent can be downloaded below

Icon for pdf Solent Nutrients June 2020 [2.41MB]

Icon for pdf Solent Nutrient Advice - Non-Technical Summary [586.55KB]

Icon for zip Nitrogen Budget Calculator [47.33KB]

An interim development phosphate budget calculator can be downloaded below.   This is a modified version of the Natural England Solent nitrate calculator.

Icon for zip Interim NFDC Phosphate Calculator [54.24KB]

Land use leaching data has been sourced from Farmscoper, simplified for  general use, and from Natural England nutrient methodology for parts of the upper Stour catchment.  Extracts from the Stour methodology most relevant to Avon phosphorus are attached below.   

Icon for pdf Stodmarsh methodology phosphate extracts [210.48KB]

The calculator is 'interim' as further work is underway in DEFRA and the leaching rates and other assumptions in this document may be updated early in 2021.  It will however provide a general estimate of mitigation requirements for planning purposes.

Dwelling occupancy rates in NFDC

Paragraphs 4.18 - 4.19 of the NE Guidance v5 includes the following statements:

  • Natural England recommends that, as a starting point, local planning authorities should consider using the average national occupancy rate of 2.4
  • Competent authorities may choose to adopt bespoke calculations tailored to the area or scheme
  • Calculations for occupancy rates will need to be consistent with others used in relation to the scheme (e.g. for calculating open space requirements), unless there is a clear justification for them to differ.

For residential planning applications in the NFDC area the following occupancy rates will be applied, consistent with the approach for mitigating the recreational impacts of new housing on the New Forest European sites.

Dwelling sizeOccupancy per unit
Studio or 1 bed1.4
2 bed2.1
3 bed3
4+ bed3.75


The unspecified dwelling size assumes a housing mix compliant with 6.1 of Policy HOU1 in the Local Plan 2016 - 2036 Part One: Planning Strategy

For outline planning permissions, at detailed application stage we will require that the nutrient budget for the site be recalculated for the actual dwelling mix and layout. Depending on the final unit mix the number of dwellings that can be accommodated may change from the figure in the outline permission.

Other forms of overnight accommodation

Units of visitor or institutional accommodation, or other proposals that include overnight stays including campgrounds, will be calculated on a dwelling-equivalent basis.

As a starting point the occupancy rate for a studio/1-bed dwelling will be applied to a hotel, guesthouse, care home 'room' or a campsite pitch. Relevant and robust evidence on rates of occupancy, including seasonal variations or periods of closure, will be taken into account.

Permitted development rights and compliance with the habitats regulations

The General Permitted Development Order (GPDO) allows for the change of use of some buildings and land to Class C3 (dwellinghouses) with this development subject to a prior approval process. However the Habitats Regulations also apply to such developments.  We are obliged by the regulations to assume that there will be a significant effect on the New Forest and Solent SPAs.

Any development for prior approval should also be accompanied by an application for us to do a Habitats Regulations Assessment on the proposed development (please note there is a £30 fee for this). The development will need to include a mitigation package to mitigate the significant effect on the New Forest and Solent SPAs which new residential development would otherwise result in.

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