Stodmarsh Nutrient Issue Update: Up to 50,000 homes per annum affected by Nutrient Issue in East Kent

It depends on your point of view, it could be a good thing or a bad thing.

The Stodmarsh Nutrient Issue rumbles on. According to Roland Cooper of Considine the issue is “affecting the construction of 33,000 to 50,000 homes per annum” being built across the five districts, affected by the issue, with a backlog of 25,000 to 30,000.

The councils areas within the River Stour Catchment Area are:

  1. Ashford Borough Council

  2. Canterbury City Council

  3. Dover District Council

  4. Folkestone & Hythe District Council

  5. Maidstone Borough Council

So you see, it could be a good thing that up to 33,000 to 50,000 homes per annum are not currently being built across these five districts; and retaining their respective environments, wildlife, habitats, air quality etc.

However, if your a developer and employed in the industry across the Stodmarsh affected area, this hold up, may well send some developers under, causing jobs to be lost. Those who survive will be forced to add an increased cost per dwelling of between £1,500 to £4,000 to mitigate the Stodmarsh Nutrient Issue. This would mean that where viability of a scheme which is marginal, could result in the scheme not coming forward and creating a loss of developers financial contributions [s106, CIL etc] for affordable homes, community facilities, infrastructure such as schools, GP surgeries etc will be reduced. As such this has a knock on affect to us all in East Kent.

To develop or not develop that is the …


As a quick reminder, the issue is that Natural England [NE] has issued water quality advice that has had a significant impact on the ability of five local planning authorities, who site in the River Stour catchment area [see map], to permit new homes or development with overnight accommodation, eg some forms of tourism. The advice sets out that until the Stodmarsh protected site is restored to good condition, new developments cannot go ahead unless it can be shown that they will not contribute to further deterioration of water quality at Stodmarsh, caused by excessive Nitrogen and Phosphorus in the River Stour and its tributaries. Developments need to show “neutrality in two terms of two nutrients – Nitrogen and Phosphorus – which, NE has found to be causing harm to the ecology of the Stodmarsh protected area due to eutrophication (excessive algae growth which kills marine life and plant life) – which is man made ecological change. In the absence of as a yet agreed strategic solution being implemented, there has been a significant break in development activity in East Kent, which is the key growth area for the County.

The latest information avaliable makes it clear officers at each of the five affected Councils are working hard to find appropriate solutions, as it has held up approx 25,000 to 30000 homes so for these developers and Councils who must hit their building targets per annum, addressing the issue will allow planning permissions to start being granted again.

Officers of two of the councils, Canterbury & Folkestone & Hythe have found some success with finding solutions for large scale developments – 2 in Canterbury [Mountfield Park & Land at Sturry Road and Broad Oak] and one in Folkestone & Hythe District [Otterpool], whilst the solution for smaller developments and brownfield/regeneration sites necessitates a coordinated strategic solution, which is less straightforward.

A more detailed update is set out below.

Large Scale Developments – over 300 dwellings.

There has been progress with establishing a solution for the strategic sites. The solutions to date have been in the form of on-site wastewater treatment plants along with environmental enhancements that together will achieve nutrient neutrality. There is however a cost associated with providing on site treatment works.  A very rough estimate, according to developers, is in the region of around £1,500 – £4,000 per dwelling, meaning ultimately higher house prices. This would significantly impact the viability of Otterpool Park [the Council make less money], where FHDC wish to build up to 10,000 homes. This could explain why FHDC are seeking “further land acquisitions”, in the Otterpoool area; and have set aside £ 6,324,000 to fulfill these ambitions.

As we understand cost of mitigation can be borne by landowners for sites that are now coming forward. However, for sites that are now owned [Otterpool] or with established options [Otterpool] held by developers, the significant upfront cost of these works potentially will impact on the viability of housing developments and not only risk a restriction in the supply of new homes but also would reduce the ability of developers to fund vital infrastructure such as schools and affordable housing.

On-site treatment works and biodiversity enhancements have been agreed with Natural England as solutions for two strategic sites in Canterbury District. A similar approach has been agreed for the Otterpool strategic site at Folkestone. For a strategic allocation at Lenham Heathlands, it is anticipated that there will be a combination of Sustainable drainage/Green Habitat blend, private package treatment and interceptor wetland though this strategy will depend on Lenham WWTW being upgraded as part of WINEP. These sorts of measures should enable very large sites to demonstrate that they are “nutrient neutral”.

The Natural England advice recognises, however, that smaller sites and brownfield developments may be harder to mitigate. A coordinated strategic solution is required to remove nutrients from the water courses and as such to create headroom for new housing development by overall no worsening of the problem.

The districts most affected by the issue are Ashford and Canterbury and both Councils are actively investigating solutions to the problem across the catchment in the affected Districts, with a view to ensuring that a joined up strategic approach is taken to implementing mitigations schemes in order to unlock development within the wider east Kent.

As we said, Stodmarsh is impacted by both Phosphorus and Nitrogen. At this stage it is likely that the solutions for each nutrient will be different.

The five affected Councils are currently in discussion with Natural England and the Environment Agency to agree a Framework Strategy. This framework strategy will be will be set out in two Phases which will necessarily overlap. The First Phase will be to 2030 to deliver current Local Plans. The Second Phase will be developed through the new Local Plans being produced within the affected areas.

The Framework Strategy, by necessity will be a River Stour catchment-wide strategy. The reason for this amongst other things is, the Habitats Regulations require in-combination effects of the various plans or projects that would impact positively or negatively on water quality at the Stodmarsh lakes to be taken into account through Appropriate Assessments.

Both Ashford and Canterbury Councils have appointed the same consultant to carry out studies to develop a catchment wide strategy. On the 23 Sep 2021, Canterbury City Council published a tender, which closed on  Mon 25 Oct 2021 for a consultancy to assist with a “nutrient mitigation strategy” on a 25.5 month contract to the initial value of £40,000. The contract start date was the 15 Nov 2021, yet the name of the consultant has not been revealed as it must be according to the Local Government Transparency Code [2015]. The outcomes of these studies will be shared with the other affected areas to support and inform further studies within those Districts, should they be necessary. The “nutrient mitigation strategy” will be delivered by Dec 31 2023.

Dealing with Phosphorus and Nitrogen


There are a number of planned upgrades to several Wastewater Treatment Works within the River Stour catchment, due to be implemented by 2023/4. These upgrades will remove a significant amount of phosphorus from the watercourse. Also an agreement by Natural England that a strategic approach whereby nutrient “credits” from planned and potential projects in the catchment can be used as part of a long term strategy that will deliver housing in the short, medium and long term. Upgrades to the Canterbury Wastewater Treatment Works and a review of its Phosphorus permit, is currently expected to be implemented in the next investment period, 2025-30. Phosphurus credits relate to the amount of Phosphorus that will be taken out of the system by the mitigation land once agricultural production ceases.

However, those planned upgrades will not happen sooner than the 2025-30 period, given the process that needs to be followed and the necessary timescale for those. In the meantime the five affected councils are able to rely upon the headroom created by existing planned upgrades to various smaller works, creating sufficient headroom to allow for planning permissions for smaller and brownfield developments to be given on the basis that occupation of those homes will be restricted until 2024/5. This is the position regarding Phosphorus only.


At this stage, no solution is in place to mitigate the impact of nitrogen on the Stodmarsh lakes for the smaller sites. It is clear the mitigation for nitrogen will need to involve a strategic approach. The two most realistic options that are currently being explored in detail are: the removal of agricultural land from agricultural use and the creation of wetlands to remove nitrogen from the catchment. The latter being significantly more land efficient than the former.

The option of removing agricultural land from agriculture requires a significant amount of land. It can require around 0.1 hectare of land to be removed from use to create headroom for a single home, although the amount of land required will depend upon the intensity of the current agricultural use. For example the removal of land from use as poultry or pig farms would require less land than removal of land from cereal production. By far the most land efficient of these two potential solutions is the creation of wetlands which can create headroom for several hundred homes per hectare.

There is therefore the opportunity for wetlands to be created, with the express purpose of mitigating housing development, should affected Councils adopt a catchment-wide mitigation strategy. There are however different requirements depending upon the proximity of the development site to the Stodmarsh lakes, so the amount per dwelling of offsetting land required for Canterbury sites will be likely to be greater than that required for sites in the Ashford District or Folkestone & Hythe.

Mitigation options and the funding requirements

Strategic sites

The letter sent to Government in April 2021 was intended to raise the issue with Ministers and request their support in working towards a solution and to raise the issue of funding and the viability implications of the need to mitigate the problem. The letter sent to Government in April 2021 made a number of requests for funding support, including for support to fund the land purchase for wetlands and the costs of creating and maintaining the wetlands in perpetuity (80+ years). The letter also set out a request for upfront funding for the provision of on site Wastewater Treatment Works infrastructure for the strategic sites Canterbury, Otterpool. The reason for the request is to maintain the viability of sites whereby developers have purchased on the basis of connection to the main sewer and as such the land value has not reflected the additional cost of mitigation for the Stodmarsh. As yet there has been no response to the letter.

Non-strategic sites

Options for strategic wetland creation from agricultural land are being considered to deliver a catchment wide wetlands scheme to mitigate for the impacts of Nitrogen, so as to allow housing development to resume across all of the affected Districts.

Canterbury Council has potentially the largest land requirement of all the Districts for wetlands and is currently investigating potential sites for wetland within its administrative area. Ashford Council, which has identified areas of land which could be used to provide wetland to offset new development. Ultimately, a catchment wide solution will be necessary, which disregards administrative boundaries. The recent Ashford Cabinet report identified potential areas for wetland creation within Ashford District to be able to mitigate impacts on development across the wider catchment.

The cost of the wetlands to address the issue of Nitrogen is not fully known although early rough estimates are that it could be greater per dwelling than the cost of the strategic site mitigation [£1,500 to £4,000]. The letter to Government sent by the East Kent Council leaders, requested support to forward fund the cost of the Councils agreeing a strategic approach to creating wetlands to deliver housing development on the non-strategic sites across East Kent. Wetland will also have some impact in terms of the removal of phosphorus from the watercourse, albeit that phosphorus removal requires a significantly greater amount of land per dwelling than does nitrogen removal.

In order to deliver the wetland solution, it is estimated that initial upfront costs will be significant and that scheme will need to include the cost of the scheme will also include long term maintenance and management costs.

There is also a broader question about the funding available to Southern Water to provide any necessary upgrades or mitigation. This will need agreement from the regulator Ofwat and it assumed in a future letter to Government that a discussion about what the water company should fund (raised through taxpayers bills) and what will then effectively be left to the developers to fund, if not grant or other subsidy is available, with the potential impact on viability of some developments.

To date no response has been received to the April 2021 letter, although we understand that Ministers are aware of the issue and are currently looking at the issue at national level, as it is an emerging UK issue. It is considered unlikely that funding will be provided directly from the Government. The East Kent Leaders now intend to contact the new Secretary of State for the Department for Levelling Up, Housing and Local Government to highlight the matter and ask for his intervention to support us in securing a solution and to reiterate the ask for funding to support this.

Other initiatives to improve water quality at Stodmarsh

NE is responsible for the management and maintenance of the lakes. An example of this is that NE can carry out dredging to remove the phosphorus and nitrogen however, they’ve chosen not to take this course of action until such time that the source of the problem is addressed. The logic being that if the lakes are dredged and the other sources of pollution are not addressed, the problem will simply reoccur.

NE also has a wider role in coordinating initiatives that will result in improvement to the water environment. This work includes working with farmers to reduce run-off and also catchment improvement groups.

A further letter will be sent from East Kent Leaders to Government Ministers with an update on the work going on in Kent and to seek the Government position with regard to the funding requests that have been made.

The Shepway Vox Team

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5 Comments on Stodmarsh Nutrient Issue Update: Up to 50,000 homes per annum affected by Nutrient Issue in East Kent

  1. You can be sure that no new schools or GP surgeries will be built with the builders claiming all their money has been spent on the water treatment. And if you believe that you’ll believe anything .
    Their pockets and the pockets of the shareholders will be bulging

  2. Natural England contacted Folkestone and Hythe District Council on 21 May 2020 to follow up from a call they had on May 13th notifying them of the problems at Stodmarsh. The pdf was online but I can no longer find the link (I have downloaded a copy).

    It’s curious that Ashford Borough Council then rushed through the planning committee meeting for “Big Burton” aka Conningbrook Park in early June immediately adjacent to the Stour. It was approved by one vote, by everyone’s favourite councillor, Paul Clokie, despite legitimate reasons (it should not have been in the Local Plan in the first place).

    I made a FOI request to Natural England regarding any communication between them and ABC prior to that committee meeting, and they could not find anything written.

    The timing of that planning meeting seems very suspicious to me, since F&H who are much further upstream on the Upper (?) Stour, were made clearly aware of the problems at Stodmarsh at least 3 weeks before ABC’s planning committee meeting.

    The problems at Stodmarsh, would likely have been the nail in the coffin of that development if it were proposed now.

  3. @KT – exactly what I was thinking. Another excuse not to deliver infrastructure and affordable housing. The list of excuses that can be used in viability assessments has just got longer.

  4. Does the recent ban on manure spreading by farmer in the aurtum help reduce phosphate/nitrogen run off? It has certainly been imposed if only to judge by the virtual disappearance of the silage smell in our are in the last 2 months.

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