New surface area draining to an existing combined sewer

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Message last updated - Sunday 06^th April 2025

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Message last updated - Sunday 06^th April 2025

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Network Impact

The impact of additional surface water flow to a combined sewer will significantly increase the risk of flooding and pollution from the receiving network and potentially to compromise the ability of assets to operate within statutory enforced permitted limits.

Increasing the surface water catchment draining to a Combined sewerage system will require new operating permits for critical assets and therefore, the approval of the appropriate permitting authority. Detailed analysis will be necessary to demonstrate that the environmental impact can be reliably mitigated. This process could impose severe time constraints on the development programme and there could be no certainty of identifying a feasible mitigation method. It should be noted that statutory operating permits reflect volumetric loading, which could not be mitigated solely by attenuating the discharge rate.

Even with new operating permits and technically feasible environmental mitigation, the change in operation would likely require extensive network reinforcement, which may not be practicable to implement.

Should a planning application be presented that proposes an increase of surface area draining to a Combined sewer we would take the view that this would pose an unmitigable risk of pollution and flooding from the network and will raise an objection to the planning application.

Process

A new connection that increases the surface area draining to a Combined system is unlikely to be a sustainable option and would not be supported.

Network Reinforcement

Network reinforcement is not reliably sustainable.

Alternative Disposal Options

i) Other drainage infrastructure

There may be highway drainage within the vicinity of your development that could accommodate the additional flow. Subject to agreement with the Highway Authority, a connection for surface water may be made under the provisions of Section 115 of the Water Industry Act, 1991.

ii) New drainage infrastructure and outfall

The alternative is that a new surface water sewer is constructed which is used to convey your surface water to a watercourse or as part of a SuDS scheme, where appropriate. Subject to the sewer being designed in accordance with the current version of Sewerage Sector Guidance, the sewer can be put forward for adoption by Anglian Water under Section 104 of the Water Industry Act 1991.

If the outfall is to a watercourse, the applicant may be required to obtain consent to discharge via the appropriate body in addition to approval of the drainage strategy from LPA. The applicant will also need to secure a Deed of Grant of Easement, in Anglian Water’s favour for the right to convey water into the watercourse in perpetuity from the riparian land owner, prior to a sewer requisition.

Installation of offsite sewers

If your site has no means of drainage without crossing third party land then you may be able to requisition Anglian Water, under Section 98 of the Water Industry Act 1991, to provide a connection to the public sewer or an approved outfall for domestic drainage purposes. Guidance on sewer requisition under Section 98 is provided here.

Alternatively, you may wish to enter into a works agreement in accordance with Section 30 of the Anglian Water Authority Act 1977. This will allow you to design and construct the public sewer using Anglian Waters’ statutory powers in accordance with Section 159/168 of the Water Industry Act 1991.

Sewer Adoption

SuDS are classed as sewers; therefore, subject to them being designed in accordance with the Design and Construction Guidance (DCG) Sewerage Sector Guidance, the sewer can be put forward for adoption by Anglian Water under Section 104 of the Water Industry Act 1991.

A pre-design consultation service is available if you would like to further advice on the adoptable standards for SuDS features. View details on our PDSA service.

As you may be aware, Anglian Water will consider the adoption of SuDS provided that they meet the criteria outline in our SuDS adoption manual. This can be found on our website. We will adopt features located in public open space that are designed and constructed, in conjunction with the Local Authority and Lead Local Flood Authority (LLFA), to the criteria within our SuDS adoption manual. Specifically, developers must be able to demonstrate:

1. Effective upstream source control,

2. Effective exceedance design, and

3. Effective maintenance schedule demonstrating than the assets can be maintained both now and in the future with adequate access.

If you wish to look at the adoption of any SuDS then an expression of interest form can be found on our website.

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