Preparing for the new Design and Construction Guidance

March 2020

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On the 25th October 2019, the documentation submitted by Water UK concerning sewerage was approved by Ofwat. It is designed to guide water companies and developers when planning, designing and constructing foul and surface water drainage systems which are intended for adoption, as per the Section 104 agreement under the Water Industry Act 1991. The documents provide updated guidance for all standards and specifications required when designing new water or drainage infrastructure and aim to accelerate the uptake of sustainable drainage (SuDS), particularly in house building, by smoothing out the transfer of ownership, responsibility and ensure the assets are effectively managed and maintained. They will also allow English water and sewerage companies to adopt a wider range of drainage types, including those with sustainable elements. The new sewerage adoption arrangements are expected to come into effect on the 1st April 2020. However, as noted in the Sewerage Sector guidance document, reporting against the new performance metrics will be delayed for a maximum of six months from the 1st April 2020.

Water and sewerage companies are currently preparing themselves to accept adoption applications under the new standards. Once the new arrangements have come into force, all changes will be subject to approval by the new codes panel that includes equal numbers of water and sewerage companies and developers.

Water companies have been considering their role with the adoption of sustainable urban drainage systems (SuDS) ever since the government decided not to implement Schedule 3 of the Flood and Water Management Act (2010). Therefore, instead of revising the long-standing voluntary Sewers for Adoption (SfA) manual, which may have resulted in further future revisions, a decision was made to include the new guidance within the implementation of the water sectors Ofwat’s Code for Adoption Agreements. Incorporating details of the water sector’s approach to the adoption of SuDS which meets the legal definition of a sewer. Therefore, the document is no longer called Sewers for Adoption 8th Edition as initially proposed but has instead been renamed to the Design and Construction Guidelines (also known as the DCG).

Context and driver for the new guidance

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What is new?

A series of enquiries, including the Pitt Report in 2008, has identified that one of the major impediments to the increased use of SuDS is uncertainty about their long-term maintenance. This is largely due to the legal regime that water companies are operating under, which may not allow for the adoption of all SuDS and therefore results in very few examples of SuDS features and systems being adopted by water companies and a reluctance from developers to incorporate them.

Furthermore, compliance with the current version of SfA is voluntary and the supporting National Technical Standard was never enacted for SfA7 which meant both SfA6 and SfA7 were often used concurrently, leading to inconsistencies. From a design perspective, the mandatory DCG revision aims to clarify and update this confused position and have an agreed approach that is consistent and clear across all water companies.

Over time the new mandatory approach should see a significant increase of SuDS assets being adopted by water companies as sewers.

Domestic Foul design flow to be calculated in accordance with BS EN 12056-2.

The hydraulic design of pipelines and other conduits should be designed in accordance with BS EN 16933-2.

Bridges the gaps in adoption related to SuDS in surface water management

General update of standard details to reflect design code changes

Elucidate the legal responsibilities of Water Companies for surface water

Connects to several CIRIA documents including the SuDS Manual to strive for common standards in the adoption of SuDS

The new DCG is more aligned to and has the familiar structure of SfA7 but incorporates the following:

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As the DCG is aimed at developers planning, designing and constructing foul and water surface water drainage systems, it only applies to the adoption of assets used for drainage from buildings or paved areas that belong to those buildings. Although it is the water and sewer companies that will ultimately apply the criteria to assets that are being offered for adoption, the new DCG document covers additional new sewers and lateral drains which are being offered for adoption under S104.

Practically and in terms of SuDS, the basic criteria that need to be achieved for a surface water drainage system to be “adoptable” or “not adoptable”, will mainly require the following.

The developer is expected to make arrangements to ensure the future operation and maintenance of any component not adopted by the sewerage company. They are also expected to provide details of these arrangements in their S104 application because components managed by another body could adversely impact on the sewerage company’s system. Ultimately, it is for the water and sewerage company to apply these criteria to assets that are being offered for adoption.

Criteria

Adoptable Not adoptable

A. It is constructed for the drainage of buildings and yards appurtenant to buildings

A. Watercourses as defined in law (these included rivers, streams and can include some ditches)

B. It has a channel (a depression between banks or ridges with a definite boundary)

B. Components build primarily for the drainage of surface water from streets or the drainage of land

C. It conveys and returns flows to a sewer or to asurface water body or to groundwater

C. Components built to manage groundwater

D. It has an effective point of discharge, which must have lawful authority to discharge into a watercourse or other water body or into land. As with conventional piped systems, this right to discharge must be secured by the devloper and transferred to the sewerage company on adoption

D. Components which are part of the structure of a building or yard (e.g., green roof, pervious driveway or guttering and rainwater pipes attached to the building)

E. Components which are an integral part of the structure of a street (e.g., a pervious street or channel formed by kerb of a conventional road or channel formed by a depression in the centre of a street

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Adoptable SuDS

The following are examples of adoptable sewer elements in public spaces that serve more than one property and meet the criteria set out in the guidelines. As stated, early discussion with the relevant company and authorities to determine what will be maintained as a public surface water sewer feature and what will be maintained as public open space is essential.

An adoptable swale will usually include the side and base of the channel, any vegetation that is part of the function of the swale and any under-drainage including any liner, check dam, flow control or erosion control measure.

An adoptable rill will usually include the material forming the sides and base of the channel and any check dam or flow control device.

Swales

Rills

An adoptable Bioretention system will usually include the whole area used for temporary ponding of water and the inlet and outlet structures and any engineered soil structures, including the vegetation.

An adoptable pond & basin will usually include the inlet and outlet structures (including flow controls). Water companies will adopt the entire area of the pond, including any banks that are designed to retain water, any storage below the ground surface, impermeable liners and under drains.

Bioretention systems

Ponds and basis

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Non-Adoptable SuDS

Any system that only provides highway drainage will not be adopted by the water and sewerage company. Developers should speak to their local Highway Authority to discuss the adoption of assets that solely serve a highway. If a system accepts some highway drainage it may still be adoptable, early discussions with both the water and sewerage company and Highway Authority for sewerage systems that serve both a highway and a property are essential At present, there needs to be an agreement in place for highway drainage to be discharged through a sustainable drainage feature that is a sewer.

Private drainage SuDS features, such as water-butts, cisterns, water-barrels; permeable paving; rainwater harvesting systems and rainsave planters; and green or blue roofs are classed as building drainage, even where flows from more than one property are conveyed. These cannot qualify as public sewers and will remain the responsibility of the homeowners. Their use, however, plays a crucial role in an integrated approach to water management. Capturing rainwater is an important way of securing future water supplies and dealing with the increasing pressures of climate change. These source control features reduce the volume of water draining to the sewer system. Moreover, collecting this water in water butts and rainwater harvesting systems provides an important supply of water to use around the home, helping to reduce demand.

An example of a drainage network made up of adoptable and non-adoptable assets

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The DCG only covers new sewers and lateral drains which are being offered for adoption under S104. To achieve the most effective design and reduce delays the designer must coordinate with a diverse set of stakeholders from the earliest stage of the design process. It’s strongly advised that designers engage early with local authorities; both local planning authorities (LPAs), lead local flood authorities (LLFAs) and the water and sewerage company to agree on a drainage strategy and maintenance plan before making planning or S104 applications. Where sewers proposed for adoption discharge into a watercourse, statutory consent and other permissions should be obtained by relevant bodies, which may include the Environmental Agency, Canal and River Trust, Internal Drainage Boards, landowners etc.

The surface water drainage applications are expected to explore the surface water hierarchy and provide evidence to support alignment with both national and local flood risk strategies and policies before connections to any existing sewers are considered. Spearheaded by the National Planning Policy Framework (NPPF), the SuDS Manual (C753) local policies and supplementary planning documents, SuDS is expected to be used as first preference in developments of any size, with additional priority given to the use of sustainable drainage systems in areas at risk of flooding.

The designer should submit construction drawings and calculations to show how the proposed design satisfies the requirements of all stakeholders, with confirmation of the arrangements for the operation and maintenance of the system in perpetuity. For additional support, there is a substantial amount of guidance on SuDS design in the Appendix to the DCG.

Implementation

“To achieve the most effective design and reduce delays the designer must coordinate with a diverse set of stakeholders from the earliest stage of the design process’’.

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The remit of adoption

Water companies

Water companies will be responsible for adopting drainage features for conveyance and storage purposes for assets predominantly used for drainage from buildings or paved areas belonging to those buildings. Although there is no exhaustive list of SuDS components suitable for adoption, water and sewerage companies are likely to produce a list in the future. Surface water sewers adopted by sewerage companies are likely to include all surface water sewers and lateral drains being connected to the surface water sewer. These will exclude any sewers that are adopted by the highway authority or other bodies. As previously stated, the management of other components are likely to be covered by a separate agreement.

The DCG is designed to be read in conjunction with the Sewerage Sector Guidance published by the sewerage undertakers under the Code for Adoption Agreements for water and sewerage companies operating wholly or mainly in England. This will likely cover the extent to which individual water and sewerage companies can deviate from the approach set out in DCG. The expected variations are related to the use of land transfer or easements that may be used by the water and sewerage companies to adopt and maintain drainage features of a sewer. The other probable variation is regarding health and safety assessment requirements. Although the DCG outlines “health and safety associated with any open water should be assessed and managed in accordance with Chapter 36 of CIRIA Report C753 ‘The SuDS Manual’, some water and sewerage companies may deviate from this to meet their legal requirements as an owner or occupier of land operating as a public surface water sewer.

Local authorities

Local authorities have a key role in determining the surface water drainage arrangements. The LPA approves the surface water drainage arrangements for new developments and redevelopments in accordance with the NPPF, local policies and any supplementary planning documents. The LLFA guides the LPA as statutory consultee in all major developments (in the case of residential developments, those of 10 units or larger). The Local Drainage Authority (LDA) regulates any work carried out in or in close proximity to non-main rivers (ordinary watercourses) except in areas where there is an internal drainage board. In areas where there are both district and county councils, the district council is the LPA and the county council are both the LLFA and the LDA.

Internal drainage boards

In some areas there are internal drainage boards (IDBs) which regulate any work carried out in or in close proximity to non-main rivers (ordinary watercourses).

Environment Agency

The Environment Agency (EA) guides the LPA in areas that are designated critical drainage areas, coastal and fluvial flood risk areas and sites within 20m of a main river as a statutory consultee. It should also be noted that approvals for discharges to “controlled waters” will also be required form the EA.

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Design and Construction Guidance - https://www.water.org.uk/wp-content/uploads/2019/03/Appendix-C-to-draft-sewerage-Sector-Guidance-Design-and-Construction-Guidance.pdf

The CIRIA SuDS Manual (C753) 2015 – https://www.susdrain.org/resources/SuDS_Manual.html

Guidance on the construction of SuDS. CIRIA, 2017 - https://www.susdrain.org/resources/ciria-guidance.html

Code for adoption agreements. Ofwat, 2017 - https://www.ofwat.gov.uk/wp-content/uploads/2017/06/Code-for-adoption-agreements-Nov-2017.pdf

Protocol for correctly classifying Culverted Watercourses and Sewers Water UK 2018 - https://www.water.org.uk/publications/water-industry-guidance/protocol-correctly-classifying-culverted-watercourses-and

National Planning Policy Framework Ministry of Housing, Communities and Local Government, 2019 -https://www.gov.uk/government/publications/nationalplanning-policy-framework--2

Ministry of Housing, Communities and Local Government, 2019 -https://www.gov.uk/government/publications/national-planning-policy-framework--2

Non-statutory Technical Standards for Sustainable Drainage Systems, Defra, 2015 - https://www.gov.uk/government/publications/sustainable-drainage-systems-non-statutory-technical-standards

Non-Statutory Technical Standards For Sustainable Drainage - Practice Guidance Association of SuDS Authorities (formerly known as the Local Authority SuDS Officer Organisation (LASOO) - https://www.suds-authority.org.uk/wp-content/uploads/2018/12/non-statutory-technical-standards-guidance.pdf

COMMERCIAL COST AND VALUE MANAGEMENT, AND THE ASSOCIATED REPORTING, HAS ALWAYS BEEN SEEN AS THE KEY TO ANY BUSINESS - THE CONSTRUCTION INDUSTRY IS NO DIFFERENT. IN MANY WAYS IT IS BROUGHT EVEN MORE TO THE FORE AND SEEN AS THE MAIN WAY OF MANAGING A PROJECT AND IDENTIFYING OVERSPEND OR UNDER PRODUCTION, BASED ON ANY CURRENT PROJECT POSITION.

Appendix

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