Housing, Poudbury, Dorset

Design of Sewers for Section 104 Agreement

Design of sewers for adoption

Morton-Roberts has the capability to design sewers to be adopted under a section 104 agreement for new development sites in both England and Wales. In addition we can undertake or assist in the negotiations with the water company for the preparation of the section 104 adoption agreement itself. Similarly, we can also either undertake or assist in the negotiations with the water company for any sewer diversions (section 185) or off-site sewer requisitions (section 98). The various section numbers refer to the Water Industry Act 1991.

As regards to the design work, we use Micro Drainage System 1 and, where relevant, Simulation software for the hydraulic design of sewerage systems and AutoCAD software for the production of the construction drawings. The final drawings themselves would include 1:500 scale layout plans and long-sections of the proposed drainage infrastructure together with details of the associated ancillaries such as manholes, pumping stations, rising mains, etc.

In summary, Morton-Roberts has the capability to design the drainage for new developments in both England and Wales, please contact us for more details.


The background to the design and construction standards for new sewers is outlined in the following sections.

Background - Mandatory adoption of new sewers

Following the transfer of most existing private sewers to the water companies on 1 October 2011, DEFRA and the Welsh government planned to ensure that no further new private foul sewers were created in the future. Although the mandatory adoption of new sewers is already in operation in Wales, no progress has been made in England and there are doubts that DEFRA will ever introduce the measure.

An integral part of the mandatory adoption process would be both English and Welsh versions of national build standards for new gravity foul sewers and lateral drains. A draft version for use in England was published by DEFRA in December 2011 but no further progress has been made. The Welsh build standards will be considered in the next section.

Background - Mandatory Adoption (Wales only)

In Wales mandatory adoption applies to both proposed foul and surface water sewers which will connect to an existing public sewer. It does not apply to SUDS systems which would require approval under Schedule 3 of the Flood and Water Management Act 2010 if and when that schedule is implemented.

Guidance on the implementation of mandatory adoption was published by the Welsh Government in July 2012 while 'The Welsh Ministers standards for new gravity foul sewers and lateral drains' was published in the following October. Mandatory adoption of foul sewers and laterals was then implemented on 1 October 2012 and applies to water companies operating wholly or mainly in Wales. This means that new sewers in the parts of England served by Dwr Cymru Welsh Water (DCWW) will be adopted under the Welsh system while new sewers in the parts of Wales served by Severn-Trent Water will be adopted under the English rules.

Background - Sewers for Adoption

Mandatory adoption would have important implications for the scope and layout of sewers to be adopted. Significant changes were therefore incorporated into the seventh edition of Sewers for Adoption which was published in August 2012. This edition of Sewers for Adoption and the draft national build standards were compatible but in view of the uncertainty, an addendum to Sewers for Adoption was promised if the final versions of the national standards differed from the draft editions.

Overall there is a fair degree of uncertainty with at least one of the nine main English water companies allowing a developer to choose to design new sewers to either the sixth or seventh edition of Sewers for Adoption. When carrying out drainage design in areas covered by the main English water companies it is therefore important to clarify the standards to be used.

Background - Summary

In areas served by DCWW (mainly Wales), the gravity foul sewers and lateral drains for a new development would be designed to the Welsh national standards. Surface water sewers, pumping stations and rising mains would be designed to the seventh edition of Sewers for Adoption together with the DCWW Pumping Station Addendum. The sewers, lateral drains and any ancillaries such as pumping stations would have to be offered to DCWW for adoption.

In England the sewerage system and lateral drains for adoption would be designed to either the sixth or seventh edition of Sewers for Adoption as required by the relevant water company or as decided by the developer if appropriate. The developer would not have to have the sewers adopted if not required by the site's planning permission. Please note that the application of mandatory adoption of sewers is based on the area served by DCWW not the border between England and Wales, see 'Background - Mandatory Adoption (Wales only)' section above.


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