New design and construction guidance for the sewage sector replaces SfA7
Ofwat has now approved new guidance from Water UK for use by developers when planning, designing and constructing foul and surface water drainage systems intended for adoption under an agreement made in accordance with section 104 of the Water Industry Act 1991.
This new guidance (DCG) will come into force from April 2020 and will be different from previous sewers for adoption guidance as compliance by water companies in England will be mandatory.
The guidance is significant as it provides the mechanism by which water companies can secure the adoption of a wide range of SuDS components that are compliant with the legal definition of a sewer. There are however some notable exceptions to the adoptable components including green roofs, pervious pavements and filter strips. These components may form part of the drainage design as long as they are upstream of the adoptable components.
It is hoped that this new mandatory guidance will help to enable more sustainable new developments that also deliver a range of multi-functional benefits to communities. It has the potential to deliver better managed and more integrated surface water systems that align more closely with government and regulatory policy and incorporate the four pillars of SuDS including amenity, biodiversity and water quality.
The new guidance states that the layout of the whole development including the drainage layout should be considered at the earliest stages of the design as it is fundamental to the performance and affordability of the drainage system as well as the wider urban design including the character of the development, amenity, biodiversity, connectivity and use of the site.
Other key points in relation to the design and construction of new surface water drainage systems include:
- The successful design requires the designer to liaise with a variety of stakeholders from the earliest stages in the design of the development.
- The location of adoptable drainage components should take account of the need to provide appropriate access to each component for maintenance.
- Health and safety risks should be assessed and managed in accordance with Ciria C753 SUDS manual and a copy of the principle designers risk assessment submitted to the water company.
- Provided there is provision for the flows to reach a particular feature, surface SuDS features designed to take 1 in 100 year rainfall event plus climate change will normally be adoptable.
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