What’s so interesting about changes to sewers?
Sounds dull, doesn’t it… but bear with us… within some new sewerage guidance, there’s potentially a substantial benefit to sustainable drainage systems (SuDS) that hasn’t been talked about nearly enough. We want to try and put it in plain English and let the world know!
New rules (April 2020) mean that SuDS elements such as swales, basins, soakaways, and ponds, are officially recognised as ‘surface water sewers’ and can be adopted by water companies in England.
This is potentially game-changing. The issue of adoption has been an historical barrier to many SuDS projects.
If we, as NFM and SuDS advocates and designers, can work effectively with landowners/clients and Yorkshire Water (or the relevant Water Company in the area), we can use the new rules to encourage the implementation and adoption of SuDS.
What was the problem with getting SuDs schemes implemented?
Educated parties have long recognised that SuDS elements are good things for the water management train overall. As well as contributing to flood alleviation, they provide additional Green Infrastructure benefits, such as air quality, amenity value, biodiversity. They generally cost less to build than traditional systems. So why wouldn’t they be everywhere?!
The issue has often been one of ongoing management and maintenance. In theory, the maintenance is simply that of looking after the landscape, which somebody would have to do anyway. Perhaps mow the grass, maybe clear a filter or de-silt once in a while, depending on the intervention.
However, landowners don’t want to take on what they might consider to be ‘additional’ maintenance of a drainage asset, whereas, if they discharge the water to a pipe in the ground it becomes somebody else’s (the water company’s) problem. Similarly, the water company didn’t want (or wasn’t allowed) to adopt a piece of landscape that normally would be maintained by the landowner. Only the most forward thinking of cash-strapped Local Authorities or Highways Agencies would adopt an asset that didn’t need to be their problem.
So, some of the very best designs fell at the final hurdle, because nobody was prepared to take long term responsibility for them.
How have we got to this point?
The Pitt Review in 2008 made recommendations that were taken up by The Flood and Water Management Act 2010 in an attempt to overcome the issues – including a presumption for SuDS, and ‘SuDS Approval Bodies’ (SABs) that would be responsible for their approval and adoption.
However, ‘Schedule 3’ ultimately wasn’t implemented, despite many local authorities doing all the work to set up SABs. This meant that the intended system, whereby local authorities would adopt SuDS systems, has never fallen into place (except in Wales, where, admirably, they have taken it upon themselves to implement Schedule 3: All new developments are now required to include Sustainable Drainage Systems which comply with National Statutory SuDS Standards. Developers must gain approval for their drainage from a SuDS Approval Body (SAB) before construction can begin.)
Water Companies have historically been able to “adopt” new sewerage assets built by others so that they become part of the national sewerage network and are looked after as such.
The water companies recognised that, since the last iteration of their ‘Sewers for Adoption’ (SfA) guidance, Schedule 3 had fallen by the wayside in England, and that the CIRIA SuDS Manual had offered a widely accepted new way of thinking about surface water management. They drafted a new version of the SfA guidance, to include the idea of adopting (taking over responsibility for) certain SuDS features by categorising them as ‘surface water sewers’.
The recently published documents have been enshrined as mandatory by the government (Section A2.8.), whereas previous SfA iterations have been voluntary), hence the confusing name change.
What are the changes, and how can SuDS schemes benefit?
The newly published Sewerage Sector Guidance documents (SSG) (1 st April 2020) contains ‘Appendix C – Design and Construction Guidance v2’ (DCG), which is the key document we are concerned with. (People who were used to the old ‘SfA’ format might refer to this as ‘Codes for Adoption’, ‘Sewers for Adoption’, or simply ‘The Code’, which the new lengthy title on the cover page acknowledges!)
Key points are as follows:
- Discusses holistic design, including the need for early involvement of all parties in the design process, i.e. thinking about SuDS at master planning stages (which is best practice anyway, but welcome!)
- Emphasises the role of the lead local flood authority (LLFA) and planning authority, in terms of dictating standards and determining maintenance arrangements. In our case both roles are held by Calderdale Metropolitan Borough Council (CMBC)
- Contains a long list of important definitions
- Reiterates the idea in previous guidance, that land drainage will not usually be adopted and ‘street’ (i.e. not connected with properties) drainage does not have to be adopted. It does say, however, that “acceptance of this (street) runoff into the works and, ultimately, the public sewer system, is only by agreement, which will not be unreasonably withheld”
Sets out the new definition of a sewer(bold = Slow The Flow (STF) emphasis):
“ a component is potentially adoptable as a sewer (or lateral drain) if all of the following apply (please note that this is a non-exhaustive list and not all structures that meet the following criteria will be adoptable):
a) it is constructed for the drainage of buildings and yards appurtenant to buildings;
b) it has a channel (a depression between banks or ridges with a definite boundary);
c) it conveys and returns flows to a sewer or to a surface water body or to groundwater;
d) it has an effective point of discharge, which must have lawful authority to discharge into a watercourse or other water body or onto or into land. As with conventional piped systems, this right to discharge must be secured by the developer and transferred to the sewerage company on adoption.” (C3.4)
– Draws attention to exclusions (bold = STF emphasis):
“The following components are not adoptable as sewers:
a) watercourses as defined in law (these include rivers, streams and can include some ditches);
b) components built primarily for the drainage of surface water from streets or for the drainage of land;
c) components built to manage groundwater;
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); and
e) components which are an integral part of the structure of a street (e.g., a pervious street or the channel formed by the kerb of a conventional road or a channel formed by a depression in the centre of a street). (C3.5)
– Acknowledges “Providing a route for adoption allows the four pillars of SuDS design to be properly considered and utilised, with the production of resilient surface water systems that integrate all four. This will enable new development to be more sustainable and deliver a wider range of multi-functional benefits.” (C3.3)
The following table, based on that in section 7 of the CIRIA SuDS Manual, considers potentially adoptable components according to Part C:
|SuDS component type||Description||Adoptable?|
|Rainwater harvesting systems||Rainwater is collected from the roof of a building or from other paved surfaces in an over-ground or underground tank for use on site. Depending on its intended use, the system may include treatment elements. The system should include specific storage provision if it is to be used to manage runoff to a design standard.||No|
|Green roofs||A planted soil layer is constructed on the roof of a building to create a living surface. Water is stored in the soil layer and absorbed by vegetation. Blue roofs store water at roof level, without the use of vegetation.||No|
|Infiltration systems||These systems collect and store runoff allowing it to infiltrate into the ground. Overlying vegetation and underlying unsaturated soils can offer protection to groundwater from pollution risks.||Yes|
|Proprietary treatment systems||These subsurface and surface structures are designed to provide treatment of water through the removal of contaminants.||Yes|
|Filter strips||Runoff from an impermeable area is allowed to flow across a grassed or otherwise densely planted area to promote sedimentation and filtration.||No|
|Filter drains||Runoff is temporarily stored below the surface in a shallow trench filled with stone/gravel, providing attenuation, conveyance and treatment (via filtration).||Yes|
|Swales||A vegetated channel is used to convey and treat runoff (via filtration). These can be “wet”, where water is designed to remain permanently at the base of the swale, or “dry” where water is only present in the channel after rainfall events. It can be lined, or unlined to allow infiltration.||Yes|
|Bioretention systems||A shallow landscaped depression allows runoff to pond temporarily on the surface, before filtering through vegetation and underlying soils prior to collection or infiltration. In its simplest form it is often referred to as a rain garden. Engineered soils (gravel and sand layers) and enhanced vegetation can be used to improve treatment performance.||Yes|
|Trees (within other SuDS components)||Trees can be planted within a range of infiltration SuDS components to improve their performance, as root growth and decomposition increase soil infiltration capacity.||Yes|
|Trees (on their own)||Alternatively they can be used as standalone features within soil-filled tree pits, tree planters or structural soils, collecting and storing runoff and providing treatment (via filtration and phytoremediation).||No|
|Pervious pavements||Runoff is allowed to soak through structural paving. This can be paving blocks with gaps between solid blocks, or porous paving where water filters through the block itself. Water can be stored in the sub-base and potentially allowed to infiltrate into the ground.||No|
|Attenuation storage tanks||Large, below-ground voided spaces can be used to temporarily store runoff before infiltration, controlled release or use. The storage structure is often constructed using geocellular or other modular storage systems, concrete tanks or oversized pipes.||Yes|
|Detention basins||During a rainfall event, runoff drains to a landscaped depression with an outlet that restricts flows, so that the basin fills and provides attenuation. Generally, basins are dry, except during and immediately following the rainfall event. If vegetated, runoff will be treated as it is conveyed and filtered across the base of the basin.||Yes|
|Ponds and wetlands||Features with a permanent pool of water can be used to provide both attenuation and treatment of runoff, where outflows are controlled and water levels are allowed to increase following rainfall. They can support emergent and submerged vegetation along their shoreline and in shallow, marshy zones, which enhances treatment processes and biodiversity.||Yes|
What does Yorkshire Water say?
Our own Yorkshire Water appears to be completely on board, and encouraging of this new approach. Information at https://www.yorkshirewater.com/developers/sewerage/sewer-adoptions even includes guidance on retrospective sewer adoption – i.e. landowners could apply for Yorkshire Water to adopt SuDS elements that are already built.
The language of their ‘Developers Guide to the Adoption and Vesting of New Sewers (S104)’ is encouraging:
“There are many types of SuDS components, which means that sustainable drainage can be delivered anywhere. A developer can choose a number of different SuDS components and tailor the overall composition of an adoptable surface water scheme to the local context.”
We are pleased to note that Yorkshire Water is enthusiastic about implementing the new guidance. They have told us that they are training staff to ensure that they are capable of dealing with SuDS systems, and are encouraging developers to think about SuDS at early stages of design, including having an ‘open door’ to discussing proposals with developers at any stage.
What does Calderdale Council say?
CMBC have appointed one of the UK’s first NFM officer roles, which is welcome and indicative of the organisation’s support for SuDS and NFM. We at STF are trying to help them to ensure that this support is understood and embraced throughout their large organisation.
CMBC have produced a draft Flooding Supplementary Planning Guidance (Flooding SPG) document, to accompany the emerging Local Plan, which STF has been able to have some input into, and goes some way to encouraging SuDS.
The flood team at Calderdale Council have said:
“We welcome the new DCG and will be working with the Planning team to review our Flooding SPG to maximise the potential for incorporating SuDS in developments that can meet the standards for adoption by Yorkshire Water.”
How can we make sure that this potentially bright future is a reality?
The opportunity has been created, it is now necessary for local authorities, designers, developers, and water companies to embrace the change. Locally, we have a strong group of willing parties in Calderdale. We need to ensure that all are well educated and aware of the issues.
“The NPPF gives an expectation that sustainable drainage systems (SuDS) should be used as first preference in developments of any size. The Ministry of Housing, Communities and Local Government (MHCLG) has also issued practice guidance to support the NPPF in a number of areas.” (SSG DCG C1.6.)
The Planning system will be a useful tool in implementing the changes. From the NPPF downwards, there is a presumption in favour of SuDS. Now we have a new system to help overcome the biggest historical hurdle and make widespread urban SuDS a reality.
We hope that CMBC will be able to amend their flooding SPG to make clearer that locally, the requirement for SuDS applies to all developments (not only those over 10 houses, and in Flood Zone 2 and 3), and perhaps make other amends to refer explicitly to the new SSG DCG, in order to encourage more developers to implement adoptable SuDS.