6. SUDS
The WEWS Act makes provision explicitly for the vesting of sustainable urban drainage systems ( SUD systems or SUDS).
SUD systems are a relatively new form, or series of forms, of drainage, which has considerable environmental benefits. Best practice is to address what is now often called the SUDS triangle: the slowing of flows (related to flooding), reduction of diffuse pollution, and amenity (which may include nature conservation). SUDS can play a part in a sustainable flood management strategy, as identified by the Avoidance sub group of the Flooding Issues Advisory Committee ( FIAC), set up by the Scottish Executive in 2005 . The Executive is committed to promoting the use of SUDS, both in public open spaces and within private curtilages, and has given effect to this policy with the introduction of General Binding Rule 10 (d)(i) in the Controlled Activities Regulations (2005, amended in 2007).
In the WEWS Act, and thus for the purposes of the 1968 Act as amended, a SUD system is defined as a drainage system which "(a) facilitates attenuation, settlement or treatment from two or more premises (whether or not together with road water), and (b) includes one or more of the following: inlet structures, outlet structures, swales, constructed wetlands, ponds, filter trenches, attenuation tanks and detention basins (together with any associated pipes and equipment)". S33 of the WEWS Act inserts this definition into section 59(1) of the 1968 Act.
The SUDS concept is one of working with natural processes, and this is often contrasted with heavily engineered systems. A key concept of SUDS is of the "treatment train", whereby features are constructed at different stages on the source-pathway-receptor progression and combine to attenuate, settle and treat surface water.
This paper deals with the issue of public SUDS in their context. For SUDS to be a success in Scotland it is recognised that effective implementation must involve the co-operation of several bodies within an integrated planning framework. This issue is discussed in this paper, although it has been previously identified that there is a need for further constructive dialogue between all parties involved in SUDS; this is provided at national level by the Sustainable Urban Drainage Scottish Working Party ( SUDSWP). SUDSWP is convened by SEPA. Scottish Water, developers (through Homes for Scotland) and the Scottish Executive are represented; local authorities have representation through the Society of Chief Officers for Transportation in Scotland ( SCOTS).
Whereas water supply and "foul" sewerage have long been core functions of Scottish Water, and there are well-established arrangements for the adoption of such facilities, there are concerns about the vesting of SUDS.
- Scottish Water has concerns that poorly designed SUDS might have adverse effects on the rest of the drainage system for which they are responsible or that they will be committed to excessive maintenance costs; or that if the system does not function properly they may have to replace the whole asset.
- SEPA has concerns that poorly designed or constructed SUDS will be ineffective in their primary purpose of protecting the environment.
- Developers wish to have certainty that the SUD systems they construct to agreed standards will be adopted by Scottish Water and thus will function as useful components of the drainage systems managed by Scottish Water.
Scottish Water, through a firm of consultants, has commissioned a revision of the technical manual, SfS 2. The Executive does not consider that the manual can simply be put into regulations, but it would be practical for agreements between Scottish Water and developers to be based on the manual's requirements as regards SUDS.
The environmental protection provisions under the WEWS Act (specifically GBR 10 in Controlled Activities Regulations) require the use of SUDS for new developments. Whilst this requirement can be met by the provision of public SUDS serving a development, it is better if the technology is applied as close to source as possible (for example at each property or alongside roads): source control. Where public SUDS are provided by developers as part of a treatment train, the source control SUDS can reduce the size of, for example, a pond or basin that is to be vested in Scottish Water, and allow a more cost-effective drainage option.
Construction in Scotland is subject to the building regulations which prescribe mandatory standards, several of which control the design and installation of drainage systems within the curtilage of a building. The Scottish Building Standards Agency has a policy of continuous review of the standards and there is, at present, a Building Standards Advisory Committee Working Party in the process of reviewing the standards and guidance relating to flooding and surface water drainage.
Full details of any source control SUDS that connect directly to a public system, including drawings and calculations, together with maintenance provisions, should be supplied to Scottish Water by developers, for evaluation as indicated in SfS 2. This should enable Scottish Water to make an overall assessment of the drainage system, and it may indicate that enhanced source control would make a public SUDS more effective and acceptable.
The Executive proposes that:
- SUDS should be constructed to good industry standards, set out in the Sewers for Scotland 2 (SfS 2) manual, which is based on the same body of knowledge as is in the new SUDS Manual (C697) published by CIRIA.
- They should be designed and constructed to be cost-effective.
- If constructed in this way, where drainage is the responsibility of Scottish Water, public SUDS should be vested in Scottish Water.
- Details of any source control SUDS should be supplied to Scottish Water by developers, for evaluation, as indicated in SfS 2, of the whole drainage system.
QUESTION 2. Do you agree with this statement of policy? If not, what alternative would you propose? Are there any modifications or additions you would like to see?
QUESTION 3. Do you think the proposal for assessment of source control SUDS is likely to be an effective means of ensuring that the components of a drainage scheme which will not be vested (eg source control) are adequate?
The SUDS philosophy is to mimic natural drainage through the treatment train, a series of features from source control to receptor. Scottish Water is responsible for sewerage and thus for SUDS in public spaces. However, the SUD systems for which Scottish Water will be responsible will be affected by drainage facilities elsewhere. For instance, if source control is practised, it may be possible to limit the size of pond or other SUDS feature that is needed downstream. Similarly if there is an element of pre-treatment in the drainage from a road, there will be less of a diffuse pollution load in the public drainage facility. The Executive re-affirms that it is important that all parties responsible should contribute to the development of the SUDS treatment train.
Previous advice has been that the parties concerned in a SUDS development should meet at an early stage and agree on the form of SUDS that should be constructed as part of a development. Agreement is important, but it can be time-consuming, and the Executive would like to see standard procedures used to improve administrative efficiency.
Scottish Water is planning to bring the approval of SUDS designs and the vesting of these assets into their existing process for approval of sewerage infrastructure. The process entails issuing an approval letter, which covers both foul water and surface water sewerage. It is proposed that this be expanded to include SUDS systems. Developers would not need, and presumably would not wish to have, separate discussions for foul sewerage and surface water sewerage and SUDS. The Executive considers such an arrangement should be the standard situation: a developer designs (and constructs) SUDS for a new development in accordance with standards, normally those set out in SfS 2, which are consistent with the CIRIASUDS Manual (C697).
QUESTION 4. Do you consider that this proposal should be regarded as the standard situation and that it gives effect to the purpose of the provisions on SUDS in the WEWS Act? If not, what alternative would you propose to implement the intention in the Act's provision that arrangements should be made for the development and the ongoing maintenance of SUD systems?