The Multiple Benefits of the new CIRIA SuDS Manual (2015)

The CIRIA SuDS Manual details the latest research, industry practice and guidance on sustainable drainage. Its 2015 update is recognised by ICE’s Chris Binnie Award for Sustainable Water Management

The Manual emphasises why collaboration is important to delivering high quality places and open space.
The Manual emphasises why collaboration is important to delivering high quality places and open space.

Sustainable drainage systems (SuDS) are a critical part of the planning, design and implementation of green infrastructure.

CIRIA's new C753 SuDS Manual (2015) strongly emphasises the need for a collaborative approach in SuDS design. It demonstrates that using an interdisciplinary team up-front will support the delivery of multiple benefits.

This involves civil and drainage engineers collaborating with those involved in flood risk management at lead local flood authority level, plus highway engineers, ecologists, infrastructure and development engineers, urban designers, other spatial planners and professionals involved in the master planning, design and development process of open space.

The 2015 SuDS Manual is an update from the original 2007 edition. The update aimed to ensure that the Manual continued to:

  • be the key reference document for SuDS delivery in the UK
  • be used by decision-makers and practitioners
  • provide a comprehensive and up-to-date source of good practice in SuDS design, based on the latest R&D, experience and guidance available in the UK and internationally

The Manual is available on the CIRIA website, with 9,500 copies downloaded for free since its launch in November 2015. The project team's work in producing the update was recognised by the ICE Chris Binnie Award for Sustainable Water Management 2016.

Context

As our climate shifts and as urban populations continue to rise rapidly, the effective management of surface water runoff becomes of crucial significance to the future sustainability of our urban areas.

The philosophy of the new Manual is that drainage system design should always aim to:

a) maximise the benefits afforded by considering surface water as a valuable resource

b) minimise potential risks associated with its uncontrolled discharge to the environment

As a resource, surface water can add to and enhance biodiversity and the amenity value of buildings, places and landscapes. Incorporating water and vegetation into urban spaces can help reduce temperatures, reduce energy use and improve air quality – delivering urban spaces that are more resilient to the changing climate, healthier, safer and of higher value.

Integrating surface water management with areas serving other functions (such as recreation, transport corridors, traffic management and car parking) reduces costs and increases opportunities. Delivering these objectives is a fundamental part of the guidance.

The Manual is now established as the definitive technical resource for the planning, design, construction and operation of SuDS and is referenced widely in both national policy and local authority guidance. It covers the technical design criteria and evaluation of SuDS components, best practice planning, design, construction processes and long-term maintenance and management.

Background

The updated Manual was much anticipated in the UK, even more so after the publication of the non-statutory national standards in England. This left many feeling that SuDS were being undervalued by the current Government, and disappointed that Schedule 3 of the Flood and Water Management Act was not being implemented for England.

Both internationally and in the UK, industry is in no doubt of the value of SuDS and the importance of effectively facilitating their delivery. The government's intended review of non-statutory standards may present further opportunity over the coming months to consider the case for legislating SuDS, and how effective the local planning process has been in encouraging their uptake.

Making it happen

The breadth of the project steering group (56 members, plus contributions from a further 36 individuals) and funding bodies (19 organisations) reflects the manual's significance and its impact whilst demonstrating a recognised need across industry.

Participants ranged from drainage engineers to landscape architects, ecologists, highways engineers, urban planners, water utilities, environmental regulators, researchers, manufacturers, software companies and house builders.

The interdisciplinary authoring team was led by HR Wallingford with input from the Environmental Protection Group, Illman Young Landscape Design, Grant Associates and Ecofutures.

The authors had a strong mandate from the project steering group that they should not be swayed by current Government policy, but to focus on the overall objective of being the definitive guidance document on good practice, which would be equally relevant in all UK regions.

Taking account of current regional differences in policy, the updated Manual aims to bridge the gap between national standards/guidance and the realities of surface water management faced by decision-makers and practitioners throughout the UK. To support this it provides flow charts, check-lists, case studies, development "typologies" and a 50 page design example.

Using the SuDS Manual

Navigation of the Manual was a very important consideration, due to its sheer size and the need for different users to be able to readily access relevant information. Figure 1 represents the overall structure of the Manual and Figure 2 shows how key questions regarding SuDS design are answered by different chapters:

Figure 1: SuDS Manual Structure
Figure 1: SuDS Manual Structure
Figure 2: Key Questions
Figure 2: Key Questions
 

Principles and objectives of SuDS design

The overarching principle of SuDS design as defined in the Manual is that surface water runoff should be managed for maximum benefit.

The types of benefits that can be achieved are be dependent on the site, but fit broadly into the four categories shown in Figure 3.

For many years SuDS design was based around the SuDS triangle, which lumped amenity and biodiversity together. However, it was recognised that each had a very distinct objective, so they have been separated in order to encourage consideration of each.

Figure 3: The four pillars of SuDS design
Figure 3: The four pillars of SuDS design

Managing surface water runoff

The core of the Manual retains the fundamental reasons for managing surface water management:

Figure 4: Why managing surface water runoff is important
Figure 4: Why managing surface water runoff is important

SuDS and the planning system

The Manual recognises the need to better integrate drainage design into the planning process, if SuDS are going to stop being a last minute design detail and have only limited benefit. Figure 5 shows how this integration and alignment can be realised:

Figure 5: The drainage system design process: links with land use planning
Figure 5: The drainage system design process: links with land use planning

SuDS component sizing

The design of SuDS components to ensure appropriate peak runoff rate and volume control needs to consider a number of factors. The Manual provides clarity as shown in Figure 6:

Figure 6: Site and sub-catchment scale component sizing for outline design
Figure 6: Site and sub-catchment scale component sizing for outline design

Urban development typologies

A key requirement of the Manual was to provide a range of ideas for suitable SuDS design, as shown in Figure 7:

Figure 7: Examples of commonly used SuDS for different development types
Figure 7: Examples of commonly used SuDS for different development types

A set of nine typologies was developed to represent a range of urban conditions and to demonstrate the opportunities for integrating SuDS into their design. Figure 8 illustrates some of the potential opportunities for elevated spaces and Figure 9 for neighbourhood streets:

Figure 8: Typology 6 - Elevated spaces
Figure 8: Typology 6 - Elevated spaces
Figure 9: Typology 7 - Neighbourhood street
Figure 9: Typology 7 - Neighbourhood street
 

Checklists (Appendix B)

The Manual provides a series of checklists that can be used by designers or drainage system approving bodies to ensure that all relevant design, construction and maintenance considerations have been taken into account and documented in a consistent way.

Design example: Rosetree Estate (Appendix C)

The Manual provides a design example for a hypothetical site, developed to demonstrate the design process and the detailed hydraulic and treatment design of individual components.

The example works through the conceptual design of the scheme to meet the design criteria, as presented in the Manual, and sizing of a number of representative SuDS components. Figure 10 shows an overview of the site.

Figure 10: Overview of proposed SuDS components and Management Train
Figure 10: Overview of proposed SuDS components and Management Train

Conclusion

Internationally, the promotion and uptake of SuDS/Low Impact Development/Green Infrastructure is gaining significant momentum. These mechanisms are seen as crucial to future urban existence in light of climate change and population growth. The new Manual is already being referenced internationally and will help keep the UK at the forefront of design expertise in this field.

After an intensive three year work programme, the Manual was published on 12 November 2015. The launch was held at the House of Commons and included a keynote speech by Lord Krebs.

Achieving consensus on principles and good practice for SuDS delivery, and producing a document of this depth and scope, was an enormous task. The result is a unique piece of guidance that places collaborative planning and design at the heart of SuDS delivery, and extols the opportunities and multiple benefits that can arise from interdisciplinary collaboration and this approach.

Recognition that all have a role to play in delivering high quality places and open space will ensure SuDS is accepted as a key consideration at the outset of every development.

The SuDS Manual (2015) received the highly commended category of the ICE Chris Binnie Award for Sustainable Water Management 2016.

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