SRA Annual Report 2020-21: Sustainable Drainage Systems (SuDS)
Activities in 2020-21
SuDS guidance
Somerset-specific guidance on Sustainable Drainage Systems (SuDS) has been produced to encourage the creation of high quality, multi-benefit, integrated SuDS at new sites across the county. This project was led for Somerset Rivers Authority by Somerset County Council using contractors JBA Consulting.
Work in 2020-21 centred on the preparation of draft Somerset Local Standards for new housing developments, commercial properties and community facilities. New developments must not increase flood risks. They must also prepare for future climate change.
The Somerset Local Standards draw upon problems identified and lessons learned through the SRA-funded Somerset SuDS Review. Between 2016 and 2018, 20 recently-built sites were inspected for the SRA by the county council, working closely with SRA partners and contractors JBA Consulting. Sites included big housing estates, retirement apartments, industrial units and offices, an arts centre, and a hotel and pub. In total, 438 elements of 113 SuDS features were inspected.
The Somerset SuDS Review found that developers focus predominantly on matters concerning amounts of water, that is on water quantity. There was little evidence of developers actively considering water quality, biodiversity and amenity in their designs. Amenity means features such as paths for walking around SuDS or play areas making imaginative use of rainwater. Some sites had missed opportunities.
More could be done across Somerset to use SuDS to their full potential. The new Somerset Local Standards cover six main issues. These are:
- water quantity
- water quality
- biodiversity
- climate change
- amenity, health and safety
- maintenance and construction
The Standards set out key principles and specify requirements.
A technical example: the Lead Local Flood Authority (Somerset County Council) will “strongly resist” the use of deep bore soakaways as opposed to shallow infiltration SuDS techniques such as swales, basins, raingardens, shallow soakaways and permeable paving. This is because “deep bore soakaways are not an acceptable infiltration SuDS technique. They do not represent a natural drainage process and do not deliver the multiple benefits of SuDS”.
A long-term example: the question of who maintains SuDS has long concerned the SRA Board and the public. The Somerset Local Standards call for the production of a full maintenance and operation management plan for the entire life of a development. They state that records of all maintenance activities, including repairs and replacements, should be retained for as long as a development exists, because such records may help with statutory Flood Investigations. Developers should also explain how the operation and maintenance of SuDS will be affected by climate change over the lifetime of a development and how any impacts will be minimised. Wherever possible, SuDS should contribute to the aims and objectives for climate change mitigation and adaptation set out in the Somerset Climate Strategy Framework.
A community example: the Standards say that SuDS should be integrated as part of local landscapes and made accessible to people. Residents should be able to meet each other, play, exercise and enjoy nature. In practice this means creating more imaginative public spaces such as car parks and recreation areas. It means offering people chances to boost their health and wellbeing through features such as paths for walking around SuDS and play areas that make use of rainwater.
The Somerset Local Standards are due to be published by autumn 2021. As local government in Somerset may be reorganised, with one or two unitary councils being created, instead of the current county council and four district councils, the Standards’ formal adoption as supplementary planning guidance will be postponed until matters become more settled. The SRA and its partners also want to allow some time for people to work with the Standards as a kind of final prototype, to see if any elements could usefully be refined.
A comprehensive Somerset SuDS website is being created.
Four main groups of users are envisaged:
- property developers
- scheme designers
- council planners
- local communities
Subjects covered include:
- different elements of SuDS
- a detailed guide to the planning process for different kinds of developments, including the important pre-application stage
- design standards
- design challenges
- local design considerations (with special attention paid to Internal Drainage Boards, different districts, and Exmoor National Park Authority)
- case studies
- construction
- inspection
- operation
- maintenance
A section for residents describes how homeowners can play a role a role in bringing SuDS to Somerset, by, for example, replacing paved surfaces with ones which allow water to soak through.
SuDS inspections
Also following on from the Somerset SuDS Review, which noted some inadequate site management practices and site defects, an SRA-funded SuDS Inspections service has allowed local councils to check developments while they are being built.
This service is led for the SRA by Somerset County Council’s Flood Risk Management team, working closely with district council planners and experts seconded from the county council’s Highways Department.
Very few formal SuDS inspection processes are in place across England: Somerset is at the forefront.
Sites are inspected at various points, either through proactive engagement with developers, or by following up notifications from local planning authorities.
The aim is to ensure that SuDS are built and work as they were designed and approved through the planning process.
Local planning authorities have the power to enforce changes to constructed SuDS schemes, if need be.
SuDS inspectors check schemes for compliance against 16 different criteria. Scores are generally best for water quantity, design requirements, health and safety, and system blockages. They are more middling for water quality and structural components, and they are lower for biodiversity, materials, vegetation and future maintenance arrangements.
Developments recently inspected have been in the Taunton area, Beckington, Crewkerne, Ilton and North Petherton.
Somerset Sponge 2020
Between 2016 and 2020, the SRA part-funded Somerset County Council’s involvement in the EU- backed Interreg 2 Seas Somerset Sponge 2020 project. The county council was one of nine project partners based across the UK, the Netherlands and Belgium. Another was Westcountry Rivers Trust. The council and the Rivers Trust focused on Taunton.
The aim of Sponge2020 was to encourage ‘innovative participatory adaptation solutions to reduce the risks of and damage from urban flooding… at considerably lower costs’.
Given Taunton’s designation as a Garden Town, the county council collaborated with Somerset West and Taunton Council on the design and construction of additional SuDS at the Coal Orchard riverside redevelopment site.
In 2020, GreenBlue Urban tree pits were installed to bring water storage and water quality benefits. Tree pits protect trees’ roots and help them to become established and grow.
Good quality mature trees will be put into the pits as late as possible to minimise the risks of them suffering any damage from nearby building works. The trees will enhance the regeneration of this high-profile town centre site.
Highway SuDS retrofit trial
Eastwick Road in Taunton is being considered for a Highway SuDS Retrofit Trial. The planted chicanes or the grassed area at the bottom of the hill could show how some simple SuDS can deal with surface water and deliver more benefits than traditional drainage schemes.
The project is being led for the SRA by the County Council’s Flood Risk Management Team working in partnership with the Highways Department.
Design is scheduled for 2021-22, construction 2022-23.