SRA Annual Report 2018-19: Urban Water Management (W3)
A unique 747-page review of Somerset’s Sustainable Drainage Systems (SuDS) has been published, and a contract let for the production of Somerset-specific guidance for property developers to help them create high quality SuDS at new sites across the county. A SuDS inspections service has been funded; responsibility for rain garden facilities in Taunton handed over; progress made on plans for a storage pond in Yeovil; and a second phase of works completed at Wirral Park balance pond and pumping station in Glastonbury.
In built-up areas, rain often falls on hard impervious surfaces such as roads, roofs and pavements so it runs off fast and cannot infiltrate into the ground. This can increase local flood risks. The SRA’s Urban Water Management lets partners focus on thorough, joined-up and distinctively local approaches to tackling flooding problems.
In 2018-19, this workstream’s outstanding achievement was the publication of a massive review of Sustainable Drainage Systems (SuDS) across Somerset. The scope of this SuDS Review is unmatched anywhere else in the UK. Locally, its findings are now being used to inform the production of Somerset-specific SuDS guidance for developers, funded by the SRA. Nationally, the review is providing an unprecedented level of hard evidence for ongoing debates about SuDs and stimulating widespread interest: see, for example, this blog by W3 leader Dan Martin on the industry-leading Susdrain website: https://www.susdrain. org/community/blog/somerset-suds-review/
As part of the review, 20 recently-built sites were inspected for Somerset Rivers Authority by Somerset County Council, working closely with Wessex Water, local planning authorities, district council drainage engineers, the Environment Agency, Somerset Drainage Boards Consortium and contractors JBA. Sites were assessed to ascertain whether they were adequately designed, constructed as designed, have any deficiencies, and are being adequately maintained. They included big housing estates, retirement apartments, industrial units and offices, an arts centre, and a hotel and pub. Run-off was considered in detail.
Generally, in terms of being able to cope with basic flows of water, and allowing for climate change, over three-quarters of the sites surveyed were satisfactory or better.
However, 6% were rated poor or very poor. In these cases, little was known about who was responsible for maintenance or what the maintenance regime should be. Inspections at some developments still being built showed inadequate site management practices, allowing sediment and pollution to enter surface waters. Individual defects were also identified, such as poorly- constructed permeable paving, non-native vegetation, and road and car park levels being higher than the entrances to properties, thereby raising the risk of water flowing into them.
Overall, the review showed that not enough is being done across Somerset to use SuDS to their full potential. SuDS are not just about managing the quantity of water, they offer wider benefits that enhance communities as a whole. They can play a key role in reducing pollution and improving water quality, make places much more attractive for people to live as well as creating habitats for wildlife.
The review found little evidence of consideration of water quality treatment in designs, although several sites did include features that would improve water quality. It also found little evidence of the deliberate provision of biodiversity and amenity benefits in drainage designs, and some sites had missed potential opportunities.
One example of good practice was Clarks’ Houndwood development in Street (pictured). This considered SuDS at an early stage, and incorporated SuDS into the design brief and through the master planning stage. It used surface SuDS features to provide amenity and biodiversity benefits, including reed bed channels, tree pits and bio-retention planters in public and semi-public amenity areas.
The SRA and its partners want to encourage more high-quality design and better place-making across Somerset.
Other W3 activities in 2018-19
An SRA-funded SuDS Inspections service has allowed local councils to check sites while they are being built. Learning lessons from the SuDS Review, team members have been fine- tuning checklists and reporting mechanisms.
Somerset County Council has let an SRA-funded contract for the production of Somerset-specific guidance for property developers, to help them create high quality, multi-benefit, integrated SuDS at new sites across the county. The guidance will incorporate specific requirements from all partners involved in the planning process and draw upon some of the challenges identified through the SuDS Review. The aim is to have detailed guidance completed by spring 2020 for adoption by Somerset’s Local Planning Authorities.
Responsibility for the maintenance of new rain garden facilities at Middleway and Kilkenny Court in Taunton was formally handed over to Taunton Deane Borough Council (as was; now Somerset West and Taunton Council). The SRA and Wessex Water funded the creation of several planters in 2017-18, to serve as small demonstrations of what could be achieved. Somerset County Council worked with Westcountry Rivers Trust on the planters, as part of the EU-backed Somerset Sponge 2020 project. The aim of Sponge 2020 is to encourage ‘innovative participatory adaptation solutions to reduce the risks of and damage from urban flooding… at considerably lower costs’. The SRA has been part-funding the development of Somerset County Council’s Sponge 2020 plans for car park retrofits in Taunton.
A second phase of SRA-funded improvement work has been completed by Mendip District Council at Wirral Park balance pond and pumping station in Glastonbury. This was built in 1989 to help to protect more than 200 homes and four hectares of industrial estate from flooding. The SRA previously funded the replacement of life-expired one-way flap valves and gate valves, and the removal of two skips full of silt and debris from the inlet channel. Now Wirral Park’s dated electrical control system has been updated to meet current regulations and to allow remote monitoring should the need arise.
In a Yeovil scheme supervised by FWAG SW for the SRA, Yeovil Rivers Community Trust (YRCT) has designed a pond in the grounds of Preston Academy, along the Preston Brook. This will help to reduce flooding downstream. It will also benefit pupils’ education and improve the area for wildlife. The school’s governors have approved the pond, subject to various conditions. It will need, for example, to be constructed over school holidays.
Above: An artist’s impression of the proposed Preston Academy pond by Yasmin Khan of Yeovil Rivers Community Trust.