On stream: the leisure services unit at Borough of Poole in Dorset have been trialling and developing sustainable drainage systems (SUDS) techniques in its public open spaces since 2000.
Project: Retrofitting sustainable drainage systems in an urban catchment
Project Team: The Bourne Stream Partnership
The locally renowned Bourne Valley dragonflies can claim responsibility for the first SUDS in Poole. The council's nature conservation team was keen to take every opportunity to enhance the valley's stream and heathland habitat at a time when the achievements of SUDS projects abroad, and to some extent in Scotland, were just beginning to be discussed at a local level. The timing also coincided with an Environment Agency R&D project which viewed the Bourne Stream as an opportunity to better understand how SUDS might be retrofitted into a small, densely urbanised catchment, and the associated maintenance and cost implications. The Bourne Steam Partnership was formed and, working with a flexible but relatively small SUDS budget, has in the last eight years managed to create five systems of varying capacity, design and purpose.
The Bourne stream is a narrow, steep and heavily modified watercourse flowing just seven kilometres through a shallow valley from Canford Heath in Poole, to Bournemouth Pier at one of the south coast's premier resort beaches.
A relatively extensive length of the stream runs in culverts and it is the receiving waterbody, via 62 discharge points, for the surface water drainage of a heavily urbanised catchment of some 12[km.sup.2].
During heavy rainfall, flow increases quickly and dramatically as water discharges into it from surrounding roads and other impermeable surfaces. At the same time its pollutant loading increases sharply and localised flooding is common. Other impacts include occasional discharge from combined sewage overflows (CSOs) and grey- and black-water misconnections in residential developments.
Lagoons and wetlands
The first of the SUDS was created in March 2000, in a little-visited, low-lying and naturally boggy area in the upper reaches of the stream catchment, immediately downstream of the busy A35 commuter route. In approximately one hectare of what was once Dorset heathland, and at a cost of approximately 7000 [pounds sterling] total, trees were felled, a series of five on-line lagoons excavated and the run-off from surrounding highways diverted into them. Originally planted with 450[m.sup.2] Phragmites australis (Common Reed) which was soon eaten by the two ponies that graze the area, they have now been colonised by Typha latifolia (commonly known as Reed Mace).
In March 2001 a shallow off-line wetland was constructed a short distance upstream of the lagoons, in an area measuring some 2500[m.sup.2]. The wetland now provides initial treatment for the highway run-off from the A35, and is intended to deal with first-flush waters containing a high level of pollutants. On leaving the wetland area stream water is diverted into the lagoons for further treatment.
The lagoons and wetland were created at a time when design guidance was thin on the ground and as Poole's Capital Works Manager, Stuart Terry, explains: "At the time there were no readily available design criteria in the UK. The best advice was collected from websites in the US and Scandinavia. Saying that, we approached this project believing that anything we did would be an improvement and the physical site restrictions from such things as gas mains, foul sewers and ground levels actually dictated the size and shape of the end result".
The partnership's Project Officer, Sarah Austin adds: "The first SUDS were a learning curve for everyone involved. Much of the valley is of national and international importance and designated SSSI and SPA. Neither Natural England nor I wanted any concrete used in the design of these SUDS and Poole's engineers have been very open minded to developing a 'soft' approach to engineering works. On subsequent projects, however, I have come to appreciate the inherent energy of fast-running water, and we have had to compromise in some areas where the stream channel and SUDS design was under threat of erosion".
It's an approach that appears to work; Environment Agency analysis of water quality downstream of the SUDS in 2003 showed that 'significant decreases' in levels of faecal coliforms, ammonia, BOD and suspended solids had been achieved. Separate surveys and regular monitoring also revealed benefits in terms of wildlife habitat, particularly for birds and dragonflies, and public enjoyment of the area. There are insufficient studies into the treatment of highway run-off (hydrocarbons) for the partnership to comment on its success in this area.
Work on the SUDS produced a further, unexpected benefit too. During tree clearance, the team discovered an old and leaking foul sewer, which is understood to have been overspilling into the watercourse for some time and was able to rectify the problem.
Since completion the project regularly attracts interest from Bournemouth University's School of Conservation Sciences, with students annually monitoring and evaluating the ecological success of the SUDS.
In the public arena
Three further projects followed the success of the lagoon and wetland, two of which had a significant impact on the amenity value of local open spaces and required the 'education' and support of residents. The latest, and most extensive of these has taken more than three years to achieve, the first half of which was simply spent in consultation with the local community and other stakeholders, and hunting down the necessary 175,000 [pounds sterling] funding. The project involved the transformation of 15 hectares of low-lying (often waterlogged), abandoned sports pitches in the centre of a densely populated area in Alderney, Poole and between two large schools. Finally completed in October 2007 and, since renamed 'Bourne Valley Park', the new landscape features what the public enjoy as a reinstated (deculverted) stream, 800m of footpaths and cycleways, seating, litter bins and a small fishing lake. In essence, however, it is a large stormwater storage system which detains some 3500[m.sup.3] of water and, to date, appears to help prevent flooding of residential property downstream.
In a neighbourhood known to experience higher than average levels of social problems, the project links communities and gives them a focus for recreation and informal play. Several community members have already taken ownership of the project, acting as informal 'wardens' for the watercourse, new amenities and the fishery. There has been a huge increase in usage by local people of all ages and plans are being made for a programme of summer events and angling coaching and competitions for the under 16s.
A large part of the funding was provided by Bourne Stream partner organisation Wessex Water who embraced the opportunity to address local flood risk in an integrated and relatively inexpensive way. The length of stream that now takes the place of what was a surface water sewer, has been adopted by the local council as part of the deal.
Excavations were complicated by the fact that the culvert lay on average two metres below the ground level due to the fact that the area had been landfilled in the 1970s. Trial holes were dug throughout the site, confirming the belief that the landfill comprised inert materials, so there were no worries about contamination. Nevertheless, surely a shallow (in dry weather) stream running two metres below the grassland areas is hardly an attractive prospect? Not so explains Sarah, "It was a concern at first, but Environment Agency and other stream restoration guidance recommends a wide 'terraced' channel offers a good degree of stability and allows for a variety of marginal vegetation. This suited our needs well, and we had the space to do it. The stream channel is 21m wide at the top, and the terracing at the one metre mark has created an informal stream-side walkway for those that like to be close to the water".
Apart from transplanting some heathland turfs from the nearby Canford Heath, which have already bedded in well, and some Yellow Flag Iris donated from neighbours' own gardens, nature has been left to do her own thing. The project team and residents have enjoyed watching the various habitats evolve in the past 14 months, and the wildlife that has been attracted to it. The lower stream channel now boasts quite a variety of aquatic vegetation. "We will need to ensure it's properly maintained though, because there's a risk the channel will become over-vegetated which will spoil things for those that enjoy the open water aspect" continues Sarah.
Another consideration when excavating a stream channel and lake is what to do with the spoil. In recent years it has become increasingly expensive to transport it off site. At Poole there was a large quantity of rubble to remove, but soil was reused to regrade other areas of the park and to form a 'viewpoint' at one end of the park, from where visitors can enjoy a long view of the entire site, with the Bourne Valley Nature Reserve in the distance.
Further contributions for Bourne Valley Park were supplied by Poole council's S106 Planning Obligations funding and by the Environment Agency's anglers rod licence income (for the fishing lake). Much of the cost of the footpath network, the seating, litter bins, planting and interpretation came from Biffaward, an environment fund managed by the Royal Society of Wildlife Trusts (RSWT), which utilises landfill tax credits donated by Biffa Waste Services.
Cllr Peter Adams, Cabinet Portfolio Holder for Leisure and Culture, Borough of Poole, said: "This project has made a valuable and quite unique contribution to one of the largest open spaces in Poole, changing its use for local people and enhancing it for wildlife. If it wasn't for the enthusiasm of local residents and ward councillors, and the willingness of the funding partners to take on something really different, this site would never have achieved its full potential."
All SUDS projects in Poole have been accompanied by public awareness initiatives with local communities and school children, from a 'Use Water Wisely' drive with the local water company, to a two-year 'Yellow Fish' campaign. Yellow Fish is an idea 'imported' from Canada and Australia, involving the spray painting of a yellow fish design beside road gullies. Leaflets distributed throughout the neighbourhoods targeted impress upon residents that the 'drain is just for rain' and that oil, soap suds and other pollutants entering gullies is carried directly to the stream. This has been an important message for the project; early research in the catchment revealed that more than 55% of local residents believed road drains led to a water treatment plan, while 20% hadn't thought about it.
The SUDS projects completed in the last seven years deal with diffuse pollution within the stream's upper catchment in Poole, but 30% of the watercourse lies downstream in Bournemouth where it flows through formal English Heritage grade II* listed gardens. Creating space-hungry and 'naturalised' SUDS in these open spaces will be more problematic than anything carried out so far. There are some that are not keen to see the formality of Bournemouth's popular gardens compromised and any work is likely to be an 'end-of-pipe' solution which would aim to spill peak flows overland to deposit suspended matter during heavy rainfall and flood events.
Until then, diffuse pollution will continue to be an issue in the Bourne Stream but good results have been achieved in terms of localised stream water quality and Poole's residents continue to reap the benefits of the improvements to their recreational spaces.
Borough of Poole contacts: Sarah Austin, Project Officer, on 01202 261325 or email@example.com
Stuart Terry, Capital Works Manager on 01202 261329 or firstname.lastname@example.org
The Bourne Stream Partnership comprises 11 local public/ private organisations--Borough of Poole, Bournemouth Borough Council, Environment Agency, Bournemouth & West Hampshire Water, Wessex Water, Natural England, Bournemouth University, Dorset Wildlife Trust, Dorset Coast Forum, Bournemouth Oceanarium and Greenlink.
Detailed project information at www.bournestreampartnership. org.uk
Sarah Austin spent 25 years in sales & marketing before turning her career completely on its head to become a mature student at Bournemouth University. In 2002 she was awarded a Masters Degree in Coastal Zone Management and the next four years was spent with the Bourne Stream Partnership. Since 2006 she has continued work on partnership projects as part of her remit as Project Officer with the Borough of Poole's Leisure Services unit.
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|Date:||Mar 1, 2008|
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