Water & Wastewater Treatment

20 | march 2015 | WWT | www.wwtonline.co.uk Project focus: sustainable drainage the constraints of the landscape. While it only had limited SuDS spend- ing approved by Ofwat for AMP5 - £3M for three specific schemes - Welsh Water's conviction about the concept, combined with its ethos as a not-for-profit organisation, meant its board was willing to back an enlarged programme and provided £15M for the purpose. A thorough analysis of the sewer network and catchment using ad- vanced modelling techniques allowed O'Brien and his colleagues to identify where to concentrate their efforts. De- signers Arup and contractors Morgan Sindall are key partners in RainScape, and were involved throughout in de- veloping and implementing solutions. An early success was at Stebon- heath Primary School in the town, where permeable paving, strategically placed plant boxes and a redesigned playground featuring green elements were combined to achieve a dramatic reduction in surface run-off. Where previously run-off from the site would have been 53 litres per second in a one-in-five-year storm, it is now just 2 litres per second, and a total of 3 mil- lion litres a year have been removed from the sewer network. Completed in summer 2013 and costing £500,000, the scheme achieved a high level of community engagement, with chil- dren asked to play a part in the design process. "The headmaster, Julian Littler, was fantastic and is a very enthusias- tic champion; the school governors got engaged in this very quickly as well, and the children too," says O'Brien. "We were able to go in there and hold a session explaining what it was all about. We gave the children sheets of paper and asked them to draw a picture of what they'd like to see. We worried they'd come back with slides and swings and things, but they understood what we were doing immediately. The woodland walk, the pond, all these were things that they actually identified and were benefi- cial to what we were proposing to do. They have now become advocates for the idea of the programme and that engagement that we got there, that ownership, means that those assets should continue to operate well and look great for years to come." The programme's biggest piece of infrastructure so far is the £850,000 swale in Queen Mary's Walk. Com- pleted in Autumn 2013 and with a ca- pacity of 220 cubic metres, the gravel and grass swale takes water from five nearby road drains and slows its entry to the network with the help of plants and shrubs. It was designed to remove 4400 cubic metres of surface water a year via the natural process of evapotranspiration, but has been performing even better than expected, O'Brien explains. "We expected that figure to be met only once the planting that we put in there had matured, but in fact, it hap- pened immediately," he says. "Last winter, when we had terrible storms, we found that in the first 6/8 weeks of monitoring alone we took out nearly 4000 cubic metres of water. We were reducing the run-off from the area not by 75 litres a second, but by 95 litres per second. "We also found we could make further improvements to the design: the 100 ml pipe leading off the site was actually too big and was allowing water to drain out too quickly. So we put a flow restrictor in, and now we're getting an even better performance from the swale, the equivalent of 125 litres per second run-off reduction in a 1-in-5-year storm. Overall, it's taken 10,000 cubic metres of water out of the network through evapotranspira- tion in the first year, and that will improve further over the next 3 or 4 years as the planting matures." Retrofitting success Since then, RainScape has stead- ily progressed with street-by-street improvements. Basins, planters and grass channels have introduced more vegetation to the area and new pipework and channels have been put in just under the surface of roads to direct surface water to these new green spots. O'Brien says it is a myth that sustainable drainage requires big areas of green space to deal with the water: many of the new green addi- tions are only a square metre or two in size. In some cases, existing trees that were entirely surrounded by tarmac had their bases opened up so that flows could be directed towards them. Throughout the programme cus- tomer engagement was crucial, par- ticularly since many of the customers most impacted by the work were those with houses higher up in the catch- ment which are not directly affected by any flood risk. As well as holding six public exhibitions and five drop-in sessions about the plans, the project team has knocked on 1,000 doors and sent 8,500 letters to local people. "Because it's such a densely populated area and people don't have gardens or driveways, car parking was • Perspectives Emyr roberts, chief Executive of Natural resources Wales: "This scheme is a fantastic dem- onstration of how investing in our natural environment can produce multiple benefits. Greener spaces can help to provide long-term, sus- tainable solutions to the problems we face like flooding, water quality and climate change, and make our towns and cities better places live and work. This kind of natural solution in Llanelli is a blueprint where the natural environment can provide benefit to the community, the local economy and wildlife." construction underway for Queen mary's Walk Swale, which was completed in autumn 2013

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