Damning approach to catchment preservation
Rather than invest in expensive technology to tackle the growing problem of high-colour in the raw water entering five treatment works, Natasha Wiseman reports on a different approach being taken by Yorkshire Water
The decline in the quality of water reaching some of its reservoirs is thought to be as a direct result of the increasing degradation of surrounding peatland areas, which has led to rainwater picking up more break-away debris on its reservoir bound journey. As a result, the company was increasingly finding itself spending more and more money and time treating the highly coloured water entering a number of its major works, with no prospect of the problem abating in the near future.
Although extra treatment may be required in the short term, the company has decided that prevention is the way forward, and is tackling the source of the problem by managing local peatland. Two years of pre-monitoring work for the Oakfield project took place was completed in November 2010. Researchers from Leeds University mapped the moor and monitored water quality in the area to identify which areas generate the most colour and are most in need of restoration.
Yorkshire Water's catchment development leader, Andrew Walker, explained to WWT that Oakfield was the trial site because it is the only one of the five owned by Yorkshire Water. He said that liaison with tenants was absolutely key to the project working, especially balancing the needs of the water company with those of sheep grazing.
Walker said: "Where land is privately owned, it is my job to persuade people that catchment management is good for climate change and good for them. We need to demonstrate to private land owners that we have managed our own sites to the best of standards."
Restoration works for the Oakfield site took place in December and January. The main emphasis is to transform the vegetation from heather towards the original bog-forming species of cottongrass and sphagnum, which formed the peat in the first place. Man-made drainage channels, or grips, created for sheep grazing after the Second World War have caused a lowering of the water table and heightened erosion. Yorkshire Water is now using grip-blocking - a series of peat dams anchored into the drainage channels every 7-15m - to help slow run-off.
Ground penetrating radar is being used to identify 'peat pipes' under the ground. To stop erosion from the bottom up, interlinked recycled plastic piling is being inserted under the peat mass itself to intercept underground drainage. Helicopters were used to deliver the piling to the site on Keighley Moor, which is a Site of Special Scientific Interest, to minimise damage from vehicles. The piling and damming should direct the water through the aboveground vegetation, rather than through the peat, reducing erosion and stabilising colour in the long term.
Walker explained that keeping the water table higher slows the rate of aerobic breakdown of the peat - keeping it wet means destructive bacteria do not become dominant. Five years of post project monitoring is now under way in Keighley. But the full impact and cost benefit of the intervention may not be known for many years. Instrumentation to monitor the water table, temperature and vegetation analysis has been installed across the project area. The project team has now entered into negotiation with landowners at the other sites and implementation plans are expected to be ready by 2013 for the start of works. Walker is keen to stress the wider ecological and carbon benefits of the scheme.
"We recognise that we have the opportunity to make a huge difference to some of Yorkshire's most iconic landscapes by restoring them back to health, boosting local biodiversity and benefiting the thousands of visitors and user groups who currently derive enjoyment or income from them," he said. "Our work will also have wider environmental benefits too, as we'll be protecting and enhancing peatland which serve as some of the largest natural carbon reservoirs in the UK."
Now considered rarer than rainforest, concern is growing around the condition of heather peatland in the UK, with climate change experts forecasting it to become increasingly warm and dry in the UK over the next 50 years - the worst possible conditions for peatland to thrive. Dried up areas of peatland across the UK are now reckoned to release the equivalent of 10M tonnes of carbon dioxide every year - that's roughly the same as the emissions from a million households.
Ofwat and the Drinking Water Inspectorate have a sustainability duty and water companies now have to prove that a catchment solution would not work before extra treatment is considered. All water companies have put this into their plans. Yorkshire Water's efforts will no be closely observed by the whole industry. The company has employed the services of two specialists in moorland restoration, Penny Anderson Associates and Dinsdale Moorland Services, to carry out the work.