WET News

wwtonline.co.uk | MAY 2018 WET NEWS 9 Natural flood defences offer added benefits W e have always modi- fied our rivers to grow food, generate energy and harness water supplies. In most cases, changes to river catchments have been car- ried out to meet the specific needs of the local population or nearby urban centres. There has rarely been holistic catchment planning that sup- ports a joined-up strategy across a river basin to tackle multiple yet interlinked issues such as water quality, biodiver- sity and risk of flood and drought. The increasing impacts of cli- mate change and development pressures for new housing mean it is more important than ever to properly integrate our approach. More holistic man- agement of catchments will help us protect and improve our natural environment and ensure we can support eco- nomic growth. Working with natural pro- cesses, also known as nature- based solutions (NBS), will be key to integrated catchment management. In practice, this means working to enhance nat- ural hydrological processes in a small-scale way that also has other positive impacts. In the UK, the main economic driver behind this is currently flood alleviation. The Environ- ment Agency recently pub- lished new guidance on natural flood management to reduce flood and coastal erosion risk by "implementing measures that help to protect, restore and emulate the natural functions of catchments, floodplains, riv- ers and the coast". But working with natural processes will bring wider envi- ronmental and societal benefits which may even outweigh the benefit in flood risk reduction. It can take many different forms and applied in both urban and rural areas. Examples include planting trees on hillsides which will 'roughen' the landscape, mak- ing it harder for water to flow straight downhill. As a result, more water will filter down into aquifers. The leaves on trees also intercept rain as it falls, meaning more water evaporates before reaching the ground. The wider benefits here are improved water quality – cross- slope woodlands can filter out sediment and nutrients in run- off – carbon sequestration and the creation of new woodland habitats. Similarly, creating buffer strips alongside watercourses will roughen the river corridor, making water in streams flow more slowly. It will be then less likely to converge on towns downstream and peak flood levels could be reduced. The added value of this approach is that the strips will help filter out nutrients in run- off and if fenced can stop live- stock damaging the channel banks which leads to sediment and water quality issues down- stream. It will also provide a corridor where nature can thrive, linking together a land- scape that is oŽen fragmented for flora and fauna. Moorlands in upland areas of northern England have been drained by digging artificial channels to dry them out, oŽen to boost the grouse population on shooting estates. This has resulted in water flowing a lot faster off the moors, severely degrading and eroding the peat. The water is also heavily dis- coloured. With many water supply reservoirs located downstream of peat moorlands, water companies have to spend a lot of money on removing this discolouration. Blocking moor- land drains will therefore reduce sediment run-off, pro- tecting what is a very important store of carbon, and may even help to lower customer bills. Two methods that will improve biodiversity as well as reducing and delaying flooding downstream are so-called 'leaky' dams, small-scale engi- neered features on streams that hold back water during periods of heavy rainfall, and modifica- tions to the channel or flood- plain to allow more flood water to be stored on the floodplain. In the case of the latter, this could include a structure in the channel to deflect river flow onto the floodplain and/or structures across the floodplain to trap deeper floodwater. All these ideas have been proposed before. But what is new is a growing realisation that linked benefits can be attached to each one, giving multiple benefits across the hydrological cycle and through- out a river basin. It shows what we can achieved if all stakeholders work together – the co-opera- tion of farmers and landowners will be especially important. Working with nature will help us to manage extreme drought and flood risk, as well as improving the water quality and geomorphology of our watercourses to allow rivers and their catchments to sup- port a more diverse and abun- dant array of wildlife and plantlife. Communities involved in nature-based solutions will be more resilient to climate change and better places to live. This will support the govern- ment's vision that we become "the first genera- tion to leave our environment better than we found it since the Industrial Revolution". OPINION • Working with natural processes will not only reduce flood risk but also bring wider environmental and societal benefits, writes Emma Wren, principal hydrologist at Mott MacDonald Wedeco Spektron UV Wedeco LBX UV Reactors Sanitaire Aeration Grids Hydroejectors & Radial Aerators Flygt Jet Aerators & Mixers Flygt Mixers AVAILABLE FROM XYLEM WATER TREATMENT 24/7 HIRE RAPID BESPOKE DESIGN SOLUTIONS DIRECT FROM THE MANUFACTURER FOR ULTIMATE PEACE OF MIND • Cost effective temporary treatment installations • Plant refurbishments | Repairs | Seasonal Overloads Drought Alleviation • Portable containerised systems available for larger projects • Planned, bespoke and reactive maintenance solutions • PLUS monitoring, control and analytical equipment also available 0845 707 8012 fgb.rental@xyleminc.com | www.xylem.com/uk flygt_sanitaire_wedeco treatmentl advert aug 2017_Layout 1 04/08/2017 15:18 Page 1

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