Water & Wastewater Treatment

TECHNICALLY SPEAKING Case study: River Roding catchment The upper catchment of the River Roding is a very rural area in the London Green Belt, where there is very little property or other development. If maintenance in this part of the channel is stopped, reeds and water vegetation will grow, trees will fall into the river and the flow of water will generally be slowed. In time of flood, this will slow the run-off of rain from the catchment and so reduce flood peaks in the river further downstream where it passes through the suburbs of London. As the river passes through east London, the reduced flood flows improve the standard of protection and there are more biodiversity gains to be had by reducing maintenance. Fortunately, despite the expansion of London through the last century, the flood plain of the River Roding has remained largely intact. This allows maintenance of some parts of the channel to be stopped, particularly in areas where the river has been over zealously canalised in the past to minimise flood risks. Modelling ies affected if maintenance was withdrawn Modelling showed that if these channels are allowed to develop naturally, without maintenance, there could be a reduction in flood risk to the surrounding properties because of the reduced flood run-off from the upper catchment. Of course the flood plain must be retained and all the bridges across it maintained to ensure there is a clear route for floodwaters down the river valley to where it joins the Thames. The Roding strategy is expected to reduce flood risk to over 900 properties and show a whole life cost saving of £40M. Although there are good efficiency and biodiversity gains through reduced maintenance, effects on the local community too need to be understood. In the Roding catchment, some properties will experience increased flood risk as a result of the new policy. The reasons for the change in maintenance spending and the possible effect on individual flood risk have been explained to all those affected. Guidance and support is being provided to help them make their own arrangements for flood protection. Responsibility d in the decision on how assets are maintained and paid for wwtonline.co.uk The transfer of responsibility for maintenance of any flood defence from public to private funding must be handled sensitively. Local landowners and the communities they belong to need time and help to adjust to their changed circumstances. Initially those affected are often angry, but eventually can usually be persuaded to start thinking constructively about how best to take responsibility for maintaining the defences. Withdrawal of maintenance can also have positive impacts on flood risk. In the River Roding that drains parts of east London and Essex in England, Black & Veatch has developed a strategy to reduce expenditure, reduce flood magnitude, improve flood protection and contribute to improving biodiversity. This work received the Environment Agency Project Excellence Award for Asset Management in 2013. Withdrawing public funding from flood defences is never a popular policy, nor is it a no-cost option, as it requires significant engagement with communities. Heavy demands of patience, perseverance and an understanding of the consequences for local communities are made on those required to implement this policy. This task can be made a little easier if communities understand their flood risk and the actions they can take themselves to minimise this risk. Community education plays an ongoing vital part of a sustainable flood risk management policy. Withdrawal of maintenance is an important tool in the armoury of a public body trying, with limited funds, to obtain the maximum benefit for society as a whole from its investment in flood defence. In a century when climate change is expected to increase flood risk, rationalising expenditure to concentrate on the most valuable assets is likely to become increasingly important. nnn January 2014 Water & Wastewater Treatment 29

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