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Natural measures to prevent floods valuable but not ‘a silver bullet’, say researchers



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Oxford Martin restatement finds claims that natural flood management will alleviate the worst floods are not supported by scientific evidence

Natural measures to manage flooding from rivers can play a valuable role in flood prevention, but a lack of monitoring means their true potential remains unclear, researchers say.

Such measures, including river restoration and tree planting, aim to restore processes that have been affected by human activities such as farming, land management and house-building.

Natural flood management is an area of increasing interest for policy makers, but its implementation can present a complex balancing act between the needs of different groups, including the public, farmers and land owners. Mixed messages about the efficacy and scalability of natural flood management measures add to the uncertainty surrounding their benefits.

Now a team of experts, led by Dr Simon Dadson of the University of Oxford, has compiled the evidence on natural flood management, in order to better inform policy decisions and show where crucial gaps in knowledge lie. Published today in the Proceedings of the Royal Society A, the restatement clarifies the scientific evidence available from a variety of sources, ranging from field data to model projections and expert opinion.

Dr Dadson said: “Flooding is an extremely costly natural hazard in the UK, and we expect it to increase in the future as climate change leads to more extremes in our weather. The period between 1960 and 1990 was relatively flood-poor compared with what we’ve seen since and with what we are likely to see in the future.

“What we’ve found is that when it comes to natural flood management, there are some interventions for which there is very strong evidence, but these tend to be in small-scale river catchments. One of the main problems decision-makers face is that differences between catchments make it difficult to transfer evidence from one location to the other – and we don’t yet know whether the effects in small catchments can be extrapolated to larger ones.”

The authors say natural measures have proved useful at preventing flooding after minor rainstorms, and can be a worthwhile component of a larger package of flood prevention measures. For measures such as tree planting that aim to change the way rainfall runs off the land, the evidence of the impact on flooding is mixed. Meanwhile, measures to restore natural floodplains by “making room for the river”, for example by removing flood walls and other obstacles, have been shown to reduce flood water levels.

“There are always going to be some extreme floods, like we saw after Storm Desmond, that are simply overwhelming”. said Dr Dadson. “Natural flood management can help if implemented well in carefully chosen locations, and it can bring important benefits to landscapes and wildlife, but it’s not a silver bullet for the problem of flooding.”

The restatement calls for increased monitoring and measurement of flood management impacts, with evidence gathered within a comprehensive framework.

“Our message to Defra and the Environment Agency is that they need to establish more systematic large-scale surveys and monitoring programmes, and feed natural flood management into planning at the catchment scale” added Dr Dadson. “It’s also really important that catchment-based schemes that have been instigated by communities and local wildlife or river trusts are monitored and evaluated so that the right lessons can be learned for the future.”

  • Download the full paper, A restatement of the natural science evidence concerning catchment-based ‘natural’ flood management in the United Kingdom

  • Dr Simon Dadson is Associate Professor in Physical Geography at Oxford University’s School of Geography and the Environment. His co-authors are Jim Hall and Anna Murgatroyd, University of Oxford; Edmund Penning-Rowsell, University of Oxford and Middlesex University London;  Mike Acreman and Nick Reynard, Centre for Ecology & Hydrology, Wallingford; Paul Bates, University of Bristol; Keith Beven and Louise Heathwaite, Lancaster University; Joseph Holden, University of Leeds; Ian P. Holman, Cranfield University; Stuart N. Lane, University of Lausanne; Enda O’Connell, Newcastle University; David Sear, University of Southampton; Colin Thorne, University of Nottingham; and Rob Wilby, Loughborough University.

  • Oxford Martin Restatements review the natural science evidence base underlying areas of current policy concern and controversy. Written in policy neutral terms and designed to be read by an informed but not technically specialist audience, restatements are produced by a writing team reflecting the breadth of opinion on the topic in the science community and involve wide consultation with interested stakeholders. The final version of the restatement is peer-reviewed prior to publication. For more information visit http://www.oxfordmartin.ox.ac.uk/policy/restatements/