Oxford Martin School research says claims that natural flood management can improve the worst floods are not supported by scientific evidence. Their research in the Proceedings of the Royal Society A concludes that natural measures to manage flooding from rivers can play a valuable role in flood prevention. However, a lack of monitoring means their true potential remains unclear.

Measures such as river restoration and tree planting aim to restore processes that have been affected by human activities like 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 their effectiveness and the scale needed to implement natural flood management measures successfully add to the uncertainty surrounding their benefits. Now a team of experts, led by Dr Simon Dadson of the School of Geography and the Environment at the University of Oxford, has compiled evidence on natural flood management to inform policy decision-making and show where there are still crucial gaps in knowledge. The article shines a light on the scientific evidence available from a variety of sources, ranging from field data to model projections and expert opinion.

One of the main problems that decision-makers face is that differences between catchments make it difficult to transfer evidence from one location to the other.

Dr Simon Dadson from the Oxford Martin School

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 that 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 showing their effect 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, are 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.'

His research publication calls for increased monitoring and better ways of measuring the effects of flood management, and a gathering of evidence within a comprehensive framework.

'Our message to Defra and the Environment Agency is that they need to establish more systematic large 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.'

Dr Simon Dadson is Associate Professor in Physical Geography at Oxford University’s School of Geography and the Environment. The Oxford coauthors on the paper are Professor Jim Hall, Anna Murgatroyd, and Edmund Penning-Rowsell, also from the School of Geography and the Environment.