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 - including Professor Keith Beven and Professor Louise Heathwaite of Lancaster University - 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, the restatement clarifies the scientific evidence available from a variety of sources, ranging from field data to model projections and expert opinion.
Professor Louise Heathwaite, Lancaster Environment Centre, Lancaster University said: “Currently, there is limited evidence that natural flood management interventions work at scale but we must not lose sight of the co-benefits these interventions offer in terms of meeting important environmental goals, such as storing carbon, reducing soil erosion and boosting wildlife quality.”
“There is no silver bullet solution to flooding based on natural flood management, except perhaps at small scales and for smaller flood events. We need also to work towards helping people make themselves more resilient to flooding. There are good examples of people learning from their experiences and acting to reduce the impact of the next flood on their own home or business."
“Brexit could offer the chance to think afresh about the priorities for managing flood risk at scales relevant to the UK. It also provides us with an opportunity for joined-up thinking on the large scale opportunities for using and managing land across river catchments more effectively to respond to challenges such as increasing flood risk.”
Dr Simon Dadson of the University of Oxford, who led the expert team, 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.”