This paper describes a project to provide a succinct summary of the natural science evidence base concerning the effectiveness of catchment-based ‘natural’ flood management in the UK. While it is recognized that implementation of Catchment-Based Flood Management (CBFM) or Natural Flood Management (NFM) can produce multiple co-benefits, it is not easy to establish the precise nature and extent of those benefits. Often a complex set of trade-offs exists between costs and benefits that accrue to different stakeholder groups within and outside the catchment.
The aim of this restatement is to review the scientific evidence for the impacts of CBFM and NFM strategies on downstream flood hazard in the UK. This paper draws attention to some important evidence gaps and highlights the following immediate priorities:
- Maintenance and enhancement of monitoring systems should pay particular attention to the accurate measurement of high water levels and out-of-bank flows;
- It is important to investigate whether models' findings can be extrapolated to regions larger than those for which they have been evaluated;
- The lack of monitored baselines and experimental controls creates a risk that the wider and scale-dependent impacts cannot be properly investigated or used to inform decision-making;
- The performance, longevity and operation and maintenance of CBFM/NFM should be systematically compared with traditional engineering solutions;
- A practitioner toolkit would help to share practical experience (while noting context-specific issues), paying attention to appropriate design criteria;
- Improve communication and collaboration between groups undertaking research in river catchments (e.g. water quality, sediment transport, river restoration, biodiversity, agriculture and forestry), which are all relevant to flood risk management.