The potential of runoff attenuation features as a Natural Flood Management approach

Natural Flood Management (NFM) is receiving much attention in the UK and across Europe and is now widely seen as a valid solution to help sustainably manage flood risk whilst offering significant multiple benefits. However, there is little empirical evidence demonstrating the effectiveness of NFM interventions in reducing flood hazard at the catchment scale. The Belford Burn catchment (~6km²) in Northern England provides a focus for this paper, and utilises observed data collected throughout the NFM project’s monitoring period (2007-2012). 
This study discusses the introduction of catchment-wide water storage through the implementation of runoff attenuation features (RAFs), in-particular offline storage areas, as a means of mitigating peak flow magnitudes in flood-causing events. A novel experimental monitoring setup is introduced alongside an analytical approach to quantify the impact of individual offline storage areas, which has demonstrated local reductions in peak flow for low magnitude storm events. Finally, a physically-based model has been created to demonstrate the impact of a network of offline storage areas to enable assessment of storage thresholds required to mitigate design storm events, thus enabling design of an NFM scheme. The modelling results have shown that peak flow can be reduced by more than 30% at downstream receptors.