Assessment of the effectiveness of natural flood management in medium scale lowland catchments

Over the last decades, there has been much interest in natural flood management (NFM). However, there is still a lack of evidence on the effectiveness of NFM in general and particularly land and soil management based NFM in medium to large scale catchments. This study investigates the effects of soil and land management based NFM in the lowland Pang and Blackwater catchments in the UK. It uses the Soil and Water Assessment Tool (SWAT) to model the effects of broadscale land use and crop rotation scenarios on peak flows in selected catchments, while considering uncertainties. The broadscale land use scenarios consisted of the conversion of the catchments’ land to broadleaf woodland and cropland, respectively, except for water and urban areas. The results indicate that the NFM effects vary across the catchments and depend on landscapes characteristics. In addition, the blanket conversion to broadleaf woodland or cropland has a larger effect on small peak flows than on large floods such as those of January 9 and February 6, 2014. Afforestation leads to a reduction of 10 to 16% of the modelled 2014 winter flood events. In contrast, implementing crop rotation scenarios increases the peak flows, with the increase depending on the crops used and tillage practice. These findings suggest that via bespoke woodland planting and farming practices, combined with other measures that can reduce the amount of flow reaching the river channel or delay the timing of the peak flow (eg. leaky barriers), flood risks can be minimized. The results of this study provide information that can benefit future decision making on flood risk reduction in suitable catchments.