What impact do semi-natural woodlands have on flooding in the UK?

Flooding is one of the most costly and widespread climate-related natural hazards, causing substantial risk to communities across the UK. The frequency of flood events has increased and future climate change is expected to cause even more intense rainfall, further increasing the risk of flooding. In response, the interest in natural flood management, in particular woodland creation, has grown as a way of reducing flood risk by storing more water and slowing the flow of water across the land. However, despite well-known connections between woodlands and water there is still low confidence in using woodlands as a flood mitigation method due to limited empirical data, particularly for broadleaf woodlands and at the catchment scale.
This thesis examines the impact of woodland on flooding in the UK using a range of approaches including; field monitoring, laboratory experiments, modelling and data analysis. Field monitoring, implemented in Naddle, Cumbria, found small (< 0.2 km2) catchments consisting of semi-natural woodland exhibited more muted responses to storm events when compared to pasture catchments. Hillslope-scale overland flow velocity investigations found wood pasture dominated by bracken reduced overland flow velocity when compared with established semi-natural woodland. The extent and spatial distribution of woodland cover impacted peak discharge simulated for a 1 in 50-year storm using SD-TOPMODEL; cross slope and riparian woodland resulted in peak discharge reductions up to 3.93 % for a 10-percentage-point increase in woodland cover compared to catchment woodland. At the catchment-scale, land cover, with the exclusion of woodland, was found to be of significance to catchment active storage when flow data from the NRFA for 418 catchments across the UK was analysed. Although not significant, woodland cover still had high relative importance to catchment active storage. Overall, the findings of this thesis confirm that woodland has an important role in mitigating future flood risk, even at larger scales.