A rainfall-runoff model based on the Soil Conservation Service (SCS) Runoff Curve Number method has been applied to the catchments draining to Omagh, Northern Ireland, to assess the potential effect of woodland creation on flood flows. Realistic woodland creation targets that would extend woodland cover to 13.8% of the catchment was predicted to reduce more frequent flood events (1 in 5 year) at Omagh by 13%, reducing to 8% for more extreme storms (1 in 100 year). The existing 6% woodland cover was predicted to be making a relatively small contribution to flood alleviation, decreasing peak flows by between 1% and 3% (for the 100 year and 5 year flood, respectively).

Modelled runoff maps were created for the different land use scenarios to allow identification of areas which generate the largest amounts of runoff. Unfortunately, the scope for woodland planting in these target areas was often constrained, requiring investigation of opportunities for improved management or suitability for other natural flood management measures. Where woodland creation is not possible, management of the existing land cover should be considered in order to help reduce runoff. This is particularly relevant on upland heather and heather-grassland for example, since woodland creation opportunities are very small on both land areas. Heather cover itself is effective at reducing runoff, having a high surface area, thus increasing evapotranspiration rates, and its root systems allows increased infiltration, compared to other land uses.

As with all modelling, the results need to be treated with caution since the SCS method remains to be validated for UK conditions. However the potential reductions in flood peak predicted lie within the range of values generated by other modelling studies and therefore add to the growing body of evidence that woodland creation and management may have a significant role to play in flood risk management. The SCS method provides a potentially powerful tool for evaluating the impact of land use change and management on runoff, as well as for identifying areas where such measures could be most effective.