Strathard ecosystem services project : Assessing the effect of implementing Natural Flood Management measures in the Duchray Water catchment

The Strathard Ecosystem Services project aims to achieve multiple benefits of land and water management; by identifying opportunities within the Strathard Project area to influence forest and land management operations and design to reduce flood risk. A key goal of the partnership is to slow the flow in the Duchray Water catchment, using natural flood management. The catchment was modelled using the Soil Conservation Service (SCS) Runoff Curve Number method to assess the impact of implementing Natural Flood Management measures on flood flows. Suitable reaches for NFM measures such as instream debris dams and floodplain storage areas were identified in the catchment using GIS techniques. If all the NFM measures were implemented in the catchment (some 448 debris dams, 18 ha of floodplain storage, and 70 ha additional storage in the catchment), as much as a 20% decrease in peak flows was predicted for more frequent 1 in 5 year rainfall events while a slightly lower 16% decrease was predicted for more extreme 1 in 200 year events. A 5% increase in catchment storage volumes were predicted, while peak timing increased by as much as an 1 hour 7 minutes for a 1 in 5 year rainfall event, to 53 minutes for a more extreme 1 in 200 year event. These numbers need to be treated with caution since the SCS method remains to be validated for UK conditions, however they support growing evidence that woodland creation and management could have a significant role to play in flood risk management.