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Evidence that intensive farming leads to increased runoff rates has been established. Fast, well connected flow paths are clearly contributing to the 'muddy floods' observed at the local scale. By targeting runoff in fields and farm ditches then a significant component of flood generation can potentially be managed at the catchment scale. The Belford Burn (Northumberland, UK) catchment is a small rural catchment with a catchment area of 6 km 2. Normal flood defences are not suitable for this catchment as it failed the Environment Agency (EA) cost benefit criteria for support. There was a desire by the local EA Flood Levy Team and the Northumbria Regional Flood Defence Committee at the Environment Agency to deliver an alternative catchment-based solution to the problem. Four different types of mitigation feature have been created in the catchment to reduce flood risk whilst also benefiting water quality and ecology. These measures include bunds disconnecting flow pathways, diversion structures in ditches to spill and store high flows, 'Beaver dams' placed within the channel and riparian zone management. Evidence collected from these features, along with construction advice and management issues, has helped to create the first draft of a Runoff Attenuation Features Handbook.

There is increasing interest in distributing small-scale interventions across the landscape as an alternative means of reducing flood risk. One such intervention, the leaky barrier, is introduced in channels to slow down high flows and encourage temporary storage on the floodplain. While these barriers have been implemented widely, there is still resistance to their use at the scales required to impact significantly on flood risk, at least partially due to an evidence gap. In particular, there is no standard method for representing leaky barriers in hydraulic models. This study sets out a methodology for developing mathematical models which capture the hydraulics of leaky barriers accurately, allowing key questions about their combined behaviour in catchments to be answered. A 1D Godunov-type scheme is set up and leaky barriers incorporated with internal boundary conditions. This model is tested against benchmarks from the literature and new steady-state data, and then run predictively on transient cases. The method will help to answer key questions about the optimal leakiness of small-scale interventions, the limits to their usefulness, and how combinations of barriers may or may not cause synchronisation problems when the effect of multiple barriers is aggregated.

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