Stormflow behaviour in blanket peat catchments affected by severe wildfire: implications for natural flood management

The restoration of damaged UK peatlands is a major conservation concern, and landscape-scale restoration is extensive in areas of upland Britain. Peatland headwater catchments are important areas of hillslope runoff production, and over the last decade there has been increasing focus on how restoration schemes can reduce downstream flood risk through natural flood management (NFM). Stormflow in degraded catchments can be incredibly flashy, as water is quickly evacuated from hillslopes across bare peat surfaces and through erosional gullies, but there is increasing evidence that restoration by revegetation and damming of channels can significantly slow the flow of water.

Recent major peatland wildfires in the UK have focused attention on the effects of wildfire and post-wildfire restoration on the hydrology of peatland catchments, but to date, relatively little is known about the effects of wildfire on peatland flood hydrology. Current understanding is largely drawn from process studies, with evidence suggesting that severely burnt peatlands will have flashier hydrograph responses to rainfall events, with higher peak flows relative to unburnt peatlands. This assumption is based on three key factors which promote rapid overland flow: (i) the development of hydrophobic crusts due to high intensity fires, (ii) the clogging of peat pores by ash, and (iii) removal of vegetation cover reducing surface roughness. Further influences on runoff production could result from changes in water table or post-fire peat shrinkage and cracking.

This paper details stormflow characteristics from nine gullies in an area of peatland affected by the high-severity Saddleworth wildfire which burned over 1000 hectares of UK peatland in June and July 2018. This field area is upstream of the community of Stalybridge, which the Environment Agency had highlighted as a priority community at risk of flooding. We compare this behaviour to catchments that were unaffected by the fire. Preliminary findings suggest that the fire affected gullies produce highly variable stormflow behaviour, with some sites producing discharges similar to bare peat sites, while others are more similar to relatively intact catchments. The planned restoration of this area has great potential to provide NFM benefits.