NFM Webinar: Peatland Catchments and Natural Flood Management

Today I attended a webinar on peatland restoration for Natural Flood Management (NFM). 145 people attended the call, where Tim Allott from the University of Manchester presented on what restorative action could be taken to help benefit both the peatlands, and slow the flow of water and runoff, to benefit downstream flood risk.

Tim started by discussing the advancement in the scientific understanding of peatland restoration, and the flood benefits downstream.

Peatlands make up ~10% of UK land cover and ~60% of uplands. Few are in a natural or ‘intact’ state (~20%), as many have been degraded, managed or damaged. There is a strong history of management of peatlands including land drainage, which has led to accelerating investment in peatland restoration. For example, the Scottish Budget 2020-21 has allocated £20million for peatland restoration, for multiple benefits including biodiversity and erosion. The importance of peatlands is becoming clearer, as they are areas of carbon store and water regulation functions, raised by NFM and water quantity issues.

Tim pointed out there is a gradient of confidence about the extent to which peatland restoration will help alleviate downstream flooding. In order to encourage investment in peatland restoration for NFM, the benefits need to be demonstrated. He continued by discussing the review which looked at establishing our current understanding of NFM in peatland catchments, and how restoration can benefit hydrological processes.

There are different types of peatland restoration, which aim to restore ecological function of peat, reduce and delay peak flows across the wider catchment, and make a difference to downstream flood risk. The 2 main aims for peatland restoration are:

• Storing more water so that it doesn’t pass through the system, via local ponding and interception.
• Delay the conveyance of flow through establishing vegetation cover to increase surface roughens of the landscape. In peatlands, stormflow is dominated by overland flow so the surface of peat is very important. Aim to create longer travel times by introducing roughness, and delay the release of water.

There are several types of peatland restoration:

1. Bare peat restoration – significant reduction in peak flow if revegetate bare peat, as surface roughness effect slows the flow.
2. Sphagnum moss – crucial, keystone species in upland peats, helping slow runoff processes. Has disappeared through north Pennines due to air pollution, and now there are many areas you would expect to see it, but it has disappeared. Plug plants can be used to help re-establish this species.
3. Drainage blocking – mixed reviews here, as field studies suggest reduced peak flows, but modelling indicates increased peak flows in some cases. Ditch orientation is important, and affects the results. For example, if you block downslope drains, water is directed onto surrounding hillslopes, increasing travel time, and reducing peak flows. Modelling studies however considered drains running across the slope, where there is the possibility that blocking drains actually shortens travel time of water, and increases peak flows, as water can enter watercourses more quickly. This shows there are lots of factors to consider, as different drains and orientation might react differently to blocking.
4. Gully Blocking – these gullies increase the transition of water and increase peak flows. At a small scale, gully blocking reduces peak flows, although further research and evidence is needed.
5. Restoration of afforested peats – removing forested areas and restoring to a pre-forestation state to benefit the landscape. There are complexities are drainage under the surface needs to be considered. Also, need to consider the scale of the catchment that might be impacted by the restoration. Recently, there has been a lot of interest in forested peatlands, particularly in Scotland.
6. Burning on peatlands – substantial impact on peak flows and runoff levels. Still a lack of data regarding the impacts at a catchment scale.

Tim’s key messages were that peat restoration techniques will be site specific and scale dependent. Many catchment scale studies have looked at how the hydrograph changes in response to restoration actions. Most modelling studies are at larger scales, whilst field studies tend to be across smaller catchments. However, there remains a lack of data on many restoration types, and we need a better understanding of responses over longer time periods.

Thanks to Tim for this really informative webinar. It was really interesting to see an overview of what techniques are available to reduce flows in the uplands, slow flows, and benefit habitats and flood risk.