University Urges Stability Checks When Rewetting Deep Peat
Quick summary
University of Nottingham says rewetting remains essential, but wants stability assessed in deep peat and on slopes.
That caution comes from the University's press release regarding a new study.
Modelled stable thickness drops from 3.87 metres on flat ground to 0.27 metres at 12°.
In Scotland, the deepest peat on record already sits right at the limit the model allows.
The University of Nottingham says rewetting remains essential for restoring damaged peat. It also says the changes in water that rewetting brings could affect peat stability in some places, particularly deep peat and slopes. It wants that risk assessed as part of restoration planning.
The University makes these points in its press release announcing a new study. The study itself looks at how thick peat can grow before its own weight makes it unstable.
Researchers at the Bandung Institute of Technology in Indonesia and the University of Nottingham carried it out, and it is published here.
Rewetting and stability: what the University says
"The research also noted that whilst rewetting remains essential for restoring damaged peat and reducing carbon emissions, the resulting changes in water levels and water movement could affect mechanical stability in some settings, particularly in deep peat or on slopes, so this risk should be assessed as part of restoration planning."
The University is not questioning whether rewetting should happen. Its point concerns how rewetting is planned on certain ground.
What the study did
The team grew virtual peat over thousands of years. Their model tracked water and decay as the peat built up. It also calculated how the growing mass squeezed and strained the layers beneath.
Each run placed peat on a 500-metre hillside section ending at a river. The slope ranged from flat to 12°. According to the press release, peatlands cover 3% of the world's land surface and 12% of the UK's.
The researchers compared the stresses inside the peat with published strength measurements. They looked for two kinds of failure. In tensile failure, peat is pulled apart, causing cracks or bog bursts. In shear failure, one layer slides over another, causing a peat slide.
They checked the results against records of real peat landslides. They also compared them with Scottish peat depths from NatureScot's Peatland ACTION database, which holds more than 116,000 observations. Sites classed as actively eroding were removed first.
Key findings
The authors applied their flat-ground thresholds to peat-depth data from the world's main peat regions. They estimate peat can grow to about 1.48 times its current global volume before mechanical limits intervene. Existing projections assume a 1.71-fold increase. This estimate assumes the ground beneath does not subside over the long term.
Using the full published range of peat strengths, maximum stable thickness was about 3.87 metres on flat ground, 0.44 metres at 6° and 0.27 metres at 12°. Real landslides tended to happen in deeper peat than this first version predicted, so the team recalibrated. Its global comparison uses a flat-ground stable limit of 4.7 metres.
Failure becomes highly likely once peat on flat ground passes 6.9 metres. On a 12° slope, that point comes at 1 metre.
Shear failure (sliding) dominates on slopes steeper than 5.8°.
In Scotland, on slopes gentler than 5.8°, the deepest recorded peat (around the 92nd–93rd percentile) closely tracks the model's boundary. On steeper ground the two diverge. The authors suggest rougher ground beneath the peat explains this.
Carbon schemes and long-term security
Professor David Large, who led the study, links the findings to carbon credits:
"Our comparison with UK peat-depth data indicates that many of our peatlands are already at or beyond their modelled limits of mechanical stability. This is relevant to restoration and carbon-credit schemes such as the IUCN UK Peatland Code. Peat depth, slope and stability may need to be considered when assessing whether carbon benefits will be secure over the long term."
The authors note that where peat erosion is widespread, its cause is often unclear, because the influence of land management is hard to separate out. They describe mechanical failure as a natural trigger for erosion. In Scotland's blanket peatlands, they write, accumulation appears to be approaching that threshold.
The press release closes with Professor Large:
"Many peatlands may be closer to their natural storage limits than previously recognised, because the weight of the peat itself can eventually cause instability, erosion and carbon loss. This research demonstrates the need to consider peat depth, slope and stability when assessing whether carbon benefits will be secure over the long term."
Why this matters
Rewetting remains central to restoring peat, and the University's call to assess stability in deep peat and on slopes points to restoration planning that starts with depth and slope measured on the ground, site by site.
