Peatland gully restoration with stone and timber dams (Kinder Plateau, UK)

Blanket peat erosion is widespread in the British Isles. Eroded gullies have formed largely from the action of running water, with anthropogenic influences thought to have initiated and accelerated erosion. Currently, many blanket peatlands are undergoing restoration using aerial applications of lime, seed, fertiliser, and hand spreading of heather mulch (LSFM) on bare peat flats and blocking gullies with dams. Dams help stabilise areas of bare peat, trap sediment, reduce runoff velocities, raise water tables, and promote the re-vegetation of peat-forming plant species. Few studies have examined how gully blocks change over time and what this means for the functions they provide. We randomly sampled 500 of >2500 small stone and timber dams 8–9 years after installation in an eroding blanket peatland. We measured: vegetation cover and abundance, sediment accumulation behind dams, and available water storage capacity in dam pools as determined by gully morphology. On average, 92% and 93% of gully floors and 85% and 95% of gully walls were fully vegetated, while mean sediment depths were 22 and 20 cm, representing 42% and 44% infill for stone and timber dams, respectively. 2% of dams had failed, suggesting that failure is rare within the first decade. Most retained upstream pools, filling 18% (stone) and 44% (timber) of remaining storage. Sediment accumulation depths (and, conversely, available storage) did not differ significantly between stone and timber dams (95% CI) nor with distance down the gully. Results showed broadly consistent storage depth behind blocks independent of gully properties or dam design. These results suggest that sedimentation depths behind dams quickly reach equilibrium with subsequent sediment inputs balanced by the flux over the dam. Runoff attenuation functions from gully blocking were maintained for almost a decade. Therefore, re-vegetated gully blocked systems likely represent a stable equilibrium condition for the restored peatland so that the restored functions are a long-term benefit of peatland restoration.