Peatland restoration is increasingly used for natural flood management (NFM). In the restoration of heavily degraded blanket peatland sites, erosional gully blocking is used to capture sediment and rewet peat in smaller peat gullies. There is limited prospect for restoration of wider late-stage erosional gullies, however these have potential for large water storage capacities for NFM barriers. A new type of peatland gully block, Large Cobblestone Dams (LCDs), designed to create large temporary in-storm storage volumes are evaluated here. Different modifications to LCD design, including dam-face modification and drainage outlets are tested. Observations of dam pond levels and input discharge are used to evaluate storage functioning. LCDs achieve temporary in-storm storage volumes to the order of 10-100 m3. Bare cobblestones were too permeable, with peat turfed dam faces improving storage utilisation. A drainage outlet is essential for inter-storm drainage to enable storage availability for following storm events. Opening of drainage holes and blocking of the outlet was observed immediately following peat turfing, however this stabilised following 1 year. With an optimised design, LCDs can provide relatively large dynamic storage volumes in peatland gullies which are not restoration priorities which with targeted design could provide NFM benefits to downstream communities.

Field-scale experiments have shown the Natural Flood Management (NFM) potential of peatland restoration. The likelihoods of effectiveness are yet unknown at scales and storms large enough to impact human lives. Using GMD-TOPMODEL, we upscale a rare Before-After-Control-Intervention empirical data set to a 25 km(2) catchment with >600 properties at flood-risk, and test storms of up to a 1,000-year return period (RP). Under these scales/storms, we find that it is not necessary (nor feasible) to delay the outlet flow-peak to meaningfully attenuate it. Enhancing catchment "kinematic" storage, for example, through restoration, can be sufficient to reduce flow magnitudes without detectable changes to peak-flow timing. NFM benefit increases exponentially with restoration area size under smaller storms, but linearly under larger storms. At RP <= 100 years, longer-lasting frontal-type storms are more challenging to defend against via NFM, but at RP > 100 years shorter-duration convectional-type events become more challenging. In the order of 1,000-10 years storms: (a) revegetating the bare-peat areas in 15% of the catchment is 31%-61% likely to reduce peak-flows by >5%; (b) revegetating & damming the erosion gullies in similar to 20% of the catchment is 42%-71% likely to reduce peak-flows by >5%; (c) Growth of Sphagnum in the dammed gullies of similar to 20% and similar to 40% of the catchment increase the likelihoods of >5% peak reductions to 65%-86% and 90%-98%, respectively. The numerical evidence of significant NFM benefit due to Sphagnum re-establishment is an important finding, because it shows that meaningful flood-risk mitigation in headwater catchments under scales/storms relevant to communities at risk can be delivered alongside other ecosystem benefits of Sphagnum re-establishment.

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 peatforming 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.

&lt;p&gt;Extensive erosional gully networks are commonplace in degrading peatlands. Gullying produces local water table drawdown and the increase in drainage density associated with gully networks increases hydrological connectivity between hillslope and channel. Peatland restoration methods commonly involve blocking of gullies with peat or timber dams to limit further erosion and promote higher water tables. Blocking is also demonstrated to attenuate channel flow in peatland catchments, suggesting that gully blocks can provide Natural Flood Management (NFM) benefits. Block design can be further optimised for flood attenuation purposes, such as including an outlet pipe through the block to provide dynamic in-storm storage.&amp;#160;&lt;/p&gt; &lt;p&gt;This paper compares the hydrological functioning of standard peat dams and piped-peat dams optimised for NFM from neighbouring microcatchments (&lt;2.5 ha) in the Peak District National Park, UK. Pre-restoration discharge was monitored for 12 months prior to installation of 6 standard peat dams in one microcatchment and 10 piped-peat dams in the other. Bottom of reach discharge and individual dam pool height was recorded for the following 12 months. The series of piped-peat dams are demonstrated to have a higher impact on catchment discharge than standard peat dams, reducing peak discharges and increasing lag times. Standard peat dams provide little storage volume during storm events compared to the dynamic storage provided by the outlet in piped-peat dams. However, the requirement for maintenance of pipe-peat dams is identified, with pipe blockages compromising dynamic storage. These findings have implications for understanding of NFM benefits from standard and NFM optimised peat dams.&amp;#160;&lt;/p&gt;

Across the world restoration of degraded peatlands involves manipulation of peatland hydrology. Often this includes blocking of drainage and changing of land cover types. These landscape scale interventions in the peatland system have the potential to significantly modify runoff from peatland systems and so to be incorporated into schemes of natural flood management. In this paper we report on results from the 4 year PROTECT project which aims to optimise peatland restoration to support NFM benefits in the degraded peatlands of upland Britain. Field experiments based on a BACI analysis of over 20 peatland microcatchments along with hydrological and hydraulic modelling approaches have underpinned a series of key findings including: reductions in peak discharge and longer lag times for runoff from re-vegetated peatlands particularly associated with sphagnum growth; Reductions in peak discharge associated with optimised peat dams which allow partial drawdown between storm events; continued delivery of NFM benefit from restoration at timescales in excess of 10 years; and identification of a key role for dam permeability in optimising NFM benefits from drainage line blocking. Taken together these data support the potential role of peatland restoration in NFM schemes and suggest that with careful optimisation synergies between the needs of peatland restoration and flood protection in headwater communities can be realised.

&lt;p&gt;Many degraded UK blanket peatland sites have been subjected to restoration using dams in eroded gully systems to trap sediment, slow the flow of water and promote revegetation of bare peat surfaces. There are few studies on how gully blocks evolve with time, what this means for changing ecosystem functions, and the natural flood management benefits of restoration. This study focuses on gully block evolution on the Kinder Scout Plateau, where the blanket peatland was restored in 2011/12 and &gt;2500 gully blocks installed.&lt;/p&gt;&lt;p&gt;&amp;#160;&lt;/p&gt;&lt;p&gt;We took a random sample of 500 small stone and timber dams 8-9 years following restoration, representing c.20% of the total number of blocks. We measured sediment accumulation behind the dams, vegetation cover and abundance and their propensity to continue to store water with respect to gully morphology. Principal component analysis suggested dam dimensions, channel, and wall slope are associated with sedimentation and change in water storage behind the dams, while other gully attributes were more associated with the change in vegetation cover. Dams installed in gullies with steeper walls and channel slopes typically accumulated more sediment. There was more variability in the evolution of stone dams, typically installed in wider, deeper gullies with shallower peat substrates and larger contributing areas than timber dams. 72% of surveyed dams were actively pooling water, and only two had visibly collapsed. On average, gully floors had 93% vegetation cover, whereas gully walls and dam tops had 90% and 45% vegetation cover, respectively. Sediment accumulation was not significantly different between the stone and timber dams at the 95% confidence interval. A random sub-sample of 26 gullies found no significant difference in sediment depths between subsequent dams in the same gullies (&lt;em&gt;p&lt;/em&gt; = 0.255). Comparisons with an earlier survey suggest most sediment accumulation happens in the first year, rapidly reaching an equilibrium. As such, dams may exhibit similar properties regardless of the materials used and gully attributes. Dam top vegetation cover was positively correlated with gully dimensions, and 21% of dams were completely covered by vegetation. However, on average, 58% of the storage available after installation remained behind dams. Therefore, remaining storage combined with additional channel surface roughness may provide more favourable conditions for attenuating runoff 8-9 years after installation than the first year after restoration. We conclude that despite the differences between stone and timber dams, the gully blocking outcomes are very similar 8-9 years after restoration. Perhaps the most striking outcome was the high vegetation cover in channel floors and gully walls which will likely benefit peatland ecosystem functioning and natural flood management.&lt;/p&gt;&lt;p&gt;&amp;#160;&lt;/p&gt;

Nature Based Solutions (NBS), including Natural Flood Management (NFM) schemes are becoming an important component of many governmental and organisation responses to increases in flood and aridity risk. NFM structures may take multiple forms to slow, store, disconnect and filter distributed overland flow pathways within a catchment that coalesce to generate a flood-wave downstream and runoff rather than infiltrate gmundwaters. To date few studies have conducted observations pre- and post-installation monitoring at river reach-scales, despite widespread and frequent installation, to investigate the efficacy of willowed engineered log jams (WELJs) interventions used in abating flood-flows, through backing-up flood-pulses with consequent reductions in downstream discharges. This paper examines the efficiency, before and after installation of five 1 m high WELJs incorporating 1,000 Bay willow (Sa!ix pentandra) saplings supporting the dead horizontal timber, across a total of 130 linear metres spanning the floodplain of a decommissioned reservoir. One rain gauge, two fixed point time-lapse wildlife cameras and three water level stations were installed: upstream-of, within, and downstream-of all WELJs. The findings demonstrate a substantial reduction is achieved for most events, with an average of 27.3% reduction in peak discharge being achieved post-installation. The time to peak is little impacted, however there is demonstrable evidence of a longer and higher recessional limb to the events. These findings quantify for the first time the role that WELJs can play in a move towards re-naturalisation of water level regimes, with lower peak water flows achieved, and waters released from the river-reach more slowly. Furthermore, baseflow during dry periods is also elevated by 27.1%, offering greater resilience to dry periods and droughts. Consequently, over the river-reach scale (0-130 m), WELJs play an important role in alleviating flood and drought risk through suppressing flood peaks and increasing baseflow during low flows; steps towards improved hydro-morphological quality overall.

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.