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The dramatic badland landscapes of severely eroded peatlands represent significant degradation of the ecosystems, which when intact, provide a range of regulating ecosystem services including carbon sequestration and runoff regulation. Increasing efforts are being made to restore these landscapes through re-vegetation and gully blocking. Restoration has been driven by the aims of restoring biodiversity and carbon storage but the transformation of hillslopes and channels also has significant impacts on hillslope runoff. This paper reports on a major project from the uplands of the UK which has been studying the generation of hillslope runoff in restored peatlands and the potential to optimise restoration approaches to mitigate downstream flood risk. Peatlands are highly productive of runoff so that these approaches have the potential to deliver multiple benefits including Natural Flood Risk management for headwater communities.Our work has demonstrated that whilst static storage of water behind gully blocks is one component of the NFM benefit, dynamic storage on hillslopes during storm events is enhanced by increased surface roughness in restored catchments and is the larger component of the overall NFM benefit. Gully blocks with pipes or slots which enable drawdown between storms maximise static storage whilst the planting of sphagnum moss dramatically increases dynamic storage on the hillslopes.Taken together these data support the potential role of peatland restoration in NFM schemes and suggest that restoration of gully-eroded peatlands can deliver flood protection in headwater communities alongside wider benefits.

The UK supports 15% of the world’s blanket peat cover but much of this vital resource is significantly degraded. In damaged peatlands runoff is quickly evacuated from hillslopes across bare peat surfaces and through erosional gullies, exacerbating downstream flooding. The restoration of damaged UK peatlands is a major conservation concern, and landscape-scale restoration by revegetation and damming of gullies is extensive in areas of upland Britain. There is increasing evidence that the restoration techniques can significantly slow the flow of water in addition to providing other ecosystem service benefits. More recently, focus has shifted from stabilising eroding surfaces to the reintroducing Sphagnum moss as part of multi-benefit restoration initiatives.This paper reports the results of long-term post-restoration monitoring on the Kinder Plateau in the southern Pennines of the U.K. Two sites were revegetated using lime-seed-fertiliser-mulch in 2011 and one of the sites was also gully blocked in 2012 and had a further phase of restoration in the form of intensive Sphagnum planting in 2015. A third unrestored control site was also monitored. We present post-intervention biogeomorphological changes spanning 10 years, showing the long-term trajectories of vegetation cover, runoff, sediment production, and water table.The trajectories of recovery for different functions differ in form and rate. At both treatment sites, vegetation cover increases rapidly then slows as full cover is approached. Sediment production is quickly reduced to levels comparable to intact peatlands within two years and bare peat cover becomes negligible after ~7 years. Key runoff metrics (e.g. peak discharge and lag time) show similar immediate step changes as a result of increased surface roughness from the rapid vegetation expansion, followed by more gradual improvements as species richness develops through time. The addition of gully blocking enhances the impact of re-vegetation alone, amplifying the step change, but there are no further benefits apparent in the longer-term trajectory. The introduction of Sphagnum provides further roughness, leading to marked increases in lag times and attenuation of runoff. There is also preliminary evidence that the Sphagnum inhibits surface drying, providing resilience to future climatic and anthropogenic stressors.This study provides the first evidence that the reintroduction of Sphagnum in degraded headwater peatlands can provide additional Natural Flood Management benefits compared to standard restoration techniques aimed at stabilising eroding surfaces. We also show that water table recovery is not at odds with flow attenuation. We also note the importance of control assessing the impact of restoration interventions and the need for investment in longer-term (>10 year) monitoring to better understand the recovery of restored peatlands.

Erosion gullies are a common feature of degraded blanket peatlands and in recent years gully blocking has been increasingly employed as a restoration approach. The stated aims of gully blocking are typically to stabilise eroding gullies and to rewet the adjacent peatland by raising water tables, but in recent years the potential benefits of gully blocking for natural flood management (NFM) have also been recognised. However, data on the hydrological effects of gully blocking and for different gully blocking techniques are sparse.We report on a before-after-control-intervention (BACI) experiment of gully blocking in peatland micro-catchments (hectare scale) in the Peak District National Park, UK. Three different gully blocking interventions were made in March 2020: impermeable peat dams, permeable cobble dams, and peat dams with a restricted diameter bypass pipe. The first two interventions represent standard restoration techniques, whereas the piped peat dams are specifically designed to be optimal for natural flood management benefit. The micro-catchments were monitored for one year before and two years after gully blocking for: rainfall, discharge, depth to water table proximate to the gullies (within 2m) and depth to water table distal from the gullies (>10m away). Storm hydrograph data (peak discharges and lag times) were extracted for >120 storms from the rainfall-runoff data. All intervention data were analysed relative to data from a control micro-catchment.After blocking for all interventions there were significant declines in median depth to water table proximate to the gullies, with the magnitude of the rewetting benefit in the following order: peat dams > piped peat dams > cobble dams. There were no significant changes in depth to water table at the distal locations. Peat dams led to a slight increase in storm peak flows but no change in hydrograph lag times. Stone dams led to no change in peak flows but increases in lag times. Piped peat dams resulted in the greatest changes to storm hydrographs, with substantial declines in peak flows and increases in lag times once the pipe diameter had been optimised to the discharge regime.Peat dams maximise the rewetting benefits of gully blocking but appear to have limited NFM potential, whereas once optimised, piped peat dams provide maximum NFM benefit and greater water table recovery than stone dams. These findings are important for restoration practitioners when making decisions on which gully blocking techniques to employ to balance the co-benefits of peatland restoration.

Many upland headwaters of the UK drain areas of blanket peat, much of which has been degraded through atmospheric deposition of pollutants, vegetation change, peat extraction, artificial drainage and erosion. These areas are increasingly the focus of interventions to restore some of the multiple-benefits lost through degradation. Understanding their runoff generation processes underpins analysis of their wider benefits including their potential to mitigate downstream flooding.Using a series of multivariate analysis techniques we examine controls on storm runoff in ten blanket peat catchments of 0.2-3.9 hectares all within 5 km of one another. We find that: 1) rainfall intensity is the dominant hydro-meteorological driver for both magnitude and timing of peak discharge for all ten catchments, with antecedent rainfall only relevant in small storms; 2) most of the inter-catchment variability in discharge predictability from rainfall can be explained by catchment characteristics, particularly catchment area; 3) runoff responses, particularly in small storms, are sensitive to scale even in an apparently homogenous and saturation-excess overland flow dominated peatland landscape; 4) peak discharge in large storms is strongly controlled by attenuation processes associated with the travel time distribution, and thus drainage network geometry; 5) peak discharge in smaller storms underlines the importance of hydrological connectivity at scales Together these results suggest a switching in rainfall-runoff behavior within these catchments where peak discharge is controlled by: catchment storage, connectivity and antecedent conditions in small storms; but runoff attenuation, travel time and thus and network structure and scale in larger storms. In the context of Natural Flood Management, our findings suggest that enhancing depression storage by creating distributed shallow peatland pools in addition to existing restoration methods could raise the threshold storm size below which catchment storage, antecedent conditions and connectivity remain important. However, changes in surface roughness and other measures that target runoff velocities are likely to be more effective in the largest (and thus most flood relevant) storms.

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 >2500 gully blocks installed. 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 (p = 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.

Before-after monitoring of small-scale restoration activities in blanket peatlands, e.g., revegetation and gully blocking, suggests they can also deliver significant Natural Flood Management (NFM) benefits (reduce and delay floodpeaks). However, we still lack a clear understanding of the underlying processes driving NFM effects; and doubts remain about whether interventions will retain their impact when implemented at scales large enough to reduce flooding in downstream communities. We examine the impact of the two interventions at a range of scales from the 1 hectare micro-catchment scale at which a Before-After-Control-Intervention (BACI) study has been undertaken, to the 40 km2 scale (at which flooding begins to affect residential properties). We calibrate the Generalised Multistep Dynamic (GMD) TOPMODEL rainfall-runoff model to different BACI experimental catchments each representing an intervention scenario. Through numerical experimentation with the calibrated parameters, we estimate the impact-magnitude of different process drivers. Our findings confirm the NFM benefits of these restoration-focused interventions at the micro-catchment scale. In both interventions and in our largest storms, floodpeak attenuation is primarily due to roughness reducing the floodwave speed and thus thickening the overland flow (kinematic storage). More conventional, static storage (i.e. interception + ponding + evapotranspiration), becomes important only in smaller storms. Finally, we use the parameter-sets identified by calibrating to the BACI catchments to extend our findings to the 40 km2 Glossop catchment. Glossop has experienced several damaging floods in the last 50 years and has received appreciable recent restoration activity. Here we use GMD-TOPMODEL in a second set of modelling experiments to estimate downstream impact of existing interventions and to examine the impact of alternative scenarios of spatially distributed intervention configurations.

Flooding is costly and disruptive in the UK and worldwide. Leaky barriers (LBs), small-scale blockages to streamflow, provide multiple environmental benefits. Depending on design, and if installed in sufficient numbers, they could also play an important role in reducing downstream flooding. Leaky barrier installation is proceeding at pace, thousands of cobble dams have been installed in peat gullies across the South Pennines (UK). However, the hydraulics of LBs in general and these cobble barriers in particular is poorly understood. Here we develop a simple model coupling two classical engineering flux estimates: Darcy/Casagrande equations for matrix flow and Colebrook equation for pipe flow (where drains are installed). We test this model against observed stage and discharge measurements for four study features with and without drains to: identify stage-discharge relationships; evaluate model performance for individual features; and apply it to model chains of features of varying design (i.e., LB density, matrix permeability, and pipe diameter). We find that: 1) stage-discharge relationships for cobble dams are concave up and are generally well captured by our simple model; 2) current designs offer relatively little attenuation because they are too permeable; 3) instead, optimal designs have low matrix permeability with pass-forward pipes at their base of a diameter tuned to design flow. Based on these results we hypothesise that LBs will perform best where they are designed to have negative permeability-depth relationships (and thus convex up stage-discharge relationships) and where the form and magnitude of the relationship is optimised to accommodate peak flood discharges.

The UK supports 15% of the world’s blanket peat cover but much of this vital resource is significantly degraded. Damaged peatlands lose their hydrological integrity, depressing water tables and exacerbating downstream flooding as water is quickly evacuated from hillslopes across bare peat surfaces and through erosional gullies. The restoration of damaged peatlands is a major conservation concern, and landscape-scale restoration by revegetation and damming of gullies is extensive in areas of upland Britain. There is increasing evidence that the restoration techniques can raise water tables and significantly slow the flow of water in addition to providing other ecosystem service benefits. More recently, focus has shifted from stabilising eroding surfaces to reintroducing Sphagnum moss as part of multi-benefit restoration initiatives, but to date there is limited empirical data to evidence its impacts.This paper reports the results of long-term post-restoration monitoring on the Kinder Plateau in the southern Pennines, UK. Two sites were revegetated using lime-seed-fertiliser-mulch in 2011 and one of these sites was also gully blocked in 2012 and had a further phase of restoration in the form of intensive Sphagnum planting in 2015. A third unrestored control site was also monitored. We present post-intervention trajectories spanning 10 years showing the long-term recovery of vegetation, water tables, runoff generation, water quality, and sediment production.The trajectories of recovery for different functions differ in form and rate. At both treatment sites, vegetation cover and diversity increased rapidly then expansion slowed as full cover was approached. Sediment production was quickly reduced to levels comparable to intact peatlands within two years and bare peat cover became negligible after ~7 years. Key runoff metrics (e.g. peak discharge and lag time) showed similar immediate step changes as a result of increased surface roughness from the rapid vegetation expansion, followed by more gradual improvements as species richness developed through time. The addition of gully blocking enhanced the short-term impacts of re-vegetation, amplifying the step change, but on longer timescales there were no additional benefits relative to the revegetation only site. Water tables recovered gradually at a constant rate and there is no sign of this slowing after 10 years. Water quality (DOC and colour) was highly variable throughout the study period and the long-term impact of restoration is inconclusive. The introduction of Sphagnum provided additional hydrological benefits, most notably through further increases in lag times and attenuation of runoff. There is also preliminary evidence that the Sphagnum provides resilience to surface drying.This study provides the first evidence that the reintroduction of Sphagnum in degraded headwater peatlands can provide additional natural flood management (NFM) benefits compared to standard restoration techniques aimed at stabilising eroding surfaces. We also show that water table recovery does not counteract the benefits of flow attenuation. We emphasise the critical importance of control in assessing the impact of restoration interventions and the need for investment in longer-term (>10 year) monitoring to better understand the hydrological recovery of restored peatlands.

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.

Upland blanket peat is widespread in the headwaters of UK catchments, but much of it has been degraded through atmospheric pollution, vegetation change and erosion. Runoff generation in these headwaters is an important element of downstream flood risk and these areas are increasingly the focus of interventions to restore the peat ecosystem and to potentially mitigate downstream flooding. Here we use a series of multivariate analysis techniques to examine controls on storm runoff behavior within and between ten blanket peat catchments all within 5 km of one another and ranging in size from 0.2-3.9 hectares. We find that: 1) for all 10 catchments, rainfall intensity is the dominant driver for both magnitude and timing of peak discharge, and that total and antecedent rainfall is important for peak discharge only in small storms; 2) there is considerable inter-catchment variability in: runoff coefficient, lag time, peak runoff, and their predictability from rainfall; however, 3) a significant fraction of the inter-catchment variability can be explained by catchment characteristics, particularly catchment area; and 4) catchment controls on peak discharge and runoff coefficient for small storms highlight the importance of storage and connectivity while those for large events suggest that surface flow attenuation dominates. Together these results suggest a switching rainfall-runoff behavior where catchment storage, connectivity and antecedent conditions control small discharge peaks but become increasingly irrelevant for larger storms. Our results suggest that, in the context of Natural Flood Management potential, expanding depression storage (e.g. distributed shallow water pools) in addition to existing restoration methods could increase the range of storms within which connectivity and storage remain important and that for larger storms measures which target surface runoff velocities are likely to be important.

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.

This study presents input–output budgets of total dissolved nitrogen (TDN), dissolved organic N (DON) and dissolved inorganic N (DIN) for a reservoir in a peatland catchment in the south Pennines (UK). This site receives high levels of atmospheric inorganic N deposition, in the range of 26 kg N ha−1 yr−1. The results show that the reservoir retains ~21 to 31% of the annual TDN input (8806 ± 741 kg N). Approximately 39 to 55% of DON (3782 ± 653 kg N) and 6 to 13% of DIN (5024 ± 349 kg N) were retained/processed. A long water retention time (104 days), average annual pH of 6.5, high concentrations of DIN in the reservoir water and a deep water column suggest that denitrification is potentially a key mechanism of N retention/removal. The results also demonstrate that DON is potentially photodegraded and utilized within the reservoir, particularly during the summer season when 58 to 80% of DON input (682 ± 241 kg N) was retained, and a net export of DIN (~34 kg N) was observed. The findings therefore suggest that DON may play a more crucial role in the biogeochemistry of peat-dominated acid sensitive upland freshwater systems than previously thought. Reservoirs, impoundments and large lakes in peatland catchments may be important sites in mediating downstream N transport and speciation. Copyright © 2016 John Wiley & Sons, Ltd.

Understanding the nature and fate of nitrogen (N) in freshwater systems is crucial for assessing the risk of eutrophication. However, there is a paucity of information on the characterization of fluvial N in upland peat-dominated environments. Here, we employ a combination of field sampling and tangential flow ultrafiltration (TFU) to investigate the concentrations and fluxes of low molecular weight (LMW) and high molecular weight (HMW) dissolved organic N (DON) in a peatland stream-reservoir system in the south Pennines (UK). Our TFU results show that ∼26% of DON concentration is LMW DON and represents an estimated fluvial flux of 3.07 ± 22 kg N ha-1 during the study period. Our mass balance results reveal that the reservoir retains 71% of LMW DON input, which accounts for ∼25% retention of bioavailable (dissolved inorganic N + LMW DON) N. Our study suggests that current understanding of inorganic N as the sole source of bioavailable N with eutrophic significance in upland freshwaters requires a reappraisal. Evaluation of ecosystem response to increased loading of N needs to include a consideration of LMW DON.

This study investigates seasonal concentrations and fluxes of nitrogen (N) species under stormflow and baseflow conditions in the peat dominated Kinder River catchment, south Pennines, UK. This upland region has experienced decades of high atmospheric inorganic N deposition. Water samples were collected fortnightly over one year, in combination with high resolution stormflow sampling and discharge monitoring. The results reveal that dissolved organic nitrogen (DON) constitutes ~ 54% of the estimated annual total dissolved nitrogen (TDN) flux (14.3 kg N ha− 1 yr− 1). DON cycling in the catchment is influenced by hydrological and biological controls, with greater concentrations under summer stormflow conditions. Dissolved organic carbon (DOC) and DON are closely coupled, with positive correlations observed during spring, summer and autumn stormflow conditions. A low annual mean DOC:DON ratio (