Diffuse pollution, globally affecting water quality by delivery of sediment, nutrients, pathogens and agro-chemicals from farmland, often has dominant flowpaths connecting to discrete channel delivery points, where field-edge mitigation can be optimally targeted. Accurate representation of field convergent flow paths (CFPs) can inform decisions on riparian mitigation planning. For three fields in Wexford, Ireland, we combined literature, catchment data, field-survey and spatial data methods to derive sediment and P exports (7.4–18.7 tonnes sediment/year and 0.9–6.9 kgP/year), runoff areas and watercourse delivery points (one to six CFPs per field). We moderated exports according to the ratio effective riparian buffer area: CFP contributing area and compared 3 mitigation levels. Low buffer to CFP area ratios highlighted limitations of narrow buffers for larger CFPs. Linear grass buffers (2 m, level 1) were predicted to retain 2–17

Agricultural mitigation measures should be correctly designed and sited to make effective barriers for diffuse pollution. Landscape contexts of soils, slope, erosion and surface runoff generation differ across scales, farm types and management. A diversity of mitigation measures are being developed to improve trapping of key pollutants. There is a need to integrate knowledge on the functioning of these measures according to site context. We provide the narrative of concepts, evidence, workflow and testing of a decision support tool for selection between 16 field edge, riparian mitigation measures for protection of water quality. The tool uses question groupings to implement concepts of severity of runoff and erosion, surface and subsurface flow paths, waterbody and riparian condition. Landscape characterization provides scoring to rank or reject between the measures. The tool is intended for use by famers, advisors and catchment officers and is coded into an openly available webpage user interface.

Water quality has declined globally over recent decades. The riparian interface is a key location for mitigation measures to support water quality and wider ecosystem services (ES). With new, multi-functional, riparian mitigation measures being designed and implemented, there is a need for evidence on the functioning of such measures with respect to delivery of ES. This study incorporated the judgements' of experts, to assess the effectiveness of various riparian measures to deliver 14 individual ES. In total 24 experts (covering a range of expertise and nationalities) completed a bespoke questionnaire (and follow-up workshop) to assess their opinion on the effectiveness of 16 mitigation measures (e.g. grass buffers, wooded buffers, integrated buffers, sediment fence) to deliver the identified ES (e.g. water quality, habitats, carbon, recreation). The results highlight the significant variance in effectiveness of the 16 mitigation measures across the 14 individual ES. Wooded buffers were the most effective mitigation measure for seven of the fourteen individual ES and in most cases were deemed highly effective at delivering that service. Linear grass buffer strips consistently scored amongst the least effective measures. The results indicate that riparian mitigation measures are consistently less effective at delivering ES relating to pesticides and biomass production than they are for other ES. This study highlights that there is no ideal riparian mitigation measure capable of delivering the wide range of ES. Future policy/research could focus on developing and implementing bundles of mitigation measures along the source-pathway receptor continuum, by means of a "treatment train" approach.

River woodlands can play a critical role in supporting healthy and biodiverse riverscapes, providing essential ecosystem services such as flood mitigation, drought resilience, carbon storage, and biodiversity. In Scotland, 50% of national riparian length is designated as degraded, which underscores the urgency of restoring and conserving river woodlands. These ecosystems are pivotal in addressing the twin crises of biodiversity loss and climate change while supporting local resilience and livelihoods. However, the creation and conservation of such healthy and resilient river systems through enhanced riparian and floodplain management with woodlands in Scotland is held back by lack of evidence and complex trade-offs of benefits for multiple stakeholders.This project aimed to address these challenges by working with diverse stakeholders—including restoration practitioners, businesses, policymakers, and researchers—across Scotland to (1) identify evidence gaps across key benefit areas including flood and drought mitigation, addressing water and air pollution, carbon storage, biodiversity, food and biomass production and utilisation, and health, wellbeing, heritage and community involvement (2) appraise scientific evidence and stakeholder perceptions for these key benefit areas and (3) and uncover evidence needs and other barriers to river woodland restoration practice.Through a literature review and engagement with 115 stakeholders via surveys, workshops, interviews, and focus groups, we identified key gaps in knowledge, barriers and opportunities for progress. Our findings highlighted a need to:Integrate the quantification of the diverse benefits of river woodlands to optimise restoration designs and avoid unintended consequences. Have robust spatial baseline data on water quality and biodiversity for planning, while long-term pre- and post- intervention monitoring is critical for evaluating restoration outcomes. Acknowledge the role of place and scale (both in space and time), and thereby transferability of benefits, especially as data gaps persist for large-scale effects like downstream flood mitigation. Address challenges posed by grazing pressures, fragmented policy frameworks, limited financial incentives, and integration with agricultural systems that hinder large-scale implementation. Improve governmental targets for river woodland coverage and cross-sector collaboration to advance multifunctional river woodland landscapes. Build on the new stakeholder network created for improved alignment and efficient communication between stakeholder needs and research focus. This project brought together a comprehensive understanding of diverse stakeholders' perceptions and priorities regarding river woodland restoration. It has provided a step-change towards the realisation of river woodland restoration by developing a new research agenda and setting out recommended pathways to address these and other barriers. Key pathways identified include developing integrated monitoring strategies, leveraging citizen science, and fostering engagement and communication to align efforts across sectors. Our multi-disciplinary approach provides a successful method that could be applied to support various other environmental restoration efforts that deliver long-term ecosystem, social and economic benefits.

Purposely placed in‐stream wooden leaky barriers (LBs) with lower gaps to facilitate flow during average conditions have become a popular type of nature‐based intervention in catchments for flood risk mitigation. Empirical evidence on their effectiveness remains rare, however. The hydro‐geomorphic effects of 16 LBs were monitored over three years on the Elm Sike, a small upland stream (catchment area: 0.33 km 2 ) in the Scottish Borders, UK. The aims of the structures were to: (1) increase water storage and roughness and, in turn, attenuate and delay flood peaks; and (2) trap and store coarse sediment to reduce sediment‐related problems downstream. Annual topographical surveys were conducted to assess geomorphic changes, and continuous 5‐minute water levels were recorded to assess changes in peak flow travel times. Two‐dimensional hydraulic modelling (HEC‐RAS 2D) was undertaken to assess the hydraulic impact of the structures and geomorphic changes. The LBs had no effect on peak flow travel time and rate of stage rise or fall based on 22 events with an Annual Exceedance Probability (AEP) of ≥ 3.7%. Hydraulic modelling showed limited velocity reduction and expansion of inundation extent due to the LBs for 50% AEP flows, but slightly greater effects for larger 5% AEP flows. However, for 50% AEP flows, inundation extent increased and velocities decreased more significantly due to morphological changes initiated by the structures. The limited hydrological and hydraulic impacts were related to the small size of the structures, close spacing and the steep, confined valley setting that limited water storage capacity. At the end of the three‐year period, a reach‐wide net deposition response of 3.49 ± 0.36 m 3 and a 5.3% loss of total LB backwater storage were observed, but local geomorphic response due to the LBs was spatially variable. Backwater capacity at 10 structures was reduced, and the lower gap increased at eight structures due to bed scour, indicating accelerated underflow. Multivariable analysis showed that gap height change was inversely related to backwater shear stress, channel cross‐section area and channel slope. No factors explained backwater sediment deposition, but a threshold lower gap height of ≤0.4 m for initiating deposition was evident. These hydro‐geomorphic observations have implications for the design and placement of LBs in river restoration and flood risk management projects.

Nature-Based Solutions (NbS) and ecosystem restoration are often conflated, but cannot be assumed to be identical. Understanding and choosing between these different framings is important. It affects our ambitions for reinvigorating natural systems, the range of actors and resources that can be drawn on to achieve them, and every part of how interventions are planned, delivered and appraised.To explore the differences and relationships between NbS and restoration we focus on freshwater catchment management initiatives, but our points are relevant to initiatives in other settings or framed in other terms. We firstly identify the potential differences by analysing accepted definitions of restoration and Nature-Based Solutions; and we then illustrate these with examples of catchment management in UK and Ireland, with which we are familiar from our own work and collaborations.These real-world cases demonstrate that the framings of restoration and NbS can lead to different priorities for how ecosystems and natural processes are managed; and who is involved and how projects develop. The cases also show that interventions may be somewhere on a continuum somewhere in between the two concepts, and potentially shift over time. There is often a lack of clarity over why these terms are used, causing sometimes unacknowledged confusion and potentially missed opportunities to improve catchment management.Different stakeholder groups involved in catchment management could benefit from more opportunity to explicitly reflect on preferred goals, and the implications for how to achieve this. We need more explicit reflection on the purpose of an intervention, and then different actors from site-managers to policy and other enabling groups can plan to achieve that vision. Given the time lags between interventions and outcomes, it is particularly important to use these insights in adaptive approaches to understand the changing drivers shaping current and future action.

Abstract. Stable isotope ratios of hydrogen (δ2H) and oxygen (δ18O) are crucial for studying ecohydrological dynamics in forests. However, most studies are confined to single sites, resulting in a lack of large-scale isotope data for understanding tree water uptake. Here, we provide a first systematic isotope dataset of soil and stem xylem water collected during two pan-European sampling campaigns at 40 beech (Fagus sylvatica), spruce (Picea abies), or mixed beech-spruce forest sites in spring and summer 2023 (Lehmann et al., 2024). The dataset is complemented by additional site-, soil-, and tree-specific metadata. The samples and metadata were collected by different researchers across Europe following a standardized protocol. Soil samples were taken at up to 5 depths (ranging from 0 to 90 cm) and stem xylem samples from three beech and/or spruce trees per site. All samples were sent to a single laboratory, where all analytical work was conducted. Water was extracted using cryogenic vacuum distillation and analyzed with an isotope laser spectrometer. Additionally, a subset of the samples was analyzed with an isotope ratio mass spectrometer. Data quality checks revealed a high mean total extraction efficiency, mean absolute water amount (> 1 mL), as well as high analytical accuracy and precision. The water isotopic signature of soil and stem xylem water varied as a function of the geographic origin and changed from spring to summer across all sites. While δ2H and δ18O values were strongly correlated, the soil water data plotted closer to the Global Meteoric Water Line (GMWL) than the stem xylem water. Specifically, the δ2H values of the stem xylem were more enriched than those of the soil water, leading to a systematic deviation from the GMWL. Isotopic enrichment of the stem xylem water was larger for spruce than for beech trees at mixed forest sites. This dataset is particularly useful for large-scale studies on plant water use, ecohydrological model testing, and isotope mapping across Europe.

Temporary storage areas (TSAs) are a type of Natural Flood Management measure or nature-based solution that can provide additional storage during flood events by intercepting and attenuating surface runoff. Pressures on land use and an increase in climate change induced storms means there is a need to create additional storage within multifunctional rural landscapes. Implementation of small-scale TSAs is slowly gaining momentum, but practitioners still require further evidence on their functioning during different storm events. Here we present the TSA Drainage Rate Analysis tool (TSA-DRA tool), a novel data-based mechanistic method that only requires rainfall and TSA water level data to describe individual TSA drainage rates. We developed and then used the TSA-DRA tool to perform a multi-site assessment of different TSAs, allowing comparisons of TSA functioning across different types or time-variable factors. TSA design and outlet were found to be the dominant controls on drainage rates when the feature is full. Meanwhile, time-variable differences in functioning were more evident at lower water levels, when soil infiltration was the main TSA outflow. Results from a modelling experiment using observed time-variable TSA drainage rates suggested that these can impact the TSAs flood mitigation effectiveness. Specifically, for a particular event, soil conditions of a TSA in NE Scotland were more effective during spring than winter in attenuating surface runoff. Understanding spatial and temporal differences in TSA drainage rates will help optimise existing and future TSA designs, ensuring small-scale headwater TSAs are successfully integrated within rural catchments to mitigate an increasing exposure to hydrological extremes.

Stream temperature is directly and indirectly affected by climate change. To be able to project future changes in stream temperature, historic trends and factors influencing these trends need to be understood. There is a demand for daily data to analyse historical trends and future changes in stream temperature. However, long-term daily stream temperature data are rare and observations of coarse temporal resolution (e.g. once-a-month) do not allow for robust trend analyses. Here, we present a methodology to reconstruct a national long-term daily stream temperature record (1960-2080) from 40 years of once-a-month observations (for 45 Scottish catchments). This involved implementing climatic and hydrological variables in generalized additive models. These models were then used in combination with regional climate projections (UKCP18 Strand 3 - RCP8.5) to predict future spatio-temporal temperature patterns. The results indicate that for the Scottish dataset (i) in addition to air temperature, the dominant environmental controls on stream temperature are unique combinations for each catchment; (ii) a general increase of up to 0.06 °C/year in historic stream temperature over all catchments resulted mainly from increases in spring and summer stream temperatures; (iii) future spatial patterns in stream temperature are more homogenous and differ therefore from the past where temperatures in N Scotland were relatively lower (iv) future changes of up to +4.0 °C in annual stream temperature are strongest in those catchments which show lower stream temperature in the past (NW and W Scotland). These results are important in the context of water quality and stream temperature management. The methodology can be applied to smaller scale sites or to other national/global datasets enabling the analysis of historic trends and future changes at a high temporal resolution.

ABSTRACT Water resources management during drought is a significant challenge worldwide, particularly for upland areas. Additionally, variations in water availability are becoming more extreme with climate change. Nature Based Solutions (NBS) e.g. Runoff Attenuation Features (RAFs) could provide an alternative to hard-engineering. Using more natural processes, flow pathways are intercepted and attenuated in features during wet periods, increasing infiltration opportunity and thus water availability for use later. NBS research has primarily focused on flood mitigation, but little is known about low flow impacts; knowledge is required on where and at what scale to implement NBS. To explore these questions, we used a physically-based catchment model (MIKE SHE) integrated with a hydraulic river model (MIKE 11) to evaluate scenarios with varying RAF volumes and locations. We applied this to an intensively monitored upland Scottish catchment (0.9 km2) where 40 RAFs (∼2m3 storage each) were installed for low flow enhancement. Model results showed installed RAFs increase recharge (∼0.1%), groundwater contribution to streamflow (∼4%) and low flows (∼1%) and reduce high (∼5%) and mean flows (∼2%), suggesting RAFs could be used to mitigate extreme flows. The scenarios revealed that RAF location (primarily soil type) and scale (total storage volume and spread of features) were both important. Doubling installed RAF volumes increased impact on low flows by ∼25% and high flows by ∼40%, although lower additional benefits were predicted with further storage increases. RAFs had greater impact in freely-draining soils than poorly-draining, however distributing the same storage volume across many smaller RAFs over greater areas (both soil types) provided the largest effect. Absolute changes observed were relatively small, and given model uncertainty, should be treated with caution. Nevertheless, the direction of change was clear and given ecological systems and water supply rely on small margins of change, even slight increases in low flows will likely be beneficial.

To monitor aquatic habitats and understand physical and biogeochemical processes, the analysis of high-resolution spatial patterns in water temperature is of outmost importance. The spatial resolution of remotely sensed thermal infrared (TIR) data ranges from cm-scale for airborne to m- and km-scale for spaceborne observations, enabling the analysis of a variety of hydrological processes. However, while remotely sensed TIR data reflects temperatures emitted from the direct surface, the temperature of waterbodies may also vary significantly with depth. Hence, there are limits to relying purely on remotely sensed water temperature data to understand 3D water temperature patterns, leading to the need of high-resolution 3D water temperature data.Here, we combined a novel self-build in-situ sensor system with remotely sensed TIR data to explore high-resolution, natural and anthropogenically influenced 3D spatio-temporal patterns in river water temperature. The study site involved a ~780 m long stretch of a river in the Northeast of Scotland, with a smaller section (~50m long) that is influenced by cooling water being discharged from a local distillery. We applied our new observation system to gain a better understanding on the 3D extend of a thermal plume and how this local anomaly compares to and affects the overall thermal variability within the river. Three surveys were conducted (during April-June 2021) to measure the surface water temperature of the river with an UAV based TIR camera. We additionally installed the novel in-situ sensor system to measure 3D water temperature during each survey. The surveys were planned to acquire data under contrasting ambient conditions as well as at a time when no cooling water was being discharged, allowing us to also observe spatio-temporal thermal variability under natural conditions. While the acquired TIR datasets give an overall view of the thermal variability at the surface, subsets of the TIR datasets were merged with the corresponding data from the in-situ sensor system to spatially interpolate high resolution 3D water temperature of the area influenced by the thermal plume. The results show that (I) the combination of remote sensing and sensor system can detect pattern in 3D in high spatial resolution, (II) surface temperatures and their spatial patterns differ from temperatures and their spatial patterns at greater depth and (III) at this site, local anomalies due to cooling water releases do not alter the overall thermal variability within the river.The combination of the novel sensor system with remotely sensed TIR data has the potential to be used to observe a broad range of hydrological processes in natural and artificial aquatic environments and to contribute to the understanding of overall energy budgets, infiltration, limnology, groundwater surface water exchange or similar processes.

Temporary storage areas (TSAs) represent a category of soft-engineered nature-based solutions that can provide dispersed, small-scale storage throughout a catchment. TSAs store and attenuate surface runoff, providing new additional storage during flood events. The need for such additional catchment storage will become more urgent as the frequency and magnitude of extreme hydrological events increases due to climate change. Implementation of TSAs in headwater catchments is slowly gaining momentum, but practitioners still require further evidence on how such measures function during flood events. This review focuses on the role of relatively small-scale (<10,000 m(3)) TSAs in headwater catchments for flood risk management. It also explores the potential wider benefits for implementing these as part of an integrated catchment management approach. TSA flood mitigation effectiveness is primarily determined by the TSA's available storage prior to the event. At the local scale, this can be represented by the relationship between TSA inputs, outputs and total storage. Factors influencing the local functioning and effectiveness of TSAs are discussed, with potential considerations for optimizing future TSA design and management. Hydrological models have suggested that TSAs could be used to effectively attenuate high magnitude events. However, future considerations should involve addressing the lack of empirical evidence showing TSA catchment scale effectiveness and how local TSA functioning might change in time. Small-scale headwater TSAs offer a holistic and sustainable approach to catchment management that can deliver both local benefits to landowners and wider flood risk mitigation for society.This article is categorized under:Engineering Water > Sustainable Engineering of WaterScience of Water > Water ExtremesScience of Water > Hydrological Processes

Natural Flood Management (NFM) and catchment-based solutions for flood risk management and environmental problems are wide-ranging and complex. Management of fluvial flood risk in the UK is undergoing a fundamental shift, with a change in emphasis from solely working with structural defences to considering catchment-based measures which attenuate flood runoff. At the heart of this change are NFM and nature-based solutions. One key type of intervention is the Runoff Attenuation Feature (RAF): a class of features that targets runoff flow pathways and creates new temporary flow storage (such as ponds and leaky barriers). However, there is currently a lack of evidence for the effectiveness of NFM and RAFs at larger catchment scales and for managing extreme flood events. Nevertheless, there is a strong evidence base to suggest that well-designed RAFs deliver a range of ecosystem services if installed in the correct location. This paper reviews and critiques the role of RAFs and NFM as an interventionist and holistic approach to lowering runoff rates. The link between RAF design types and their relationship to land use and scale is made. Recent novel innovations and attempts to scale up RAFs are discussed. The role of antecedent conditions, groundwater and the change in residence time of processes is highlighted. The uncertainty and complexity of proving NFM effectiveness underpin a view that new thinking in catchment flood management is needed. New research is required, and many questions are raised about RAFs and NFM. The direction of travel is that a positive and proactive NFM community can now embrace the problem. Proof that RAFs and NFM can address flood management is not likely to be resolved without a great deal of further research but confidence that RAFs do beneficial work is growing and an argument for greater amounts of runoff attenuation is made.

The impact of stormwater drainage and detention ponds on flooding is assessed using statistical analysis and physically based computer simulation of a 45-year case study for a peri-urban catchment. In 1978, the 54 km(2) Ouseburn catchment in Newcastle upon Tyne was impacted by the connection of a new 2.1 km(2) residential development, directly to the Ouseburn River, via a stormwater drain, which reduced the time to peak and increased flood risk. Further residential developments of 1.6 km(2) have been built since 2004, again with separated sewer systems, but this time linked to stormwater detention ponds before draining into the Ouseburn River. Detailed analysis of the data, confirmed with computer simulation, shows that in contrast with the 1978 intervention, these new developments had only a minimal effect on the flows in the Ouseburn River, in fact achieving a small reduction in peak flows for large events. This study assesses the post-construction efficiency of such systems, and we show that the stormwater detention ponds are working as designed.

Floodplain reconnection can potentially improve the hydrogeomorphology of river corridors and attenuate flood peaks. However, empirical evidence of its effectiveness - needed to inform future restoration - is limited. A 70 m long flood embankment was lowered on the upper River Dee, a medium sized gravel bed river in north-east Scotland to reconnect a backwater and floodplain. Comparison of two years pre- and three years of post-restoration hydro-geomorphic monitoring, shows the lowering and subsequent adjustment, assisted by several floods including a <1% annual exceedance probability event, have altered the morphology and hydrological dynamics. Channel aggradation of up to 1 m occurred. Erosion of the bank by up to 0.41 m in depth and deposition of gravel or sand within the backwater and the floodplain were the dominant geomorphic responses elsewhere. The channel adjustment, unexpected in the restoration design, improved hydrological connectivity with the floodplain; annual median water table levels were on average 0.037-0.089 m higher post-restoration although the correlation between river discharge and floodplain water levels did not change. Based on 1D modelling, the threshold river discharge for backwater connection decreased by 55% from 93 m3 s-1 (discharge exceedance percentile: Q0.4) to 42 m3 s-1 (Q8). Thus, overspill frequency increased. For a given peak discharge, floodplain water levels were higher on average by 0.25 m with a statistically significant difference (Mann Whitney U test: p < 0.05), due to improved hydrological connectivity. The monitoring demonstrates that localised but significant improvement of channel to floodplain hydro-geomorphic connectivity can result from targeted embankment lowering. Such actions could enhance future catchment resilience by improving water storage and biogeochemical processing.

Water temperature is one of the key factors controlling aquatic ecosystems and influencing physical, chemical and biological processes. Detailed observations of spatial and temporal patterns in water temperature are important for assessing e.g. variations in thermal refugia, impacts of climate change and for developing appropriate management strategies. Freshwater temperatures are still mostly analysed based on single point measurements, but these do not reflect the spatial thermal variability within waterbodies (i.e. stream and lake) and therefore could lack information on thermal refugia. 2-D images of freshwater temperature in varying spatial resolution are increasingly obtained by space- and airborne methods such as UAV (unmanned aircraft vehicles). While these UAV methods offer the necessary spatial resolution at the surface, they require in situ measurements to obtain absolute temperature values and don’t provide information on vertical thermal variability. Approaches that bridge this gap do exist (e.g. fibreoptic cables), but high demand on resources and high costs limit widespread use. The aim of this work was to develop a low-cost, custom-build, fully flexible 3-D temperature sensor system that can be used for calibration and validation of thermal UAV observations, but also adds information on water temperature with depth. The design of our floating sensor system (with a maximum of 72 sensors) offers high flexibility in horizontal/vertical spacing and logging time intervals (ms to h). Here we present the first results of our prototype, which was calibrated using Solinst Leveloggers (accuracy ± 0.05ºC) and tested under various ambient conditions, both in the laboratory and in a lab-in-field experiment in a relatively shallow lake (maximum measurement depth of 1.50 m) in NE Scotland. We also evaluated the use of this system with UAV imagery at the lake. The results show a quick response of the individual sensors to temperature changes and indicate suitability of the system for validating and calibrating thermal UAV images. For a set-up with 12 vertical arrays (6 sensors at different depths for each array) and arranged as a grid, preliminary data indicated the value for a 3-D approach as not all thermal patterns at depth were captured by surface measurements. Next, the transferability of the sensor system to a stream will be tested and applied to a stream water management case. Together with UAV thermal imagery, the new sensor system could have the potential for a wide range of research and management applications (e.g. thermal habitats, groundwater upwelling, infiltration of cooling water).