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Water surface roughness (SR) is a highly relevant parameter governing data reliability in remote sensing applications, yet lacking appropriate methodology in riverine habitats. In order to assess thermal accuracy linked to SR of thermal imaging derived from an unmanned aerial vehicle (UAV), we developed the SR Measurement Device (SRMD). The SRMD uses the concept of in situ quantification of wave frequency and wave amplitude. Data of nine installed SRMDs in four different fluvial mesohabitat classes presented a range of 0 to 47 waves per 30 s and an amplitude range of 0 to 6 cm. Even subtle differences between mesohabitat classes run, riffle, and no-/low-flow still and pool areas could be detected with the SRMD. However, SR revealed no significant influence on the accuracy of thermal infrared (TIR) imagery data in our study case. Overall, the presented device expands existing methods of riverine habitat assessments and has the potential to produce highly relevant data of SR for various ecological and technical applications, ranging from remote sensing of surface water and habitat quality characterizations to bank stability and erosion risk assessments. [ABSTRACT FROM AUTHOR]

Human activities and climate change threaten coldwater organisms in freshwater ecosystems by causing rivers and streams to warm, increasing the intensity and frequency of warm temperature events, and reducing thermal heterogeneity. Cold‐water refuges are discrete patches of relatively cool water that are used by coldwater organisms for thermal relief and short‐term survival. Globally, cohesive management approaches are needed that consider interlinked physical, biological, and social factors of cold‐water refuges. We review current understanding of cold‐water refuges, identify gaps between science and management, and evaluate policies aimed at protecting thermally sensitive species. Existing policies include designating cold‐water habitats, restricting fishing during warm periods, and implementing threshold temperature standards or guidelines. However, these policies are rare and uncoordinated across spatial scales and often do not consider input from Indigenous peoples. We propose that cold‐water refuges be managed as distinct operational landscape units, which provide a social and ecological context that is relevant at the watershed scale. These operational landscape units provide the foundation for an integrated framework that links science and management by (1) mapping and characterizing cold‐water refuges to prioritize management and conservation actions, (2) leveraging existing and new policies, (3) improving coordination across jurisdictions, and (4) implementing adaptive management practices across scales. Our findings show that while there are many opportunities for scientific advancement, the current state of the sciences is sufficient to inform policy and management. Our proposed framework provides a path forward for managing and protecting cold‐water refuges using existing and new policies to protect coldwater organisms in the face of global change. [ABSTRACT FROM AUTHOR]

Fine particle clogging and faunal bioturbation are two key processes co‐occurring in the hyporheic zone that potentially affect hyporheic exchange through modifications in the sediment structure of streambeds. Clogging results from excessive fine sediment infiltration and deposition in rivers, and it is known to decrease matrix porosity and potentially reduce permeability. Faunal bioturbation activity may compensate for the negative effect of clogging by reworking the sediment, increasing porosity, and preventing further infiltration of fines. Although both processes of clogging and bioturbation have received significant attention in the literature separately, their combined effects on streambed sediment structure are not well understood, mostly due to the lack of a standard methodology for their assessment. Here, we illustrate a novel methodology using X‐ray computed tomography (CT), as proof of concept, to investigate how, together, clogging and bioturbation affect streambed porosity in a controlled flow‐through flume. By visualising gallery formations of an upward conveyor macroinvertebrate; Lumbriculus variegatus as a model species, we quantified bioturbation activity in a clogged streambed, focusing on orientation, depth, and volume at downwelling and upwelling areas of the flume. Gallery creation increased the porosity of the streambed sediment, suggesting a potential improvement in permeability and a possible offset of clogging effects. We illustrate the promising use of X‐ray CT as a tool to assess bioturbation in clogged streambeds, and the potential role of bioturbation activity supporting hyporheic exchange processes in streambeds, warranting further studies to understand the extent of bioturbation impacts in natural systems. [ABSTRACT FROM AUTHOR]

Interdisciplinary approaches are required to tackle complex environmental issues as freshwater ecosystems face unprecedented pressures globally. The emerging Ecohydraulics field of research should, therefore, take steps towards developing true interdisciplinarity to adapt to a continuing changing world. This study contributes to the ongoing discussion on interdisciplinarity in Ecohydraulics and shapes its growth by identifying key actions, actors and implementation strategies that can strengthen it. Based on an online questionnaire and a workshop involving over 150 early and established careers, we present a list of 20 prioritised actions that will help engage the research community towards specific goals and will result in increased interdisciplinary outcomes. While early career researchers (ECRs) have taken the lead on creating this roadmap, its implementation should be a joint responsibility of both ECRs, established career scientists, groups, and institutions within Ecohydraulics. The list of identified actions and assigned responsibility should, therefore, be considered a conversation starter. Continued revision of the here-stated approaches will be required in the future as the field of research and its community progresses. With this contribution, we resume a critical reflection on where the Ecohydraulics field of research and community stand today and suggest where resources should be invested in the long-term to consolidate the inherent interdisciplinarity in Ecohydraulics. [ABSTRACT FROM AUTHOR]

Antonetti et al. ([6]) simulates the 2D hydro and thermal dynamics in a small braiding flooplain showing the influence of river morphology in shaping the hydro-thermal landscape, hence the habitat conditions, in hydropeaking rivers. The economic value of the South Saskatchewan river to the city of Saskatoon:(iii) value of alternative minimum river water flow. Hydropower represents the largest renewable energy source (Ritchie et al., [38]) with an increasing number of hydropower dams, especially in the Global South (Zarfl et al., [44]). Literature on hydropeaking covers impacts on bio-chemo-physical processes such as the river hydrological and thermal regime, the flora and the fauna of river corridors and their natural habitats, oxygen saturation and river metabolism, and the transport of sediments and contaminants. [Extracted from the article]

An increase in the demand for renewable energy is driving hydropower development and its integration with variable renewable energy sources. When hydropower is produced flexibly from hydropower plants, it causes rapid and frequent artificial flow fluctuations in rivers, a phenomenon known as hydropeaking. Hydropeaking and associated hydrological alterations cause multiple impacts on riverine habitats with cascading effects on ecosystem functioning and structure. Given the significance of its ecological and socio‐economic implications, mitigation of hydropeaking requires an inter‐ and transdisciplinary approach. An interdisciplinary network called HyPeak has been conceived to enrich international research initiatives and support hydropower planning and policy. HyPeak has been founded based on exchange and networking activities linking scientists from several countries where hydropeaking has been widespread for decades and numerous studies dedicated to the topic have been carried out. HyPeak aims to integrate members from other countries and continents in which hydropower production plays a relevant role, and grow to be a reference group that provides expert advice on the topic to policy‐makers, as well as researchers, stakeholders, and practitioners in the field of hydropeaking. [ABSTRACT FROM AUTHOR]

Hydropower is considered an important form of renewable energy, often involving hydropeaking. While the effects of hydropeaking on aquatic communities in areas downstream the dam are well understood, there is a lack of studies investigating potential impacts on tributaries located further upstream. In this study, we tested the effects of hydropeaking operations on upstream tributaries in a restored area of the Danube River, with a focus on the periods of backlog and release of water (up‐ramping and down‐ramping, respectively) during the filling and release of the reservoir. We used brown trout egg and larval mortality, linked to hydraulic, sedimentary and physiochemical changes in spawning grounds as an indicator. We compared hydropeaking‐affected versus non‐affected sites in upstream tributaries using HydroEcoSedimentary Tools (HESTs) loaded with clean gravels and brown trout eggs. Egg and larval mortalities were significantly higher in the hydropeaking‐affected site with more than 80% egg mortality and almost 100% larval mortality compared to values of 55–63% and 80–85%, respectively, in non‐affected sites. Spawning ground quality was significantly altered in the hydropeaking‐affected site, where the highest mortalities were observed. Overall, duration of time periods with flow velocities close to zero were a key variable, potentially decreasing oxygen supply for eggs and larvae. Such periods of close to zero flow velocities were driven by backlog periods during the filling of the reservoir, revealing that such events can severely impair ecological integrity of spawning sites in tributaries upstream of dams by slowing the flows in upstream tributaries. Such altered processes can reduce fish population recruitment and need to be considered in future restoration projects. [ABSTRACT FROM AUTHOR]

Increased deposition of fine sediments in rivers and streams affects a range of key ecosystem processes across the sediment–water interface, and it is a critical aspect of river habitat degradation and restoration. Understanding the mechanisms leading to fine sediment accumulation along and across streambeds and their effect on ecological processes is essential for comprehending human impacts on river ecosystems and informing river restoration. Here, we introduce the HydroEcoSedimentary tool (HEST) as an integrated approach to assess hydro‐sedimentary and ecologically relevant processes together. The HEST integrates the estimation of sedimentary processes in the interstitial zone, as well as hydraulic, geochemical and ecological assessments, with a focus on brown trout early life stages. Compared to other methods, the HEST expands the possibilities to monitor and quantify fine sediment deposition in streambeds by differentiating between vertical, lateral and longitudinal infiltration pathways, and distinguishing between the depth (upper vs. lower layers) at which interstitial processes occur within the sediment column. By testing the method in two rivers with different degrees of morphological degradation, we detail the possible measurements and uses of the HEST, demonstrate its feasibility and discuss its reliability. [ABSTRACT FROM AUTHOR]

Environmental flows aim to mitigate the impacts of modification of riverine flow regimes by restoring components of the natural flow regime. Explicit evidence-based cause-effect relationships between flow regimes and fish responses are required for defensible flow recommendations. However, flow recommendations are typically based on expert opinion rather than a rigorous test of the available evidence. We used rapid evidence synthesis to systematically review the literature on responses of several native Australian fish to flow-related and other important environmental variables, and tested 13 explicit hypotheses. The hypotheses were related to the condition, reproduction and survival of pygmy perches, carp gudgeons, blackfish and flat-headed gudgeons. The evidence was insufficient to reach strong conclusions for all but three of our hypotheses. Late-spring high flows are associated with increased survival of pygmy perches and carp gudgeons, and exotic fish are associated with decreased survival of these fishes. The evidence that warmer spring water temperatures enhance their reproduction was inconsistent. The dearth of evidence to support or refute most hypotheses points to substantial gaps in our understanding of hydro-ecology of these native Australian fish, highlighting the need for targeted monitoring and research to further understand key flow relationships for these fish species. [ABSTRACT FROM AUTHOR]

Hydropeaking power production has the potential to pose serious challenges towards hydrology, water quality and ecology in the downstream water bodies. The effects of such abrupt changes of flow in hyporheic exchange have been explored in a few cases in the literature. This paper extends previous works with a study of finer time resolution in a river of a smaller size and with different climatic characteristics, adding to the current knowledge of peaking-hyporheic interactions. A high-frequency logging field experiment measuring hyporheic flow and temperature was conducted on a ~30 × 20 m gravel bar frequently exposed to dry conditions because of fast and abrupt flow changes. This study demonstrates that hyporheic processes are sensitive to hydropeaking with respect to rates of change, durations and temperature. Differences BETWEEN individual events, seasons, watering and dewatering processes and positions in the river bed that can be potentially relevant to ecology were investigated. Understanding the complexity of those processes at the fine scale from the physical point of view is both important for the judgement of potential ecological impacts and for the future management of such regulated systems. Copyright © 2014 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

This paper presents a cost-effective approach to predict dynamic variation of mesohabitat classes or hydromorphological units (HMUs) in the context of a peaking scenario. Predicting dynamic mesohabitats has been a challenge in the last 20 years. This is mainly due to the fact that mesohabitat changes do not show a simple relationship with varying discharges. The HMUs Simulation Method, by using a one-dimensional hydraulic model as a basis, proved to be a promising tool to simulate HMUs at four varying discharges in a Norwegian river. Low flows and surface pattern criteria were the most challenging to simulate and best modelling results were achieved for the higher flows. Further development on this approach should follow, but at present the method shows promising results towards the prediction of dynamic HMUs at the river scale. [ABSTRACT FROM AUTHOR]

Understanding stream thermal heterogeneity patterns is crucial to assess and manage river resilience in light of climate change. The dual acquisition of high-resolution thermal infrared (TIR) and red–green–blue-band (RGB) imagery from unmanned aerial vehicles (UAVs) allows for the identification and characterization of thermally differentiated patches (e.g., cold-water patches—CWPs). However, a lack of harmonized CWP classification metrics (patch size and temperature thresholds) makes comparisons across studies almost impossible. Based on an existing dual UAV imagery dataset (River Ovens, Australia), we present a semi-automatic supervised approach to classify key riverscape habitats and associated thermal properties at a pixel-scale accuracy, based on spectral properties. We selected five morphologically representative reaches to (i) illustrate and test our combined classification and thermal heterogeneity assessment method, (ii) assess the changes in CWP numbers and distribution with different metric definitions, and (iii) model how climatic predictions will affect thermal habitat suitability and connectivity of a cold-adapted fish species. Our method was successfully tested, showing mean thermal differences between shaded and sun-exposed fluvial mesohabitats of up to 0.62 °C. CWP metric definitions substantially changed the number and distance between identified CWPs, and they were strongly dependent on reach morphology. Warmer scenarios illustrated a decrease in suitable fish habitats, but reach-scale morphological complexity helped sustain such habitats. Overall, this study demonstrates the importance of method and metric definitions to enable spatio-temporal comparisons between stream thermal heterogeneity studies. [ABSTRACT FROM AUTHOR]

Excess fine sediment, comprising particles <2 mm in diameter, is a major cause of ecological degradation in rivers. The erosion of fine sediment from terrestrial or aquatic sources, its delivery to the river, and its storage and transport in the fluvial environment are controlled by a complex interplay of physical, biological, and anthropogenic factors. While the physical controls exerted on fine sediment dynamics are relatively well‐documented, the role of biological processes and their interactions with hydraulic and physicochemical phenomena has been largely overlooked. The activities of biota, from primary producers to predators, exert strong controls on fine sediment deposition, infiltration, and resuspension. For example, extracellular polymeric substances associated with biofilms increase deposition and decrease resuspension. In lower energy rivers, aquatic macrophyte growth and senescence are intimately linked to sediment retention and loss, whereas riparian trees are dominant ecosystem engineers in high energy systems. Fish and invertebrates also have profound effects on fine sediment dynamics through activities that drive both particle deposition and erosion depending on species composition and abiotic conditions. The functional traits of species present will determine not only these biotic effects but also the responses of river ecosystems to excess fine sediment. We discuss which traits are involved and put them into context with spatial processes that occur throughout the river network. While strides towards better understanding of the impacts of excess fine sediment have been made, further progress to identify the most effective management approaches is urgently required through close communication between authorities and scientists. This article is categorized under: Water and Life > Nature of Freshwater EcosystemsWater and Life > Stresses and Pressures on EcosystemsScience of Water > Water and Environmental Change Controls on the delivery, transport and storage of fine sediment, and the resulting ecological responses in river networks. From the sediment sources in the landscape to the ecological impact in the river, the transport of particles and the responses of biota are subject to potential lags and delays as sediment is temporarily stored and time is taken for local populations to reach critical life‐stages where fine sediment limits survival. [ABSTRACT FROM AUTHOR]