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Centuries of beaver extirpation, deforestation, and other anthropogenic impacts have disconnected North American rivers from their floodplains and concentrated more hydraulic energy within their channels, degrading aquatic habitat and making the streambed more prone to erosion. Rivers naturally adjust via systematic downcutting, bank erosion, channel widening, bar building, and the gradual recovery of geomorphic equilibrium with well‐connected benches that dissipate hydraulic energy and restore a more natural streambed disturbance regime. The life histories of two endangered freshwater mussels, the fanshell (Cyprogenia stegaria) and snuffbox (Epioblasma triquetra), suggest they have evolved to and depend on the natural disturbance regime. Young juveniles excyst from their host fish in early summer, burrow into the top few millimeters of the streambed, and then need ca. 3 months of streambed stability prior to growing large enough to be less vulnerable to streambed mobilization. We propose a conceptual model that suggests a potential prerequisite to supporting fanshell and snuffbox populations is a geomorphically recovering (i.e. at least one stable bank and a wide enough channel corridor for at least partially vegetated bars/benches) or recovered (i.e. stable banks and vegetated benches) channel and floodplain corridor that sufficiently dissipates its hydraulic energy to maintain seasonal streambed stability during typical (non‐hurricane) summer/autumns. To explore this conceptual model, we conducted mussel and geomorphic surveys in a reach of the Rolling Fork River that spanned a range of channel conditions from chronically failing streambanks to a geomorphically recovered channel with wide, vegetated benches. Our analyses documented increasing mussel species richness, including the presence of the endangered fanshell or snuffbox, with increasing width of seasonally stable streambed habitat. [ABSTRACT FROM AUTHOR]

The plant diversity of riparian zones has significantly deteriorated due to human disturbances, making their restoration a key focus in research. However, restoration efforts often fail due to the lack of available propagules. Hydrochory, i.e., plants dispersed via water, which plays a critical role in transporting propagules downstream and is pivotal for riparian habitat recovery. Although hydrochory is closely related to the establishment and restoration of downstream riparian vegetation, most previous studies have concentrated mainly on the species richness and the number of propagules dispersed by water, but have overlooked the functional diversity. We explored the temporal variations in functional traits composition and functional diversity of hydrochorous propagules in three upland rivers within the upper Yangtze River catchment, situated in a humid subtropical monsoon climate. We find that during the high flows of summer, these rivers transport more species and exhibit higher functional diversity. This underscores the critical role of high summer flows for breaking the dispersal bottleneck of species with limited dispersal ability, and emphasizes the importance of hydrochory during the flood season for the recovery of riparian vegetation and maintaining high river flows is a critical strategy for restoration in the era of global flow regulation. [ABSTRACT FROM AUTHOR]

Water temperature is a critical factor for aquatic ecosystems, influencing both chemical and biological processes, such as fish growth and mortality; consequently, river and lake ecosystems are sensitive to climate change (CC). Currently proposed CC scenarios indicate that air temperature for the Mediterranean Jucar River will increase higher in summer, 4.7 °C (SSP5-8.5), resulting in a river water temperature increase in the hotter month; July, 2.8 °C (SSP5-8.5). This will have an impact on ecosystems, significantly reducing, fragmenting, or even eliminating natural cold-water species habitats, such as common trout. This study consists of developing a simulated model that relates the temperature of the river with the shadow generated by the riverside vegetation. The model input data are air temperature, solar radiation, and river depth. The model proposed only has one parameter, the shadow river percentage. The model was calibrated in a representative stretch of the Mediterranean river, obtaining a 0.93 Nash–Sutcliffe efficiency coefficient (NSE) that indicates a very good model fit, a 0.90 Kling–Gupta efficiency index (KGE), and a relative bias of 0.04. The model was also validated on two other stretches of the same river. The results show that each 10% increase in the number of shadows can reduce the river water temperature by 1.2 °C and, in the stretch applied, increasing shadows from the current status of 62% to 76–87% can compensate for the air temperature increase by CC. Generating shaded areas in river restorations will be one of the main measures to compensate for the rise in water temperature due to climate change. [ABSTRACT FROM AUTHOR]

Natural river landscapes can be biodiversity hotspots but are one of the most human altered ecosystems with habitats significantly damaged around the world, and a third of fish populations threatened with extinction. While riparian ecosystems have been negatively altered by anthropogenic activities, effective planning and restoration strategies can reverse negative impacts by improving habitat quality. However, restoring rivers requires appropriate data on current riparian health while also considering priorities for different stakeholders. To address this, a Geographic Information System (GIS) was used to create a new and transferable restoration priority model based on a section of the river Linth in Switzerland as a case study. The restoration priority model is founded on connectivity, river condition, national priority species and species hotspots. Landscape change of the riparian zone was analyzed using aerial imagery and landscape metrics. Almost a quarter of rivers within the study area were considered high or very high restoration priority, with many aquatic species set to benefit from restoration. From 1946 to 2019, the riparian landscape became highly fragmented due to significant growth in impervious surfaces and a concomitant loss of agricultural land. The GIS model provides a tool by which environmental agencies can manage natural features over large scales, while also planning priorities and targeting conservation strategies to the areas of greatest need. [ABSTRACT FROM AUTHOR]

Increasing organic carbon storage in river corridors (channels and floodplains) is a potential cobenefit of some river restoration approaches, raising the possibility of using restoration to produce carbon credits and, therefore, increase restoration funding. However, the uncertainty already associated with existing carbon credits is compounded in river corridors, which are dynamic on daily, seasonal, annual, and longer timescales. We currently do not know how much river restoration approaches could increase carbon storage or how significant increased organic carbon storage from restoration would be compared with other forms of climate mitigation. We also do not know whether river corridor carbon credits could meet market needs for quickly established, stable, and simple credits. Therefore, we argue that biophysical and political economic uncertainties make river corridor restoration carbon credits currently unfeasible but that research on river restoration projects would demonstrate whether restoration carbon credits could be feasible in the future. [ABSTRACT FROM AUTHOR]

Aquatic ecosystems are affected by multiple stressors, including hydrological and morphological degradation, high nutrient loading, and chemical pollution. To improve freshwater habitats, hydromorphological restorations have been increasingly implemented. However, follow‐up assessments often show little to no improvement in ecological status, even years after restoration measures have been implemented. The success of restoration projects can be compromised by other stressors, such as insufficient water and sediment quality, which often receive less attention compared to nonchemical stressors. In this study, the impact of chemical stress on the outcome of five river restorations was evaluated ecologically, chemically, and ecotoxicologically. Overall, the habitat structure was considerably improved through the restoration measures, whereas the species communities did not show a consistent trend toward an improved ecological status. Effect‐based methods were used for an integrative assessment of the exposure to chemical mixtures in water and sediment samples of restored stream sections. Differences in toxicity between restored and non‐restored sections were found but did not show a consistent trend among the applied assays. In contrast, the chemical analysis showed that the sections of the same stream were similar in their chemical composition, and differences within a stream were primarily due to sediment contamination. The results of this study suggest that chemical pollution is a relevant factor preventing the success of restoration measures and, ultimately, the improvement of the ecological status of rivers. They also demonstrate the applicability of EBMs in water quality monitoring to detect mixture toxicity in streams and link chemical and ecological assessment. [ABSTRACT FROM AUTHOR]

Understanding the relationship between a dam's size and its ecological effects is important for prioritization of river restoration efforts based on dam removal. Although much is known about the effects of large storage dams, this information may not be applicable to small dams, which represent the vast majority of dams being considered for removal. To better understand how dam effects vary with size, we conducted a multidisciplinary study of the downstream effect of dams on a range of ecological characteristics including geomorphology, water chemistry, periphyton, riparian vegetation, benthic macroinvertebrates, and fish. We related dam size variables to the downstream–upstream fractional difference in measured ecological characteristics for 16 dams in the mid‐Atlantic region ranging from 0.9 to 57 m high, with hydraulic residence times (HRTs) ranging from 30 min to 1.5 years. For a range of physical attributes, larger dams had larger effects. For example, the water surface width below dams was greater below large dams. By contrast, there was no effect of dam size on sediment grain size, though the fraction of fine‐grained bed material was lower below dams independently of dam size. Larger dams tended to reduce water quality more, with decreased downstream dissolved oxygen and increased temperature. Larger dams decreased inorganic nutrients (N, P, Si), but increased particulate nutrients (N, P) in downstream reaches. Aquatic organisms tended to have greater dissimilarity in species composition below larger dams (for fish and periphyton), lower taxonomic diversity (for macroinvertebrates), and greater pollution tolerance (for periphyton and macroinvertebrates). Plants responded differently below large and small dams, with fewer invasive species below large dams, but more below small dams. Overall, these results demonstrate that larger dams have much greater impact on the ecosystem components we measured, and hence their removal has the greatest potential for restoring river ecosystems. [ABSTRACT FROM AUTHOR]

From the early 2000s, many forestation projects were carried out in the flooding areas of the Po River to preserve abandoned or damaged riverbanks and establish natural populations of Populus nigra L. for species conservation and future seed collection activities. Different clones of P. nigra, belonging to a collection of the Centre for Forestry and Wood (CREA-FL), were planted. The group named 'POBIA' comprises 35 selected clones chosen for their survival ability and fast growth. After plantation and a few essential cultural inputs, four establishments were left undisturbed. This study highlights the survival, growth, and performance results of the 'POBIA' group compared to other not-selected clones. The 'POBIA' clones showed a higher survival than the not-selected clones. Moreover, the 'POBIA' groups showed a significantly higher C sink performance in three of four establishments, reaching 278.6 t ha−1 of CO2 obtained in thirteen years in one site. The management of 'POBIA' clones in reforestation projects agrees with the EU recommendations for a vital ecosystem service. [ABSTRACT FROM AUTHOR]

Habitat suitability modeling is a commonly used methodology to plan and assess in‐stream habitat enhancement in rivers, such as for the key fish life stages spawning and juvenile development. However, their use only allows modeling the spatial distribution of habitats, but not their connectivity. By integrating micro‐scale habitat modeling and a larval drift model, we assess the functional connectivity between spawning and larval nursery habitats for four rheophilic and litophilic fish species in a channelized and hydropower impacted reach of the lower Inn River (Bavaria, Germany), in which two restoration measures, a bypass channel and an island side‐channel system, have been constructed to improve longitudinal connectivity and habitat conditions. The study aims to (a) map spawning and larval nursery habitats, (b) quantify their connectivity, and (c) optimize functional habitat connectivity through an alternative bypass channel location. Results show that the channel's morphological complexity influences quantity and quality of available spawning and nursery habitats and their connectivity. Despite the presence of nursery habitats across the analyzed channel, the slow lateral larval dispersion during drift limits their accessibility to only the left river bank, making only 33% of available habitats useable. The degree of functional connectivity and hence the percentage of useable habitats can however be increased up to 95.3 % when considering different spatial configurations of habitats, which were explored in two alternative restoration scenarios. The results demonstrate the importance of considering functional habitat connectivity in habitat assessments and restoration planning. Key Points: Spawning to nursery functional habitat connectivity was quantified using a larval drift modelMorphological complexity affects habitat availability and functional connectivityConnectivity can be improved by optimizing spatial distribution of spawning sites [ABSTRACT FROM AUTHOR]

While urban river restoration has become mainstream in the Global North, it remains scarce in Latin America, where most literature focuses on water quality, stream habitats, and watershed assessment, but planning and implementation lag behind. Colombia is undergoing a paradigm shift after pioneering the integration of green and blue infrastructure (GBI) into urban planning in the early 2000s (namely Estructura Ecológica Principal). A surge in river renaturalization initiatives is underway, with large and intermediate cities planning and executing projects. We systematically assessed the integration of rivers and GBI into local policies (Planes de Ordenamiento Territorial) and found widespread and strong recognition of streams, wetlands, and ecosystem services in urban planning, higher than previously reported. Most cities emphasize river multifunctionality, ecological connectivity, public space, and recreation, as well as disaster risk reduction, advancing toward sustainable urban water and drainage systems. However, significant gaps persist regarding climate change resilience, participation, and social justice. In a region marked by high inequality, pre-existing spatial exclusion could be amplified by urban renewal, greening, and tourism due to unfair resettlement conditions and gentrification. Such trade-offs can undermine the ecological and social benefits of restoration. We highlight the crucial role of civil society and grassroots activism in protecting and defending urban commons and conclude by recommending a critical examination of GBI and river restoration efforts in Latin America. Colombia's case can serve as both a reference and a cautionary tale for other cities in the region to achieve outcomes that promote equity and justice amid pressing social and environmental challenges. [ABSTRACT FROM AUTHOR]

Since 2001, the Indonesian government has formulated and implemented several restoration programs to improve the Citarum's water quality. However, these programs were often contested, particularly concerning the meanings of 'water quality' and how those informed approaches to responsibility and involvement. This paper problematises river restoration in view of these controversies towards improving people's lives and their environment. Our investigation found (1) a selective use of scientific knowledge of water quality and related responsibilities; (2) a tension between broader inclusion and military involvement in river restoration; and (3) a diverse host of informal restoration practices that largely remain unnoticed in view of the government programs. The findings indicate that river governance can benefit from recognising and tuning into below-the-radar restoration practices to tackle river pollution. [ABSTRACT FROM AUTHOR]

Moving from an era of dam building to dam removal brings additional perspectives to indigenous water governance and hydrosocial relations in the Klamath River Basin (US). This collaborative research initiative with the Karuk Tribe builds greater understanding of the sociocultural impacts of Klamath dam removal and river restoration through Karuk knowledge. Addressing a knowledge gap around the social dimensions of dam removal, we held focus groups and interviews with Karuk cultural practitioners, tribal leaders, and tribal youth in the six-month period leading up to demolition. Extending beyond a focus on infrastructure removal or single-species restoration, we consider how Indigenous environmental relations and cosmologies are embedded in dam removal and river restoration. Specifically, Karuk knowledge shifts the significance of dam removal by elucidating deeply interconnected ecological, cultural, and ceremonial relations that are co-constituted with the Klamath watershed, thereby recasting dam removal as a holistic eco-cultural revitalization initiative. This reconfigures dam removal goals to include improving community health and well-being, enhancing spiritual elements of river restoration, responding to colonial legacies, and engaging tribal youth. In the Klamath case, restorative justice becomes possible through Karuk participation in river restoration to facilitate the revitalization of reciprocal relations held between Karuk people and the Klamath River—including Karuk eco-cultural and ceremonial practices for restoring balance in the world. [ABSTRACT FROM AUTHOR]

Rock-sills are instream low-head structures generally used to stabilize the riverbed. Their presence causes the formation of pools and riffles along the river, thus improving the aquatic habitat and creating resting spots for aquatic species. In this study, the riverbed morphology due to the rock-sill configuration installed at river bends was experimentally analyzed under clear-water condition, with a uniform, granular bed material. Tests were conducted by varying the inclination of sills with respect to the radial direction in three curved bends. Experimental evidence confirmed that the curvature of the channel bend plays a fundamental role, i.e., scour features significantly differed from those occurring in straight channels. Likewise, the inclination of the sill and its shape affect the scour morphology. The presence of the sill and the curvature of the channel caused an asymmetric distribution of the flow in the radial direction, possibly resulting in a shift of the scour hole toward the center. The analysis of experimental data allowed us to provide practitioners with a useful formula to predict the maximum scour depth. Finally, interesting insights on scour dynamics and features at equilibrium are also presented. [ABSTRACT FROM AUTHOR]

This paper evaluates the effectiveness of restoring open‐water area in a wetland via a geographical framework that goes from a general perspective to a detailed view. The methodology relies on diachronic cartography, remote sensing through Landsat satellite imagery validated by in situ hydrological data (2000–2022), and details from field work. We analyzed the water surface area of Comana freshwater marsh in Southern Romania. The water surface area recorded a statistical change point synchronous to the restoration actions. The water surface area increased due to restoration actions in 2011 and then became relatively stable. Post‐restoration, the mean monthly discharge of Neajlov River correlates statistically with the water surface area. The water has low depths in the marsh; yet, the area covered by vegetation appears to be stable. The persistence of the effects for over a decade recommends Comana Marsh as a demonstrative case study in South‐Eastern Europe and for further monitoring activities. [ABSTRACT FROM AUTHOR]

A philosophical and communication shift is needed in river management if we are to meet sustainable development goals and tackle environmental challenges brought about by ongoing anthropogenic and climate change. In some parts of the world, recovery‐enhancement approaches to river management have been adopted, communicated and used for many years. At the heart of these approaches lies an understanding of the biogeomorphic forms, processes and evolutionary trajectories of rivers that differs philosophically from notions of restoration, rewilding or creation of a utopian natural state. Instead, recovery‐enhancement approaches aim to improve the biogeomorphic condition of rivers, recognising that they are dynamic entities and new evolutionary trajectories and novel ecosystems are being created that are now part of the environment. Accepting shifting baselines and moving targets is inherent as boundary conditions (water, sediment and vegetation interactions) continue to be altered under the influence of anthropogenic and climate change, and the impacts of 'unprecedented' wildfires, floods, heatwaves and drought are manifested on the ground. The river management sector has not yet fully adapted to this reality with large amounts of applied science and on‐ground practice still focussed on restoration, re‐engineering and rewilding, words which in themselves produce a false impression of the aims, visions and achievability of river management. Embracing recovery‐enhancement approaches to river management requires a conscious shift in communication strategies and terminology to present more realistic expectations and possibilities for river condition improvement, a responsibility that is incumbent upon us, the scientists and practitioners, who work in the applied science and river management profession. In this Short Communication, I use a case study from eastern Australia to illustrate what biogeomorphic river recovery can look like. I use this to discuss the potential for adoption of a recovery‐enhancement approach to river management more broadly, and call on scientists and practitioners to make a conscious philosophical and communications shift when working in applied science and river management. [ABSTRACT FROM AUTHOR]

Channel migration, furcation, and vegetation succession are characteristic processes of braided gravel rivers in Alpine regions. These are associated with a frequent turnover of large parts of the active floodplain. However, more than one century of river regulation has reduced or destroyed most of these ecosystem dynamics. More recently, there have been attempts to restore at least some sections of degraded rivers, while there is little monitoring of the biogeomorphological dynamics of such rivers. Thus, we did a four‐year analysis of four representative sections of the upper River Isar in Southern Germany differing in their degree of naturalness. Dynamics of channels, gravel bars, and vegetation were recorded by drone images, and braiding and gravel indices were calculated. When comparing the near‐natural, semi‐natural, degraded or restored sections, there was a gradient of decreasing channel migration, gravel bank expansion, and bank erosion due to a reduced turnover frequency. Biogeomorphological variation among years correlated with log peak discharge within the four sections. In addition, the cover and height growth of vegetation increased with river degradation, and channel migration was positively related to the braiding index. The total turnover of the active river corridor and of the vegetation were positively correlated with log peak discharge within the four sections. The floodplain dynamics of the restored section were improved compared to the degraded section but did not reach a near‐natural state. Thus, Alpine river sections with contrasting degrees of naturalness differ in terms of habitat turnover and vegetation succession, and these characteristics can only partially be restored by local measures. [ABSTRACT FROM AUTHOR]

Biogeomorphological responses to river restoration are rarely reported. Despite a transition in the emphasis and priorities of river management over the last 40 years from controlling river channel forms and processes to restoring and supporting natural processes, forms and functions, remarkably little information is available on project outcomes. Here, using the example of Beverley Brook within Wimbledon Common, Greater London, UK, we illustrate how standardised detailed monitoring information can be assembled at a very low cost using the citizen science MoRPh survey and we demonstrate the importance of having a pre‐project vision of likely outcomes that can be tracked by the monitoring programme. We show how a pre‐project and five post‐project surveys undertaken over 4 years according to a before‐after‐control‐impact (BACI) design provides scientifically robust data. Analysis of the survey data quantifies the nature, abundance and spatial distribution of restoration interventions, the immediate responses to those interventions, and the ensuing trajectory of biogeomorphological adjustments. Changes in the persistence, size, position, abundance and evolution of habitats reveal the degree to which the restoration achieved the pre‐project biogeomorphological vision and why the recovery trajectory progressed at the observed rate and to the observed end point over 4 years. Our approach has enormous potential for monitoring the outcomes of river interventions. Whilst our project was limited in its spatial scale and focus on physical habitats, we suggest how these limitations could be overcome whilst still containing costs. [ABSTRACT FROM AUTHOR]

Recent river studies in the United Kingdom have observed an increase in riparian vegetation and its potential impact on river channel change and sedimentation. Here, we quantify changes in floodplain and riparian vegetation during the first two decades of the 21st century along reaches of eight gravel‐bed rivers in England and Wales that exhibit varied active and stable, single and multi‐thread planforms. The analysis employs information drawn from open‐access sources including national LiDAR surveys and the photographic analysis of repeat aerial and satellite imagery. Most reaches show an increase in woody vegetation across their floodplains reflecting both natural colonisation and deliberate planting, and all but one of the reaches show an increase in woody riparian vegetation cover along their riverbanks. Of the six reaches that have exposed riverine sediments, five show a reduction in exposed sediment area as a result of vegetation encroachment. Contrasts in the rate, extent and location of riparian change were associated with the stability of the channel planform, with differences seen between stable and more active reaches. The significance of riparian woodland in promoting riverbank stability is demonstrated. Riparian vegetation development varies between river reaches, largely in response to differing rates of channel movement but also because of multiple and diverse local decisions regarding the management of in‐channel and channel‐adjacent vegetation by landowners rather than a single national policy. We consider the relevance of our findings and the value of remote monitoring for future river management interventions. [ABSTRACT FROM AUTHOR]

River restoration projects often involve vegetation planting to retain sediment and stabilize riverbanks. Laboratory experiments have explored the impact of rigid emergent vegetation canopies on bed morphology. Inside canopies, bed erosion is attributed to vegetation‐induced turbulent kinetic energy (TKE). Based on the in‐canopy local TKE and the criteria for sediment movement, a method is established and validated for predicting the length of the bed erosion region. In the bare channel, bed erosion is related to the ratio of canopy length to flow adjustment distance, L/LI, and exhibits two trends. At L/LI < 1, the maximum depth, ds(bare), and length, Ls(bare), of the bed erosion region increase with increasing canopy length. At L/LI ≥ 1, ds(bare) and Ls(bare) are not influenced by the canopy length and remain constant. In vegetated regions with the same length and plant density, discontinuous canopies (streamwise interval s ≥ canopy width D) yield weaker bed erosion than continuous canopies. The mutual influence between two canopies must be considered if the canopy interval satisfies s < 3D. These results provide insights for designing vegetation canopies for river restoration projects. Key Points: The impact of canopy length on bed morphology inside and outside the canopy is clarifiedA method for predicting the length of the bed erosion region inside canopies is establishedDiscontinuous canopies produce weaker bed erosion than continuous canopies for the same vegetated region length and plant density [ABSTRACT FROM AUTHOR]

In the first half of the 2000s, one project to restore the former Danube floodplain was carried out in Belene, a marginal town on the Bulgarian Danube. The aim of this article is to record the practices that were already in place before the interventions on the Danube, as part of a heterogeneous local knowledge that had an alternative vision to the scientific knowledge of experts involved in the restoration project. The data comes from qualitative interviews with locals and experts implicated in this project, as well as ethnographic observations from the fieldwork I carried out in 2013–2014, 2020 and 2022. The conclusion is that without attempting to replace the scientific knowledge, the locals aim to impose, through their local knowledge, a sort of slow ecology that eases the pace of the restoration of the former Danube floodplains. [ABSTRACT FROM AUTHOR]

This study investigates the effect of large woody debris (LWD) on the abundance of juvenile Atlantic salmon (Salmo salar, L.) and anadromous brown trout (Salmo trutta, L.) in semi‐alluvial side channels of the river Aurlandselva (Norway) using point electrofishing and microhabitat mapping. Not the presence of LWD, but stream bed shelter availability and the distance to spawning grounds affected the fish abundance (fish/point), independent of other habitat components. LWD showed only an effect on fish abundance when in interaction with other habitat components. This discrepancy can be explained by the availability of cavities in the shelter‐rich coarse substrate which provide sufficient cover and territory for juvenile fish at the given carrying capacity of river Aurlandselva. Whilst LWD may be most effective to provide shelter in lowland streams (bed slope <0.005), maintaining or restoring shelter‐rich coarse substrates should be considered a key priority in steeper salmonid rivers and associated semi‐fluvial streams. [ABSTRACT FROM AUTHOR]

Alpine rivers are among the most heavily modified ecosystems in Europe. Following massive interventions in the 18th and 19th centuries, many plant species specialized in these challenging environments declined and are now endangered or even locally extinct. Today, attempts are being made to reintroduce these species as part of restoration measures, but only a few are successful. The selection of potential sites for reintroduction is commonly intuitive and based on practical considerations, while a prior scientific assessment of habitat availability and habitat connectivity is lacking. To increase the success of future reintroductions, we employ a habitat suitability model and subsequent habitat connectivity analysis to identify promising regions and patches for reintroduction within a riverscape. We demonstrate this approach using the Alpine river specialists Chondrilla chondrilloides and Myricaria germanica in three differently degraded and one restored section of the large Alpine river Isar. All river sections provide habitats for both species, but with increasing degradation, habitats become fewer and less connected. For the species with a narrower habitat niche and lower dispersal ability, suitable and connected patches that support a self-sustained metapopulation are only found in the near-natural sections. Despite an improvement in the habitat situation, the patch size in the restored section is too small, and the patches are too scattered to support a successful reintroduction of the species. We show that this evidence-based approach outperforms an intuitive selection of out-planting sites. The results further underline the importance of using scientific habitat analysis to increase the success of reintroduction measures.

The Periyar River, a vital component of Kerala's ecosystem in India, serves as a lifeline supporting agriculture, hydropower generation, and ecological equilibrium. This study adopts a multifaceted approach to address critical challenges in the Periyar basin, with a primary focus on flood mitigation due to the region's susceptibility to devastating floods. Covering a length of 67.85 km, the study intricately segments the Periyar River into distinct reaches for a comprehensive steady flow analysis, considering factors such as seasonal monsoon fluctuations, diverse catchment topography, and human-induced alterations. Utilizing advanced modeling techniques, particularly HEC-RAS software, the study effectively predicts and simulates shifts in hydraulic behavior. The results, including velocity plots and cross-sectional maps, offer accurate insights into critical parameters, enabling the identification of areas with high velocity occurrence. This information proves instrumental in making informed decisions for the construction of river restoration structures, crucial for mitigating the impact of floods. The study's findings contribute valuable tools for future forecasting and sustainable management of the Periyar River, addressing the complex interplay of natural and anthropogenic factors. HIGHLIGHTS One dimensional steady flow analysis is performed in this study.; Velocity plots were generated to get clear idea about velocity of each station.; Terrain plots were generated from HEC-RAS.; Critical flood prone area identification can be done by analysing velocity plots.; HEC-RAS modelling is effective for flow studies.;

ABSTRACTNature-based solutions (NBS) are actions that help communities address social-ecological challenges such as flooding and polluted groundwater. Nevertheless, research shows that in practice, NBS confront several barriers in planning and implementation, many of which are related to the different attitudes of political and administrative actors. There is knowledge missing on their viewpoints on NBS. We used Q-methodology to explore the attitudes towards the implementation of a constructed wetland as NBS, interviewing decision-makers from the Tárcoles River Basin Commission in Costa Rica, the administrative body in charge of the integrated management of the river. We determined three recognizable viewpoints: ‘the nature lover’, ‘the cost concerned’, and ‘the participation seeker’. Although all members of the commission shared a common vision, it was clear that their priorities differed. Regarding the ways of implementing NBS, interviewees agreed that the country urges a paradigm shift in policy design towards ecosystem-based approaches and emphasized the need for more cooperation among bodies of administration in river basin decision-making. We reflect on the lessons learned to improve planning and implementation of NBS, such as the importance of increasing knowledge and awareness of NBS, the support from all governance levels as well as the cooperation of researchers and policy-makers, and the consideration of NBS financing by private companies.

Migration is critical for life‐cycle completion in diadromous fish species. River connectivity is vital in facilitating these large‐scale movement events, but the extent of present‐day river fragmentation can interfere with these migrations. Fish passage solutions (FPSs) are commonly implemented with the aim of improving river connectivity. In our study, we investigated the performance of two types of FPSs, spill regimes and complete dam removal, on Atlantic salmon (Salmo salar) smolt migrations. We used acoustic telemetry to monitor migration behavior and passage success of 120 wild smolts released in three different groups/sites: one group with two dams to pass to reach the river mouth, a second group with one dam to pass, and a control group without any barriers to pass (upstream of a recently removed hydroelectric dam). Smolt passage probabilities were similar for the two studied dams (87% and 86%) but showed variation in path choice, delay times, and loss rates. Passage success was influenced by several factors, such as body size, diel period, and water temperature, but not flow. Cumulative passage success to the river mouth was 61%, with most individuals being lost within lentic river stretches, either in the forebays of hydroelectric power stations or in naturally wide river stretches. Within the recently rehabilitated river sections (post dam removal), passage speeds were significantly faster than all other sections of the river (post‐rehabilitation x¯ = 56.1 km/day) with significantly faster speeds compared to pre‐rehabilitation (pre‐x¯ = 28.0 km/day). Our findings provide valuable information on the benefits of dam removal and highlight the need for further rehabilitation measures in upriver reaches where barriers still affect downstream passage. [ABSTRACT FROM AUTHOR]

Cool‐water habitats provide increasingly vital refuges for cold‐water fish living on the margins of their historical ranges; consequently, efforts to enhance or create cool‐water habitat are becoming a major focus of river restoration practices. However, the effectiveness of restoration projects for providing thermal refuge and creating diverse temperature regimes at the watershed scale remains unclear. In the Klamath River in northern California, the Karuk Tribe Fisheries Program, the Mid‐Klamath Watershed Council, and the U.S. Forest Service constructed a series of off‐channel ponds that recreate floodplain habitat and support juvenile coho salmon (Oncorhynchus kisutch) and steelhead (O. mykiss) along the Klamath River and its tributaries. We instrumented these ponds and applied multivariate autoregressive time series models of fine‐scale temperature data from ponds, tributaries, and the mainstem Klamath River to assess how off‐channel ponds contributed to thermal regime diversity and thermal refuge habitat in the Klamath riverscape. Our analysis demonstrated that ponds provide diverse thermal habitats that are significantly cooler than creek or mainstem river habitats, even during severe drought. Wavelet analysis of long‐term (10 years) temperature data indicated that thermal buffering (i.e. dampening of diel variation) increased over time but was disrupted by drought conditions in 2021. Our analysis demonstrates that in certain situations, human‐made off‐channel ponds can increase thermal diversity in modified riverscapes even during drought conditions, potentially benefiting floodplain‐dependent cold‐water species. Restoration actions that create and maintain thermal regime diversity and thermal refuges will become an essential tool to conserve biodiversity in climate‐sensitive watersheds. [ABSTRACT FROM AUTHOR]

Elevated fine sediment accumulation in a river system's gravel bed is known to cause detrimental ecological impacts. Current sediment targets and approaches to mitigation have failed due to the oversimplification of geomorphological processes controlling fine sediment accumulation and the lack of relevant scientific knowledge underpinning them. This is particularly apparent in chalk streams (groundwater‐dominated systems) which regularly exhibit high rates of sediment accumulation despite low suspended sediment yields. A necessary first step is to better characterise their sedimentology; thus, the novelty of this study was to determine the sedimentological characteristics of chalk stream gravel beds, specifically the quantity and distribution of fine sediment with depth. We collated published and unpublished freeze‐core data, encompassing 90 sites across 11 UK chalk streams. Results showed average quantities of fine sediment (<2 mm) in chalk stream gravel beds were 25% by weight, with >75% of beds exceeding thresholds for ecological degradation. Quantities of fine sediment increased with increasing depth into the bed, with an average increase between surface and subsurface layers of 54%, and 89% of the gravel bed over‐saturated with fine sediment. Regional differences were attributed to differences in stream power and local sediment sources, including surficial geology and catchment land use. Additionally, a major contrast was identified between experimental conditions in flume studies used to establish models describing interactions/mechanisms of fine sediment infiltration into immobile gravel beds and the natural conditions observed in chalk streams. As such, the use of such models as a basis to explore sediment management scenarios is unlikely to predict the outcome of such management techniques correctly in a real‐world situation. [ABSTRACT FROM AUTHOR]

This research evaluates natural flood management strategies in a mountain basin, the Olivares-Minitas creek in Manizales, Colombia, to quantify the effectiveness of their application in reducing floods. Hydraulic and hydrological modeling was performed simultaneously in Iber software. Multiple scenarios were proposed for three natural flood management alternatives: (1) making room for the channel, eliminating contractions and structures limitations, (2) changing the vegetation cover of the upper part of the basin, increasing the ground roughness, and (3) reconnect the stream with their floodplains, allowing the stream to dissipate flow and energy. Applying these strategies, the simulations resulted of the decrease the high discharges and the delay in peak times for the hydrographs. In conclusion, from natural solutions like rehabilitating, recovering the water body, and their ecosystem, is possible to manage and reduce the flooding risk, Attaining benefits through long-term reduction of flooding and enhancement of the river and its ecosystem. [ABSTRACT FROM AUTHOR]

How rivers restored for aquatic biota such as Pacific Salmon (Oncorhynchus spp.) will evolve under shifting management and climate regimes is unknown. To inform this, we tracked the evolution of a highly impacted, regulated river reach following habitat restoration and subsequent drought and flood hydrology using a suite of data to better understand how created habitat evolves over time. Topographic change detection, riffle creation and persistence, substrate, and Chinook Salmon spawning and rearing habitat were evaluated for the three epochs. Sediment transport regimes and velocity outputs from the numerical flow model were used to interpret channel change associated with the flood season the site experienced. Salmon spawning observations and habitat suitability modeling demonstrated that habitat improved following restoration for both salmon spawning and rearing. Chinook Salmon spawning activity and the relative site utilization compared to escapement increased post Project. These benefits were largely maintained during drought and flood events, despite an absence of upstream coarse sediment supply. We hypothesize this was because the restoration design incorporated riffle-pool maintenance theories and the use of emergent islands that served as a local sediment source. Extrapolations of bioturbation by spawners suggest that if population targets for the river are met, topographic change due to spawning activity could exceed that caused by river flow under drought conditions and provide a modest contribution during flood years. Thus, this study demonstrates that river restoration can not only improve physical habitat, but also engage ecosystem engineers such as spawning salmonids to contribute to future habitat evolution. [ABSTRACT FROM AUTHOR]

Dam removal has become one of the most widespread tools for river restoration; however, these projects can be conflictual. Our aim in this paper is to question the disconnection between the ecological project and the territorial project and to evaluate its role in the emergence of conflicts. Conceptually, we draw on a hydrosocial territory perspective to link the sociopolitical and economic context to the production of a new materiality sustained by power relationships. We focus on the removal of two large dams on the Sélune River in Normandy, France, which has fueled a conflict that has lasted for a decade. By combining multiple data sources (semi-directive interviews, focus group, archives), we highlight five successive and overlapping phases since the dams' construction at the beginning of the 20th century. Each of these periods are characterized by the (dis)empowerment of certain stakeholders, the evolution of the material environment, and the fluctuation of the hydrosocial territory scales. The case of the Sélune highlights the importance of including long-term historical perspectives in the concept of hydrosocial territory, i.e. thinking about hydrosocial heritages. Hydrosocial heritages constitute a new way to approach non-human actors by taking the historical and contemporary relationships between humans and non-humans into account. It also helps situate the dynamics of a conflict in a deeper historical process, revealing how past dynamics shape contemporary situations. [ABSTRACT FROM AUTHOR]

It is currently unclear how river restoration based on hydro-geometrical modifications, dredging, and creating a barrier instead of its removal on a river would affect the water quality in urban rivers. This work attempts to fill this gap in our understanding by simulating the water quality of a highly critical 22-km-long Delhi stretch of river Yamuna in terms of DO, BOD, and total coliform after the implementation of these river restoration measures. Four scenarios were conceptualized based on these restoration measures and water quality simulated. These are: scenario I: simulate the impact of varying the width uniformly for all reaches of the study stretch on the water quality, scenario II: simulate the impact of increased depth by controlled dredging. Scenario III (a) closing the ITO barrage gate and then simulating river water quality from Wazirabad barrage to ITO barrage and (b) closing the ITO barrage and simulation of water quality from ITO barrage to Okhla barrage. Results reveal that the water quality improved significantly in scenario I and scenario II. Scenario III did not yield desirable results in terms of water quality improvement. To the best of the author's knowledge, this is the first attempt involving river morphometry changes using the QUAL2k model for the Delhi stretch of river Yamuna. [ABSTRACT FROM AUTHOR]

Wood accumulations influence geomorphic, hydraulic, and ecologic functions within a river corridor, but characterizing these accumulations presents challenges across a range of field and remote sensing methodologies. We evaluate the ability of handheld lidar scanners, specifically lidar‐scanning capabilities of a fourth‐generation iPad Pro, to collect three‐dimensional wood accumulation data, which can be used to inform measurements of wood volume, porosity, complexity, and roughness. We discuss the potential and limitations of this novel methodology for river research and management. We found that handheld lidar presents a cost‐effective input for data‐processing workflows that field measurements of wood accumulation dimensions cannot as easily replicate including (1) a user‐friendly means of data collection and visualization; (2) accurate comparisons of wood volume over time; (3) integration into workflows to measure porosity parameters; and (4) potential use in informing hydraulic and morphodynamic models. Consideration of study area constraints and intended use of scans are prerequisites to using handheld lidar as an effective tool. We identified some specific limitations of using handheld lidar scanners in wood‐rich river corridors, including (1) scanners perform poorly when wood is under water or surrounded by dense vegetation; (2) scanners require physical access to areas of interest at distances less than 5 m; (3) scans need to be manually georeferenced; and (4) scans require manual measurements for any dimensional data, which still have associated user time and error. Handheld lidar as a scientific tool is rapidly developing and there is substantial room for expansion of applications, utilization, and advances in the use of this tool in river research and management. [ABSTRACT FROM AUTHOR]

Unnatural changes in river flow patterns resulting from peak‐operating hydropower plants adversely impact freshwater ecosystems. In particular, the rapid dewatering of shoreline habitats during artificial flow down‐ramping puts early fish life stages at a high risk of becoming stranded if they fail to follow receding water levels in time. While extensive research has been conducted on the effects of hydropeaking on salmonid species, there is limited knowledge on the diverse cyprinid family, particularly on vulnerable early life stages. Hence, this study aims to compare the larval stranding of two cyprinid species, the common barbel (Barbus barbus L.) and common nase (Chondrostoma nasus L.), in response to bank dewatering. We conducted larvae experiments in near‐natural mesocosms, simulating single flow down‐ramping events with varying down‐ramping rates (0.3–1.8 cm·min−1) during the day and at night to quantify stranding rates, also including water temperature and fish development. Our results reveal distinct diurnal patterns for both species, with higher stranding rates during the night than during the day in all experimental scenarios. The data also show higher stranding rates at faster down‐ramping, with interaction effects between down‐ramping rates and time of day. The stranding rates between the two species are similar across most of the scenarios. Scenarios with colder water temperatures show that nase larvae tend to strand more frequently than with warmer temperatures. In conclusion, the study results contribute to the ongoing discourse on hydropeaking mitigation by providing new perspectives on flow‐reduction effects on early cyprinid life stages. Mitigation measures should prioritize the periods during early larval development and factor in prevailing water temperatures. Lowering down‐ramping rates, especially during nighttime, will help minimizing negative impacts on aquatic ecosystems, particularly when combining flow rules and habitat restoration measures. [ABSTRACT FROM AUTHOR]

Introduction: Alterations in river systems are inevitable and affect the environment. Rivers have played a very important role in creating and maintaining life on the earth since a long time ago. In other words, rivers are vital for sustaining life and ecosystems, providing essential freshwater for irrigation, drinking, and industry. However, human interventions including changes in land use patterns, construction near rivers, exploitation of water resources, and flood and storm management have significantly impacted on these crucial environmental systems. They can actually alter the spatial distribution and velocity of geomorphological processes such as sediment transport, erosion, and deposition, consequently leading to significant changes in river morphology. Therefore, assessing their morphological quality is important for their management and restoration. In this study, morphological assessment from the upstream to the midstream of the Talar River as a pilot has been conducted using the Morphological Quality Index (MQI) to evaluate the morphological status. Material and Methods: First, Talar River was divided into two landscape units, three segments and 23 reaches based on the hierarchical approach and according to the physiographic condition. Then, geomorphological functionality, artificial structure and Indicators of channel adjustment have been assessed by MQI which includes 28 parameters. Results and Discussion: The results obtained from 28 MQI parameters in 23 reaches showed that about 15% of the reaches have a "good" condition; almost 35% have a "moderate" condition, and more than 50% have "poor" and "very poor" conditions. Based on the assessment along the Talar River, the areas that are in the urban area due to a large amount of agriculture, urban development and road crossing have poor and very poor morphological quality class, and the areas that are in the forest area are natural and have good morphological quality. Also, the results of the assessment indicate that the average quality class of the investigated reaches is in "moderate" conditions. Conclusion: The results show that most reaches of Talar River require urgent measures for its restoration. In addition, although the MQI method can be an appropriate and effective tool in diagnosing hydromorphological challenges. However, it is not still enough for an integrated management and restoration, and it should be integrated with other indices regarding human pressures i.e. water quality, hydrological and biological pressures. [ABSTRACT FROM AUTHOR]

Codornices Creek is a small urban stream in Alameda County, California, that flows along the border between the cities of Albany and Berkeley. The creek provides habitat for Oncorhynchus mykiss, a species of salmonid known as steelhead or rainbow trout, depending on whether populations have an ocean-going life stage. Steelhead trout are a species of interest in Codornices Creek because they are listed as threatened under the Endangered Species Act. Populations in the creek have fluctuated over the past 30 years due to impacts from restoration projects, urban pollution, and climatic conditions. Previous reports have suggested that water temperature may be limiting steelhead trout success in some reaches, prompting our investigation into water temperature and potential drivers in Codornices Creek.We analyzed spatiotemporal trends in water and air temperature recorded at eight sites along Codornices Creek during a 5-month period (June - November 2022), including potential drivers for water temperature trends such as rainfall and canopy cover. We analyzed canopy cover using spatial analysis and field observations. We obtained water temperature data from long-term monitors, a local stream gauge, and a thermocouple for instant field measurements. We downloaded air temperature and rainfall data from the National Weather Service weather station located at the Oakland International Airport (June - November 2022) and additional rainfall data from a local rainfall gauge (October - November 2022). We then calculatedlong-term water temperature suitability as maximum weekly average temperature and maximum weekly maximum temperatures. We compared water temperature to air temperature, rainfall, and canopy cover to determine primary drivers of water temperature. To evaluate canopy cover, we brought National Agriculture Imagery Program satellite imagery into ArcGIS and calculated the normalized difference vegetation index within a 30-meter buffer along open stream sections of Codornices Creek. We supplemented this analysis with field observations at each study site using a densiometer.  Our investigation indicated that air temperature affected long-term trends in water temperature, rainfall affected short-term water temperature trends, and canopy cover tended to moderate the effects of air temperature. Despite water temperatures in the upper half of the watershed being slightly cooler than downstream temperatures, water temperatures throughout Codornices Creek were generally within suitable range for steelhead trout. Only one location downstream reached temperatures stressful for steelhead trout. This location may require further investigation, as air temperature, rainfall and canopy cover do not explain elevated temperatures. Locating and addressing the source of elevated temperature may benefit steelhead trout populations.

The Nooksack Dace (Rhinichthys cataractae sp. cataractae) is a federally endangered riffle specialist endemic to the lower Fraser Valley of British Columbia, Canada, with historic population declines associated with riffle loss from stream dredging, channelization, and excessive sediment inputs. To assess the effectiveness of riffle restoration as a recovery strategy, gravel and cobble riffles were constructed in two replicate tributaries of the Nooksack River as a before-after-control-impact experiment, measuring dace abundance, substrate composition, and invertebrate biomass before and one year after restoration. Nooksack Dace density increased significantly in cobble (but not gravel) treatments relative to control riffles. Dace abundance was strongly associated with increased availability of interstitial refuges rather than substrate effects on invertebrate prey abundance, suggesting that interstitial space limits adult dace abundance. Young-of-the-year dace were not observed in one of the two restored streams despite riffle restoration, indicating increased dace density due to aggregation in higher-quality restored riffles. This recruitment limitation indicates persistence of a population bottleneck at an early life history stage that is not addressed by successful restoration of adult riffle habitat.

Large dam removal can trigger changes to physical and biological processes that influence vegetation dynamics in former reservoirs, along river corridors downstream of former dams, and at a river's terminus in deltas and estuaries. We present the first comprehensive review of vegetation response to major fluvial disturbance caused by the world's largest dam removal. After being in place for nearly a century, two large dams were removed along the Elwha River, Washington, USA, between 2011 and 2014. The exposure, erosion, transport, and deposition of large volumes of sediment and large wood that were impounded behind the dams created new fluvial surfaces where plant colonization and growth have occurred. In the former reservoirs, dam removal exposed ~290 ha of unvegetated sediment distributed on three main landforms: valley walls, high terraces, and dynamic floodplains. In addition to natural revegetation in the former reservoirs, weed control and seeding and planting of desirable plants influenced vegetation trajectories. In early years following dam removal, ~20.5 Mt of trapped sediment were eroded from the former reservoirs and transported downstream. This sediment pulse, in combination with transport of large wood, led to channel widening, an increase in gravel bars, and floodplain deposition. The primary vegetation responses along the river corridor were a reduction in vegetated area associated with channel widening, plant establishment on new gravel bars, increased hydrochory, and altered plant community composition on gravel bars and floodplains. Plant species diversity increased in some river segments. In the delta, sediment deposition led to the creation of ~26.8 ha of new land surfaces and altered the distribution and dynamics of intertidal water bodies. Vegetation colonized ~16.4 ha of new surfaces: mixed pioneer vegetation colonized supratidal beach, river bars, and river mouth bars, and emergent marsh vegetation colonized intertidal aquatic habitats. In addition to the sediment-dominated processes that have created opportunities for plant colonization and growth, biological processes such as restored hydrochory and anadromous fish passage with associated delivery of marine-derived nutrients may influence vegetation dynamics over time. Rapid changes to landforms and vegetation growth were related to the large sediment pulse in the early years following dam removal, and the rate of change is expected to attenuate as the system adjusts to natural flow and sediment regimes. [ABSTRACT FROM AUTHOR]

Geomorphic river design strives for natural resilience by encouraging geomorphic form complexity and morphological processes linked to greater habitat diversity. Increasing availability of high‐resolution topographic data and spatial feature mapping methods provide advantages for morphological analysis and river restoration planning. We propose and evaluate an approach to quantifying topographic variability of geomorphic form and pixel‐level surface roughness resulting from channel planform geometry differences using spatially continuous variety computation applied to component metrics including flow direction, aspect and planform curvature. We define this as the geomorphic form variation (GFV) approach and found it scalable, repeatable and a multi‐stage analytical metric for quantifying physical aspects of river‐bed topographic variability. GFV may complement process‐based morphological feature mapping applications, hydraulic assessment indices and spatial habitat heterogeneity metrics commonly used for ecological quality evaluation and river restoration. The GFV was tested on controlled synthetic channels derived from River Builder software and quasi‐controlled sinuous planform flume experiment channels. Component variety metrics respond independently to specific geometric surface changes and are sensitive to multi‐scaled morphology change, including coarser‐grained sediment distributions of pixel‐level surface roughness. GFV showed systematic patterns of change related to the effects of channel geometry, vertical bed feature (pool‐bar) frequency and amplitude, and bar size, shape and orientation. Hotspot analysis found that bar margins were major components of topographic complexity, whereas grain‐scale variety class maps further supported the multi‐stage analytical capability and scalability of the GFV approach. The GFV can provide an overall variety value that may support river restoration decision‐making and planning, particularly when geomorphic complexity enhancement is a design objective. Analysing metric variety values with statistically significant hotspot cluster maps and complementary process‐based software and mapping applications allows variety correspondence to systematic feature changes to be assessed, providing an analytical approach for river morphology change comparison, channel design and geomorphic process restoration. [ABSTRACT FROM AUTHOR]

The placement of wood in rivers is a common restoration method used to locally affect hydraulic and morphologic conditions to create habitat. Laboratory experiments demonstrated that wood placements can also promote surface declogging, that is, removal of fine sediment from a gravel bed, thereby restoring spawning grounds for fish. Logs of different size and submergence level were placed on a gravel bed clogged with fines. Surface declogging was observed in regions of elevated turbulence in the log wake and elevated velocity adjacent to the log. A criteria for declogging was identified based on a modified non‐dimensional Shields parameter combining mean and turbulent velocity at the bed. The footprint of declogged bed scaled with log dimensions. Emergent logs produced a larger declogging footprint compared to submerged logs of the same length, due to their stronger influence on the flow field. Logs were also shown to prevent clogging over similar areas. Plain Language Summary: Placing wood in rivers is a common way of improving river health and creating regions for fish and small aquatic animals to live. This method involves the placement of individual wood pieces (logs) at the side or in the center of a river. In this study, we explored how the positioning of logs could be used to remove fine sediments from gravel beds by changing the way water flows. This is important because excessive deposition of fine sediments in the bed, defined as riverbed clogging, can make the channel bed too compact. This makes it harder for fish to find good spots to lay their eggs. Using laboratory experiments, we observed that the logs generated regions with strong water turbulence (swirling) and faster flowing water in their surroundings, both of which removed fines from the gravel bed surface. We identified specific conditions necessary for effective removal of fines, which were related to both the turbulence and water velocity. The size of the cleaned area on the gravel bed was proportional to the size of the log. Key Points: Deliberate wood placement can promote declogging adjacent to and downstream of logsDeclogging was correlated with elevated turbulence downstream of logs and elevated velocity adjacent to logsEmergent logs declogged a greater surface area than submerged logs [ABSTRACT FROM AUTHOR]

This study attempts to back-calculate Manning's roughness coefficients by repeating a two-dimensional flow simulation to fit the spatially and temporally dense river water-level data observed in Japan's Yamatsuki River, a typical mountainous river with an average riverbed gradient of 1/50 and an average river width of 17.9 m. Furthermore, we aim to clarify the influence of the in-channel physical parameters on the coefficient of roughness obtained through the above method. In the Yamatsuki River, 16 water-level gauges were installed at intervals of about 40~80 m in the longitudinal direction in the study reach. Manning's roughness coefficients were back-calculated by repeating two-dimensional flow simulations to match the observed water levels of a flood in 2021 (the estimated maximum flow rate is 11.5 m3/s). The back-calculated roughness coefficients approached a constant value in the range of 0.05 to 0.1 s/m1/3 as the relative water depth increased, indicating that the roughness coefficient can be considered a constant value when performing plane two-dimensional flow calculations for flooding. The roughness coefficient during flooding was found to be correlated with the slope and step height (H)-step length (L)- channel slope (S) ratios (H/L/S). An equation for predicting the roughness coefficient during flooding based on the physical parameters of the channel is also proposed. [ABSTRACT FROM AUTHOR]

Missing cooperation between farmers and nature conservationists is an obstacle to conflictive social-ecological transformation processes of agro-systems in Germany. Conflict psychology research shows that agonistic conflict frames play a crucial role in the parties' response to and perception of conflicts. However, the role of conflict frames regarding farmers' response to conservation conflicts in Germany, which are a recurrent expression of social-ecological transformation, is yet unclear. To address this knowledge gap, we investigate whether farmers have different agonistic conflict frames and whether these are related to their perceptions of specific conflicts. To answer these questions, we developed a cluster analysis of farmers' attitudes towards conflicts over river restoration in order to find indications for different conflict frames. We used data from a telephone survey from 2021 that was conducted with 300 farmers on the topic of river restoration conflicts. We captured conflict frames using four categories: rejection of others' attitudes, perceived threat, perceived integrated potential, and delegitimization. In the second and third steps, we looked for differences between the groups with regard to the perception of concrete conflict and economic factors. The results of this explorative study show that it is possible to distinguish six agonistic conflict frames within the four categories. Moreover, the six groups show differences in how they perceive a concrete river restoration conflict. In five out of six groups, the perceived threat is indicated as high. The findings show that farmers have different perspectives on the conflict, indicating possible differences in needs and differences regarding the openness to communicative strategies. The groups differ in their concrete conflict perception, and only weak characterization with regard to the economic situation could be found. This knowledge can help policymakers and practitioners find practical and communicative strategies that constructively address farmers' different conflict frames. [ABSTRACT FROM AUTHOR]

Riffles are heterogeneous habitats that support diverse assemblages in natural streams. They are often constructed as part of stream restoration practice, including in degraded urban stream ecosystems, despite larger scale limits to ecological state. Such restoration practices fail to consider ecological theory, and their outcomes have rarely been robustly monitored and assessed. We assessed the effects of constructed rock riffles on habitat heterogeneity and on macroinvertebrate assemblages in six urban streams (4%–32% effective imperviousness). We compared habitat heterogeneity, and taxon abundance and richness of the six streams before and after (1 and 5 years) riffle construction and in three control streams without riffles. Riffles increased habitat heterogeneity. In contrast, macroinvertebrate assemblages in all streams were dominated by tolerant, cosmopolitan, and invasive taxa before and after riffle construction. Riffles reduced the abundance and richness of tolerant taxa in less urbanized streams and increased their richness in more urban streams. These changes had no effect on measures of biodiversity. Urban stormwater runoff can affect the degree to which rock riffles increase habitat heterogeneity through sediment transport and increased physical disturbance. In highly urban streams, increased habitat heterogeneity is likely to primarily favor cosmopolitan species that can tolerate frequent chemical and physical disturbance. Riffle construction may reduce the abundance of cosmopolitan species and increase the abundance of more sensitive species, but only if catchment‐scale impacts of urban stormwater runoff are adequately controlled. Robust experiments such as this add to general understanding of the effectiveness of restoration practice, reducing the need for ubiquitous monitoring of restoration projects. [ABSTRACT FROM AUTHOR]

ABSTRACT On January 2022, the Carmo River (a tributary of the Doce River) was affected by an extreme hydrological event, with 50-yr return interval. This event was 50% higher than that associated to one of the largest tailing dam failures ever reported that took place in the Gualaxo do Norte River. This delivered to Doce River, through the Carmo River, in a Y-shaped confluence, the contaminated tailing slurry. In order to understand the role of tributaries in the recovery of the Doce River, 2D hydrodynamic and 2D sediment transport models were applied at the confluence of the Carmo River with the Piranga River. Our results, based on hydraulic modeling, remote sensing, and in-situ measurements, indicated that significant amounts of sediments were trapped on the riverbanks and stone banks, making this confluence an important site for the retention of contaminated sediments, influencing sediment budgets and downstream water quality. Therefore, this confluence deserves special attention from water engineering in order to prevent the sediments retained in this area from being transported downstream during extreme events in the coming years. These results can contribute to decision-making, to identify reaches with greater susceptibility to erosion and sediment deposition and to plan the restoration of these rivers.

Tributaries play a vital role in fish spawning and recruitment, significantly influencing mainstem river fish populations. However, in the Anthropocene era, tributaries within river networks suffered ecological degradation due to fragmentation and channelization. This has led to reduced distribution ranges and declining populations of various riverine species, underscoring the urgency of conservation and rehabilitation efforts. Our study explores the potential for reintroducing fish from the mainstem Danube River into the Wien River, an urban tributary that has undergone partial rehabilitation. We assessed habitat use and movement patterns of 20 adult barbel (Barbus barbus), a species classified as ‘near threatened’ in Austria, collected from the Danube River during the spawning season. These barbel were tagged with radio telemetry tags and relocated into the upper reaches of the Wien River, surmounting several artificial barriers in the lower sections. Although spawning activity was not observed among the barbel, possibly due to prevailing water temperatures, our data suggest that the Wien River could function as a viable temporary habitat. Barbel were notably inclined to inhabit deeper pool and run habitats. Their daily movements and home ranges were relatively limited, ranging from 0.0 to 1.1 km and 100 m to 2.9 km, respectively. One contributing factor to restricted movement was the presence of beaver and knotweed dams, which created temporary migration obstacles. On average, the barbel remained within the system for more than a month. Most of these fish migrated downstream at the onset of a significant high-flow event. Our assessment suggests that while the Wien River may not serve as a permanent habitat, it could function as a temporary habitat for migratory fish. However, to ensure accurate assessments of the restored Wien River as a spawning habitat, it is imperative to reevaluate the findings under stable spawning conditions and gather comprehensive data on relevant abiotic factors. This study advocates for the restoration of longitudinal connectivity between tributaries and mainstem rivers as a means to counteract biodiversity loss in Anthropocene river ecosystems.

River re-naturalisations are at the forefront of conservation efforts. The hope is that these interventions will benefit both local ecosystems and facilitate flood mitigation. While hydrological modelling has been a standard procedure in assessing the outcomes of river re-naturalisations, vegetation modelling has not always been performed as part of these assessments. We hypothesised that the use of potential vegetation modelling, i.e. the modelling of self-sustainable vegetation that can survive after the intervention, can provide insight into vegetation outcome of river re-naturalisation and can thus support vegetation restoration and conservation planning. We investigated the utility of potential vegetation modelling under a specific, widespread element of river re-naturalisation: river floodplain widening at three study sites along the Tisza River in Hungary. We applied potential vegetation modelling, in addition to hydrological and groundwater modelling, to assess the expected vegetation outcome of the river floodplain widening. Flood frequency and duration were assessed by the HEC-RAS hydrological model. Based on the output this hydrological model provided, expected values of the water-related explanatory variables (including groundwater level) were calculated. Statistical relationships encompassed by the existing mulitple potential vegetation (MPV) models of Hungary were applied to the environmental variable sets corresponding to conditions before and after floodplain widening (pre- and post-treatment, respectively), including water-related and other explanatory variables. This resulted in predicted potential vegetation distribution for pre-treatment and post-treatment conditions, which were then compared via ordinations and PERMANOVA. At two of the study sites, post-treatment potential vegetation prediction typically showed vegetation types requiring wetter and less saline conditions when compared to the pre-treatment potential vegetation distribution. This pattern corresponds to general expectations given river floodplain widening. However, at one of the sites, the potentiality of saline and non-saline steppe vegetation was actually more pronounced under the expected post-treatment conditions than those before widening. The strengthening of the potentiality of dry vegetation types can be explained by the minor environmental differences related to the microrelief. As the studied sites were all located in the lowlands where geomorphological variation is small, the effect of these minor geomorphological differences on post-treatment potential vegetation would have remained hidden without applying MPV models. In conclusion, scenarios that employ MPV models help predict river restoration outcomes more accurately and can help identify factors that might otherwise be overlooked. Thus, when combined with physical modelling of river flow, their use can aid in the restoration and landscape planning decisions in river re-naturalisation projects.