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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]

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]

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]

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]

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.

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]

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]

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]

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]

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.

In the context of the requirements of the Water Framework Directive to reinstate a river’s good ecological status after being severely altered by human pressures, river restoration became a major topic in the last decade in the EU and the number of projects implemented especially on hydromorphology increased. However, it is still uncertain whether these restoration measures have positive cumulative effects, i.e. hydromorphological effectiveness, when compared to reference conditions and expectations of stakeholders, because of inconsistent methodologies. Therefore, the goal of our project is to develop a methodology to evaluate the hydromorphological effectiveness of river restoration, based on standardised indicators, at various spatial scales, appropriate for implemented measures and for restored river types, weighting the expectations of actors and adapted to case studies in Romania. This methodological protocol could become also a useful tool to create a strategy and make decisions in the practice of river restoration. Moreover, this kind of analysis could contribute to clarifying the issue of standards in environmental projects.

Background: In Korea, riparian zones and some floodplains have been converted into agricultural fields and urban areas. However, there are essential for maintaining biodiversity, as they are important ecological spaces. There are also very important spaces for humanity, as they perform various ecosystem services in a changing environment including climate change. Due to the importance of rivers, river restoration projects have been promoted for a long time, but their achievement has been insignificant. Development should be pursued by thoroughly evaluating the success of the restoration project. Ecological restoration is to accelerate succession, a process that a disturbed ecosystem recovers itself, with human assistance. Ecological restoration can be a test bed for testing ecological theories in the field. In this respect, ecological restoration should go beyond a ‘simple landscaping exercise’ and apply ecological models and theories in restoration practice. Results: The cross-section of the restored stream is far from natural rivers due to its steep slope and artificial material. The vegetation profiles of the restored streams did not reflect the flooding regime of the river. The species composition of the vegetation in the restored stream showed a significant difference from that of the reference stream, and was also different from that of an unrestored urban stream. Although species richness was high and the proportion of exotic species was low in the restored stream, the effect was offset by the high proportion of gardening and landscaping plants or obligate terrestrial plants. Conclusions: Based on both the morphological and ecological characteristics of the river, the restoration effect in the restored stream was evaluated to be very low. In order to solve the problems, a systematic adaptive management plan is urgently required. Furthermore, it is necessary to institutionalize the evaluation of restoration effects for the development of river restoration projects in the future.

The removal of the two dams on the Sélune River since 2019 has led to profound changes in the aquatic ecosystem. Lentic habitats bordered by forest had shifted to new conditions (running water and sparsely vegetated riverbanks) therefore shaping organisms’ assemblies. We studied how the reestablishment of aquatic lotic habitats in interaction with riparian vegetation could mediate the restoration of important ecological functions in the new river. Six stations located along the river continuum were surveyed for 3 years after dam removal: two control stations upstream the former reservoir, three restored stations within the former reservoir, and one control station downstream. We monitored physico-chemical characteristics, phytobenthos biomass and the river’s benthic metabolism, and assessed the functional composition of macroinvertebrate communities. We compared the recorded variables among upstream, downstream and restored sampling stations. We observed a rapid recolonization by invertebrates, but a still low phytobenthic primary production in restored stations. Such a low primary productivity was also reflected in the functional composition of invertebrate communities. Three years after dam removal, there was still a significant time lag between communities recovery and expected ecosystem functioning restoration. We observed a quick colonization by aquatic running-water invertebrate communities of new lotic reaches, but a slower recovery of important ecological functions rates such as those observed in control stations.

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 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.

Abstract 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.

On 5–6 July 2017, an unstable atmospheric condition caused an unusual concentration of rainfall above the Northern part of Kyushu Island, triggering a set of hydro-meteorological hazards. Within the affected area, the mountainous subwatershed of the Akatani River was significantly impacted by numerous landslides combined with debris flow and floods. National and local agencies deployed a plan of reconstruction to restore the floodplain and protect inhabitants. Regarding the hydrosystem in the Akatani watershed, this reconstruction project mainly focuses on the restoration of damaged protection systems and the construction of new infrastructures. Thus, this paper aims to explain the restoration plan of the Akatani River in terms of the strategic Japanese River System Sabo and then as a model of a national-scale spatial plan. It draws on (i) a literature review based on the historical evolution of Japanese protection systems and the River Sabo System; (ii) field surveys in 2019, 2022 and 2023, in conjunction with (iii) interviews with local, regional, and national officials; and (iv) a Geographical Information System analysis of previously and newly built protection systems through aerial photograph interpretation and geospatial data. Sabo works implemented in the Akatani watershed illustrate the engineering vision of Japanese river management. They also constitute a comprehensive system and include a downstream–upstream logic which echoes that of the River System Sabo. In addition, the disaster of July 2017 and the government's response emphasize the continuous adaptation and improvement of the Japanese disaster management system, which mitigates severe disasters. [ABSTRACT FROM AUTHOR]

In the context of the requirements of the Water Framework Directive to reinstate a river's good ecological status after being severely altered by human pressures, river restoration became a major topic in the last decade in the EU and the number of projects implemented especially on hydromorphology increased. However, it is still uncertain whether these restoration measures have positive cumulative effects, i.e. hydromorphological effectiveness, when compared to reference conditions and expectations of stakeholders, because of inconsistent methodologies. Therefore, the goal of our project is to develop a methodology to evaluate the hydromorphological effectiveness of river restoration, based on standardised indicators, at various spatial scales, appropriate for implemented measures and for restored river types, weighting the expectations of actors and adapted to case studies in Romania. This methodological protocol could become also a useful tool to create a strategy and make decisions in the practice of river restoration. Moreover, this kind of analysis could contribute to clarifying the issue of standards in environmental projects. [ABSTRACT FROM AUTHOR]

Constructed floating wetland (CFW) is an ecotechnology used to improve water quality using emergent macrophytes on a floating mat structure. The goals of this research were to design and evaluate a low-cost field-scale CFW for revitalization of a polluted lentic section of an urban stream, located in the subtropical coastal region of South Brazil. To attain these goals (i), the design parameters were selected from field-scale applications in the literature, and (ii) the influence of the meteorologic and hydraulic data over the CFW performance to improve water quality were analyzed during five months. Macrophyte leaves grew 1 cm·day−1. Biochemical oxygen demand (BOD) (72%), total phosphorus (TP) (52%), turbidity (53%), total solids (TS) (60%), dissolved oxygen (DO) (39%) and water temperature (WT) (0.4 °C) showed statistically significant reductions. The HRT was sufficient to reduce dissolved carbonaceous organic matter. HRT and solid particles-related parameters showed reductions both on high and low HRT. The resulting loading rates can be used for the design purposes of similar CFW field applications. The CFW promoted water quality improvement, attractiveness of fauna, temperature regulation, carbon sequestration, and is a potential ecotechnology towards the depollution of river basins in urban areas. [ABSTRACT FROM AUTHOR]

Despite millions of dollars being spent annually to restore degraded river ecosystems, there exist relatively few assessments of the ecological effectiveness of projects. An evidence-based synthesis was conducted to describe river restoration activities in Newfoundland and Labrador. The synthesis identified 170 river restoration projects between 1949 and 2020. A practitioner's survey was conducted on a subset of 91 projects to evaluate ecological success. When the perceived success of managers was compared to an independent assessment of ecological success, 82% of respondents believe the projects to be completely or somewhat successful whereas only 41% of projects were evaluated as ecologically successful through an independent assessment. Only 11% of practitioners' evaluations used ecological indicators, yet managers of 66% of projects reported improvements in river ecosystems. This contradiction reveals a lack of the application of evidence to support value-based judgments by practitioners. Despite reporting that monitoring data were used in the assessment it is doubtful that any meaningful ecological assessment was conducted. If we are to improve the science of river restoration, projects must demonstrate evidence of ecological success to qualify as sound restoration. River restoration is a necessary tool to ensure the sustainability of river ecosystems. The assessment conducted in this study suggests that our approach to planning, designing, implementing, monitoring, and evaluating projects needs to improve. An integrated-systems view that gives attention to stakeholders' values and scientific information concerning the potential consequences of alternative restoration actions on key ecosystem indicators is required. [ABSTRACT FROM AUTHOR]

Abstract Fish physical habitat models are a tool for guiding restoration efforts in lotic ecosystems, but often they overestimate restoration outcomes because currently they do not incorporate habitat connectivity. This persistent issue can, in extreme cases, result in little or no improvement to fish populations after the restoration, wasting valuable conservation resources. We present a case study where practitioners applied a fish habitat model for multiple life stages of gravel spawning fishes to a 52‐km stretch of the Iller River but did so at a microscale implementation by setting up a model based on cross sections with a maximum of 200 m distance from each other. This approach provided an opportunity to assess the connectivity of habitats for gravel spawning fishes, that is, European Grayling (Thymallus thymallus) and Common Nase (Chondrostoma nasus), integrating probabilities to find suitable habitats for all life‐history stages and seasonal movements. We used the assessed habitat estimates (availability of distinct habitat types within reaches defined by the 200 m cross sections) to calculate the minimum distance a fish would need to overcome to change from one habitat type into the other as it hypothetically ‘grew up’ from egg to full spawning adult. This approach can be interpreted as a life cycle habitat check as it considers all habitat types that are necessary to fulfil the life cycle of gravel spawning fishes including their size, distance and flow direction‐related orientation (e.g. larvae habitats only used when downstream of spawning areas). Our results show that the assumption of complete connectivity would require long movement distances for vulnerable life stages to find suitable habitat. This puts the high priority on the creation of migration corridors and passability of migration barriers in question. Without consideration of habitat types for all life stages of a species and their spatial context, restoration will not be successful. Shortly said: A perfect migration corridor does not necessarily provide habitat connectivity. We recommend the application of the habitat connectivity approach when predicting the effect of restoration measures and particularly setting the priority of measures for mitigation of fish migration.

The dam removal movement is resulting in numerous projects worldwide, especially in Western countries. Whether completed or in progress, these undertakings often trigger conflict. Nearly 30 years after the initiation of the first major projects, this article examines the conditions for the local appropriation of dam removal projects. From the perspective of two pioneering and emblematic projects in France (Sélune River) and the United States (Elwha River), this article highlights the geographic specificities of dam removal projects carried out in European rural areas. The aim is to discuss how to implement ambitious ecological projects without running the risk of local people losing their sensitive relationship (history, experience, landscape) with the areas once they have been restored. In other words, ecological restoration should not result in a loss of meaning and quality in the relationship between local people and newly restored spaces; it should instead enrich it. In fact, the removal of a dam is not just a technical project; it profoundly affects landscapes, disrupting uses and creating new places. We identify the modalities by which a new space is produced and appropriated by local populations based on a comparison of the relevant spaces (national park vs. rural agricultural space), the populations involved (river users, Native American tribes, residents, and NGOs), and, finally, the governance processes and interactions between expertise and politics, all to highlight the need to take geographical context into account. Based on a detailed knowledge of the formation of the Sélune dam removal project, which has been the subject of continuous participant observation since 2011, we examine these projects’ singularities and commonalities to identify the factors that contribute to their success. This study highlights the importance of the spatial scale at which the dam removal project should be framed, the role of government, and the importance of considering people’s attachment to local places. Finally, this comparison makes recommendations for improving the socio-territorial quality of ecological projects, especially in Europe, with the aim of ensuring their sustainability and success.

Modeling fish community responses to dam removal is an emerging field of study as dam removals become more common, but uncertainties concerning recovery time and community stability remain. In Europe, an EU-wide biodiversity strategy plans to restore around 25,000 km of rivers to free-flowing status, which emphasizes the importance of being able to predict fish community responses after dam removal. We developed a multi-species size spectrum model for a fish community in the Mörrum River in Sweden to identify possible outcomes after a dam was removed in 2020. Electrofishing monitoring before the dam removal was used to calibrate the model. We projected multiple scenarios into the future to explore patterns of community stability, individual species responses, and recovery time while varying parameters related to dam removal mortality, base resource rate change, and maximum recruitment change. We created 30 hypothetical scenarios using an abrupt change perspective (parameters are step-based) and 30 scenarios using a gradual change perspective (parameters are smooth). In both perspectives, dam removal mortality and a decreasing resource rate reduced community biomass and delayed recovery time compared to pre-dam removal conditions. Our results demonstrate that recovery from a dam removal scenario is not necessarily a benefit for all species. In scenarios where dam removal practices or dam failures cause high mortality events and sustained impacts on base trophic level resources, recovery of pre-removal biomass may take decades, while community stability may be unstable for twice that time-period. Our study shows that size spectrum models can be applied to dam removal scenarios to explore potential recovery outcomes, particularly from a risk avoidance perspective. A benefit of using such an approach is the relatively low data requirements needed to perform projections (e.g., present species, fish growth rates, relative fish abundance). Implementing this model in other river systems, particularly at the reach scale, can help river restoration and management assess tradeoffs associated with different habitat restoration approaches prior to committing to a dam removal plan.

In the milieu of escalating flood occurrences, the concept of community resilience has garnered considerable attention. A series of studies recommend a river restoration approach to encourage the participation of all relevant stakeholders to manage floods to improve community resilience. However, existing studies have not sufficiently unraveled the intricate interplay of drivers shaping such participation. Therefore, using the Moat System Restoration Project in Tianchang City as the empirical conduit, this study elucidates the relationship between the drivers that drive stakeholder participation in river restoration in the context of improving community resilience. The Theory of Planned Behavior was employed to extend additional independent variables such as stakeholder attitudes, priorities, risk perception, trust in government decisions, knowledge, motivation, and intentions. A sample of 473 local residents involved in the Moat System Restoration Project was evaluated by Structural Equation Modelling. The empirical results revealed the salient influence of stakeholder attitudes, knowledge, and priorities on their behavior and risk perception where harnessing perceptions of priority has the potential to significantly improve community resilience. Notably, the study dispelled the presumed influence of trust on risk perception, a revelation that deviates from some existing literature. The findings further demonstrate a strong association between stakeholder motivation and both risk perception and intentions, a relationship underappreciated in previous studies. Theoretically, this study unearths the intricate dynamics of stakeholder participation in river restoration projects, thereby extending the Theory of Planned Behavior to the sphere of stakeholder participation, which adds a critical dimension to the understanding of flood management and community resilience. Practically, this study provides a valuable lens for practitioners as it illuminates pathways to foster stakeholder participation in river restoration initiatives, guiding the development of strategies to foster stakeholder participation in similar projects. [ABSTRACT FROM AUTHOR]

River rehabilitation and ecological engineering are becoming critical issues for improving river status when ecological habitats and connectivity have been altered by human pressures. Amongst the range of existing rehabilitation options, some specifically focus on rebuilding fluvial forms and improving physical processes. The aim of this contribution is to illustrate how geomorphological expertise and process-based thinking contribute to river rehabilitation success. This semantic contribution is intended to feed the rehabilitation debate, particularly concerning the design of actions and the proposed references for monitoring target reaches and evaluating rehabilitation effects empirically. This article is also based on lessons learned from practical cases, mainly in gravel-bed rivers. Geomorphic understanding is needed at a local level to achieve an adequate diagnosis of river functioning, estimate human impacts and potential remnant river responsiveness, and to assess the gains and risks from rehabilitation, as well as to appraise success or failure through several pre- and post-project assessment strategies. Geomorphological studies can also be upscaled in a top-down manner (from high-order controls to small-scale processes, understanding detailed processes in their regional or basin-wide context), providing large-scale information at the regional, national, or even global level, information that can be used to diagnose the health of riverscapes in relation to local site-specific contexts. As such, geomorphological studies support strategic planning and prioritization of rehabilitation works according to specific contexts and river responsiveness, so as to move from opportunistic to objective-driven strategies. [ABSTRACT FROM AUTHOR]

Peri-urbanization changes the natural dynamics of fluvial processes. Human intervention can be seen in the riverbeds and also in land use changes, vegetation cover variations, and the capture of water resources. As a result, hydrogeomorphological indicators have become relevant for evaluating these impacts. In this article, the hydrogeomorphological quality of the Napostá Grande stream in the peri-urban area of Bahía Blanca, Argentina, is evaluated. The Hydrogeomorphological Index (IHG) was applied to functional sectors in order to analyze fluvial behavior against human intervention on a section scale. We compared the values obtained in 2016 and in 2021. Over the last five years, the hydrogeomorphological quality decreased mainly in the parameters of the quality of the riparian corridor and the quality of the channel. Likewise, variations intensify as the stream descends towards the more urbanized sectors. In terms of river health, the evaluations of the index and processes such as streamlining the channel show signs of deterioration that may require river restoration measures. [ABSTRACT FROM AUTHOR]

Vortex rock weirs (VRW) are often used in natural channel design applications to maintain channel form and function, provide physical channel stability, and enhance aquatic habitats. A balanced approach is required to address (often) conflicting goals of VRWs, which include providing erosion protection and grade control while facilitating fish passage for target species. This research evaluated a sequence of modified VRWs in a small-scale watercourse in Southern Ontario, Canada. To determine passage suitability for the target fish species, the water level, water temperature, and channel geometries at 10 VRWs and 11 adjacent pools were monitored under different water level conditions. The structural dimensions and velocity at each VRW were compared to the burst swim speed of local small-bodied fish species to determine fish passage suitability and identify the best practices for VRW design and construction. The results concluded that VRWs provided suitable passage for small-bodied fish species through gap and over-weir flow pathways, particularly during low water level conditions. Further, appropriate design considerations based on the VRW gradient, VRW width, keystone size, and pool length contributed to 100% fish 'passability' under all water level conditions. The methodology is provided for predicting the velocity and small-bodied fish passage suitability through VRWs, informing the best practices for VRW design and construction while balancing the requirements for channel stability and fish passage, and contributing to fish population management strategies. [ABSTRACT FROM AUTHOR]

The effects of channelization with low in-stream barriers in mountain rivers on macroinvertebrate communities are still weakly recognised. We aimed to assess the differences in structure and density of benthic macroinvertebrates between two north Carpathian mountain rivers: one channelized with a cascade of concrete sills and the other one with block ramps. Water was collected five times for physicochemical analysis. Macroinvertebrate fauna and fine bottom sediments were collected three times (spring, summer, autumn) from different habitat types: glides, runs, pools and riffles of the estimated channel surface. The in-stream barriers altered the channel gradient and flow velocity, reducing the area of pools and riffles as well as extending the area of glides with slow current velocities, associated with the highest rate of fine sediment deposition. Channel modifications induced a general shift of investigated fluvial systems toward lentic habitat conditions. Macroinvertebrate communities characteristic of slow-flowing rivers and pools became dominant, while those characteristic for the riffles of mountain rivers were confined to only small areas. The studied section of the Porębianka River channelized with block ramps exhibited greater diversity in the macroinvertebrate community between habitats and significantly higher macroinvertebrate density than the Mszanka River which was channelized with concrete sills. [ABSTRACT FROM AUTHOR]

Highly modified riverbeds are not able to spontaneously reproduce natural processes. The restoration of natural river systems is an important challenge to modern river engineering. Various procedures and solutions, both technical and non-technical, are applied in this process. This involves looking for simple solutions that are close to nature and that interfere with river ecosystems to a minimal extent. One of these solutions is deflectors, which constitute a type of simplified spur. This study presents the results of the research on the transformations of hydromorphology and macrophytes on selected sections of the Flinta River, which represents the most common type of river in the Central European Lowlands (a small river with a sandy substrate). Two neighbouring sections of the watercourse were selected. The first one has not been subject to any regulatory measures for over 30 years and is undergoing spontaneous restoration, while the second one was significantly altered (straightened, cleared of hydrophytes, and desilted) ten years ago. Three deflectors were introduced in this section in the years 2017–2018. Research conducted on both sections enabled the determination of the possibility of initiating renaturalisation processes by way of implementing simple solutions in the form of low-cost wooden deflectors. It also provided the basis for the assessment of the impact the measures taken had on the hydromorphological status of the watercourse and on macrophytes. Based on the studies conducted, it was possible to determine the size, dynamic, and scope of the changes taking place in the river under various conditions of its transformation, including those resulting from anthropopressure. [ABSTRACT FROM AUTHOR]

The Water Framework Directive set for European Union countries the objective of restoring the ecological and/or sediment continuity of rivers, as the latter is relevant for providing suitable habitats for the former. Indeed, abiotic fluxes and variables shape riverine ecological habitats and are likely to be modified by barriers such as dams. Two dams were removed from the Selune River (northwestern France) from spring 2017 to summer 2022. The objective of this study was to describe and quantify how the dams modified abiotic parameters and fluxes, as well as the dynamics of these fluxes during dam removal. We monitored coarse and fine sediments, water temperature and nutrient concentrations in the Selune River from upstream to downstream of the dams from 2015 to 2023. The results showed that coarse sediments of the riverbed are a legacy and that current hydrodynamic conditions are not sufficient to move them much, with or without the dams. In addition, it appears that at this early stage after the removal some downstream parameters, especially nutrient concentrations and water temperature, have already converged towards upstream signals, while fine sediment stored in the dam’s reservoirs are still destocking. Restoring ecological continuity of the Selune River will involve dynamics of abiotic parameters over longer time scales, in response to removal of the dams, and over larger spatial scales, in response to climate and other global changes.

Dam removals are occurring more frequently with the rising cost of maintaining aging infrastructure, public safety concerns, and growing interest in river restoration. So far, most dam-removals have been unsystematic in their approach. Given the several thousand dam removals expected over the coming decades, a systematic approach to plan future dam removals holds potential for aligning and delivering multiple benefits. Despite multi-sector factors driving decision-making, most existing prioritization frameworks tend to operate within single or related disciplines. Here we present a hierarchical, multi-disciplinary decision-support framework to prioritize dam removals based on opportunistic factors (Tier 1), hydro-ecological variables (Tier 2), and socio-cultural considerations (Tier 3). This framework integrates multiple decision criteria under data availability constraints, incorporates value-driven weights, and can be applied to a portfolio of dams at various spatial scales. The final output facilitates the identification of dam removal projects that align opportunistic, environmental, and social benefits. We recommend the application of this framework as a critical first step to identifying high-priority candidates for removal, recognizing that removal decisions will ultimately require detailed feasibility studies and stakeholder engagement. To illustrate its utility, we apply this framework to California's North Coast region and identify a small number of “good” candidates to be considered for removal. We conclude with recommendations for filling critical knowledge gaps and advancing systematic dam removal planning in the United States and beyond.

Nationwide biodiversity indicators based on landscape heterogeneity have been developed primarily for terrestrial ecosystems, but not well for freshwater ecosystems worldwide. A plausible reason for this limitation is the difficulty in the fine discrimination of freshwater environments by remote sensing. However, in recent years, Geographic Information System (GIS) vector data of freshwater land cover are classified in detail (i.e. rice paddy fields, other marshy wetlands, rivers, ponds and lakes) in Japan. Using these GIS data, we developed an index for freshwater landscape heterogeneity with 1 km square as the spatial unit, which was named the ‘Satogawa’ Index (SGI). The SGI formula consisted of two-component terms, one reflecting the diversity of freshwater land covers, and the other representing their spatial shapes. We calculated the SGI at a central region in Japan and found significant relationships with the species richness of Odonata (dragonflies and damselflies) and freshwater fish. The amounts and spatial patterns of freshwater landscape elements by which the SGI was estimated were different among regions in Japan; however, the SGI may be adapted to other regions as a surrogate of aquatic species richness, a typical measure of freshwater biodiversity. Although several modifications are underway that may have negative consequences for freshwater biodiversity, land use has been changed to prevent flood damage and improve the freshwater environment. The SGI may reveal the influences of the changes in land use on freshwater biodiversity and may identify the type and amount of lotic and lentic environment that should be supplemented to improve freshwater biodiversity at a certain location.