As stream habitats change from upstream to downstream, choice of spawning redd sites by brown trout may shift as habitat availability changes. In a previous study, we examined the importance of overhead cover in redd site selection. Here, we examined spawning site habitat use and selection by brown trout by assessing physical characteristics at redd sites in a 4.8-km reach of Garvin Brook during each of five spawning seasons, 2016–2020. We measured redd dimensions, water depths, and current velocities, and compared these among four separate sections (900–1900 m in length) of the stream. We also assessed available habitats within each section to examine possible selection of habitats by spawning trout, plus quantified the size distribution of gravel substrate at redd sites within two stream sections. Habitat availability varied dramatically among stream sections. After analyzing 1844 redds from the five spawning seasons, brown trout displayed strong selection for water depths between 10 and 29 cm and current velocities between 10 and 49 cm/sec when choosing redd locations. Preferred/selected water depths and current velocities increased by 7 cm and 10 cm/sec, respectively, between upstream and downstream sections. All redds were placed in gravel/cobble substrates, with variations in size distributions of gravels not correlated to redd dimensions or any measured habitat variable. Spawning site preferences of brown trout can change along a stream reach of moderate length, likely in relation to changing availability of various combinations of water depth, velocity, substrate, available cover, and trout abundance.

Understanding the interactive effects of non-native species and alterations to flow regimes is important to combat threats to freshwater communities. Low-flow conditions may either exacerbate or offset influences of non-natives but the mechanisms determining the direction are poorly understood. We evaluated how stream drying affected interactions between vulnerable native non-migratory galaxiids and non-native trout in Aotearoa - New Zealand. We electrofished (December – March) paired perennial and drying reaches containing galaxiids ( Galaxias vulgaris and G. paucispondylus) to compare abundance and growth rates in streams with high abundance (n=2), low abundance (n=2) or no brown trout (n=3; Salmo trutta). Low flows greatly reduced trout abundance and size, likely reducing predatory threats to galaxiids since risk is size-related. Galaxiid densities were consistently lower in drying compared to perennial reaches of troutless streams. However, galaxiids were less affected by low flows than trout, setting the scene for an interaction between trout and low flow. In streams with high numbers of trout, galaxiid numbers were very low in perennial reaches, whereas they were moderate in drying reaches. That meant galaxiid numbers increased with decreasing flow in streams with many trout, an indirect positive effect, although their abundance never reached the high levels of trout-free perennial reaches. In low-density trout streams, there were no clear differences in galaxiid abundance between reaches of different flow type. Thus, the effects of trout on galaxiids depended on the flow regime, likely driven by harsh low-flow conditions suppressing large trout, which were more sensitive to low flow than galaxiids. Growth advantages for galaxiids possibly enhanced this interaction because galaxiids grew fastest when trout were present at low densities. Overall, although low-flow conditions likely reduced predatory effects of non-natives, populations of natives were also suppressed by low flow. Such interactive effects of flow reduction are likely common and appear controlled by relative vulnerability and size-structured interactions. Balancing maintenance of natural flows with minimising effects of non-native sports fish poses a difficult challenge, but managers should aim to both protect natural flow regimes to maintain suitable fish habitat, and actively manage non-native species in harmful situations to conserve native fish.

Vegetation overgrowth in rivers worldwide has been a significant problem due to its potential to reduce flood-flowing capacity and cause biodiversity loss. This study tried to develop a model to predict vegetation recruitment during the initial stage of secondary succession, leading to vegetation overgrowth. This study chose a logistic regression model for predicting vegetation recruitment because of its simplicity and lower computational load than machine learning. The model was designed for the Kinu River in Japan, undergoing significant vegetation overgrowth. Data for the model development was obtained from UAV (unmanned aerial vehicle) aerial surveys and public databases. To ensure the model’s applicability beyond the training rivers, we trained the logistic regression model in its performance across different river flows and geomorphic characteristics, including the normal and flood times and the gravel-bed and sand-bed. The results indicated that the logistic regression model with three explanatory variables — the distance from the river stream, the relative height, and the vegetation existence history —was optimal for all rivers with the F-measures of 0.79 to 0.85. Additionally, using UAV imagery allowed for high spatial resolution in predicting vegetation recruitment. The best model’s prediction map of the vegetation recruitment demonstrated that it could accurately predict vegetation distributions along the main river channel for the gravel and sand beds.

Erosion generally reduces the resilience of replenished gravel in rivers. This is why structures are sometimes added to modify the upstream flow and stabilize artificial spawning grounds. In particular, rows of boulders can be placed around the replenishment area to limit the transport of replenished gravel during flood events. This study aims to optimize the arrangement of these rows, based on field experiments as well as physical and numerical models. A combined hydro-sedimentary numerical model is calibrated and validated by comparing simulated and measured morphological evolutions in nine laboratory experiments. The results show that boulders downstream of the replenishment slow down the flow above the replenishment, decreasing shear stress on the gravel. Stabilization efficiency is shown to depend on the positioning of the boulders and arrangement of the replenishment surface. In order to achieve sustainable spawning, prospective scenarios with the numerical model highlight the need to limit the width of the replenishment area.

The majority of river restoration initiatives are driven by new environmental policies. However, evaluation of management styles for ecosystem services (ESs) within river policies and their implications for restoration has been rarely investigated. This paper aims to evaluate the way in which environmental policy manages river ESs and river restoration initiatives. A content analysis-based approach applied to policy documents was undertaken on China’s River Chief (CRC) policy. ESs attributes were summarized according to categories, values, relationships, and stakeholders. Subsequently, a hierarchical evaluation indicator system, along with its graded keywords, was developed. The occurrence frequencies of these keywords in policy documents were then used to measure the policy regulatory degrees of ESs indicators. The reference values extracted from literature statistics of peer-reviewed papers served as a template to clarify the ESs management style. We found that the CRC policy primarily relied on the management of ESs categories and stakeholders, followed by ESs relationships, with extremely limited consideration of river ESs values. Moreover, the bundle of those ESs incorporated into the policy significantly differ from the typical structure of the ESs provided by rivers. For stakeholders, the CRC policy relies heavily on the authorities and the farm/business operators to manage the rivers. This case study showed a partial and pattern-mismatch management style of river ESs, which will hamper the holistic restoration of rivers. We concluded that the proposed policy document-based evaluation approach can help to identify the policy deficiency in relation to river ESs management, and river restoration possibilities.

The RETERO project develops new methods to Reduce, Replace and Refine (3R-principle) animal experiments for assessing the risk of harm to fish when passing through turbines or pumps. Since behavior of fish influences the mortality risk during turbine and pump passages, knowledge about species-specific behavior and its triggers are necessary. A primary objective of the RETERO project is the study of fish behavior in hydraulic conditions similar to turbine and pump intakes. Therefore, an experimental conduit was constructed at the Hubert-Engels Laboratory of Technische Universität Dresden (Germany) specifically for the RETERO project’s study on fish behavior, equipped with a 3D camera infrared tracking system. The conduit was designed to model hydraulic conditions typical for turbine and pump intakes. In the experimental setup the effects of flow velocities exceeding the maximum swim speed of fish, as well as spatial velocity gradients and illumination conditions, on the fish behavior are studied. The data from studies involving brown trout ( Salmo trutta) allow for an analysis of how these fish react to flow accelerations and velocities surpassing their sprint speed, using quantitative metrics for movement and activity. An initial evaluation of these experiments highlights the potential of this approach for further research.

Trace elements and minerals can be important for physiological and biochemical functions in aquatic organisms and are also permanently retained in metabolically inert structures in fish, such as otoliths, which can be examined to reconstruct environmental history. Despite the importance of trace elements for biological function and environmental reconstruction, their distribution and dynamics in river systems is poorly understood. The objective of our study was to quantify trace element concentration data from across 14 river basins in Georgia, USA to create elemental concentration profiles and illustrate how spatial changes in water chemistry can be used to construct research hypotheses or make management decisions using results from chemical analyses on hard calcified parts of fish. Principal component analysis revealed substantial variation in water chemistry among and with river basins. Pairwise comparisons of Sr:Ca and Ba:Ca ratios were useful in quantifying specific differences among river systems within river basins. These data will be useful for establishing a baseline for long-term water chemistry monitoring and provides a framework for future fish chemistry research.

A document by Edward Fleming. Click on the document to view its contents.

The role of hydropower as a renewable and balancing power source is expected to significantly increase in a Net Zero Emissions by 2050 scenario. As a common phenomenon in hydropower plants, hydropeaking will become more prominent, resulting in additional stresses on the ecological status of rivers. Here we propose a novel approach to design and operate auxiliary reservoirs called re-regulation reservoirs that aims to mitigate the adverse impacts of hydropeaking on rivers. A re-regulation reservoir aims at smoothing flow fluctuations caused by hydropeaking by diverting and retaining parts of high flows and returning them back to river corridors during low flows. The regulatory performance of re-regulation reservoirs is a function of its geometry and volume availability. It is defined (and optimized) by restricting various flow components thresholds. Using actual data from a hydropeaking-influenced river system, the operation and efficiency of potential re-regulation reservoir have been investigated by employing a range of thresholds for hydropeaking mitigation. A methodology and an open-access algorithm to operate re-regulation reservoirs, by establishing a hierarchy of conditions to restrict peak flow, minimum flow, up-ramping rates, and down-ramping rates was developed. Our calculations show clear theoretical possibilities for regulating hydropeaking with re-regulation reservoirs, while offering several advantages, including greater flexibility and adaptability to changing environmental conditions, power, and water demand without increasing the operational cost of power systems.

Environmental DNA (eDNA) extracted from water is routinely used in river biodiversity research, and via metabarcoding eDNA can provide comprehensive taxa lists with little effort and cost. However, eDNA-based species detection in streams and rivers may be influenced by sampling season and other key factors such as water temperature and discharge. Research linking these factors and also informing on the potential of eDNA metabarcoding to detect shifts in ecological signatures, such as species phenology and functional feeding groups across seasons, is missing. To address this gap, we collected water samples every two weeks for 15 months at a long-term ecological research (LTER) site and at three different positions in the river’s cross section, specifically the water surface, riverbed, and riverbank. For these 102 samples, we analyzed macroinvertebrate species and molecular Operational Taxonomic Unit (OTU) richness and temporal community turnover across seasons based on COI metabarcoding data. Using Generalized Additive Models, we found a significant influence of sampling season on species richness. Community turnover followed a cyclic pattern, reflecting the continuous change of the macroinvertebrate community throughout the year (‘seasonal clock’). Although water temperature had no influence on the inferred species richness, higher discharge reduced the number of Annelida and Ephemeroptera species detectable with eDNA. Most macroinvertebrate taxa showed the highest species richness in spring, in particular merolimnic species with univoltine life cycles. Further, we detected an increase in proportion of shredders in winter and of parasites in summer. Our results show the usefulness of highly resolved eDNA metabarcoding time series data for ecological research and biodiversity monitoring in streams and rivers.

Flood-related policies for England are reviewed, updating needs in the light of recent flood-rich decades and in recognition of future climate trends. This review updates one we published in 2021- a significant year for extreme floods in Europe that were part of a continuing trend; governments now require fast-track adaptation and resilience policies. Currently, the event signals of increasing spatial and temporal variability in impacts is insufficiently incorporated in hazard/risk assessments. We advocate a transformative policy change towards place-based strategies, based on the fast-emerging evidence from three sciences: hydroclimatology, hydrology and hydromorphology. It is vital that policy actions recognise factors such as atmospheric rivers, surface water flooding, and the role of eroded and transported sediments in localised hazards and risks. Located vulnerabilities require local strategies. Attribution of extreme events to climate change, and the recognition and specification of genuinely vulnerable sites, need further refinement and extension into public decision making. Risk assessment needs reform, both from science but also for institutions and individuals, with accompanying reform of flood risk management expenditure. Data analysis, e.g. of rainfall and river flow, needs more disciplined clarity; standard sets are needed together with their variable spatial/temporal application. We further recognise sediment hazards (and other entrained debris spread in flood flows) as new and important components for the located risk of present and emerging ‘hot spots’.

A document by Behnam Balouchi. Click on the document to view its contents.

The current focus of river restoration on flow and sediment transfer without proper consideration of vegetation as a key structuring agent, beyond its stabilising effect, is too simplistic. We contend that vegetation has an essential role in shaping the physical fluvial environment and should be considered equally alongside hydrogeomorphic processes in restoration projects. In support, we introduce engineer plants as important controls, along with flowing water and transported sediments, on the morphodynamics of river systems and associated physical habitat development. The effect of vegetation on channel planform is then summarised, the influence of vegetation on hydrogeomorphic connectivity is outlined, and then the role of vegetation in landform development and habitat provision, as encapsulated in the fluvial biogeomorphic succession model, is described. We then present examples demonstrating how vegetation has contributed to the recovery of degraded rivers through biogeomorphic processes. Finally, we advance the concept of biogeomorphic river restoration by proposing principles to support a closer synthesis of the component sciences and list key areas for practitioners to focus on.

Fish stranding in rivers, due to rapid shoreline dewatering, often occurs during the down-ramping phases of hydropeaks enabling peak energy production. Multiple hydrological characteristics of hydropeaking and river morphology influence stranding, but little is known about their relative effects. The goal of our study is to identify how the combination of hydropeaking characteristics and the occurrence of morphological microstructure (e.g., puddles, scour pools) influence fish stranding. For this purpose, we used an extensive dataset of fish stranding observations collected over 3 years in spring at 48 stations along a 50 km-long river reach. We aimed (1) to characterize stranding events and their associated fish assemblages, and (2) to identify the spatial and temporal determinants of stranding. We found that the occurrence of morphological microstructures of the riverbed was the main factor explaining fish stranding. Scour pools are the most impacting microstructures, followed by scour puddles, humid zones, and alluvial puddles. Then, hydropeaking characteristics interact with morphology and modulate the intensity of stranding. Low flow ranges (low peak flow, low base flow) occurring after periods without hydropeaks induce particular “salmonid” and “super-stranding” events and other flow ranges induce regular stranding events. Salmonids are particularly subject to stranding at the beginning of the sampling period. Recommendations that emerged are (1) to act in priority on stations where stranding is most likely, by morphological operations or by installing attractive structures in the perennial area, and (2) to maintain attractive, perennial habitats in the low flow range of hydropeaks.

Fluvial hazards of river mobility and flooding are often problematic for road infrastructure and need to be considered in the planning process. The extent of river and road infrastructure networks and their tendency to be close to each other creates a need to be able to identify the most dangerous areas quickly and cost-effectively. In this study we propose a novel methodology using random forest (RF) machine learning methods to provide easily interpretable fine-scale fluvial hazard predictions for large river systems. The tools developed provide predictions for three models: presence of flooding (PFM), presence of mobility (PMM) and type of erosion model (TEM, lateral migration, or incision) at reference points every 100 meters along the fluvial network of three watersheds within the province of Quebec, Canada. The RF models uses variables focused on river conditions and hydrogeomorphological processes such as confinement, sinuosity, and upstream slope. Training/validation data included field observations, results from hydraulic and erosion models, government infrastructure databases, and hydro- geomorphological assessments using 1-m DEM and satellite/historical imagery. A total of 1,807 reference points were classified for flooding, 1,542 for mobility, and 847 for the type of erosion out of the 11,452 reference points for the 1,145 km of rivers included in the study. These were divided into training (75%) and validation (25%) datasets, with the training dataset used to train supervised RF models. The validation dataset indicated the models were capable of accurately predicting the potential for fluvial hazards to occur, with precision results for the three models ranging from 83% to 94% of points accurately predicted. The results of this study suggest that RF models are a cost-effective tool to quickly evaluate the potential for fluvial hazards to occur at the watershed scale.

Streambank erosion impacts rivers and reservoirs due to bank erosion. However, little information of stream bank is available due to the need for advanced planning. Dendrogeomorphology offers a post-hoc method to calculate streambank erosion providing information about past erosion events and processes. Bank retreat can be calculated by dendrogeomorphology where the distance from a channel bank of an exposed live root shows anatomical changes that are dated from the root’s growth rings. We estimated bank erosion for three different sized southern U.S. watersheds ranging in area from 4 to 3781 km 2 using dendrogeomorphology compared to modeled erosion based on critical velocity required for sediment transport. Erosion values ranging from 3.8 to 13.5 cm/yr for the smaller drainages with no difference found between root and modeled erosion rates. The large sub-basin had erosion ranging from 33.6 to 196.4 cm/yr with high variance associated with two prior 2-year flow events with significant differences found between root and modeled values. We also found distance to bank strongly and positively correlated with root exposure in straight sections of the channel in contrast to roots collected in meander bends attributed to erosion processes (i.e., scour, mass wasting) occurring at these locations. When compared with other erosion studies across the southern U.S. prairie, our values were similar in magnitude but with low correlation to drainage area indicating site specificity of erosion mechanisms. We confirm dendrogeomorphology provides reasonable estimate of bank erosion across multiple spatial scales, important for watershed management in areas lacking intentional and persistent monitoring.

The upper Colorado River is a highly regulated system that provides habitat for federally listed species, disproportionate number of flora and fauna and is the water supply for the western United States. River regulation has led to wide scale channel narrowing. Over the last three decades dams have been operated with a more natural hydrograph for environmental reasons. We sought to use remote imagery from 1940-2022 to examine rates of channel narrowing in the pre-dam, post-dam, and environmental flows eras along three river reaches in Canyonlands National Park. We found an increase in the vegetated area along the Colorado River (above the confluence with the Green River) and the Green River since 1940. We documented a 6.12% and 4.00% narrowing in the post-dam period and a 19.51% and 6.49% narrowing in the environmental flows period on the Colorado and Green Rivers, respectively. The Cataract Canyon reach (Colorado River below the confluence) has been stable since 1966. All three river reaches showed the slowest period of narrowing in the last 16 years of environmental flows that coincided with a large peakflow in 2011. All three reaches showed a decrease in vegetated area after the 2011 flood, followed by an increase in vegetated area to similar levels to before the 2011 flood. Environmental flows that mimic the natural hydrograph may have slowed channel narrowing, but it is clear that periodic large peaks are also necessary. Managers must be careful that any environmental flows that take from the spring peak are carefully considered.

This study was conducted to meet regulatory requirements under the Fisheries Act in Canada, specifically for a hydroelectric facility on the Yellowknife River in the Northwest Territories. The research focused on annual snorkel surveys of adfluvial fish and their spawning habitat below the facility. Initial observations of egg mortality, potentially due to overcrowding, prompted the investigation of natural and enhanced habitat for spawning Lake trout ( Salvelinus namaycush), lake whitefish ( Coregonus clupeaformis) and cisco ( Coregonus artedi) from 2016 to 2019. The design and composition of the installed habitat were based on fish utilization of the natural channel below the hydro facility and design principles from previous habitat rehabilitation projects for anadromous fishes. Pre- and post-enhancement data on egg density and survival were collected using 1 m 2 plots on both natural and artificially enhanced substrates. Three years of post-enhancement monitoring indicated higher egg densities and a greater proportion of live eggs in the artificially enhanced habitat compared to the natural habitat, with more pronounced trends observed for coregonids (lake whitefish and cisco) compared to lake trout. These findings suggest that habitat enhancement has the potential to enhance juvenile recruitment for adfluvial fish. A critical factor in the design was the substrate composition, providing adequate interstitial spaces for egg development and protection. This study represents the first documented attempt at habitat improvement in a regulated sub-Arctic river in Canada. The findings offer valuable guidance for stakeholders involved in new or existing development projects that require conservation actions to maintain fisheries productivity.