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.

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.

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.

Blue sucker ( Cycleptus elongatus) occurs in the Mississippi River and Gulf of Mexico drainages of North America and is negatively affected by habitat fragmentation and flow regime alteration caused by dams. During fish assemblage surveys in August of 2022, we collected five specimens of juvenile blue sucker (312-428 mm total length) in the Angelina River upstream of Sam Rayburn Reservoir in east Texas (46,335-hectare surface area) where the occurrence of the species was previously unconfirmed. Given this unexpected finding, we (1) analyzed blue sucker mesohabitat associations to compare habitats we sampled with reports in the literature, and (2) reviewed blue sucker occurrence in state, national, and global databases across historical (1950-1980) and contemporary (1981-2022) periods to assess occurrence across gradients of habitat fragmentation and streamflow regulation. The blue sucker population in the Angelina River upstream of Sam Rayburn Reservoir was previously unconfirmed but is within the native range of the species. Mesohabitats occupied by blue sucker were consistent with literature reports, including fast velocity, shallow depth, and coarse substrates. The low degree of regulation (19% of natural runoff stored by upstream reservoirs) and a high degree of habitat connectivity (287 rkm of mainstem habitat) for the Angelina River upstream of Sam Rayburn Reservoir matched range-wide patterns of persistence within relatively intact (unfragmented and unregulated) or remnant (fragmented but unregulated) riverscapes. Our review reveals that blue sucker populations might persist (1) in remnant river fragments where local habitat templates are appropriate and (2) where effects of habitat fragmentation and flow regulation are not coupled.

Centuries of human development have altered the connectivity of rivers, adversely impacting ecosystems and the services provided. Significant investments in natural resource projects are made annually with the goal to restore function to degraded rivers and floodplains and protect freshwater resources. Yet restoration projects often fall short of their objectives, in part, due to the lack of systems-based, strategic planning. To evaluate channel-floodplain (dis)connectivity and erosion/incision hazard at the regional scale, we calculate Specific Stream Power (SSP), an estimate of the energy of a river, using a topographically-based, low-complexity hydraulic model. Other basin-wide SSP modeling approaches neglect reach-specific geometric information embedded in Digital Elevation Models. Our approach leverages this information to generate reach-specific SSP-flow curves. We extract measures from these curves that describe (dis)connected floodwater storage capacity and erosion hazard at individual design storm flood stages and demonstrate how these measures may be used to identify watershed-scale patterns in connectivity. We show proof-of-concept using 25 reaches in the Mad River watershed in central Vermont and demonstrate that the SSP results have acceptable agreement with a well-calibrated process-based model (2D Hydraulic Engineering Center’s River Analysis System) across a broad range of design events. While systems-based planning of regional restoration and conservation activities has been limited largely due to computational and human resource requirements, measures derived from low complexity models can provide an overview of reach-scale conditions at the regional level and aid planners in identifying areas for further restoration and/or conservation assessments.

Floodplain restoration can enhance capacity for carbon sequestration by facilitating higher water tables, deposition of fine sediment, and increased input and residence time of organic matter. We measured floodplain soil organic carbon stocks in nine stream restoration projects across the western United States and compared them to nearby degraded and reference condition floodplains. Degraded floodplains had the lowest soil mean carbon stocks in the majority of floodplains measured (range 161-894 Mg C/ha), and reference stocks had the highest stocks (range 391-904 Mg C/ha) of those with statistically significant differences between the three categories. Across all sites measured, stream restoration sites, referred to as treatment sites, had stocks (range 203-1028 Mg C/ha) similar to degraded condition floodplains but the largest range. When modeled under degraded conditions, four out of nine of the treatment sites had significantly higher OC stocks than predicted. Climate and geologic variables are most influential in predicting carbon stocks, and floodplains in the interior western USA have the highest carbon stocks. As the demand for carbon sequestration increases due to climate change, ecologically responsible floodplain restoration provides a significant opportunity for carbon storage. However, despite the statistically significant relationships we observed in this dataset, the variations within the data in relation to degraded/treatment/reference categories illustrate the uncertainties in quantifying the effects of restoration on floodplain carbon stocks.

Salt dilution is a well-established streamflow measurement method in creeks, which works particularly well downstream of turbulent flow sections as mixing of the salt tracer is enhanced. Usually salt dilution measurements are performed manually, which considerably limits the observations of rare peak flow events. However, these events are particularly important for constructing robust rating curves and avoiding large uncertainties in the extrapolation of river discharge values. An additional challenge is the variability of the river cross-section, especially after larger discharge events, leading to non-stationary rating curves. Therefore, discharge measurements well distributed over time are needed to both construct a reliable streamflow-water level relationship and to detect changes caused by erosion and deposition processes. To overcome these two issues, we used an automated streamflow measuring systems at three different sites in the Alps for event-based discharge measurements. This system allowed us to measure close to the highest peak flows at all three sites in the observation period (2020-2021) and to detect abrupt changes in the rating curve. Based on a very large data set of almost 300 measurements, we were able to evaluate the reliability of the system and to identify the main sources of uncertainty in the experimental setup. One key aspect was the site selection for the downstream electrical conductivity sensors as measurement location strongly controls the signal-to-noise ratio (SNR) in the recorded breakthrough curves.

Mapping fluvial hydromorphology is an important part of defining river habitat. Mapping via field sampling or hydraulic modelling is however time consuming, and mapping hydromorphology directly from remote sensing data may offer an efficient solution. Here we present a system for automated classification of fluvial hydromorphology based on a deep learning classification scheme applied to aerial orthophotos. Using selected rivers in Norway, we show how surface flow patterns (smooth or rippled surfaces versus standing waves) can be classified in imagery using a trained convolutional neural network. We show how integration of these classified surface flow patterns with information on channel gradient, obtained from airborne topographic LiDAR data, can be used to compartmentalize the rivers into hydromorphological units that represent the dominant flow features. Automated classifications were consistent with those produced manually. They were found to be discharge-dependent, showing the temporally dynamic aspect of hydromorphology. The proposed system is quick, flexible, generalizable, and free from researcher-subjectivity. The deep learning approach used here can be customized to provide more detailed information on flow features, such as delineating between standing waves and advective diffusion of air bubbles/foam, to provide a more refined classification of surface flow patterns, and the classification approach can be further advanced by inclusion of additional remote sensing methods that provide further information on hydromorphological features.