Fish guidance structures (FGS) with adjacent bypasses can provide safe downstream passage at hydropower plants. To regulate bypass discharge, gates with partial openings are installed at bypass inlets. This study examines how flow constriction at such openings affects fish behaviour and bypass entrance efficiency (BEE). In a physical model, we quantified upstream velocities with acoustic Doppler velocimetry for gates configured with either a bottom (BO) or top opening (TO) under three approach-flow velocities U-o: Ethohydraulic tests with brown trout (Salmo trutta) and common barbel (Barbus barbus) assessed their ability to locate and enter the bypass. Hydraulic measurements showed high bypass inflow velocities U-by,U- in up to 2.0 m/s, velocity ratios U-by,U-in=U-o up to 6.7, and streamwise velocity gradients SVG(x) up to 21 s(-1), exceeding common design recommendations. U-by,U- in and SVG(x), linked to opening location and geometry, emerged as key parameters associated with BEE and fish behaviour. Both species frequently avoided strong currents at the openings, with significantly lower and delayed passage through the TO. Brown trout tended to enter the BO more often and earlier than barbel, indicating species-specific preferences. Overall, BEE was low (BO: 27-59%; TO: 8-21%). Findings highlight that unfavourable hydraulics can impair FGS-bypass performance. Design recommendations are provided.
The design of fishways for an entire fish community is challenging. Different species and fish sizes have different demands, especially on flow velocities. We were interested if flow fluctuations that occur in the vertical slot of fishways influence the passage of small fish. In a flume experiment, we tested the passage of small roach (Rutilus rutilus) and gudgeon (Gobio gobio) through a slot of 0.4 m width for three flow fluctuation treatments: constant mean flow velocities with (A) small random fluctuations, (B) strong random flow fluctuations, (C) periodic intervals of reduced flow velocities. Contrary to our expectations, passage success did not differ significantly between these treatments for either species, with gudgeon having fewer passages than roach across all treatments. However, roach preferred passage during periods of reduced flow in the periodic treatment. The findings suggest that flow fluctuations as they occur in vertical slot fishways neither hinder nor improve passage, but that species-specific characteristics and also group dynamics may play a crucial role in the passage success of upstream migrating fish.
This research examines the influence of abutments placement near the inner and outer walls, alongside the deployment of convergent-vertical and divergent-vertical bridge pier groups. Three positions 60, 90, and 120 degrees out of a 180-degree bend were selected and tested. Additionally, the impact of varying flow conditions in three states: clear water, incipient motion, and live bed, on bed changes and scour rate was examined. The findings revealed that, under incipient motion conditions, when piers were positioned at 60 degrees, the deepest scour of the main hole occurred near the piers; however, when placed at 120 degrees, this deepest scour shifted to the area around the outer abutment. The greatest scour depth under incipient motion conditions was observed in the convergent pier groups positioned at 90 degrees, reaching about 1.3 times the flow depth. At this position, the maximum depth of the second scour hole and the sediment ridge height were higher compared to the 60 degrees and 120 degrees positions. When piers and abutments were positioned at 90 degrees, the deepest scour of the second hole and the sediment deposit height increased as the ratio of average flow velocity to the critical velocity for bed particles rose from 0.87 to 0.98 and 1.03.
Mesoscale habitat approaches are increasingly popular and all rely on a definition and delineation of geomorphic (GU) and hydraulic (HU) units. Traditionally, experts perform GU-HU delineation in the field, but unsupervised algorithms are increasingly being developed. Such algorithms typically assume that the parameters selected for HU delineation (mostly water depth and flow velocity) are of equal importance. This study challenges that assumption by investigating the consequences of weighting parameters in the automatic delineation of HU. Using simulated hydraulic variables, we applied algorithmic HU delineation under various conditions and tested different parameter weightings. The resulting HU were compared to GU delineated using a field-based field approach. Additionally, a synthetic habitat suitability criterium was used to evaluate how parameter weights influence final habitat assessments. We found that weighting parameters influences the algorithmic HU delineation and the amount of predicted habitat; assuming equal importance for all parameters can lead to inaccurate conclusions in habitat assessments. We show that field- and algorithmic-based approaches used for mesohabitat delineation are not interchangeable, but rather are complimentary. This work contributes towards the integration of field- and algorithmic-based approaches.
Instream boulder placement is a widely adopted technique for restoring degraded streams to enhance instream complexity, aquatic habitat quality, fish passage, and overall ecological value. However, biological responses to these structures have been evaluated less frequently and with lower consistency as compared to physical/hydraulic habitat assessments. This experimental study examines the impact of instream boulder placement on the behavior of juvenile Atlantic salmon (Salmo salar) and rainbow trout (Oncorhynchus mykiss), focusing on their movements upstream through a flume. The experimental setup featured seven boulder arrangements, including rock-ramp (areal densities from 0.0% to 8.3%) and cluster formations (V- and I-weirs), under two flow rates. Top-down and underwater cameras recordings were analyzed using AI-driven object-tracking algorithms document the movement behavior of the fish. We found that juvenile salmonids in fast flowing water have prolonged resting periods in favorable microhabitats created behind boulders. Atlantic salmon moved upstream most readily with the I-weirs, while rainbow trout did so with the V-upstream weirs. The results revealed strong predictive relationships between dimensionless ground speed and both Froude number and dimensionless swimming speed. Moreover, this study identified strong nonlinear relationships between habitat-scale hydrodynamic complexity metrics and key fish behavioral responses, including resting time, ground speed, passage time, and passage efficiency. The findings of this study enhance our understanding of fish behavior in complex hydraulic environments and offer empirically-based design guidance for more effective, species-specific fish passage and habitat restoration efforts. The study also demonstrates the utility of experiments using live fish in flumes to test fish passage structure designs.
Rheotactic behavior of fish, which is physiologically associated to the animal's lateral line sensory system, has a strong influence upon fish behaviour in the wild. However, criteria for flows that inform the rheotaxis of native fish species in Central Europe are lacking. Thus, it was the aim of the presented study to investigate rheotaxis of brown trout (Salmo trutta) and grayling (Thymallus thymallus) using a novel experimental setting. Sediment Impact Assessment Flumes (SIAFs) allowed us to determine the orientation of fish at different velocities within the flumes. Because the flumes could be discharged from clockwise and counterclockwise, the threshold criterion for rheotaxis was marked to the active 180 degrees turn of single- or group of fish when the direction of the velocity was changed. A strong rheotactic behaviour was documented above 8 cm s-1, a partial reduction at lower current velocity, with a clear drop off below 2 cm s-1. The findings of this experimental design were related to the natural flow velocity variations in selected riffle-pool reaches during low flow conditions of European rivers. It could be shown, that the flow velocities in pools were beyond the threshold criteria even for small brooks.
Turbulence is heterogenous in riverine habitats. The ability of individual zebrafish (Danio rerio) to regulate swimming under turbulent conditions has not been investigated. We examined age- and sex-specific behavioural responses using a controlled jet-stirred tank that generated turbulence levels spanning turbulence kinetic energy (TKE) values from 3.5 & times; 10-& sup3; to 2.4 & times; 10-2 m2 s-2 (where 3.9 & times; 10-& sup3; to 8.6 & times; 10-& sup3; m2/s2 are used for fish swimming observations), comparable to natural streams. Twenty-two zebrafish were tested individually across three turbulence conditions and still water. Three-dimensional swimming trajectories were reconstructed with stereoscopic imaging, and swimming speeds were quantified. We found that live zebrafish exhibited up to two orders of magnitude higher instantaneous swimming speeds, compared to dead controls, with median values of 7.4-11.5 cm/s that remained stable across turbulence levels, indicating strong behavioural self-regulation. However, these speeds were higher than commonly reported cruising speeds in the literature, which suggest that zebrafish may expend greater effort when swimming in near-zero-mean-flow turbulence. Nonparametric statistical tests revealed significant differences between sex and age groups but weaker differences within groups across different TKE values. Two-year-old females consistently swam faster than one-year-old females, while males showed intermediate swimming speeds. These findings suggest that zebrafish combine individual resilience with group-level diversity in locomotor responses, providing insight into how small-bodied fishes may adapt to anthropogenic flow modifications and climate-driven changes in hydrodynamics.
Freshwater mussels are a highly imperiled, mostly sessile, benthic fauna that rely on stable sediments for their habitat. The subadult life stage is most often used in reintroduction efforts but very little is known about their physical habitat requirements. Here, 20-mm and 40-mm 3D printed subadult mussels are developed as a proxy for live subadult mussels for four common mussel species in the southeast United States: Pustulosa pustulosa (pimpleback), Quadrula verrucosa (pistolgrip), Amblema plicata (threeridge), and Lampsilis teres (yellow sandshell). These mussels were used in a flume study to identify the mobilization thresholds and calculate a new metric, the mussel mobilization index (Tm), based on observed mussel shear stress and sediment critical shear stress. A set of live L. teres subadult mussels was used to corroborate the morphometrics and thresholds of printed L. teres mussels, with 20-mm mussels matching well dimensionally. For 20-mm lengths, live mussels had higher mobilization thresholds than similar sized printed mussels. Overall, small sediments provided higher mussel mobilization index values, but larger sediments produced more stable mussels. The 3D printing of mussels provides an opportunity for managers to assess potential habitat without the risk of losing live specimen.
Hydropower is a globally important renewable energy source with profound impacts on aquatic organisms, including direct injury and mortality to fish that move through hydropower facilities. While it is expected that the characteristics of turbine design and operation influence the type, frequency, and magnitude of injuries suffered by entrained fish, few direct comparisons exist to illustrate differences in fish survival outcomes for conventional and novel turbine designs. This study evaluated blade strike-associated injury and mortality rates for juvenile white sturgeon (Acipenser transmontanus) passed through a model-scale turbine equipped with a runner having conventional blade profiles (thin, straight leading edges) and the same turbine equipped with a runner designed for improved fish survival (thick, slanted leading edges). In both trials, head and turbine runner rotational speeds were matched to produce five blade peripheral speeds between 15.0 and 27.6 m/s. High-speed video was captured for all turbine passage events. Fish were assessed for injuries following passage, and mortalities were assessed immediately after passage and after 48 h. Conventional runner passage resulted in 42% to 78% survival after 48 h, with approximately one-third of all tested fish killed by severing. Under the same test conditions, immediate and 48 h survival rates through the novel runner were 100% except at the highest speed condition (95.6% survival at 48 h). These results clearly indicate that turbine design has a profound effect on fish survival, and suggest that thoughtful redesign of hydropower equipment could significantly ameliorate the risks of blade strike mortality.
Sand mining plays a vital role in meeting construction demands and maintaining river sediment balance; however, unregulated extraction can significantly alter river hydrodynamics, morphology, structural and ecological stability. This study investigates the influence of different floodplain sand mining pit configurations on flow velocity, secondary currents and vorticity structures in a sinuous channel using FLOW-3D Hydro simulations validated through laboratory experiments conducted at the IIT Guwahati Fluvial Hydro-Ecological Laboratory. The experimental channel was 18 m long with a sinuosity of 1.1 and operated under subcritical flow conditions. Two mining scenarios were examined: (i) two consecutive floodplain pits and (ii) two consecutive pits with an additional pit on the opposite floodplain. Results indicate that streamwise velocity was consistently higher near the inner bank in both scenarios, while the second configuration produced a narrower high-velocity core. Secondary currents were concentrated near the outer bank and within the mining pits; however, their intensity was stronger in the first scenario, suggesting that it may have a higher potential for pit migration and bank erosion. Vorticity in the streamwise direction was concentrated within the mining pits in both scenarios. Vertical vorticity dominated near the inner bank and within the pits, whereas lateral vorticity prevailed near the bed in the main channel and inside the pits. The combined vorticity field exhibited anticlockwise circulation near the outer bank and clockwise rotation near the inner bank. The findings contribute to sustainable sand mining practices by improving understanding of channel hydrodynamics and reducing potential environmental impacts in sinuous river systems.
The hydrodynamic and sediment processes in the Yellow River are profoundly amplified during the flood season, significantly influencing the habitat suitability of aquatic species. This study evaluates the impact of these processes on the habitat of two indicator species, Cyprinus carpio and Misgurnus anguillicaudatus, using a 2D hydrodynamic and sediment transport model, MIKE 21, coupled with the habitat suitability model (HSM). Habitat suitability curves (HSCs) for water depth (SId), velocity (SIv), water temperature (SIt) and suspended sediment concentration (SSC) (SISSC) were developed to assess the habitat suitability based on weighted usable area (WUA) and overall suitability index (OSI). Three model configurations were tested: (1) Conventional SSC (SId, SIv, SIt, SISSC). (2) Incorporation of the severity of ill effect (SEV) index (SId, SIv, SIt, SISEV) and (3) Excluding sediment stress (SId, SIv, SIt). The results indicate that habitat suitability is significantly decreased by sediment stress under maximum discharge. The SEV-based test showed a slightly increased OSI compared to the conventional method by 1% under maximum discharge, reflecting more physiologically realistic sediment stress effects. Although OSI was higher at minimum discharge across all methods, excluding the sediment variable improved OSI by 13% to 27%, resulting in a higher WUA, representing substantial but unrealistic improvements. Hydrodynamic indices showed both species thrived at a depth of (5-8 m) and velocities between 0.8 and 2 m/s. These findings highlight the significance of managing sediment and hydrodynamic conditions for biodiversity conservation in the Yellow River during flood conditions.
Hyporheic exchange across salmonid redds plays a critical role in embryo development and biogeochemical cycling. Using fully coupled numerical models validated against measurements from non-invasive high-resolution optical techniques in large-scale open-channel laboratory experiments, we examine how streambed permeability governs the transition from pressure- to advection-driven hyporheic flows. Our results show that hydraulic conductivity K = 0.2 m/s (order of 10(-1) m/s) represents a critical threshold: below this value, sequential surface-subsurface models adequately capture bulk hyporheic fluxes, while above it, fully coupled modeling becomes essential due to significant momentum exchange between flow domains. The experimental validation at K= 0.17 m/s, achieved through simultaneous calibration against both surface flow patterns and subsurface velocity measurements, provides direct evidence of flow regime transition mechanisms near this threshold. At higher permeabilities present in highly porous formations, feedback between surface and subsurface flows becomes significant, reducing near-bed pressure gradients by up to 80%, altering surface hydraulics, and substantially changing hyporheic exchange morphology. We propose a correction factor to extend existing predictive models to high-permeability regimes, accounting for the transition from pressure-driven to advection-dominated flow conditions. These findings highlight the importance of dynamically coupled modelling for assessing ecohydraulic processes in permeable streambeds and inform habitat assessments, restoration strategies, and evaluations of fish-built structures as ecosystem engineers.
Although angled bar racks are increasingly used to guide fish at water intakes, their efficiency for potamodromous species during downstream migrations remains poorly quantified, particularly under varied structural configurations. In this study, the behavioral responses of fish to hydraulic conditions were experimentally investigated using the Oppermann fine screen, with and without an elliptical guidance wall. The tests were conducted at a 45 degrees screen angle, with a bar spacing of 10 mm for two potamodromous fish species, Colchic nase (Chondrostoma colchicum) and Sakarya bleak (Alburnus escherichii). Results showed the guidance wall significantly enhanced passage success for Alburnus while improving passage trends for Chondrostoma. Total body length was found to be a highly significant predictor of success for Chondrostoma, but not for Alburnus. Consequently, including fish length in predictive models dramatically increased their classification accuracy for Chondrostoma. The guidance wall decreased downstream transition time for Chondrostoma and slightly increased it for Alburnus. Both experimental measurements and CFD model results revealed that the guidance wall reduced Reynolds shear stresses, eddies, recirculation, and stagnant areas upstream of the screen, improving downstream bypass passage. These results highlight the value of incorporating guidance walls into fish passage structures to enhance migration efficiency of potamodromous species in regulated river systems.
This paper investigated the influence of the deterioration of water quality in processed potable water distributed to the public from the Lower Usuma Dam Water Treatment Plant (LUD-WTP) in Abuja, Nigeria. Laboratory results revealed that the physiochemical parameters of the water samples were within the guidelines set by the World Health Organization (WHO) and the Nigerian Standard for Drinking Water Quality (NSDWQ). However, analysis of the bacteriological content of the water samples collected from locations serviced by the LUD-WTP revealed the presence of E. coli, Enterobacter aerogenes, and Klebsiella. Through water age simulation, the water distribution system in Abuja is supply-driven rather than demand-driven, which leads to an intermittent supply of water in certain areas. To prevent this issue, recommended chlorine booster locations be implemented at community tanks to re-chlorinate the water before distribution to consumers, and future designs should consider potential urban expansion.
Aquatic habitats in cities are increasingly being promoted to provide ecosystem services and adapt cities to climate change. These include protected and restored habitats, many of which as aquatic nature-based solutions (aquaNbS) focus on ponds and streams. Such habitats support diverse macroinvertebrate communities, for which knowledge gaps remain regarding their environmental drivers. We characterized macroinvertebrate composition in urban ponds and streams built as aquaNbS across four European cities under contrasting climatic conditions (Lisbon, Antwerp, Pozna & nacute;, Helsinki). Further, we tested the influence of environmental factors as two types of variation, based on a geographical scale. Results have shown that variation between cities communities were mainly associated by climate and bottom material. At the variation within cities, communities were associated by the type of aquaNbS (pond vs. stream), followed by city specific drivers: water (temperature, oxygen, water residence time), aquaNbS (bottom material, depth) and vegetation (Normalized Vegetation Index) related variables. Results suggest that NbS planning can boost urban biodiversity by ensuring the presence of a wide range of habitats as in important factor for communities. Understanding the possible drivers of communities is critical to improve the functions and management of aquaNbS and should be considered when projecting or restoring them.
The study of fish movement behavior has been greatly advanced by the development of automated visual tracking, which can provide quantitative data on movement and body posture. Software tools enable researchers to explore various ecological questions but fundamentally rely on achieving good visual contrast between the moving organism and its background. Many laboratory studies expose fish to highly artificial environments with rectangular channels, flat concrete floors, and glass walls. However, imaging fish remains technically challenging, and the absence of standardized guidelines often makes automated tracking a time-consuming process of trial and error. Clear recommendations are lacking that could help reduce imaging difficulties and improve tracking efficiency. Here, we address challenges related to tracking fish through the air-water interface while replicating natural light and flow conditions to enrich ecohydraulics studies. We demonstrate how bottom-up infrared illumination allows for high-contrast imaging of fish position and posture, and how structural features such as depressions and cobbles can mimic the complexity of natural riverbeds. Finally, we discuss challenges posed by surface waves and light refraction and provide a framework for designing flume experiments that improve tracking accuracy and thereby enhance the study of fish movement under ecologically relevant flow conditions.
Hydropeaking and invasive non-native fish species are among the most significant pressures to riverine ecosystems and freshwater biodiversity, yet, fish responses to hydropeaking and the effectiveness of mitigation measures remain largely uncharted. This study addressed this gap through an indoor flume experiment assessing how two flow events influenced the use of artificial habitats (flow refuges) by the invasive non-native common carp (Cyprinus carpio). Fish behaviour was evaluated for a base flow (continuous 7 L/s) and a peak flow (increase from 7 L/s to continuous 60 L/s). Refuge use was quantified within three regions of two flow refuges alongside physiological responses (glucose and lactate) to stress and fatigue. Results were compared with previous findings for the native Iberian barbel (Luciobarbus bocagei) tested under the same conditions. No significant differences in lactate or glucose levels were observed between flow events for either species. In contrast, both species showed significantly higher frequency and duration of refuge use during peak flow. The native Iberian barbel displayed more frequent and prolonged refuge use than common carp, suggesting a stronger dependence on these structures for hydrodynamic sheltering. These findings raise concerns that intensified competition for flow refuge use may impede native species' access to these structures.
Barriers have significantly disrupted fish movement and migration, contributing to global population declines. The Tube Fishway offers a novel solution for upstream passage that uses the flow of water through pipes to lift fish upstream. Potential design advantages include reduced water demands, and an ability to retrofit to existing barriers or sites with space constraints. This study presents the first Tube Fishway deployment that attracted and safely transported wild fish. Installed downstream of Ewen Maddock Dam (Australia), the fishway operated over 20 experimental hours and successfully transported 230 fish across eight species over a height of 3.4 m. The most effective configurations included a one-way cone trap with a 3-minute attraction interval and 0.26 m/s attraction flow (25 fish/h), or combined attraction and auxiliary flows of 0.13 m/s and 0.28 m/s, respectively (29 fish/h). DIDSON acoustic camera footage indicated auxiliary flow enhanced fish activity near the entrance, while the fishway's operational surge temporarily deterred fish activity for up to 80 s. This field validation confirms the capacity of the Tube Fishway to transport wild fish. Operational parameters including entry design, flow configuration, and timing, can influence the fishway's effectiveness. These findings support the development of the Tube Fishway as a solution for restoring riverine connectivity.
This work examines the relationships between flow restoration, natural flow regimes and riparian vegetation utilizing a case study in northern Sweden. The riparian zone is one of the most species-rich ecosystems and forms an important link between aquatic and terrestrial systems. The integrity of the riparian zone and its vegetation is harmed by flow alteration in numerous rivers, which calls for enhancing riparian management and ecological mitigation measures. Here, we take an ecohydraulic approach, combining a hydraulic model and data on inundation tolerance of riparian vegetation to evaluate the effects of reintroducing seasonal flow variation in a bypassed reach with minimum discharge. The results show that implementing the seasonal flow variation is projected to benefit riparian vegetation by extending the riparian zone and to lead to the development of distinct vegetation belts similar to riparian vegetation along free-flowing rivers. Additional simulations demonstrated that a further increase in riparian area could be achieved by increasing the magnitude of the minimum flow release. While the method assumes the riparian vegetation to be in equilibrium with the flow regime, continued monitoring is needed to assess how fast the riparian vegetation adjusts to new flow conditions.
