Downstream Passage Research Articles

Paddlefish movement and dam passage in the Ohio and Kanawha Rivers, West Virginia

The Paddlefish (Polyodon spathula), a large-bodied and highly migratory species of large river systems, has experienced population declines or extirpation in parts of its native range. As an effort to reestablish a Paddlefish population in the Ohio River of West Virginia, the West Virginia Division of Natural Resources has stocked fingerling Paddlefish in the previous two decades. Post-stocking studies could assess the status of the reintroduced population, which includes collecting information on their seasonal movements and dam passage frequency through navigation dams of the Ohio and Kanawha Rivers. Using acoustic telemetry techniques, we monitored seasonal movements and assessed dam passage of five Paddlefish in the Robert C. Byrd Pool of the Ohio and Kanawha rivers. Paddlefish were highly mobile with two individuals using the entire R.C. Byrd Pool during the 11-month study period. Most movements occurred during the expected spawning period of April and May, where all individuals frequented the upper section of the pool in the Kanawha River. Downstream passage was documented for one individual at the R.C. Byrd lock during July 2023, but no evidence of upstream passage was documented for the locks at Racine (Ohio River) or Winfield (Kanawha River). Tagging of additional Paddlefish would be beneficial to increase sample size for future assessments and continue efforts toward the long-term conservation and management of Ohio River Paddlefish.

Impacts of the High-Pressure Bratsk Hydroelectric Power Station on Fish Population of the Bratsk Reservoir

Environmental and ecological effects of the dam of the high-pressure Bratsk Hydroelectric Power Station (HPS) on the fish population and the probability of fish downstream migration from the Bratsk Reservoir have been studied. It has been revealed that thermal stratification of the water column is a significant factor in the ecological differentiation of the fish population in the upper reaches of high-pressure hydroelectric plants. According to hydroacoustics data, most of the ichthyomass, consisting of “warm-water” representatives of the Percidae (65%) and Cyprinidae (22%) families, is concentrated in the relatively warm layer of the epilimnion. Juvenile fish from 30 to 50 mm in size (up to 70% of the total fish number in this layer) are also concentrated here. In the cold-water hypolimnion, the fish population is represented by large single individuals of whitefish (Coregoninae). The data on distribution of fish in the lower and upper reaches of the dam, fish nutrition patterns, growth rate, and the presence of injuries that occur when fish pass downstream through hydroelectric plant dams are presented. Revealed differences in the growth rate of perches from the upper and lower reaches are associated with their constant inhabiting of water masses with contrasting temperatures. Net catches in the lower reaches over the four seasons of research lack injured individuals. These facts prove the absence of mass downstream passage of fish through the Bratsk HPS dam. Juveniles of cyprinids and perches accumulate in the upper warm layer of 0–10 m, i.e. outside the zone of the intake flow formation, which makes their entrance to intake openings at a depth of more than 20 m hardly possible.

Population Responses of Blueback Herring to Dam Passage Standards and Additive Mortality Sources

Abstract The management of anadromous fishes is inherently complicated because this suite of species exhibits complex life histories in multiple habitats and is subject to varying natural and anthropogenic influences during discrete ontogenetic periods. Fishery scientists and managers often adopt life history–based simulation models to help understand potential effects of management decisions on fish populations while incorporating uncertainty in life history, climate, and other components of resource management systems. We applied one such model to Blueback Herring Alosa aestivalis in the Hudson River watershed, New York, USA. Our goal was to better understand influences of historical habitat loss on anadromous fishes and determine to what extent and under what conditions novel habitat created by canal infrastructure might confer increased population abundance. We found that access to historical habitat in the upper Hudson River increased population abundance at all upstream dam passage rates with sufficient downstream survival of adult and juvenile Blueback Herring but that abundance decreased with increasing upstream passage relative to the “no passage” scenario when downstream survival through dams was not sufficiently high. Access to novel spawning habitat in the Mohawk River canal system resulted in increased abundance of Blueback Herring when downstream survival of adults and juveniles was at least 0.80/dam, and both upstream passage and probability of using the Mohawk River were greater than approximately 0.25. Both mortality during upstream passage of locks in the Mohawk River and marine fishery mortality had the potential to reduce Blueback Herring abundance below historical population abundance, despite access to novel spawning habitat. These results highlight the complexity associated with effects of upstream and downstream fish passage standards on population responses while emphasizing similarities observed in other diadromous species and watersheds.

Computational fluid dynamics simulation of passive downstream fish passage over a weir with OpenFOAM®

Many fish species are dependent on migration through river systems. Weirs are an obstacle to downstream migration, which can lead to obstruction as well as injury and mortality. The current level of knowledge about downstream migration over weirs is limited, and the current assessment of this is uncertain. This study uses a computational fluid dynamics (CFD) method for assessing the damage potential of the downstream migration over the weir, evaluating the effectiveness of the current recommendations. Two test cases were simulated using OpenFOAM® and an interFoam-based solver, extended with Lagrangian particles to represent passively transported fish. The results of the simulations show that adherence to the recommendation for a necessary tailwater level has no significant impact on the relevant hydraulic stressors, shear stress, pressure changes and collisions in certain situations. A thick nappe, however, leads to a significant reduction in collisions, especially of particles initialized near the surface. The CFD method used in this study proves to be suitable for evaluating downstream fish passage with certain limitations. This means that qualitative comparisons of different situations are possible, but not the determination of the damage potential of a specific situation. Further investigations are necessary to identify factors for safe downstream fish passage.

Challenges in downstream dam passage and the effect of dam removal on Atlantic salmon (Salmo salar) smolt migrations.

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

Fish behavior at the horizontal screen of a novel shaft hydropower plant

AbstractPreventing fish entrainment during their downstream passage at hydropower plants remains a major challenge in reducing the ecological impacts of hydropower production. We investigated fish behavior at the world's first innovative shaft hydropower plant with its novel screen concept, aiming at reducing fish entrainment due to the fully horizontal arrangement of the screen and low vertical suction effects toward the turbine. Based on ARIS sonar recordings, we assessed whether fish could move unhindered across the turbine intake area toward the bypass corridors at the sluice gate for safe downstream passage. For a range of species (Anguilla anguilla, Barbus barbus, Thymallus thymallus, Salmo trutta, and Hucho hucho) and operation modes (high/low turbine load), we assessed behavioral patterns such as screen avoidance, dwelling behavior, and search behavior at the screen. Contrary to the engineers' expectations, the innovative screen arrangement neither guided the fish away from the turbine intake to the bypass corridors nor prevented them from swimming vertically into the turbine shaft. Rather, fish freely moved near the screen and avoidance behavior was only rarely observed. Both the dwelling and active search behavior, which was particularly evident in eel, are directly linked to an increased risk of screen passage and subsequent turbine‐related death or injuries. Our findings illustrate that consideration of fish behavior at turbine inlet structures is a crucial component which needs to be integrated with other variables such as fish mortality and injury patterns for a comprehensive evaluation and improvement of fish passage at hydropower plants.

Assessment of Movement and Dam Passage of Paddlefish in the Ohio River, West Virginia.

Paddlefish (Polydon spathula), a large-bodied and highly migratory species of large river systems, has experienced population declines or extirpation in parts of its range. As an effort to reestablish Paddlefish populations in the Ohio River of West Virginia, the West Virginia Division of Natural Resources has periodically stocked Paddlefish, but post-stocking studies are needed to assess the status of the reintroduced population, including information on movements of Paddlefish or on their passage through navigation dams of the Ohio River. Using telemetry techniques, we monitored seasonal movements and assessed dam passage of five Paddlefish in the Robert C. Byrd pool of the Ohio and Kanawha rivers. Paddlefish were highly mobile with two individuals using the entire R.C. Byrd pool during the 11-month study period. The highest movement rates occurring during the expected spawning period of April and May, where all individuals frequented the upper section of the pool in Kanawha River. Downstream passage was documented for one individual at the R.C. Byrd lock during July 2023, but no evidence of passage was documented for the locks at Racine or Winfield. Tagging of additional Paddlefish is planned, which will increase sample size for future assessments and continue efforts toward the long-term conservation and management of Ohio River Paddlefish.

Downstream passage performance of silver eel at an angled rack: effects of behavior and morphology

The European eel is critically endangered due to heavy impact of anthropogenic factors, such as habitat fragmentation, overexploitation and climate change. During downstream migration, silver eels may encounter hydropower plants, which often result in delay or mortality from impingement on trash-racks or turbine passage. These problems can be mitigated with downstream passage solutions, such as angled racks that guide downstream-migrating eels to safe passage routes. The importance of bar spacing and phenotypic diversity for passage performance is, however, largely unknown. In this study, we investigated how morphological parameters (body mass, eye and fin indices) and behavioral score (open field test) influenced passage rate at an experimental intake equipped with a bypass and angled racks with either 15 or 30 mm bar spacing. Both racks were efficient in guiding eels into a bypass. There was a strong positive effect of body mass and a weak positive effect of open field test score on passage rate. Other factors such as eye and fin indices played a minor role. These results demonstrate the performance of angled racks with bypasses and form a useful starting point for further research regarding the relationships between individual variation in behavior, morphology and passage solutions for silver eels.

Emigration of post-spawned twaite shad Alosa fallax, an anadromous and iteroparous fish, in a highly fragmented river.

Anthropogenic barriers are widely known to negatively impact the spawning migrations of anadromous fishes, by delaying or preventing passage upstream. Although the impacts of barriers on emigrating post-spawned adults are less well studied, they could potentially impact the fitness and subsequent return rates of iteroparous species. In this study, passive acoustic telemetry was used to track the emigrations of 53 twaite shad Alosa fallax in the River Severn basin in their first spawning migration a year after being tagged, giving insights into their emigration movements and the impacts of anthropogenic weirs on these movements. A. fallax began their emigrations after spending varying amounts of time and migrating various distances within the river, with late-emigrating individuals moving fastest and most directly. Emigrations became faster and more direct the further downstream individuals were from their furthest upstream extent. Downstream passage delays at weirs increased emigration times by a median of 61%, with environmental conditions (i.e., temperature, flow, and tidal influence on river level) having little influence on downstream passage at weirs with no modifications to facilitate fish passage. As weir-induced emigration delays are suggested to deplete energy reserves (when energy levels are already depleted post-spawning), limit spawning opportunities (by preventing access to downstream spawning habitat), and expose individuals to increased predation risk and suboptimal conditions (e.g., high temperatures), these delays can potentially diminish the benefits of iteroparity. The evidence presented here suggests that more consideration should be given to the potential impacts of anthropogenic barriers on the emigrations of iteroparous species when assessing river connectivity or undertaking barrier mitigation.

Hedonic analysis of willingness to pay for dam removal: evidence from Plymouth, Massachusetts

This study investigates how the removal of small dams, and subsequent river restoration investments, affect residential housing prices in Plymouth, Massachusetts, selected for its unusually high density of dam removals. From 2002 to 2019, 5 dams within 1.05 miles of each other have been removed. Following removal, riverine restoration was completed, leading to improved public safety for downstream infrastructure, fish passage, and better water quality. Yet, contention exists in local government decision-making from fear of loss of property values of homes that are no longer classified as “waterfront.” To examine that charge, we evaluate sale prices of 9,710 single-family homes from 1997 to 2021, in a comparative estimation of a hedonic regression and a difference in differences model. The results indicate that the price of homes sold in Plymouth after dam removal increased, with no impact on property values of waterfront and properties within 1 mile of riverine restoration locations. For properties within a 5-mile radius of a former dam, we observe comparative difference in price of a fraction of a percent for lots around 2 of the dams, in relation to all home lots in Plymouth. We explain that this difference is due to property-specific features, rather than the impact of dam removal. The implications are that dam removal would not negatively impact waterfront property values, while it may translate into an overall environmental price premium for the community at large.

A130 RETROGRADE ENDOSCOPIC ULTRASOUND-GUIDED ENTERO-ENTEROSTOMY USING A LUMEN-APPOSING METAL STENT FOR THE MANAGEMENT OF A HIGH-OUTPUT ENTEROCUTANEOUS FISTULA AND ILEAL STRICTURE IN A COMPLEX SURGICAL ABDOMEN

Abstract Background A 26-year-old male sustained significant traumatic thoracoabdominal injuries following a gunshot. He underwent several laparotomies, small bowel resections, an extended left hemicolectomy with end-colostomy formation, and a flap to close the abdomen. He subsequently developed a high-output enterocutaneous fistula (ECF) and loss of colostomy output. CT imaging confirmed an ECF from the ileum to the anterior abdominal wall and a severe ileal stricture distal to the fistula. Aims In the context of his complex surgical abdomen and proximity of the ECF to the abdominal flap, surgical re-intervention was deemed high-risk. He was placed on total parenteral nutrition and referred for endoscopic management. Methods Under fluoroscopic guidance, we injected methylene blue & contrast dye from the skin side of the ECF. A dilated segment of small bowel was filled, with no downstream passage of contrast (Fig 1A). Retrograde ileoscopy was performed with an Olympus pediatric colonoscope via the patient’s colostomy. 90 cm from the ileocecal valve (ICV), we encountered a benign enteric stenosis that could not be traversed. Contrast was injected, with fluoroscopy revealing a 10 cm long tortuous stenosis (Fig 1B), extending to the previously filled loop of small bowel. Given the length and characterof the stricture, endoscopic balloon dilation and enteral stenting were technically infeasible. Results We proceeded to retrograde endoscopic ultrasound (EUS)-guided entero-enterostomy creation. With the aid of a guidewire, and under endoscopic, fluoroscopic and endosonographic guidance, a linear echoendoscope was advanced into the ileum via the colostomy, cecum and ICV. 50 cm from the ICV, we identified an adjacent dilated loop of small bowel (Fig. 1C). Water was instilled through the ECF, with the endosonographic view demonstrating filling, thus indicating this location to be upstream from the ECF. A 19-gauge needle was punctured through, with subsequent aspiration of methylene blue (Fig. 1D). We then created an EUS-guided entero-enterostomy using a 15mm lumen-apposing metal stent (Hot-AXIOS; Boston Scientific, Massachusetts, USA; Fig. 1E). Passage of methylene blue & contrast through the stent confirmed accurate deployment (Fig. 1F&G). With both the ECF & stricture bypassed, the patient’s colostomy output returned and ECF output diminished. Conclusions Electrocautery-enhanced lumen apposition with metal stenting is well established. It can facilitate the formation of an anchored anastomosis across non-adherent luminal structures in a single-step fashion. Herein, we have reported a novel application of this technique in the management of a complex post-surgical trauma patient with a high-output ECF and deep enteric stenosis. Figure 1: Retrograde EUS-guided entero-enterostomy Funding Agencies None

Swimming Performance of Schizothorax sp. and Planning of Fish Passages in Nepal

Swimming performance of migrating fish is crucial for the planning and design of effective fish passages. Commonly the fish swimming speeds are classified into five categories: 1) Optimum Swimming Speed, 2) Maximum Sustained Swimming Speed, 3) Critical Swimming Speed, 4) Maximum Domed Swimming Speed, and 5) Burst Swimming Speed. Swimming characteristics are related to the different species' adaptions to the environmental conditions. A variety of different factors affect the swimming capacity of fish which is directly related to fish size and species-specific morphology. A crucial abiotic factor is water temperature, which affects the fish physiology and thereby the swimming speed of the fish. This means that the fish's swimming speed can increase with increased water temperature. The swimming speed also increases with fish size. Fish often use burst speeds when passing a step in a fish ladder or entering a culvert. Burst speed is the highest speed attainable for fish, and it is the maximum energy output to be gained by using the white muscle (red muscle in salmonids). The burst speed can only be maintained for short periods of time (seconds). In the Himalayas, the main objective of many fisheries development plans is to secure future habitats and ensure up- and downstream migration of fish. Schizothorax richardsonii is often a targeted species in the area due to its importance as a food resource. If a fish passage is prepared for the upstream migration of fish, it is also crucial for the fish population development to ensure a safe downstream passage. Data on swimming performance for many of the native fish species in Nepal are scarce which complicates the design of suitable ecologically adapted fishways. In general, nature-like fish passes allow most of the species to migrate, followed by vertical slot fishways, meander fishways, and thereafter fish ladders of the pool-and-weir type. The key factor is to construct fish-passes that under all naturally required environmental circumstances can allow appropriate passage conditions of the targeted fish species.

Downstream migration and hydropower dam passage of a Danubian cyprinid, Rutilus meidingeri, at the Seeache River, Austria

Downstream passage at a hydroelectric power plant of pearlfish (Rutilus meidingeri), a cyprinid species endemic to the Danube catchment, was examined. Forty pearlfish were trapped in the fish pass during their upstream migration, tagged with telemetry transmitters and subsequently released to the upstream section of the weir. The tagged fish were monitored to determine their descending behaviour and ability to overcome the obstacle through three possible corridors: a bypass channel, the overflown weir, and a vertical slot fish pass. Pearlfish used the entire 2.7 km of the river by successfully migrating further upstream and also by descending past the obstacle back to Lake Attersee through the bypass channel (65 %), and the weir overflow (35 %). No fish utilised the fish ladder as a descent corridor, even though 82 % of the fish were registered in the vicinity of the entrance to the facility. Apart from the unfavourable positioning of the fish pass for downstream migration, the discharge conditions proved to be decisive for the choice and availability of the descent corridor as well as the behaviour during descent. Significant delays in power plant passage occur both in the forebay and at the used corridors. Even if the ability to find corridors and the passability of adult pearlfish can be proven, further measures appear to be necessary for the safe migration and protection of the endangered species.

Timing is everything; operational changes at a pumping station with a gravity sluice to provide safe downstream passage for silver European eels and deliver considerable financial savings

Catadromous European eel (Anguilla anguilla) are a critically endangered fish species due in part to in-river anthropogenic barriers (e.g., pumping stations, weirs, hydropower facilities). European legislation stipulates that safe downstream passage must be provided at hazardous intakes. Where present, gravity sluices have the potential to act as safe and low-cost downstream passage for seaward migrating silver eels at pumping station, but operational changes are required. This study used catchment-wide and fine-scale acoustic telemetry to investigate if operational changes (OC) at a pumping station (PS) with a co-located gravity sluice (GS) facilitated safe downstream passage for silver European eels. Specifically, night-time pump operations were ceased, river levels prior to sluicing were elevated and the GS was opened during key eel migration windows, i.e., at night during the new moon phase in autumn. No tagged eels passed through any pumps and the majority (2018 = 87.5%, 2020 = 88.9%) that approached the PS during OC passed downstream through the GS. Most eels approached during the first period of night sluicing after release (2018 = 73.9% and 2020 = 76.5%) and passed downstream during the first sluice event they experienced at the PS (2018 = 66.7% and 2020 = 75.0%). During the final approach prior to passage, very few retreats back upstream occurred at a median (IQR) distance of 34 (7.25) m from the GS and were predominantly a short distance (1–8 m). Overall, OC at a PS with a GS are considered a win-win-win, despite opening the sluice for <3% of the study period, given safe downstream passage was maximised, the financial benefits of sluicing water (∼£14,670 in direct operational costs over two years) and the relative ease of implementation.

FishSeg: 3D Fish Tracking Using Mask R-CNN in Large Ethohydraulic Flumes

To study the fish behavioral response to up- and downstream fish passage structures, live-fish tests are conducted in large flumes in various laboratories around the world. The use of multiple fisheye cameras to cover the full width and length of a flume, low color contrast between fish and flume bottom and non-uniform illumination leading to fish shadows, air bubbles wrongly identified as fish as well as fish being partially hidden behind each other are the main challenges for video-based fish tracking. This study improves an existing open-source fish tracking code to better address these issues by using a modified Mask Regional-Convolutional Neural Network (Mask R-CNN) as a tracking method. The developed workflow, FishSeg, consists of four parts: (1) stereo camera calibration, (2) background subtraction, (3) multi-fish tracking using Mask R-CNN, and (4) 3D conversion to flume coordinates. The Mask R-CNN model was trained and validated with datasets manually annotated from background subtracted videos from the live-fish tests. Brown trout and European eel were selected as target fish species to evaluate the performance of FishSeg with different types of body shapes and sizes. Comparison with the previous method illustrates that the tracks generated by FishSeg are about three times more continuous with higher accuracy. Furthermore, the code runs more stable since fish shadows and air bubbles are not misidentified as fish. The trout and eel models produced from FishSeg have mean Average Precisions (mAPs) of 0.837 and 0.876, respectively. Comparisons of mAPs with other R-CNN-based models show the reliability of FishSeg with a small training dataset. FishSeg is a ready-to-use open-source code for tracking any fish species with similar body shapes as trout and eel, and further fish shapes can be added with moderate effort. The generated fish tracks allow researchers to analyze the fish behavior in detail, even in large experimental facilities.

Monitoring of fish upstream and downstream passage at a screw turbine and migration screw facility

Monitoring of fish upstream and downstream passage at a screw turbine and migration screw facility

The influence of passive wedge-wire screen aperture and flow velocity on juvenile European eel exclusion, impingement and passage

The European eel (Anguilla anguilla) is a critically endangered catadromous fish. The decline has partly been attributed to water management infrastructure that abstract water from rivers for potable and industrial water supply, irrigation, hydroelectric power generation and flood defence; eels can be impinged on weedscreens and trashracks and entrained in pumps and turbines. The Eel Regulations (England and Wales) 2009 stipulates measures are required to provide safe (upstream and downstream) passage of eels past such hazardous intakes. Preventing impingement and entrainment of upstream migrating (glass eel and elver) and river-resident (yellow) juvenile eels at hazardous intakes may require fine-mesh aperture screens and low approach velocities due to eels' small size and relatively poor swimming capacity but quantitative evidence is lacking. Here, passive wedge-wire screen aperture (1, 2, 3 and 5 mm) and depth-averaged flow velocities (0, 0.1, 0.15 and 0.2 m·s−1) both influenced the fate (i.e., impingement or passage) and behaviour (i.e., migratory separation or behavioural avoidance) of two size classes of juvenile eels (60–80 mm glass eels and 100–160 mm elvers) in an experimental flume. One and 2 mm aperture screens were required to physically exclude 60–80 mm and 100–160 mm, respectively. Up to 90% and 100% of the 60–80 mm and 100–160-mm size class eels were impinged at 0.2 m·s−1 depth-averaged flow velocity, which also positively influence number of screen contacts per eel and time to eel fate (from first contact). A small proportion of 60–80 mm eels (9.2%) did not approach the screen due to migratory separation (i.e., positive rheotaxis) and eels narrower than the screen aperture did not always pass through the screen, and thus other biological or hydraulic processes may also influence screen passage. It is hoped that these findings help improve screening guidance for regulators, key stakeholders and water abstraction managers to further improve protective measures required for critically endangered eels.

Spatial-temporal evolution of tip leakage cavitation with double-hump in a mixed flow pump with tip clearance

Tip clearance in pump induces tip leakage vortex (TLV), which interacts with the main flow and leads to instability of flow pattern and decrease in pump performance. In this work, a closed-loop experimental rig with high-speed observation for a mixed flow pump is established, and the numerical simulation on tip leakage cavitation is conducted with experimental validation. A new double-hump pattern of tip leakage cavitation is first observed in the mixed flow pump. Results show that primary tip leakage vortex cavitation develops from a linear pattern to a banded pattern and, finally, to a double-hump pattern. The spatial–temporal evolution of tip leakage cavitation with double-hump can be classified into four stages: incepting stage, growing stage, merging stage, and propagating stage. The inception of the front hump is found to correspond to the periodic evolution of the specific passage vortex-tip leakage vortex (PV-TLV) pair. Affected by the propagation of the high-pressure area at the passage outlet, the PV wanders in the downstream passage, which greatly affects the intensity of tip leakage flow. The away motion of the PV from the tip clearance brings stronger tip leakage flow and results in the intensified TLV and the lower core pressure. As a result, the front hump incepts, grows, and travels downstream. Finally, it merges with the rear hump and together propagates to the downstream passage.

Downstream fish passage at small-scale hydropower plants: Turbine or bypass?

Introduction: Hydropower plants are frequently equipped with physical and behavioral fish protection barriers to prevent downstream moving fish from harmful turbine passage and to guide them to alternative bypasses. As not only diadromous but also potamodromous fish species migrate and inevitably have to pass hydropower plants, knowledge on corridor usage for a wide range of species is important to identify potential deficits and to improve bypass efficiency.Methods: In this study, the corridor usage of downstream moving fish (6,646 individuals from 42 species) was investigated at four small-scale hydropower plants with different concepts to prevent turbine entrainment and to bypass fish.Results: Despite existing bypasses and fine screens with 15 mm and 20 mm bar spacing to prevent turbine entrainment, a large proportion of fish (35%–88%) still passed the turbines. The mainly poor efficiency of the investigated bypasses was probably due to low discharge and unfavorable bypass location or detectability. The various bypass types were used by a different range of fish species and sizes due to species-specific behavior and differing fish communities between sites. The effectiveness of the investigated downstream corridors was positively correlated with the share of discharge.Discussion: To reduce the negative ecological impacts of hydropower plants on downstream moving fish, well-performing bypasses are required that consider not only current requirements regarding design, dimensioning and location, but also the site-specific fish community. Thus, bypasses should function for the widest possible range of species, which can be achieved through less selective bypass types such as full-depth bypasses, or a combination of different bypass systems. Moreover, less harmful turbine technologies and more effective fish protection systems need to be implemented, since fine screens with 15 mm and 20 mm bar spacing cannot prevent small-bodied fish species and juvenile fish &amp;lt;20 cm from turbine entrainment.

Understanding the temporal dynamics of a lowland river fish community at a hazardous intake and floodgate to inform safe operation

Entrainment and mortality of freshwater fish at hazardous pumping station intakes used for Flood Risk Management (FRM) are of global concern. Although upstream and downstream passage of diadromous fish has received considerable attention, the ecological behaviours of river-resident fish at these structures and how to protect these species from entrainment is poorly-understood. At a lowland flood-relief pumping station and floodgate situated off-channel (River Foss) to the main-river Yorkshire Ouse (York, England), multi-beam sonar (Dual-Frequency Identification Sonar: DIDSON) was used over a pluriannual (three years) period to investigate diel movements of river-resident fish in response to the variations in temperature, hydrology and pump and floodgate operation, and to determine fish-friendly management options. Diel lateral movements of thousands of river-resident fish between the main-river, floodgate operated channel (River Foss) and off-channel pump forebay were predominantly during the crepuscular period and daytime, proposing important considerations for when managers should operate pumps and associated flood infrastructure. Seasonal diel movements increased throughout winter during a baseline year (no pump operation) and overwintering behaviour was influenced by cooling river temperatures. A Generalized Linear Mixed Model (GLMM) revealed fish entered the off-channel forebay when river levels were stable and not when they were rising or falling, suggesting hydrological stability was important for the ecological function of this fish community. Two years of impact data (pumps operated) then revealed pump operations severely disrupted the ecological functions of local fish populations, which was also uniquely quantified over two independent 24h periods during which temporal fish counts were reduced by 85%. A trial period where the floodgate was lowered ahead of dawn significantly reduced fish immigration into the hazardous forebay when compared to two different hydrological periods. Modifying when the floodgate and pumps operate, including lowering the floodgate ahead of fish immigration at dawn, and starting pumps during the night (but not day), are therefore promising non-engineered management options to prevent immigration of fish into the hazardous off-channel pump forebay and to reduce entrainment and mortality risk during pump operation.