Search Results (22)

Brown trout (Salmo trutta L.) is a bioindicator species of ecological integrity in mountain rivers of northern Portugal. Habitat loss and recreational fishing justify sustainable management to balance the conservation and exploitation of these fish populations. In fact, salmonid streams in NE Portugal are low productive watercourses and fish stocking has been continuously demanded by fishermen. However, this most common management action must be analyzed carefully and determined the effective increase for local fisheries, taking into consideration the potential dispersal of stocked fish. The objective of the present study, developed in River Sabor, was to determine short- and medium-term movement and dispersal patterns and habitat preferences of wild and stocked Brown trout, using radio telemetry, during a weekly monitoring 4-month period (October to February 2026; n = 18). Fish was sampled by electrofishing at beginning and the end of the experiment. Twenty-four adult Brown trout, equally distributed by two salmonid sections, and three groups, (1) wild resident (River Sabor) (213–270 mm TL); (2) wild non-resident (from contiguous basin, River Baceiro) (200–375 mm TL) and (3) rear-captivity (Castrelos Fishfarms, ICNF) (227–365 mm TL) fish, were surgically implanted with radio transmitters. Significant differences (KW-H (2;24) = 4.67; p = 0.09) were observed for the dispersal distances, considering fish detected at least in five sampling events, ranging from 120–1437 m for the wild resident stationary group to 192–14,150 m for the stocked mobile group. Moreover, wild non-resident fish displayed higher movement in the upstream direction, in opposition to the downstream movement of stocked individuals. Wild resident and non-resident trout tended to display increased movements during November and December, probably related to spawning activity, showing preferences by riffle and run habitats. Stocked fish were detected in pool habitats (mainly weir reservoirs), exhibiting significantly lower growth rates, and increased movement during January and February, particularly during flood events. These findings are valuable information for managers related to movement patterns, habitat use and stocking management. Full article

Hyporheic zone exchange processes are strongly influenced by channel morphology, producing heat transfer patterns with distinct vertical stratification. To evaluate the effects of different channel geomorphic units on hyporheic temperature dynamics, monitoring sites were established along a segment of the Xiajiasi River (Hubei Province, China) encompassing four representative channel types: a meandering reach, a pool–riffle reach, a weir reach, and a straight reach. Hyporheic temperatures were recorded at multiple depths (0, 0.1, 0.2, and 0.3 m) during both summer and winter. The results indicate that channel morphology strongly controls the spatiotemporal distribution of hyporheic temperatures. Across all channel types, sediment temperatures exhibited depth-dependent amplitude attenuation and phase lag, with mean temperatures decreasing with depth in summer and increasing with depth in winter. The meandering reach exhibited the highest summer temperatures (28.3–30.6 °C), whereas the pool–riffle reach displayed the steepest thermal gradients (deep sediment temperatures as low as 25.6 °C). In contrast, the straight reach exhibited the weakest thermal buffering capacity. The presence of the weir markedly modified downstream thermal conditions, reducing sediment temperatures by approximately 1.6–3.2 °C during summer, whereas overall winter observations demonstrated a pronounced thermal inversion with deep sediment temperatures increasing by 1.2–2.9 °C. These findings demonstrate that distinct geomorphic units create diverse thermal niches; river managers can incorporate diverse geomorphic features into river restoration designs to create localized thermal refugia, thereby protecting temperature-sensitive aquatic species. Full article

Anthropogenic barriers fragment Portuguese rivers, threatening endemic freshwater fish communities. This study compiled national inventories and peer-reviewed research (2002–2024) to quantify fishway implementation, evolution and typology, while evaluating fish performance from published research. One hundred fishways built between 1950 and 2024 were recorded, half of which were constructed after the implementation of the Water Framework Directive in Portugal (29 Dec 2005), tripling the annual construction rate. Fishways were found to be associated mainly with weirs (46%) and small hydropower plants (44%), with typology being dominated by the pool-type design (67%), nature-like facilities (18%), fish locks and combined systems (6% each), fish lifts (2%) and a single eel pass. Forty scientific contributions addressed fishway effectiveness; three-quarters dealt with pool-type facilities, while 12.5% and 10% focused on nature-like fishways and lifts, respectively. Experimental and field studies highlighted species-specific hydraulic preferences, the benefits of vertical slot and multislot configurations, and the potential of retrofitting fishways with macro-rugosities (i.e., fixed structural elements placed on the bottom) to improve non-salmonid fish passage. However, low attraction efficiency, limited multi-season monitoring and risks of aiding invasive species remain a concern. Research needs are proposed, including the refinement of species-specific hydrodynamic criteria, and the development of standardized efficiency metrics and of selective passage solutions, to advance fishway performance under Mediterranean hydrological constraints. Full article

The placement of hydraulic elements in existing pool-type fishways to make them more suitable for Cyprinid fish is an issue of increasing interest in fishway research. Hydrodynamic characteristics and fish behavior at the representative pool of the fishway with bottom orifices and notches were assessed at the Dagdelen hydropower plant in the Ceyhan River Basin, Türkiye. Three-dimensional velocity measurements were taken in the pool of the fishway using an Acoustic Doppler velocimeter. The measurements were taken with and without a brush block at two different vertical distances from the bottom, which were below and above the level of bristles tips. A computational fluid dynamics (CFD) analysis was conducted for the studied fishway. The numerical model utilized Large Eddy Simulation (LES) combined with the Darcy–Forchheimer law, wherein brush blocks were represented as homogenous porous media. Our results revealed that the relative submergence of bristles in the brush block plays a very important role in velocity and Reynolds shear stress (RSS) distributions. After the placement of the submerged brush block, flow velocity and the lateral RSS component were reduced, and a resting area was created behind the brush block below the bristles’ tips. Fish movements in the pool were recorded by underwater cameras under real-time operation conditions. The heatmap analysis, which is a 2-dimensional fish spatial presence visualization technique for a specific time period, showed that Capoeta damascina avoided the areas with high turbulent fluctuations during the tests, and 61.5% of the fish presence intensity was found to be in the low Reynolds shear regions in the pool. This provides a clear case for the real-world ecological benefits of retrofitting existing pool-weir fishways with such flexible hydraulic elements. Full article

Local regulations control the additional runoff produced by urbanization processes. Sustainable urban drainage systems can mitigate the issues associated with increased runoff by employing infiltration basins, detention ponds, wet ponds, and constructed wetlands. Traditionally, the Water Level Pool Routing Method, which relies on an implicit calculation scheme, has been used to calculate outflow hydrographs in reservoirs. In this research, an explicit scheme for the Water Level Pool Routing Method has been developed. The proposed model is applied to a case study where the reservoir has a surface area of 9.12 hectares. The influence of weir width and the discharge coefficient is also analyzed. Additionally, the variation in time step does not significantly affect the response of the proposed model, demonstrating its adequacy as a novel method. The proposed model is compared to the traditional method, yielding similar results in an analyzed ornamental reservoir (low percentage reduction in peak flow). However, a case study with experimental data reveals that the proposed model provides better accuracy than the traditional method. In addition, the proposed model is more efficient as it reduces computational time compared to the implicit scheme (conventional method). Finally, the proposed model is simplified for small watersheds by applying the rational method for computing an inflow hydrograph. Full article

Modified Denil fishways have a centred gabion containing gravel and are intended to enable the free passage of riverbed-oriented species and invertebrates. An experimental plant was built at a small hydropower station which provided a newly arranged Denil fishway and a pool and weir fishway parallel to one another. It was possible to alternately operate the systems for monitoring purposes owing to the parallel design, allowing an appropriate comparison and analysis of the results to be carried out. The primary objective of this study is to qualitatively and quantitatively compare the size selectivity and ascent numbers between the new development and the conventional construction type. An important component of this study is the test to prove the passage of bullheads in the modified Denil fishway using an experimental set-up. The results of this study depict a similar size distribution of ascended fish in both construction types and thus provide no evidence of selectivity for small fish sizes. Likewise, no deficit of the modified Denil fishway compared with the pool and weir fishway could be proven within the scope of a monitoring. The successful passage of bullheads could be demonstrated in the experiment as well as during monitoring. Full article

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

This work aims to assess brown trout (Salmo trutta) passage through a free-flow pool-weir-type fishway with hydrodynamic notches and extreme water drops between pools. It consists of an old-school fishway design, commonly constructed in salmon rivers of Spain during the period of 1950–1980. To assess their performance, a field test was designed with confined trial conditions during the spawning migratory season. The mean water drop between pools was 0.65 m and the total water height considered for the trial was 11.8 m. The monitoring was carried out using PIT telemetry. The initial hypothesis, considering the fishway design and assessment guidelines, classified this structure as hardly insurmountable. Results showed an ascent success of 19% with a median transit time of 29.1 min/m of ascended height. Larger fish and fishway sections with lower values of volumetric power dissipation were related to a better performance in the passage. The results suggest that in certain circumstances, such as limited construction areas where other design or management options are difficult to implement (e.g., canyons), this type of fishway may be an alternative for the upstream passage of at least a small proportion of the brown trout population, although a selection effect is expected. Full article

Most freshwater fish need to move freely through rivers to complete their life cycles. Thus, river barriers that hinder or block their longitudinal movement (e.g., dams, culverts, gauging stations), directly affect their reproductive, feeding, and habitat routes. A holistic solution to these barriers would need to allow directed, undistracted, and bidirectional fish migration between different habitats; that is to say, it would need to allow two-way migration. The most extended solution that would allow upstream fish migration is a fishway. However, for downstream migration fish have alternate routes such as spillways, turbines, or bypasses. Studies and discussions about two-way migration and bidirectional movement through a fishway have been focused on large dams and reservoirs; thus, there is a lack of available data on other environments, less popular species, or smaller dams and weirs. In this sense, it is possible to hypothesize that a fishway, especially in a smaller facility, could enhance two-way migration by allowing bidirectional movement. Therefore, as a first step to analyzing the possibility, we studied longitudinal connectivity (two-way migration and bidirectional movements) through a small run-of-river hydropower plant (HPP) with a step-pool type fishway, a common and representative configuration of several small HPPs around the world. A potamodromous cyprinid—the Iberian barbel (Luciobarbus bocagei)—was selected as the target species. In this study, radio and PIT tracking data were collected for four different years and combined to characterize movement in the full system: fishway, turbines/spillways, and the river reach downstream (up to 3 km) and upstream (up to 4 km) from the HPP. The results demonstrated the existence of several types of movement with inter-annual and intra-annual variability. Several fish even returned over the years. This suggests that, in this type of HPP facility, a fishway can provide bidirectional connectivity and two-way migration, thus ensuring that a great proportion of fish complete their life cycles. Full article

Understanding the concentration and distribution of cyanobacteria blooms is an important aspect of managing water quality problems and protecting aquatic ecosystems. Airborne hyperspectral imagery (HSI)—which has high temporal, spatial, and spectral resolutions—is widely used to remotely sense cyanobacteria bloom, and it provides the distribution of the bloom over a wide area. In this study, we determined the input spectral bands that were relevant in effectively estimating the main two pigments (PC, Phycocyanin; Chl-a, Chlorophyll-a) of cyanobacteria by applying data-driven algorithms to HSI and then evaluating the change in the spatio-temporal distribution of cyanobacteria. The input variables for the algorithms consisted of reflectance band ratios associated with the optical properties of PC and Chl-a, which were calculated by the selected hyperspectral bands using a feature selection method. The selected input variable was composed of six reflectance bands (465.7–589.6, 603.6–631.8, 641.2–655.35, 664.8–679.0, 698.0–712.3, and 731.4–784.1 nm). The artificial neural network showed the best results for the estimation of the two pigments with average coefficients of determination 0.80 and 0.74. This study proposes relevant input spectral information and an algorithm that can effectively detect the occurrence of cyanobacteria in the weir pool along the Geum river, South Korea. The algorithm is expected to help establish a preemptive response to the formation of cyanobacterial blooms, and to contribute to the preparation of suitable water quality management plans for freshwater environments. Full article

Hydrological changes affect not only the physicochemical factors and habitat structure of river ecosystems, but also the structure of biological communities sensitive to environmental changes, such as zooplankton. In this study, we investigate the effects of weir opening on environmental variables and topographic structures at Sejong Weir in South Korea and monitor the resulting changes in the structure and distribution of the zooplankton community. Weir opening led to increased dissolved oxygen and decreased conductivity, turbidity, chlorophyll a, total phosphorus, and total nitrogen and increased the diversity of topographic structures (reduced pool area and increase riffle and grassland/bare land areas) in the section downstream of Sejong Weir. Prior to weir opening (2015–2016), the cladoceran community was dominated by Chydrous spaeericus and Moina microcopa. After opening (2018–2019), the abundance of other cladoceran communities such as Bosmina groups (Bosmina longiseta, Bosmina fatalis, and Bosminopsis deitersi), Ceriodaphnia sp., and Daphnia obtusa increased. In contrast, the copepod species (Cyclops vicinus and Mesocyclops leukarti) were abundant before weir opening. We conclude that artificial weir opening helped maintain the unique environmental characteristics of the river ecosystem in terms of river continuity and led to a different zooplankton community composition in the new river environment. Full article

In this study, a hydraulic analysis technique is presented for evaluating the efficiency of a pool-weir type fishway. The River-2D model with the fish physical habitat module was used for the analysis of the attraction efficiency, and the weighted usable area proposed as an index of the efficiency. For the analysis of passage efficiency, the three-dimensional model, FLOW-3D, was used as an evaluating tool to describe the fluid behavior on a hydraulic structure with a free surface. The ice-harbor type fishway at Dalseong weir in the Nakdong River of Korea was selected as a test-site, and the efficiency was estimated using the hydraulic analysis. The results of River-2D analysis showed that the location of the fishway near the right bank now was not appropriate for attracting the target fish to the fishway due to the deep water depth. The 3D analysis results presented that the flow velocity field inside the fishway showed a similar plunging flow in each pool, but various flow patterns appeared locally. Full article

Due to the construction of dams and sluices, habitat fragmentation of riverine species is an issue of concern in hydropower projects. An artificial fishway aims to restore flow connectivity and facilitate migration. As an alternative to the conventional layout with straight walls, labyrinth layouts are introduced, consisting of either triangular, trapezoidal, or rectangular weirs. Three-dimensional CFD simulations are performed to examine their influences on the fishway hydraulics. The labyrinth layouts exhibit an appreciable three-dimensional flow structure in a pool, featuring flow fluctuations in both cross- and along-channel directions, which is indicative of the potential for multiple species with distinct swimming preferences. The streamwise reduction in mean flow velocity is correlated with the Froude number, with the labyrinth weirs leading to a somewhat lower reduction than the conventional one. The dimensionless pool water depth declines with specific flow discharge. The turbulence kinetic energy is the lowest in the triangular layout and the vorticity in the conventional one. Among the labyrinth layouts, the differences in volumetric power dissipation are small. An equation is developed for dissipation estimation. All the labyrinth layouts generate higher energy loss than the conventional one. With optional weir configurations, the findings provide reference for engineering design. Full article

The water flow characteristics over an interval-pooled stepped spillway are investigated by combining the renormalization group (RNG) k-ε turbulence model with the volume of fluid (VOF) interface capture technique in the present study. The results show that the energy dissipation performance of the interval-pooled stepped spillway was generally better than that of the pooled, stepped spillways and the traditional flat-panel stepped spillway. The omega vortex intensity identification method is introduced to evaluate the energy dissipation. Due to the formation of “pseudo-weir”, the energy dissipation did not increase with the growth of the pool’s height. In addition, the average vortex intensity can characterize the dissipation rate to some extent. Full article

Although fibre-reinforced-concrete (FRC) is increasingly used, it has been occasionally applied to water-retaining structures (WRSs), and no comprehensive design guidelines are currently available for the design of WRSs with FRC. A design methodology for such applications based on available recommendations and research has been applied to three reference scenarios representing a wide range of WRSs: a flood defence wall, a weir wall, and a swimming pool wall. For each of these scenarios, alternative designs using different FRC mix designs have been compared through the statistical analysis of several relevant parameters. This study confirms that the use of FRC significantly reduces reinforcement requirements when compared to conventional reinforced concrete solutions. Clear trends have been identified between the structural performance of the resulting WRS designs, the FRC mix characteristics and the fibre type and dimensions. This study has considered not only structural performance but also the total cost and environmental footprint per unit length of WRSs, and these considerations further the case for adoption of FRC in such applications. Overall, fibre dosages below 0.75% and 2% in volume for steel and synthetic fibres, respectively, can lead to WRS designs with lower cost and carbon footprint than their reinforced concrete counterparts. Full article