Search Results (52)

Climate change is projected to significantly alter hydrological conditions across the Northern Hemisphere, with increased precipitation variability, more intense rainfall events, and earlier, rain-driven spring floods in regions like northern Sweden. These changes will affect both natural ecosystems and hydropower-regulated rivers, particularly during ecologically sensitive periods such as the grayling spawning season in late spring. This study examines the impact of extreme spring flow conditions on grayling spawning habitats by analyzing historical runoff data and simulating high-flow events using a 2D hydraulic model in Delft3D FM. Results show that previously suitable spawning areas became too deep or experienced flow velocities beyond ecological thresholds, rendering them unsuitable. These hydrodynamic shifts could have cascading effects on aquatic vegetation and food availability, ultimately threatening the survival and reproductive success of grayling populations. The findings underscore the importance of integrating ecological considerations into future water management and hydropower operation strategies in the face of climate-driven flow variability. Full article

As a critical intervention for enhancing inland navigation efficiency, waterway regulation projects profoundly modify riverine hydrodynamic conditions while optimizing navigability. This study employs the MIKE21 hydrodynamic model to establish a two-dimensional numerical framework for assessing hydrological alterations induced by channel regulation in the Hui River, China. Through comparative simulations of pre- and post-project scenarios across dry, normal, and wet hydrological years, the research quantifies impacts on water levels, flow velocity distribution, and geomorphic stability. Results reveal that channel dredging and realignment reduced upstream water levels by up to 0.26 m during drought conditions, while concentrating flow velocities in the main channel by 0.5 m/s. However, localized hydrodynamic restructuring triggered bank erosion risks at cut-off bends and sedimentation in anchorage basins. The integrated analysis demonstrates that although regulation measures enhance flood conveyance and navigation capacity, they disrupt sediment transport equilibrium, destabilize riparian ecosystems, and compromise hydrological monitoring consistency. To mitigate these trade-offs, the study proposes design optimizations—including ecological revetments and adaptive dredging strategies—coupled with enhanced hydrodynamic monitoring and riparian habitat restoration. These findings provide a scientific foundation for balancing navigation improvements with the sustainable management of fluvial systems. Full article

Submerged vegetation plays a crucial role in influencing flow hydrodynamics, generating turbulence, and shaping velocity distributions in aquatic environments. This study investigates the hydrodynamic effects of submerged rigid vegetation, specifically focusing on the local flow and turbulence alterations resulting from the removal of a single stem from an otherwise uniform vegetation array under controlled laboratory conditions. Experiments were conducted in a flume using Acoustic Doppler Velocimetry (ADV) to measure 3D (three-dimensional) flow characteristics, turbulence intensities, Reynolds shear stress (RSS), and quadrant analysis. In the fully vegetated scenario, vegetation significantly modified flow conditions, creating inflexion points and distinct peaks in velocity profiles, turbulence intensity, and RSS—particularly near two-thirds of the vegetation height—due to wake vortices and flow separation. The removal of a single stem introduced a localised gap, which redistributed turbulent energy, increased RSS and near-bed turbulent interactions, and disrupted the organised vortex structures downstream. While sweep and ejection events near the gap reached magnitudes similar to those in the fully vegetated setup, they lacked the characteristic coherent peaks linked to vortex generation. Overall, turbulence intensities and RSS were reduced, indicating a smoother flow regime and weaker energy redistribution mechanisms. These findings critically impact river restoration, flood management, and habitat conservation. By understanding how vegetation gaps alter flow hydrodynamics, engineers and ecologists can optimise vegetation placement in waterways to enhance flow efficiency, sediment transport, and aquatic ecosystem stability. This study bridges fundamental fluid mechanics with real-world applications in environmental hydraulics. Full article

Renewable energy sources such as hydropower are important to reduce the global emissions. Hydropower, however, comes with other environmental challenges by altering the ecological conditions in the rivers. Hydraulic models connected with fish habitat models could be one tool to assess the environmental impacts and evaluate mitigation measures for fish habitats. This study examines the limitations of steady-state hydraulic simulations in a low-sloping river located between two hydropower plants, where downstream regulations significantly influence the river flow dynamics. A 2D hydrodynamic model in Delft3D FM was applied to compare steady-state and transient simulations, focusing on how hydraulic variables affect the spawning habitat. The results show that steady-state models fail to capture time-dependent damping and delayed water level responses, leading to systematic underestimation of hydraulic variability. Peak bed shear stress values were under-predicted by the steady-state interpolation, which may under-predict spawning ground stability. Additionally, the steady-state approach failed to capture daily habitat fluctuations, resulting in a mean absolute error of 2910 m² in spawning habitat area per hour. This study demonstrates how errors in hydraulic calculations propagate into habitat assessments, potentially leading to misleading long-term evaluations of fish populations. This study highlights the importance of selecting appropriate hydraulic modelling approaches based on river-specific flow dynamics. Future studies should investigate the sensitivity of fish habitat models to hydraulic inputs from steady-state and transient simulations by integrating these approaches into advanced fish modelling tools, such as individual-based models. This will help determine the optimal balance between computational efficiency and accuracy in long-term habitat assessments. Full article

This study evaluates the habitat of the Bocachico fish (Prochilodus magdalenae) in the Ciénaga de Betancí, Colombia, using a habitat suitability index (HSI) model. Wetlands like the Ciénaga de Betancí are under significant pressure from anthropogenic activities, affecting biodiversity and ecosystem health. The Bocachico, a species of immense cultural and economic importance, faces habitat degradation and fragmentation. Using hydrodynamic and water quality data, a numerical model (EFDC+ Explorer 11.5), and field data collected from multiple sampling campaigns, we assessed habitat suitability based on five key parameters: water temperature, dissolved oxygen, ammonia nitrogen, velocity, and depth. The model results indicated that environmental conditions in the wetland remained relatively stable during the dry season, with an average HSI score of 0.67, where 9% of the wetland area displayed acceptable conditions, and the remaining 91% displayed medium conditions. The wet season, on the other hand, had an average HSI score of 0.64, with 7.2% of the area in the acceptable suitability range, and the remaining 92.8% in the medium category. Variations in HSI were primarily driven by ammonia nitrogen levels, water velocity, and depth. Despite limited fluctuations in the HSI, areas of low suitability were identified, particularly in regions impacted by human activities. These findings have practical implications for conservation strategies, providing valuable insights for the sustainable management and conservation of the Ciénaga de Betancí, informing strategies for improving habitat conditions for the Bocachico, and supporting wetland restoration efforts. Full article

South Korea’s River Act mandates the maintenance of instream flow to support river ecosystems. This regulation has evolved from early river management practices to more advanced, systematic approaches, including the Instream Flow Incremental Methodology (IFIM). Despite these advancements, river management in South Korea, particularly in the Seomjin River Basin, continues to face numerous challenges. In this study, a three-dimensional numerical model was developed to simulate the hydrodynamic and salinity conditions of the Seomjin River Estuary. This study proposes optimal instream flows to support critical habitats for the Corbicula bivalve, which has seen a significant decline due to salinity intrusion by environmental changes. Using the Environmental Fluid Dynamics Code (EFDC), the model simulates salinity and river discharge with calibration and validation by incorporating historical data. Subsequently, this study evaluates how river discharge affects salinity in four major Corbicula habitats (Dugok, Shinbi, Mokdo, and Hwamok). Finally, we determine the minimum flow (instream flow) needed to sustain Corbicula habitats. In short, this study found that the minimum flow rates (instream flow) required to meet target salinities varied significantly across these sites and under different tidal conditions. These findings highlight the necessity of adapting river flow management practices to preserve the ecological health for Corbicula in the Seomjin River Estuary. Furthermore, this study suggests integrating an additional water supply to be used with local water management plans by suggesting short-term and long-term alternatives in order to sustain adapting river minimum flow (instream flow). Full article

Shallow floodplains play a crucial role in river basins by providing essential ecological, hydrological, and geomorphic functions. During floods, intricate hydrodynamic conditions arise as flow exits and re-enters the river channel, interacting with the shallow vegetation. The influence and mechanism of shoal vegetation on channel hydrodynamics, bed topography, and sediment transport remain poorly understood. This study employs numerical simulations to address this gap, focusing on the Xiaolangdi–Taochengpu river section downstream of the Yellow River. Sinusoidal-derived curves are applied to represent the meandering river channel to simulate the river’s evolutionary process at a true scale. The study simulated the conditions of bare and vegetated shallow areas using rigid water-supported vegetation with the same diameter but varying spacing. The riverbed substrate was composed of non-cohesive sand and gravel. The analysis examined alterations in in-channel sediments, bed morphology, and bed heterogeneity in relation to variations in vegetation density. Findings indicated a positive correlation between vegetation density and bed heterogeneity, implying that the ecological complexity of river habitats can be enhanced under natural hydrological conditions in shallow plain vegetation and riparian diffuse flow. Therefore, for biological river restoration, vegetation planting in shallow plain regions can provide greater effectiveness. Full article

Tidal stream environments are important areas of marine habitat for the development of marine renewable energy (MRE) sources and as foraging hotspots for megafaunal species (seabirds and marine mammals). Hydrodynamic features can promote prey availability and foraging efficiency that influences megafaunal foraging success and behaviour, with the potential for animal interactions with MRE devices. Uncrewed aerial vehicles (UAVs) offer a novel tool for the fine-scale data collection of surface turbulence features and animals, which is not possible through other techniques, to provide information on the potential environmental impacts of anthropogenic developments. However, large imagery datasets are time-consuming to manually review and analyse. This study demonstrates an experimental methodology for the automated detection of turbulence features within UAV imagery. A deep learning architecture, specifically a Faster R-CNN model, was used to autonomously detect kolk-boils within UAV imagery of a tidal stream environment. The model was trained on pre-existing, labelled images of kolk-boils that were pre-treated using a suite of image enhancement techniques based on the environmental conditions present within each image. A 75-epoch model variant provided the highest average recall and precision values; however, it appeared to be limited by sub-optimal detections of false positive values. Although further development is required, including the creation of standardised image data pools, increased model benchmarking and the advancement of tailored pre-processing techniques, this work demonstrates the viability of utilising deep learning to automate the detection of surface turbulence features within a tidal stream environment. Full article

Coastal ecosystems are vital for numerous demersal and benthopelagic species, offering critical habitats throughout their life cycles. Effective monitoring of these species in complex coastal environments is essential, yet traditional survey methodologies are often impractical due to environmental constraints like strong currents and high wave regimes. This study introduces a new cost-effective Baited Remote Underwater Video System (BRUVS) design featuring a vertical structure and 360° cameras developed to overcome limitations of traditional BRUVS, such as system anchoring, overturning, and restricted frame view. The new design was compared against a previous one used on the northwest Iberian coast. Key performance metrics included species detection, habitat identification, and operational efficiency under complex hydrodynamic conditions. Findings reveal that the two designs can effectively identify the common species typically observed in the study area. However, the new design outperformed the previous by significantly reducing equipment losses and anchoring issues. This enhancement in field operations’ simplicity, operability, portability, and resiliency underscores the new system’s potential as a cost-effective and efficient tool for demersal and benthopelagic ecological surveys in challenging coastal seascapes. This innovative BRUVS design offers advanced monitoring solutions, improving habitat assessment accuracy and responsiveness. Full article

The future of marine ecosystems is at risk due to climate change and other human impacts. Specifically, due to ocean warming, some tropical species are expanding their populations while populations of temperate species are in regression, making the establishment of conservation measures imperative to maintain local biodiversity. In this study we establish a baseline on the distribution and abundance of the temperate coral Balanophyllia regia from the Canary Islands. We found that the main environmental factors determining B. regia’s distribution and abundance were sea surface temperature and hydrodynamic conditions. Areas under large wave action and colder environments enhanced this warm-temperate species’ development. Since its metabolic performance depends exclusively on the surrounding environment, we also propose a methodology to potentially monitor climate change on coastal habitats through this azooxanthellate calcified coral. Results of a tagging experiment showed that a concentration of 20 mg/mL of calcein during 6 h might be enough to in situ label polyps of B. regia without compromising corallite survival. Long-term monitoring of population abundances and growth rates of B. regia through calcein tagging will allow us to identify alterations in local ecosystems early and focus future conservation investments on the most vulnerable areas with higher ecological and economic value. Full article

Florida Bay, a large and shallow estuary, serves as a vital habitat for a diverse range of marine species and holds significant environmental, commercial, and recreational value. The salinity structure of the bay plays a key role in the bay’s ecosystem. Florida Bay receives 45% of its freshwater directly from rainfall, the largest source of freshwater, while the Taylor River is the second largest source. A hydrodynamic model was applied to determine if doubling the Taylor River flow, as currently planned, is adequate to meet salinity performance measures and protect the bay’s ecosystem health. Model-predicted salinity indicated that rainfall caused the largest reduction (10–15 ppt) followed by Taylor River discharges, and none of the predicted salinity scenario means exceeded 38 ppt. The salinity restoration target was achieved more than 70% of the time, by doubling the Taylor River freshwater discharges, only for the existing bay conditions. To protect Florida Bay’s ecosystem health and counterbalance saltwater intrusion in the Everglades wetlands, caused by future sea-level rise, additional freshwater sources needs to be identified. Yet, the question becomes, do we have enough available freshwater sources to achieve the restoration target and protect the bay’s ecosystem health now and for future sea-level rise? Full article

Agricultural drainage canals that connect upstream fish spawning areas to downstream rivers and lakes serve as crucial habitats for migrating fish. However, disconnections, such as drops and chutes, have been constructed in these canals due to agricultural modernization and flood control measures, hindering the movement of fish that find it difficult to ascend in fast-flowing currents. Portable fishways offer a promising solution to reconnect waterbodies in agricultural canals, as they can be easily removed during high water discharges to avoid impeding the canals’ drainage function. In addition to experimental assessments of fishway functionality, employing a hydrodynamic model to explore effective placement strategies for portable fishways is essential to maximize their effectiveness. This study presents a method for determining the best horizontal location of a portable fishway in an agricultural drainage canal using two-dimensional hydrodynamic simulations within the specified cases. The applicability of this method is demonstrated by addressing the positioning challenge of a portable fishway on a chute in an agricultural drainage canal in Japan. The results indicate that the proposed method allows for the selection of a suitable location, considering preferable hydraulic conditions both within the portable fishway and around its entrance. Full article

To reveal the evolution of habitat distribution for multiple fish species in the lower reaches of the Gongzui Hydropower Station, this study conducted a catch survey to determine the target species of the reach. Based on their suitability curves, a combined suitability assessment model for multiple fish species was constructed. The reliability of the model was verified by combining acoustic observations of flow fields and fish distribution in specific flow conditions. A two-dimensional hydrodynamic model was coupled to quantitatively analyze the distribution characteristics of fish habitat patches under different flow conditions. The results indicate that the correlation coefficient between the multi-species comprehensive suitability index and the number of fish is 0.676, which indicates that the model can better evaluate the distribution of multiple fish habitats in the study river reach; the weighted usable area (WUA) decreased as the discharge increased; from low flow condition (<800 m³/s) to high flow condition (>2000 m³/s), the patch area of suitable habitat decreased from 11,424 m² to 1268 m², and the connectivity between patches also showed a downward trend; and the habitat shifted to the near-shore area of the downstream wider and shallower section, which was highly correlated with the migration process of low-depth and low-velocity areas. The model proposed in this study can establish a rapid response between the suitable habitat distribution of multiple fish species and discharge conditions, which can provide a research method for quantitative evaluation of multi-species habitats in river, and make a significant contribution to the sustainable development of riverine fisheries resources and river water ecology. Full article

Modeling in ice-covered rivers is limited due to added computational complexity, specifically challenges with the collection of field calibration data. Using River2D, a 2-dimensional hydrodynamic modeling software, this study simulates depth-averaged velocity and shear stress distributions under ice cover and in open-water conditions during varying flow conditions in a small, shallow riffle-pool sequence. The results demonstrated differences in velocity distribution throughout the channel and increases in discharge were found to impact the velocity magnitude under ice cover, while the spatial distribution remained consistent. A recirculating eddy found along the pool’s left bank was exacerbated under ice cover, with potential implications for silver shiner habitat suitability. Bed shear stress magnitude did not vary significantly between ice and open water, although the spatial distribution differed notably. Model validation demonstrated success in simulating water depth and velocities, and the shear stress was estimated within a reasonable margin. Using hydrodynamic models provides valuable insight into seasonal changes in velocities and shear stress when ice is present. Full article

This study aims to analyses the response of meiofaunal organisms (foraminifera) to disturbances caused by the diffusers of domestic sewage outfall at Cigarras beach, SE Brazil. Hydrographical, sedimentological (grain size and geochemical), and living benthic foraminiferal recorded in 2006 and 2007 analyzed in ten stations were compared with the same results analyzed in two control/reference stations (sampled in 2008). The results of this work show that, in the benthic environment of the Cigarras region, moderated hydrodynamic conditions, relatively high total organic carbon, total nitrogen, total sulfur contents, oxic water column and anoxic sediments, organic matter supplied by marine productivity and from mixed sources prevail. Living foraminiferal assemblages denote that the Cigarras region is undergoing environmental degradation due to progressive organic enrichment directly influenced by the domestic sewage outfall. The effluents discharged by the domestic sewage constrained the composition of foraminiferal communities (which include mainly stress tolerant species) with probable impacts on the entire marine trophic chain. Noticeably, the tolerant species Ammonia tepida, Bolivina striatula and Buliminella elegantissima dominated at the stations under the influence of the sewage outfall. In addition, Ammonia parkinsoniana was found in moderate abundances, and the moderate level of TOC enrichment by the sewage outfall did not prevent the survival of this sensitive species. The ecological quality status inferred from the diversity index Exp(H’_bc) calculated on foraminifera showed the poor ecological status of benthic habitats in the area. Overall, this work highlighted the adverse effects of the sewage outfall on the benthic ecosystem in front of the Cigarras beach in Brazil. Future works should investigate the current ecological quality of the area to figure out if any change occurred since the present study sampling. Full article