J. Hydrol. Hydromech., Vol. 74, No. 1, 2026, p. 1 - 10, doi: https://doi.org/10.2478/johh-2026-0001
Scientific Paper, English

Vighnesh Prasad, Anil Dubey: Role of critical parameters on the rheology and pipeline transportation of concentrated non-Newtonian iron ore slurry

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• Achieving optimal flow characteristics while handling a complex slurry system in the pipeline needs greater attention. This study aims to demonstrate the role of iron ore concentration and size distribution on slurry rheology and their subsequent effect on slurry pipeline transportation. The concentrated iron ore slurries are sheared in the shear rate range between 0.1 – 500 s-1, where the experimental data is well-represented by the Bingham-plastic model. The model parameters are employed to calculate pressure drop and energy consumption. A thorough investigation through rheo-microscopy analysis reinforces the validity of the rheological hypothesis. The rheological analysis reveals the yield-pseudoplastic flow behaviour of iron ore slurries irrespective of particle concentrations and coarse particle addition. The slurry containing iron ore fines contributes to an increase in viscosity, mitigated by introducing coarse particles. Rheo-microscopy suggests that the viscosity reduction is attributed to the obstruction of floc formation and disintegration of the slurry structure. The pressure drop and energy consumption escalate with increasing slurry velocity regardless of pipe diameters. However, these entities decrease by including coarse iron ore particles in slurries. This work advocates optimizing rheology to reduce pipeline transportation costs while handling bulk iron ore with minimum environmental repercussions.
  
  KEY WORDS: Data not availableIron ore; Rheology; Rheo-microscopy; Slurry pipeline transportation; Pressure drop; Specific energy consumption.
  
  Address:
  - Vighnesh Prasad, Department of Pipeline Transport Systems & Societal Technologies, CSIR – Institute of Minerals & Materials Technology, Bhubaneswar, Odisha - 751013, India. Faculty of Engineering Sciences, Academy of Scientific and Innovative Research (AcSIR), CSIR - HRDG, Ghaziabad, Uttar Pradesh - 201002, India. (Corresponding author. Tel.: Fax.: Email: vprasad@immt.res.in)
  - Anil Dubey, Faculty of Engineering Sciences, Academy of Scientific and Innovative Research (AcSIR), CSIR - HRDG, Ghaziabad, Uttar Pradesh - 201002, India.

J. Hydrol. Hydromech., Vol. 74, No. 1, 2026, p. 11 - 19, doi: https://doi.org/10.2478/johh-2026-0002
Scientific Paper, English

Hossein Sohrabzadeh Anzani, Sameh Ahmed Kantoush, Sohei Kobayashi: Hydraulic Optimization of Symmetric Wart-Type Baffle Spacing for Fish Passage in Open-Channel Flows

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• This study investigates the role of symmetric wart-type baffles in facilitating fish passage under supercritical flow conditions in an open-channel flume. Experiments were conducted in a 7 m long, 0.5 m wide flume with a 2% bed slope at the Ujigawa Hydraulic Laboratory, Kyoto University. The impact of two baffle spacings (20 cm and 30 cm) on hydraulic characteristics was assessed and compared to a smooth channel. Velocity profiles, flow depth, and turbulence intensity were measured across ten longitudinal points to evaluate flow heterogeneity and energy dissipation. Results indicate that baffles significantly reduce flow velocity and create low-velocity resting zones critical for fish migration. The 20 cm spacing configuration proved most effective, offering a balance of reduced velocities (0.5–0.9 m/s) and sufficient hydraulic diversity to support energy-efficient fish passage. In contrast, the 30 cm spacing resulted in higher velocities and reduced low-velocity zones, potentially challenging weaker swimmers. Turbulence intensity was lowest with 30 cm spacing (TImean= 0.053), indicating smoother flow but fewer refuges compared to 20 cm spacing (TImean= 0.069). The smooth channel exhibited uniform, high velocities, unfavorable for most fish species. These findings highlight the importance of optimized baffle spacing in fishway design to enhance river connectivity and support aquatic biodiversity.
  
  KEY WORDS: Fish passage; Baffles; Barriers; Remediation; Ecohydraulics; Turbulence intensity.
  
  Address:
  - Hossein Sohrabzadeh Anzani, Water Resources Research Center, Disaster Prevention Research Institute, Kyoto University, Uji 6110011, Japan. (Corresponding author. Tel.: Fax.: Email: ho.sohrabzadeh@gmail.com)
  - Sameh Ahmed Kantoush, Water Resources Research Center, Disaster Prevention Research Institute, Kyoto University, Uji 6110011, Japan.
  - Sohei Kobayashi, Water Resources Research Center, Disaster Prevention Research Institute, Kyoto University, Uji 6110011, Japan.

J. Hydrol. Hydromech., Vol. 74, No. 1, 2026, p. 20 - 35, doi: https://doi.org/10.2478/johh-2026-0003
Scientific Paper, English

Manisha Panthi, Brian Mark Crookston, Michele Palermo: Scour evolution for steady and unsteady flow conditions downstream of Type A piano key weirs

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• For the first time a comprehensive analysis for steady and unsteady flow conditions was performed of time-dependent scour processes in non-cohesive sediment downstream of a Type A piano key weir. The evolution and progression of scour of large-scale laboratory experiments were interpreted using an empirical approach and adapting a theoretical model based on the phenomenological theory of turbulence developed elsewhere. The results were within 30% of experimental with the R-squared values of 0.972 for the theoretical model and 0.993 for a calibrated empirical model. Results of this study demonstrate consistent scour evolution kinetics between steady and unsteady flow cases, although in the latter, the maximum scour features were smaller than their steady-state counterparts. This study highlights the novelty of integrating experimental and theoretical frameworks to validate and enhance the design of complex hydraulic structures. Quantitative findings confirm the robustness of first principles-based approaches, offering practical insights and design parameters critical for addressing scour challenges in non-cohesive sediment environments.
  
  KEY WORDS: Temporal scour evolution; Non-cohesive sediment; Scour equilibrium; Stepped flood hydrograph; Unsteady flows.
  
  Address:
  - Manisha Panthi, Utah Water Research Laboratory, Dept. of Civil and Env. Engineering, Utah State University, 8200 Old Main Hill, Logan, UT 84322-8200 USA.
  - Brian Mark Crookston, Utah Water Research Laboratory, Dept. of Civil and Env. Engineering, Utah State University, 8200 Old Main Hill, Logan, UT 84322-8200 USA. (Corresponding author. Tel.: Fax.: Email: brian.crookston@usu.edu)
  - Michele Palermo, DESTEC- Department of Energy, Systems, Territory and Construction Engineering, University of Pisa, Via Gabba 22, 56122 Pisa, Italy.

J. Hydrol. Hydromech., Vol. 74, No. 1, 2026, p. 36 - 56, doi: https://doi.org/10.2478/johh-2026-0004
Scientific Paper, English

Abdorreza Kabiri-Samani, Amirhossein Fathi, Rashid Farooq: Does an Armor Layer Control Clear-Water Scour at Cylindrical Bridge Piers? A Comprehensive Experimental Assessment under Steady and Unsteady Flow Conditions

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• Local scour at bridge piers is a critical phenomenon jeopardizing structural integrity worldwide. This study presents a comprehensive physical modelling investigation into the evolution of local scour in the presence of a protective armor layer, considering both steady and unsteady (hydrograph) flow regimes. A systematic parametric analysis evaluated the effects of pier diameter, flow velocity, and sediment characteristics, the latter comprising three distinct sizes for both the underlying bed material and the armor layer. Experimental observations elucidate the initial scour mechanism: the formation of strong horseshoe vortices that first accumulate armor material upstream of the pier. Subsequent vortex strengthening induces flow instability, leading to the entrainment and downstream transport of bed sediments. Under steady-flow conditions, the maximum equilibrium scour depth shows a strong positive correlation with pier diameter. A 33.3% increase in diameter resulted in a 31.2% increase in scour depth, while a 47.6% increase led to a 46.3% increase. Conversely, the maximum scour depth is inversely proportional to the size of both the armor layer particles and the underlying bed material. For unsteady flows, the peak scour depth was determined to be independent of the sequence of hydrograph events, converging to a value equivalent to the equilibrium scour depth of a steady flow at the hydrograph's peak discharge. However, the temporal evolution of scour depth varied significantly between the flow regimes. A dimensional analysis of the experimental data identified the governing dimensionless parameters. This analysis formed the foundation for deriving new predictive equations to estimate the maximum scour depth at bridge piers protected by an armor layer under both steady and unsteady flow conditions. The proposed relationships provide practical tools for the design and risk assessment of bridge piers.
  
  KEY WORDS: Equilibrium depth; Equilibrium time; Horseshoe vortexes; Hydrograph; Image processing; Maximum scour depth.
  
  Address:
  - Abdorreza Kabiri-Samani, Department of Civil Engineering, Isfahan University of Technology, P.O. Box 84156, Isfahan, Iran. (Corresponding author. Tel.: Fax.: Email: akabiri@cc.iut.ac.ir)
  - Amirhossein Fathi, Department of Civil Engineering, Isfahan University of Technology, P.O. Box 84156, Isfahan, Iran.
  - Rashid Farooq, Department of Civil and Construction Engineering, Swinburne University of Technology, Melbourne, VIC, 3122, Australia. Department of Civil Engineering, International Islamic University, Islamabad 44000, Pakistan.

J. Hydrol. Hydromech., Vol. 74, No. 1, 2026, p. 57 - 73, doi: https://doi.org/10.2478/johh-2026-0005
Scientific Paper, English

Shahin Oodi, Alireza Khoshkonesh, Saeid Okhravi, Saeed Gohari: Numerical study of transient flow dynamics in a prismatic channel with a bed depression

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• Catastrophic floods triggered by a dam-break pose significant hazards to infrastructure due to transient flows and concentrated structural loads. These hazards are intensified where in-channel structures or variable topography redirect momentum and magnify impacts on downstream infrastructures. This study aimed to numerically predict the dam-break transient flow characteristics around a bed depression, as a specific topographic condition, in the downstream channel. The numerical model was optimized and validated against experimental results reported in the literature. Subsequently, the effects of bed depression dimensions and location along the channel on transient flow were examined in twelve cases. The validation results demonstrated that the model accurately reproduced the evolution of the free surface, flow velocity, formation of the impact jet, and impact loads. The bed depression has increased plunge-pool dissipation and reduced the peak force to 16.6–18.6 N. Accordingly, the supercritical flow was characterized by a maximum Froude number (Fr) of approximately 5.4 around this depression. Increasing the depression distance attenuated the wave front and decreased the post-depression flow depth from 0.16 m to 0.03 m within approximately 2 seconds. Overall, the framework captured sharp interfaces and transient regime shifts, enabling the prediction of jetting, nappe stabilization and impact-load envelopes. The study has implications for evaluating in-channel structures and the effects of channel topography on rapid flood hazard screening and emergency planning.
  
  KEY WORDS: Transient flow dynamics; Bed depression; Volume of Fluid (VOF); Numerical modeling; Impact loads.
  
  Address:
  - Shahin Oodi, Water Science Engineering Department, Faculty of Agriculture, Bu-Ali Sina University, Hamedan 65175-4161, Iran.
  - Alireza Khoshkonesh, Department of Geography, Birkbeck University of London, London WC1E 7HX, UK.
  - Saeid Okhravi, Institute of Hydrology, Slovak Academy of Sciences, Dúbravská cesta 9, 84104, Bratislava, Slovakia. (Corresponding author. Tel.: Fax.: Email: saeid.okhravi@savba.sk)
  - Saeed Gohari, Water Science Engineering Department, Faculty of Agriculture, Bu-Ali Sina University, Hamedan 65175-4161, Iran.