J. Hydrol. Hydromech., Vol. 73, No. 3 - Early view, 2025, p. 230 - 247, doi:
Scientific Paper, English

Reza Ahmadi, Hossein Afzalimehr, Hussam Jabbar Abed, Saeid Okhravi: Hydrodynamic effects of porous baskets on scour patterns at elliptical and hexagonal piers

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• This study investigates the effectiveness of a newly introduced scour countermeasure, the porous basket (PB), in modifying flow structure and mitigating scour around elliptical and hexagonal piers with varying length-to-width ratios (l/w). Experimental analysis of near-bed flow velocities revealed a significant reduction at the pier face, followed by velocity recovery after reattachment in the second half of the pier for both geometries. However, in elliptical piers, lateral imbalances in vortex shedding and flow separation led to localized variations in velocity profiles, while l/w had no influence on the location of flow separation. The results indicate that piers with l/w = 5 ratio experienced 50% reduction in scour volume due to lower Reynolds Shear Stress (RSS) in the downflow region. In general, increasing l/w resulted in a more confined scour area and reduced scour volume. Implementation of the PB, effectively trapped over 65% of turbulence kinetic energy (TKE), significantly reducing scour at the pier base. As turbulence dissipated and flow stabilized, RSS values approached zero. Among the tested installation distances, the smaller placement exhibited the best scour mitigation performance by enhancing localized turbulent energy dissipation. This finding highlights the potential of the PB in improving bridge pier stability and reducing local scour effects.
  
  KEY WORDS: Local scour; Length-to-width ratio; Flow structure; Porous basket; Reynolds shear stress.
  
  Address:
  - Reza Ahmadi, Faculty of Civil Engineering, Iran University of Science and Technology, Tehran, 1684613114, Iran.
  - Hossein Afzalimehr, Faculty of Civil Engineering, Iran University of Science and Technology, Tehran, 1684613114, Iran. (Corresponding author. Tel.: Fax.: Email: hafzali@iust.ac.ir)
  - Hussam Jabbar Abed, Faculty of Civil Engineering, Iran University of Science and Technology, Tehran, 1684613114, Iran.
  - Saeid Okhravi, Institute of Hydrology, Slovak Academy of Sciences, Dúbravská cesta 9, 84104, Bratislava, Slovakia. (Corresponding author. Tel.: Fax.: Email: saeid.okhravi@savba.sk)

J. Hydrol. Hydromech., Vol. 73, No. 3 - Early view, 2025, p. 248 - 259, doi:
Scientific Paper, English

Yujie Fan, Zhonghua Yang, Wenxin Huai, Shuolin Li, Peng Zhang, Xichen Wang: Effect of shape and size on the transport of floating vegetation debris: A La-grangian experimental study

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• Flood-generated floating vegetation debris can accumulate near hydraulic structures, posing risks to power generation and engineering safety. Understanding the transport characteristics of different types of floating aquatic vegetation debris is fundamental for modeling their movement. A Lagrangian experiment was conducted in a laboratory straight water channel using six models of floating vegetation debris (categorized as leaf-type and rod-type) with varying shapes and sizes. The trajectories of the models were tracked and processed using image analysis technology, and diffusion coefficients were calculated based on distribution data. Results indicate that centimeter-sized models move at the same velocity as the surface flow. The diffusion coefficient in the flow direction was approximately twice that of the spanwise diffusion coefficient. The shape and size of the debris models influenced diffusion characteristics: leaf-type models diffused faster than rod-type models, while leaf-type models with a center of mass offset showed greater spanwise diffusion. Shorter models exhibited higher diffusion tendencies in the spanwise direction. Diffusion properties in the two directions vary significantly with flow conditions and debris model characteristics. Formulas were proposed for estimating dimensionless diffusion coefficients in both directions. These findings are valuable for predicting the potential accumulation zones of floating vegetation debris under varying flow conditions.
  
  KEY WORDS: Floating vegetation debris; Lagrangian experiment; Transport velocity; Diffusion properties; Dimensionless diffusion coefficients equation.
  
  Address:
  - Yujie Fan, State Key Laboratory of Water Resources Engineering and Management, Wuhan University, Wuhan, Hubei, 430072, China.
  - Zhonghua Yang, State Key Laboratory of Water Resources Engineering and Management, Wuhan University, Wuhan, Hubei, 430072, China. (Corresponding author. Tel.: Fax.: Email: yzh@whu.edu.cn)
  - Wenxin Huai, State Key Laboratory of Water Resources Engineering and Management, Wuhan University, Wuhan, Hubei, 430072, China.
  - Shuolin Li, State Key Laboratory of Water Resources Engineering and Management, Wuhan University, Wuhan, Hubei, 430072, China.
  - Peng Zhang, State Key Laboratory of Water Resources Engineering and Management, Wuhan University, Wuhan, Hubei, 430072, China.
  - Xichen Wang

J. Hydrol. Hydromech., Vol. 73, No. 3 - Early view, 2025, p. 260 - 272, doi:
Scientific Paper, English

Aditya Nugraha Putra, Sephia Dewi Meila Chrisaputri, Cindy Monica Manurung, Michelle Talisia Sugiarto, Novandi Rizky Prasetya, Irma Ardi Kusumawati, Istika Nita Sudarto, Mohd Hasmadi Ismail, Silvia Kohnová, Kamila Hlavčová: Utilising land use scenario modeling and machine learning for mitigating drought risks in degraded landscapes

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• Land-use change is a key driver of environmental degradation and increasing drought risk. This study assesses drought dynamics in the South Malang Plateau, East Java, by integrating remote sensing data with the Random Forest (RF) algorithm. Three land use scenarios were developed: Business-as-Usual (BAU) for 2030 (predicted using the CA-ANN method in QGIS), participatory mapping (PM), and land capability classification (LCC). Using 175 stratified random field points (70% for training, 30% for validation), the analysis integrated 25 predictor variables across climatic, anthropogenic, topographic, and vegetation index factors. The RF model used for drought classification achieved an overall accuracy of 92.57%. Based on unsupervised classification of historical satellite imagery, between 2017 and 2023 multistrata agroforestry declined by nearly 50%, natural forest cover decreased by 27.6%, and settlements more than doubled. Under the 2030 BAU scenario, forest cover is projected to decline further to 9,195.16 ha. Drought analysis shows a peak in 'Severe Drought' at 18.1% in 2019, dropping to 3.1% by 2030, while 'Extreme Drought' steadily rises from 6.2% to 7.0%, particularly in deforested areas. Among the scenarios, the integrated LCCPM approach demonstrated higher potential to reduce drought vulnerability and land degradation. The integrated land capability classification- participatory mapping (LCCPM scenario) is recommended to strengthen landscape resilience and promote sustainable land management.
  
  KEY WORDS: Remote sensing; Land cover; Machine learning; Geographic information system; Water management.
  
  Address:
  - Aditya Nugraha Putra, Department of Land and Water Resources Management, Faculty of Civil Engineering, Slovak University of Technology in Bratislava, Bratislava 81005, Slovakia. Soil Science Department, Faculty of Agriculture, Brawijaya University, Veteran Street, Malang 65145, Indonesia. (Corresponding author. Tel.: Fax.: Email: aditya.putra@stuba.sk)
  - Sephia Dewi Meila Chrisaputri, Agroecotechnology Study Program, Faculty of Agriculture, Brawijaya University, Veteran Street, Malang 65145, Indonesia.
  - Cindy Monica Manurung, Agroecotechnology Study Program, Faculty of Agriculture, Brawijaya University, Veteran Street, Malang 65145, Indonesia.
  - Michelle Talisia Sugiarto, Soil and Water Management Study Program, Faculty of Agriculture, Brawijaya University, Veteran Street, Malang 65145, Indonesia.
  - Novandi Rizky Prasetya, Soil and Water Management Study Program, Faculty of Agriculture, Brawijaya University, Veteran Street, Malang 65145, Indonesia.
  - Irma Ardi Kusumawati, Yayasan Bumi Hijau Lestari, Telaga Bodas Raya, Semarang 50235, Indonesia.
  - Istika Nita Sudarto, Soil Science Department, Faculty of Agriculture, Brawijaya University, Veteran Street, Malang 65145, Indonesia.
  - Mohd Hasmadi Ismail, Faculty of Forestry and Environment, Universiti Putra Malaysia, Serdang, Selangor 43400, Malaysia.
  - Silvia Kohnová, Department of Land and Water Resources Management, Faculty of Civil Engineering, Slovak University of Technology in Bratislava, Bratislava 81005, Slovakia.
  - Kamila Hlavčová, Department of Land and Water Resources Management, Faculty of Civil Engineering, Slovak University of Technology in Bratislava, Bratislava 81005, Slovakia.