Original Article
Hydraulic
Reza Farzanpour; Salah Kouchakzadeh; Shabnam Moghispour
Abstract
Extended AbstractIntroductionHistorically, the determination of Manning's roughness coefficient, n, has relied on two approaches: (1) field measurements, and (2) laboratory experiments in flumes where quasi-uniform flow is artificially established. While field data are most realistic, they suffer from ...
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Extended AbstractIntroductionHistorically, the determination of Manning's roughness coefficient, n, has relied on two approaches: (1) field measurements, and (2) laboratory experiments in flumes where quasi-uniform flow is artificially established. While field data are most realistic, they suffer from uncontrolled variables and high costs. Laboratory studies offer controlled conditions but face a fundamental challenge: establishing truly uniform flow in a flume requires a long channel length, precise slope adjustment, and a downstream control that balances friction losses—a condition that is rarely achieved in practiceStudies by Tracy and Lester (1961) and Kazemipour and Apelt (1979, 1982, 1999) demonstrated that even in relatively long flumes, achieving true uniform flow is difficult and time-consuming. Moreover, in natural rivers, uniform flow is the exception rather than the rule; gradually varied flow dominates due to changes in cross-section, slope, and roughness along the channel.This study proposes a paradigm shift: instead of forcing uniform flow in the laboratory—which introduces uncertainty and limits repeatability— the GVF was used as the basis for estimating Manning's coefficient. The M2 profile provides a well-defined water-surface profile that can be accurately measured and compared with theoretical GVF solutions. By optimizing n to minimize the discrepancy between observed and computed profiles, we obtain a robust estimate of the roughness coefficient that is both physically meaningful and practically reproducible.The primary objectives of this research were: To develop and validate a GVF-based methodology for estimating Manning's n in a laboratory flume; To investigate the effects of three different bed roughness types on n; to quantify the influence of longitudinal slope and discharge on n; to compare the experimental results with theoretical resistance laws and assess the flow regime (hydraulically smooth, transitional, or rough); to perform a sensitivity analysis regarding the choice of reference depth for roughness-height estimation.MethodologyExperimental SetupExperiments were conducted in a rectangular flume located at the Central Water Research Laboratory of the University of Tehran. The flume has a length of 12 m, a width of 0.8 m, and a depth of 0.6 m. The flume is mounted on an adjustable platform capable of setting longitudinal slopes. Water-surface profiles were measured using data-acquisition system designed for the current research. Three bed materials, 9 longitudinal slopes, and 9 discharges were tested. Experimental Procedure and Data AnalysisFor each bed roughness the desired slope was set, and the flow was established. The downstream gate was fully opened to create a free overfall, generating an M2 gradually varied profile. After steady-state conditions were reached, the water surface elevations along the flume were recorded.Manning's n was determined by solving the standard GVF equation for a prismatic channel. For each experimental profile, the value of n was optimized to find the best match between the observed and the computed profiles. The equivalent roughness height, ks, was then calculated.Results and DiscussionThe optimized Manning's n values for all 81 runs are summarized in Tables 1–3 of the main Contrary to some previous studies (e.g., Merry, 2017; Yilmaz et al., 2023), which reported a decreasing trend of n with increasing discharge, the results did not show a systematic or monotonic relationship. For most roughness–slope combinations, n remained approximately consistent across the discharge range. Small fluctuations (typically ±0.002) were observed but did not follow a consistent pattern. This suggests that within the tested range of relative submergence, the effect of discharge on bulk resistance is secondary to the geometric roughness characteristics. Similarly, slope variations produced only minor changes in n.Computed shear Reynolds numbers ( ) revealed that both bed materials of C2 and C3 operated in the fully rough turbulent regime ( ), confirming that viscous effects were negligible. In contrast, the galvanized bed (C1) fell within the transitional regime.Because the piezometers were connected to the flume floor (i.e., below the installed mesh covers), measured depths included the physical thickness of the roughness elements. To assess whether this introduced systematic bias, the reference depth was artificially reduced by 0.5 cm, 1.0 cm, and 1.5 cm, and the entire optimization was repeated. The resulting changes in ks were consistently less than 1%, and the flow regime classification remained unchanged. This demonstrates that the methodology is robust and insensitive to minor uncertainties in vertical datum selection.ConclusionsThis study validates a novel experimental approach for estimating Manning's n using gradually varied flow (M2 profiles), which offers a practical, repeatable, and lower‑uncertainty alternative to conventional uniform‑flow methods in laboratory flumes. By leveraging gradually varied flow—which prevails in natural channels—this approach bridges the gap between laboratory studies and field applications, offering a physically relevant framework for river engineering and flood modeling.Keywords: Equivalent roughness, Longitudinal slope, Manning's roughness coefficient, Open Channels, Shear Reynolds number Conflict of Interest The authors declare that they have no conflict of interest. All authors have read and approved the final manuscript. Funding The corresponding author conducted this study as an extension of the research project entitled “Experimental Investigation of the Effects of Hydraulic Crossing Structure Geometry on the Trapping of Large Woody Debris and the Aggravation of Flood Hazards,” carried out at the Soil Conservation and Watershed Management Research Institute. The present research was undertaken to develop practical measures for reducing flood risks associated with woody debris accumulation at bridges. No financial support was received from any public, commercial, or non-profit organization for conducting, writing, or publishing this study. Data Availability Statements All relevant data and results supporting the findings of this study are presented within the article. The datasets generated and/or analyzed during the current study are available from the corresponding author upon reasonable request. Author Contribution All authors contributed to the study conception and design. Material preparation, data collection and analysis were performed by all authors. The first draft of the manuscript was written by R.F. and all authors commented on previous versions of the manuscript (R.F., S.K., and S.M.). The final revisions have been applied by S.K. and Moreover, all authors have read and approved the final manuscript.All authors contributed equally to the conceptualization of the article and writing of the original and subsequent drafts. AcknowledgementThe vice dean for research affair of the University of Tehran is Acknowledged for providing the research facility of the Central Lab for Water Research
Review paper
Irrigation network management
Nasrin Khodamoradi vatan; Hojat Ahmadi
Abstract
Extended AbstractIntroductionRiver intakes constitute critical hydraulic infrastructure for sustainable water resource management. A primary challenge in the design and operation of these structures is sediment management, as excessive sedimentation significantly impairs storage capacity and operational ...
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Extended AbstractIntroductionRiver intakes constitute critical hydraulic infrastructure for sustainable water resource management. A primary challenge in the design and operation of these structures is sediment management, as excessive sedimentation significantly impairs storage capacity and operational efficiency. The intake angle is a pivotal geometric parameter governing flow patterns and sediment transport mechanisms, exerting a substantial influence on the sedimentation process within the river–intake system. The present study provides a systematic literature review covering an 81-year period (1944–2025). We synthesized findings from 132 peer-reviewed articles sourced from reputable domestic and international scientific databases. Following a comprehensive thematic classification, the literature was analyzed using the PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) framework. Conceptual synthesis of the reviewed evidence underscores that the intake angle is a fundamental design variable for effective sediment control. These findings offer practical insights for hydraulic engineers and practitioners, facilitating the optimization of intake configurations and enhancing overall water resource management strategies.Materials and MethodsThis study employs a systematic and documentary review to analyze the hydraulic and sediment-control performance of lateral intakes in open channels. Drawing upon 132 national and international publications retrieved from reputable databases between 1944 and 2025, the research synthesizes findings from both laboratory and numerical investigations. The analysis, structured under the PRISMA framework and complemented by a conceptual review approach, identifies the key hydraulic, geometric, and sedimentary parameters affecting intake efficiency. Results indicate that optimized intake angle and position, along with geometric modifications such as sloped walls, submerged vanes, and deflector structures, substantially reduce vortex formation and sediment entry. Numerical modeling using tools such as FLUENT, FLOW‑3D, and SSIIM demonstrates high agreement with experimental data, validating its use for design optimization. Moreover, hybrid and multi‑component designs integrating vanes, sills, and guide walls achieve sediment reduction rates exceeding 70%. The study concludes that sustainable and efficient water‑diversion systems require an integrated design approach balancing hydraulic performance, sediment dynamics, and site‑specific topographic conditions, supported by advanced numerical modeling and experimental validation. ResultsThe review of eleven studies published between 1944 and 2025 revealed consistent patterns in the hydraulic behavior and sediment‑control performance of lateral intakes. Analysis of laboratory and numerical investigations indicated that variations in intake angle, channel curvature, discharge ratio, and intake geometry have the most significant impact on vortex formation, flow separation, and sediment entry. Experimental results showed that reducing the intake angle generally decreases sediment intrusion, while positioning the intake along the outer bend improves flow distribution and minimizes scour depth. Numerical simulations using CFD models such as FLUENT provided strong agreement with experimental findings, confirming the critical role of geometric configuration and shear stress in controlling flow behavior. After multiple comparative evaluations, seven major parameters were identified as the dominant factors governing intake efficiency: intake angle, bend conditions, bed shear stress, relative curvature‑to‑depth ratio, geometry and dimensions of the intake, discharge ratio, and Froude number. These parameters form a unified analytical framework for optimizing intake design to achieve minimal sediment intrusion and stable hydraulic operation.ConclusionsA comprehensive review of studies conducted between 1944 and 2025 revealed that the hydraulic performance of lateral intakes in open channels is strongly governed by geometric configuration and flow conditions. The intake angle, discharge ratio, and intake position along the channel bend are among the most influential parameters controlling flow patterns, vortex formation, and sediment entry. Findings from previous research indicate that intake angles of 45°–60° effectively minimize flow separation, while positioning the intake on the outer bend (at angles of 115°–135°) enhances flow uniformity and reduces local scour. Both numerical and physical investigations confirm that the geometry of the intake and sidewalls—particularly curved or rounded-corner designs—and regulation of hydrodynamic parameters such as the Froude number play a decisive role in sediment control. The strong agreement between laboratory observations and advanced computational models further supports the reliability of numerical approaches for optimized design.Overall, achieving stable hydraulic performance in lateral intakes requires an integrated approach that simultaneously considers optimal intake geometry and position, improved hydraulic conditions, and the use of auxiliary structures. Despite significant progress in laboratory and numerical studies, research gaps remain—particularly in field-scale investigations, sediment characterization, and interaction analyses of combined structures under complex flow conditions. Future developments in three-dimensional numerical modeling and large-scale field experiments could substantially enhance understanding of these interactions and lead to more sustainable strategies for sediment management and intake efficiency. Conflict of InterestThe authors declare that they have no conflict of interest regarding the preparation and publication of the materials and findings presented in this study. FundingThe authors received no financial support for the research, authorship, or publication of this article. Data Availability Statements The datasets generated and/or analyzed during the current study are available from the corresponding author on reasonable request. Authors’ ContributionsAll authors contributed equally to the conceptualization of the study, preparation of the original draft, and subsequent revisionsAcknowledgementThe authors wish to express their sincere gratitude to the Editor and the two anonymous reviewers for their insightful comments and constructive feedback, which significantly improved the quality of this manuscript. We also thank the Regional Water Company of Qazvin for providing the necessary data for this research.
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