Original Article
Hydraulic
Amirreza Shahriari; Mehdi Daryaee; SeyedMahmood Kashefipour; Mohammadreza Zayeri
Abstract
IntroductionSide weirs are widely used hydraulic structures in irrigation, drainage, and flood control systems. These structures allow excess water to be diverted from the main channel, helping to manage flow capacity effectively. In converging channels, the presence of guiding structures, such as flow ...
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IntroductionSide weirs are widely used hydraulic structures in irrigation, drainage, and flood control systems. These structures allow excess water to be diverted from the main channel, helping to manage flow capacity effectively. In converging channels, the presence of guiding structures, such as flow deflectors, can influence the hydraulic performance of side weirs. Recent studies have highlighted the potential of guiding structures to enhance discharge capacity. However, uncertainties persist regarding the impact of convergence and added structures on specific energy variations in the main channel. The classical assumption of spatially varied flow with lateral outflow suggests that specific energy remains constant along the weir. This study aims to evaluate the validity of this assumption in converging channels with guiding structures by investigating specific energy variations using numerical simulations. MethodologyA three-dimensional numerical model was developed using FLOW-3D to simulate flow over a converging side weir. The experimental setup by Maranzoni et al., (2017) was used as a reference for model validation. The numerical domain consisted of a converging channel with a side weir, and guiding structures were placed on the weir crest at three different longitudinal positions (upstream, middle, and downstream) with installation angles of 60°, 90°, and 120° relative to the horizontal.The Reynolds-averaged Navier-Stokes (RANS) equations were solved using the RNG k-ε turbulence model. Boundary conditions included a specified flow rate at the inlet, a pressure outlet at the downstream boundary, and wall conditions for the channel boundaries. Grid independence was ensured by testing different mesh resolutions, with the final model consisting of approximately 1.5 million cells. The numerical model was validated against experimental data, with a maximum simulation error of less than 4%. Results and DiscussionThe numerical results showed that guiding structures influenced specific energy variations along the weir. The middle position of the weir exhibited the least change in specific energy (0.8%) , making it the optimal location for installing guiding structures. In contrast, upstream and downstream placements resulted in greater energy variations, with mean differences of 1.17% and 1.37%, respectively.The effect of installation angle on specific energy variations was negligible. Across different angles, the mean variation ranged from 1.03% to 1.22%, indicating that the angle of installation had little impact on energy conservation. The influence of the inflow Froude number was also examined. For Froude numbers below 0.3, specific energy variations remained under 0.5%. As the Froude number increased to 0.45, energy variations reached 1.6%, which is still within an acceptable range. These findings suggest that specific energy variations are more sensitive to the location of guiding structures than their installation angle.The results confirm that the classical assumption of constant specific energy in spatially varied flow with lateral outflow holds even in converging channels with guiding structures. Although minor deviations were observed, they were within acceptable limits for practical applications. ConclusionsIn this study, by comparing the simulation results with experimental data, it was found that the model used for simulating flow over side weirs possesses high accuracy and reliably predicts the actual performance of these structures. One of the key aspects of this research is the accurate simulation of side weirs in converging channels. Despite numerous studies in this area, especially in recent years, certain aspects of the design and hydraulic behavior of these types of weirs still require more detailed investigation and numerical modeling.The findings of this study demonstrated that the classical concept of specific energy stability in gradually varied flow with decreasing discharge remains valid even under converging conditions and in the presence of guiding structures. The average difference in specific energy between the upstream and downstream of the weir in all simulations was 1.24%. Additionally, the influence of the Froude number on the increase in specific energy variations was clearly observed. However, within the range of Froude numbers less than 0.5, which is typically dominant in irrigation and drainage channels, specific energy variations did not exceed 3%.Finally, for future research, it is recommended to investigate the effects of factors such as the crest height of the side weir, the presence of orifices within the weir structure, and the influence of supercritical flow regimes on specific energy variations along side weirs, in order to develop a more comprehensive understanding of their hydraulic behavior. AcknowledgementWe are grateful to the Research Council of Shahid Chamran University of Ahvaz for financial support (GN: SCU.WH1402.31370).
Original Article
Irrigation network management
mojtaba noori; Rouhallah Rezaei; mohammad kazem rahimi
Abstract
Introduction Water scarcity can result from drought, a decline in water resources, or a combination of both factors. Under these conditions, the term "crisis" aptly describes the situation. The global water crisis is among the most significant threats facing humanity; ...
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Introduction Water scarcity can result from drought, a decline in water resources, or a combination of both factors. Under these conditions, the term "crisis" aptly describes the situation. The global water crisis is among the most significant threats facing humanity; it is estimated that approximately 3.5 billion people will experience water shortages by 2025, with global water demand projected to rise by 30% by 2050. To mitigate farmers' vulnerability and mitigate the impacts of water scarcity, the concept of resilience has gained attention. Resilience reflects the capacity of an individual or system to adapt effectively during critical situations and identify rational strategies to overcome crises. Today, resilience serves not only as a tool for crisis management but also as a preventive and predictive measure aimed at maintaining orderly continuity under various conditions. Notably, the agricultural sector faces earlier and more severe consequences of water scarcity than other sectors due to the direct threats it poses to farmers' livelihoods and national food security. Given this critical importance, the objective of this study is to identify and analyze key drivers that influence the development of farmers' resilience against water scarcity crises. Materials and MethodsGiven that "capacity development" pertains to future-oriented activities, this study utilized the critical uncertainty approach and the cross-effects matrix, common methods in futures research, to identify relevant drivers. Initially, a comprehensive review of existing literature was conducted to identify significant issues related to resilience against water scarcity. After summarizing, consolidating, and eliminating redundant or overlapping concepts, these factors were compiled into questionnaires and presented during semi-structured interviews with experts, specialists, and key informants.Participants rated each factor based on "importance" and "uncertainty" for the horizon of 1413 using a five-point Likert scale (very low, low, medium, high, very high). Subsequently, experts weighted and ranked these factors according to their perceived importance and uncertainty. Interaction analysis was then performed to examine interrelationships among key factors, assessing their mutual influence. This method, implemented through specialized futures research software MICMAC, is particularly suitable for analyzing variable interdependencies and compiling expert insights. MICMAC employs a matrix-based approach to elucidate the relationships among influential factors in qualitative research. ResultsUsing the critical uncertainty approach, factors identified as both highly important and uncertain were deemed key drivers. Average weights assigned to each factor were plotted onto an importance-uncertainty matrix, allowing the selection of critical factors. Identified factors included: (1) reforming policies that incentivize the production of water-intensive crops; (2) acceptance of the severity of the crisis within the agricultural community; (3) systemic governance of agricultural water resources; (4) promoting optimal water-use practices among farmers; (5) controlling excessive agricultural water extraction; (6) reforming regional cropping patterns; and (7) promoting sustainable livelihoods independent of water-intensive practices.Results demonstrated that policy reforms targeting water-intensive crop production, enhancing water-use culture among farmers, and adjusting regional cropping patterns significantly impact farmers' resilience to water scarcity. Additionally, key-dependent factors highly influenced by others were the agricultural community's acknowledgement of crisis severity, systemic governance of agricultural water resources, and regulation of excessive water withdrawals. ConclusionsThis study identified three primary drivers crucial to developing farmers' resilience in Zanjan province: recognizing the severity of the water crisis, adopting systemic governance approaches to water resources, and regulating excessive agricultural water withdrawals. These drivers are interconnected, implying that changes in one factor will inevitably influence the others. Effective management of these drivers is thus essential for advancing resilience among farmers facing water scarcity. Given the critical status of water resources in Zanjan, where five out of seven plains are classified as prohibited or critical zones, provincial administrators and planners, along with the broader agricultural community, must acknowledge the depth of this crisis. By adopting systemic approaches and managing water consumption responsibly, significant strides can be made towards building resilience to the ongoing water scarcity crisis.
