Irrigation and Drainage Structures Engineering Research

Original Article Hydraulic

Estimation of Open Channel Flow Resistance Coefficient Under the Effect of Slope and Discharge Variation Using Gradually Varied Flow

Reza Farzanpour; Salah Kouchakzadeh; Shabnam Moghispour

Volume 27, Spring , April 2026, Pages 16-1

https://doi.org/10.22092/idser.2026.373436.1652

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 ... Read More 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

A Review of Water Consumption Management Indicators of different Crops in Iran

Volume 25, Issue 94 , June 2024, , Pages 1-16

https://doi.org/10.22092/idser.2024.364605.1569

Abstract

Extended AbstractIntroduction In terms of water consumption in different sectors, in Iran as in other countries, a significant part of surface and groundwater resources is used in agricultural sector. For the amount of water consumed in Iran's agricultural sector, different numbers have been reported ... Read More Extended AbstractIntroduction In terms of water consumption in different sectors, in Iran as in other countries, a significant part of surface and groundwater resources is used in agricultural sector. For the amount of water consumed in Iran's agricultural sector, different numbers have been reported in various sources. In the past three decades, water consumption in agricultural sector in various sources and methods has been reported between 44 and 86 billion cubic meters (Movaheddanesh, 1994; Ghodratnema, 1998; Mohammad-Vali-Samani, 2005; Nasseri et al., 2017; 2018). The physical water productivity is also one of the important indicators of irrigation management, which is determined by using the amount of product produced per unit of applied irrigation water. Abbasi et al. (2017) estimated and analyzed water productivity values in Iran for different years. They estimated the values of water productivity varying from 0.94 to 1.29 kg/m3 and average being 1.07 kg/m3. Abbasi et al. (2019) also showed that water productivity index in Iran had an upward trend with a slope of 0.045 kg per year. It varied from 1.0 kg/m3 in 2008 to about 1.45 kg/m3 in 2017. Past researches regarding the estimation of water consumption in agricultural sector have been reported with estimation methods such as water balance method, which was not accurate and was associated with errors. On the other hand, the figures presented for the amount of water consumed in agricultural sector are very different and there are doubts about their accuracy. Despite the importance of the issue, accurate information on the amount of irrigation water for agricultural crops in different regions of Iran is not available and this issue has always been one of the main concerns of the water industry managers and planners. Therefore, carrying out a research work that leads to more accurate numbers about the amount of applied irrigation water for different crops, can be of great help to the decision-making of officials related to water and agriculture. The main goal of this article is a comprehensive evaluation of water management indicators in agricultural sector (including the water productivity and applied irrigation water for different crops). MethodologyField measurements including applied irrigation water and crop yield were carried out for at least one cropping season in the production hubs of each crop. Twelve crops included 12 wheat, rice, barley, fodder corn, alfalfa, sugar beet, sugar cane, beans, sunflower, cotton, rapeseed, and soybean, 17 garden crops included saffron, apple, olive, orange, tangerine, peach, nectarine, plum, lemon, fig, grape, date, pomegranate, walnut, almond, pistachio, and cherry and 6 vegetable and summer crops were tomato, watermelon, potato, cucumber, melon, and onion. These crops covered more than 85% of the cultivated area and irrigated lands in different provinces. For each crop, applied irrigation water was measured in a crop season and the yield for one year or the average of two years, but for garden plants, due to climate changes and frost damages, the average yield of 1-3 years was determined and used in the analysis. Physical water productivity of irrigation water from the ratio of crop yield to applied irrigation water and water productivity from the ratio of crop yield to water (total volume of irrigation water and effective precipitation) and gross income per unit of applied irrigation water was calculated from the product of crop yield in the sales price divided by the applied irrigation water. In this research, the cluster analysis model was used to determine the homogeneous crops. Results and DiscussionThe results showed that applied irrigation water for different crops varied from 3984 for rapeseed to 32500 cubic meters per hectare for sugarcane. So that the weighted average applied irrigation water of 35 studied crops was determined to be 8032 cubic meters per hectare. This index was 9162, 7669 and 7247 cubic meters per hectare for garden, agricultural, vegetable and summer crops, respectively. Also, the total applied water used for the 35 studied crops was estimated at 61.7 billion cubic meters and the total irrigation water for other crops that were not evaluated in this research was estimated at 9.4 billion cubic meters. The total water used in irrigated crops was estimated at 71 billion cubic meters, which was about 70% of the total renewable water in Iran. The weighted average of irrigation water productivity and water productivity of the studied crops was determined as 1.9 and 1.5 kg/m3, respectively. Saffron and pistachio provided the highest gross income per unit of irrigation water and sugarcane, soybean, barley, fodder corn, wheat and alfalfa had the lowest values. ConclusionsThe results of this research provided valuable information for managers and decision makers in different provinces of Iran.

The effect of cropping pattern modification on the physical and economic productivity of crop irrigation water in Fars province (Case study: Qaderabad-Madarsolaman plain)

Volume 25, Issue 94 , June 2024, , Pages 17-37

https://doi.org/10.22092/idser.2024.366325.1583

Abstract

Extended AbstractIntroduction The sharp drop in the water level of the underground aquifers in the plains shows the lack of a suitable approach to create synergy between all the stakeholders in the water sector in the management of water resources. On the other hand, the undeniable ... Read More Extended AbstractIntroduction The sharp drop in the water level of the underground aquifers in the plains shows the lack of a suitable approach to create synergy between all the stakeholders in the water sector in the management of water resources. On the other hand, the undeniable limitation of water resources has led to the adoption of integrated water resources management as a requirement. In this regard, in an agricultural plain, there should be a matching of underground water resources with programmable water in order to reduce the severity of the created crisis and help to balance the plain over time. Therefore, avoiding acreage expanding in the agricultural sector and increasing water productivity should be on the agenda of decision makers, especially in the planning of cropping patterns.Material and MethodThis research has been carried out with the aim of improving the cultivation pattern in improving the physical and economic productivity of water in the Qaderabad-Madarsolaman plain of Fars province. The required data of the products include crop calendar, price at the time of harvest, production cost, yield, monthly programmable amount of plain water and monthly irrigation water amount of each crop related to crop year 2021-2022, which is in the form of documents from Jihad- Agriculture Organization. and the Regional Water Company of Fars province was collected. Data analysis was done by mathematical programming method using GAMS software.ResultsThe results showed that after implementing the model and determining the optimal cultivation pattern, the number of agricultural products in the plain increased by 50%. So that the number of products reached 18 products from 12 products. Also, the area under cultivation of crops in the optimal cultivation pattern decreased by 27% and reached 3861 ha from 5303 ha. Meanwhile, the amount of irrigation water of the optimal pattern caused a 26% reduction in the consumption of underground water resources. In addition, the amount of crop production in the current and optimal model was 8,469,3000 and 6,947,060 kg, respectively, and the decrease in the cultivated area has caused an 18% decrease in this index in the optimized model. However, the economic efficiency of the entire plain in the current and optimal model was calculated as 1975.37 and 2035.60 billion rials, respectively, which indicates a three percent increase in the optimal model. With regard to the direct effects of the modification of the cultivation pattern of the Qaderabad-Madarsolaman plain, including the increase in the number of agricultural products of the plain and the introduction of six crops with the highest economic water productivity into the optimal cultivation pattern, as well as the reduction of the area under cultivation of crops in the optimal cultivation pattern, and the increase of the economic efficiency of the entire plain in this pattern, it is expected that the index of physical productivity and economic productivity of the whole plain will also change. So, the physical water productivity index of the whole plain in the current and optimal model was obtained as 2.56 and 2.84 kg/m3, respectively. In the same way, the water economic productivity index of the whole plain was calculated as 59,607 and 83,086 rials per cubic meter, respectively.ConclusionsThe modification of the cultivation pattern in the Qaderabad-Madarsolaman plain resulted in the annual saving of 8.64 million cubic meters of water, an 11% increase in physical productivity, and a 39.4% increase in the economic productivity of water. Based on this, focusing on the water productivity index in the form of improving physical and economic productivity can be followed as a suitable approach to create synergy between all stakeholders and beneficiaries of the water sector in the management of water resources in the agricultural sector. In this approach, by focusing on increasing water productivity, in a defined time period, while minimizing the amount of production reduction, and by increasing the livelihood level of the users, it is possible to reduce the agricultural water consumption in the plains to the amount of programmable water.

Investigation of Specific Energy Stability in Converging Side Weirs with Guiding Structures

Volume 26, Spring , April 2025, , Pages 18-1

https://doi.org/10.22092/idser.2025.368890.1610

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 ... Read More 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).

Investigating the volume of irrigation water and applied water productivity in Plum orchards of Razavi Khorasan province (Chenaran and Mashhad)

Volume 25, Issue 94 , June 2024, , Pages 53-68

https://doi.org/10.22092/idser.2024.366702.1586

Abstract

Extended AbstractIntroductionDue to the limitation of water resources in the production of agricultural products in the country and the need to improve water productivity in the production of horticultural products on the one hand and the economic importance of plum production in the country on the other ... Read More Extended AbstractIntroductionDue to the limitation of water resources in the production of agricultural products in the country and the need to improve water productivity in the production of horticultural products on the one hand and the economic importance of plum production in the country on the other hand, the investigation of management indicators such as the volume of irrigation water, yield and irrigation water productivity is necessary in the production of plums in the country. Plums are one of the most important orchard products, and the livelihood of a large number of farmers in different regions of the country, including Khorasan-Razavi province, depends on this product. Therefore, the current project was carried out with the aim of direct and field measurement of the water content of plum varieties in orchards under the management of local farmers in the producing regions of this product in the province. According to the latest statistics published by the Ministry of Agricultural Jihad (Statistical Yearbook of the Department of Agriculture of Khorasan Razavi Province in 2022), the area under plum cultivation in Mashhad and Chenaran regions is 328 and 75 hectares, respectively, and the yield per unit area in those two mentioned regions is 3905 and 6028 kg/ha, respectively.MethodologyIn Khorasan Razavi province, two regions with highest area under plum cultivation were selected for evaluation, Chenaran and Mashhad. To conduct this research, 10 orchards in Chenaran region and 10 orchards in Mashhad region have been selected. The volume of irrigation water was measured in these 20 orchards during the irrigation season. The measurements were carried out in different irrigation and planting methods, various soils, different salinity of irrigation water and soil, and different plum varieties during the growing season of 2021-2022 without interfering with the farmer's irrigation management. The measured values were compared with the gross irrigation water requirement estimated by the Penman-Monteith method using the last 10 years meteorological data and also with the national water document values. Plum yield was recorded at the end of the growing seaso nand water productivity was calculated as the ratio of yield to total water (irrigation applied water and effective rainfall).Results and DiscussionThe results showed that the amount of applied water, the amount of plum yield and the water productivity in Chenaran region were 10899 m3/ha, 21.73 ton/ha and 1.9 kg/m3, respectively. The volume of applied water, the amount of plum yield, and water productivity in Mashhad region were determined as 10229 m3/ha, 13.11 ton/ha and 1.42 kg/m3, respectively. The volume of plum irrigation water in the regions varied from 4999 to 16862 and its weighted average (based on the cultivation area) was 10256 m3/ha. While the average gross requirement of irrigation water in the regions using the Penman-Monteith method using meteorological data of the last ten years and the national water document was 14964 and 12173 m3/ha, respectively. The average yield of plum in the selected orchards varied from 5560 kg/ha to 89800 kg/ha and the average was 14713 kg/ha. Irrigation water productivity in selected orchards varied from 0.4 to 7.09 and the average was 1.53 kg/m3. The applied water productivity in the selected orchards was 1.51 kg/m3.ConclusionsAccording to the results of this research in Chenaran and Mashhad, the weighted average volume of irrigation water and the irrigation water productivity in plum orchards are 10256 m3/ha and 1.53 kg/m3, respectively. The volume of irrigation water to produce plum in these two regions was about 31% more than that in country and the irrigation water productivity was about 32.6% less than that in country. The volume of irrigation water, yield and irrigation water productivity in plum orchards in drip irrigation method were 9920 m3/ha, 18827 kg/ha and 1.88 kg/m3, respectively, and in surface irrigation method they were 11433 m3/ha, 14804 kg/ha and 1.31 kg/m3 respectively. The yield of plum and the irrigation water productivity in drip irrigation method, compared to the surface irrigation method, increased by 27 and 43%, respectively, and water consumption decreased by 13%. Comparing the volume of irrigation water used by farmers in the plum orchards with the gross irrigation requirement, shows that the farmers have no enough water for irrigation and unintentionally, they follow deficit irrigation in the plum orchards, and in fact, the farmers use water available for them. The average yield of plums with drip irrigation method was equal to 18.83 ton/ha, which is about 65.75% higher than the average yield of plums in the country. Based on this, plum cultivation in both regions and also the use of drip irrigation method in plum orchards cab is recommended.

Issues and Challenges of Participatory Management and Sustainable Irrigation Management Transfer in Iran

Volume 25, Issue 95 , October 2024, , Pages 110-93

https://doi.org/10.22092/idser.2024.366787.1588

Abstract

Participatory irrigation management (PIM) and at utmost level irrigation management transfer (IMT) are processes that have been carried out in the water sector of most countries all around the world for more than two decades. In Iran, such activities have also been carried out in different aspects including ... Read More Participatory irrigation management (PIM) and at utmost level irrigation management transfer (IMT) are processes that have been carried out in the water sector of most countries all around the world for more than two decades. In Iran, such activities have also been carried out in different aspects including mainstreaming of its literature; entering it into the programs, laws, and macro-level policies, the establishment of a few number of Water Users Associations (WUA), and implementing PIM on a limited scale and in some pilot projects in recent years. According to surveys, the process of this issue in the country has been slow, scattered and has faced different problems and challenges. The review of scientific sources and the investigation and analysis carried out for the problem finding regarding the subject in this study indicate that the implementation of the PIM and IMT programs have various issues and challenges in Iran, which important ones are:1) issues of being in charge of the matter, 2) lack of necessary coordination, parallel work and interference of different agencies in each other's affairs 3) absence or lack of necessary determination and will regarding the issue despite its importance and different emphasis in the laws and macro-level documents, 4) the long time passed and the necessity of various changes in the structure of water management due to the growing crisis of water shortage in the country, 5) centralization and not having or not giving the necessary place to WUA from the aspects of the structure, the description of duties and authorities and their ultimate independence, 6) weaknesses in the empowerment of WUA and necessary facilitations for their formation and sustainability, 7) lack of necessary infrastructures and inconvenience of work from various aspects such as non-volumetric delivery of water, closure and or non-implementation of some related laws and regulations, indecision of the relevant organization in doing their work, and competition of water distribution companies to create WUA and relevant conflict of interest issues, 8) lack of necessary research and field studies regarding the issue, 9) the emergence of new challenges in the objectives of the subject and the introduction of some new terms in the discourse of the definition of WUA, specifically in Iran, such as the introduction of the term “land use” into the topic, i.e., calling it as water and land exploitation associations instead of just WUA, and 10) special issues and challenges in the creation and stability of well or underground water users associations (W-WUA). A lot of time (more than three decades) has passed since the introduction of PIM to the scientific and executive literature on water management. There is a long pause in its complete and effective implementation in Iran. During this period some new debates in the country's water management such as creating local water markets, water accounting, water reallocation, etc., have emerged. Moreover, the growing shortage of water resources and the issues of climate change over this period bring the continuation of PIM in the country into a new field and environment. All these necessitate newer studies for revisions in PIM and IMT implementation methods and approaches by taking into account the socio-cultural issues of the regions and on a case-by-case basis.

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