Original Article
Irrigation network management
Seyed Hasan Tabatabaii; Seyed Majid Mirlatifi; Hosein Dehghanisanij; Ashkan Shokri
Abstract
IntroductionIrrigation should be applied in accordance with an accurate estimate of the crop water requirement and the crop growth stages (Jensen and Allen, 2014). In recent years, several meteorological forecasting models (MFM) have been developed which are capable of forecasting weather data. Such ...
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IntroductionIrrigation should be applied in accordance with an accurate estimate of the crop water requirement and the crop growth stages (Jensen and Allen, 2014). In recent years, several meteorological forecasting models (MFM) have been developed which are capable of forecasting weather data. Such data could be used to calculate and predict crop water requirements during the next few days. The performance of irrigation canals and water delivery systems can be significantly improved if future short-term demands based on the predicted crop water requirement are available. The appropriate performance of these models in the agricultural sector depends on the quality of their predictions of various weather variables. The aim of this study is to evaluate the accuracy of the predicted spring sugar beet water requirement in the Jovien region when 5-day forecasted meteorological variables by ECMWF, GFS, and MeteoBlue MFM were used as the climatological parameters in the Penman-Monteith equation. The prediction accuracy of these models was evaluated under four categories, 1. Inclusion of the three main meteorological variables involved in calculating reference evapotranspiration (ET_0), including maximum air temperature (T_max) and minimum air temperature (T_min), and maximum wind speed, 2. Inclusion of radiation term (ET_0^Rad) and advection term (ET_0^Adv) of the Penman-Monteith equation, 3. Inclusion of ET_0 and water requirement of spring sugar beet. MethodologyMeteorological forecasts for ECMWF, GFS, and MeteoBlue databases were obtained from https://www.windy.com. The meteorological variables presented by these models and used in this research were temperature, wind speed, and the degree of cloudiness. The study period was selected from May to December of 2020.ET0 was calculated using the FAO-Penman-Monteith method presented in the FAO 56(Allen et al., 1998). The first part of the FAO-Penman-Monteith (0.408∆(R_n-G)/(∆+γ(1+0.34 u_2 ) )) represents the contribution of the energy terms to the process of evapotranspiration and the second term ((γ 900/(T+273) u_2 (e_s-e_a ))/(∆+γ(1+0.34 u_2 ) )) signifies the importance of advective forces. Meteorological data obtained from the Jovein weather station was checked to take into consideration the possibility of non-standard surface cover surrounding the weather station in accordance with the method recommended in Annex 6 of FAO 56. Crop coefficients in early, developing, middle, and ending growth periods were also calculated based on the method recommended by the FAO 56.Results and DiscussionThe GFS model had the best performance in estimating T_maxwith the lowest Bias and RMSE errors of 1.4 and 2.3 degrees Celsius, respectively. Also, MeteoBlue with Bias and RMSE values of -2.2 and 1/3, respectively, had the best performance in estimating T_min. All three models underestimated the air temperature. The bias error of GFS, ECMWF, and MeteoBlue models in predicting the maximum daily wind speed in the Jovein region were 0.1, 1.3, and 1.8 m/s, respectively, and their RMSE Respectively 3.3, 3.3, and 3.4 m/s.Since the GFS model estimated Tmean and consequently vapor pressure deficit (VPD) with a higher degree of accuracy as compared with the other model, the advective term (ET_0^Adv) computed using data estimated by the GFS model was more accurate than that of the other models. The bias and RMSE errors of this model in estimating the mentioned variable were 0.4 and 0.7 mm per day, respectively. All the other three models underestimated ET_0^Adv.The bias error of GFS, ECMWF, and MeteoBlue models in estimating ET0Rad were -0.4, -0.5, and -0.2 mm/day, respectively, and their RMSE were 0.61, 0.67, and 0.65 mm per day, respectively.When the overestimated ET0Rad and underestimated ET_0^Adv terms were summed up to calculate ET_0 according to the FAO-Penman-Monteith method, the bias error of the outcome (ET_0) was significantly reduced for all the models. The bias error of the ET_0 for the GFS, ECMWF, and Meteoblue models were 0.03, -0.03, and 0.47 mm/day, respectively. Their RMSE values were 0.62, 0.58 and 0.94 mm/day, respectively.K_(c_ini ) of sugar beet for Jovein region with 4-day wetting intervals and light soil texture with an average ET_0 of 5.9 mm/day was 0.56, and K_(c_mid ) and K_(c_end ) were also calculated as 1.176 and 0.676, respectively. The seasonal water requirement of spring sugar beet for the Jovein region was 866 mm. The seasonal water requirements calculated using the outputs of GFS, ECMWF, and Meteoblue were 860, 866, and 788, respectively. However, the cumulative error of these models were 66, 65, and 101 mm, respectively, during the growing season.ConclusionA notable result in this study is the interaction of the ET_0^Adv and ET_0^Rad terms, which canceled out each other over and under estimations—all the three models underestimated and overestimated ET_0^Adv and ET_0^Rad terms, respectively. Thus the absolute value of the oblique error of the computed ET_0 was less than that of the ET_0^Adv and ET_0^Rad terms. However, the RMSE of ET_0, which indicates the noise and random behavior of the error sources, was not reduced.
Original Article
Irrigation network management
KARAMAT AKHAVAN; Nader Abbassi; Milad kheiry Ghoujeh biglou; Hedieh Ahmadpari
Abstract
Extended AbstractInvestigation on Conveyance Efficiency and Operation Issues of Precast Concrete Channels (Canalette) in Moghan Irrigation NetworkIntroductionMoghan irrigation network is also facing the problem of water losses similar to other projects. In recent years, more than 43,000 hectares of tertiary ...
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Extended AbstractInvestigation on Conveyance Efficiency and Operation Issues of Precast Concrete Channels (Canalette) in Moghan Irrigation NetworkIntroductionMoghan irrigation network is also facing the problem of water losses similar to other projects. In recent years, more than 43,000 hectares of tertiary irrigation canals has been lined using precast concrete channels (Canalette). The main purposes of the project were; improving irrigation efficiency, increasing water use efficiency, reducing waiting period to get water, and preventing water loses. But the project due to weaknesses in various stages of design, construction, operation and maintenance were faced with numerous issues and problems. In this research, the performance of construction canalette in terms of conveyance efficiency and network operation and maintenance problems have been investigated.MethodologyTo do this, 40 canalettes were chosen after various visits to the different projects area and reviewing the existing related documents. In order to calculate conveyance efficiency, the inflow and outflow values of the channels were measured. In order to estimate the waiting time for farmers to receive water, the time required for water to reach from the water dividing site to the field was measured. The amount of land losses in each project was determined according to the availability of information such as the length of the canalette and considering the average width of 2 meters for the canalette and also the specificity of the area covered by the projects. In addition, by taking photos, talking to farmers, water distributors and other relevant factors, exploitation and maintenance issues were investigated. Field observations from the study of technical and social issues, issues related to the operation and maintenance of the canalette network as well as the results of measurements were analyzed and then the necessary suggestions to improve the current situation are presented.Results and Discussion The average conveyance efficiency in the studied canalettes in the three studied projects, namely agro-industrial lands, return A canals and sub-A canal lands, respectively %89, %89.47 and %86.77, respectively. The results of the study of land losses in different projects showed that land losses in agro-industrial lands, which are segmentate in an integrated manner, are far less than farmers' lands (lands of return A canals and sub-A canal). The results of local visits regarding the issues and problems of maintenance and operation of canalettes are presented below. 1) According to the visits and studies, the lack of complete sealing of the washers is one of the main problems of prefabricated canals. As a result of inadequate performance of the washers, unprincipled sealing performed by farmers in various ways, including the use of bitumen, concrete and plastic in the network was observed in large numbers. Investigation and research to solve this problem and improve existing channels and not to repeat this problem in future projects seems necessary.2) The climatic conditions of Moghan plain are such that weeds to grow in most of the soil canals and are widely seen in the network canals. Also, in canalettes, the growth of weeds around and along the canalette and sometimes even inside the canalette, creates problems in the process of water transfer and canalette life. In addition, the transfer of weed seeds from the canal to the fields by water causes damage to the fields.3) During the visits, several cases partial and total destruction at the network level were observed. Some of these cases were due to poor design and implementation of the canalette network and also lack of attention to the geotechnical conditions of the bed. However, most of the thematic demolitions have been done intentionally by the exploiters in order to dewatering of the network. The use of canalette siphons in irrigation sub-networks has been proposed as a simple and low-cost solution. ConclusionsBased on the results, the average conveyance efficiency was found to be 89, 89.47 and 86.77 percents in three different studied areas that are agro-industrial lands, lands of return A canals and sub-A canal, respectively. Also, the waiting period of farmers and land losses were determined as 37 minutes in Km and 51.3 m2 per ha, respectively. Furthermore, inadequate performance seal washers, aquatic plant growth, damage of structures and intakes, improper operating, using overdesign rate of discharges, and other social and maintenances issues were found to be the problems in the operation of Moghan irrigation and drainage networkAcknowledgementThank all people, institutions, and companies that have supported and funded the research.Keywords: Disorganized water intake, Water use efficiency, Land losses, Farmers' waiting time, Canalette
Original Article
Irrigation network management
Abolfazl Nasseri; Fariborz Abbasi; Amir Nourjou; Jamal Ahmadaali; Mohammad Ali Shahrokhnia; Alireza Mamanpoush; majid keramati; سالومه Sepehri Sadeghian; Keramat Akhavan; Syeed Hassan Mousavifazl; Nader Abbassi; Mehdi Akbari; Javad Baghani; Mohammad Mehdi Nakhjavani; Ramin Nikanfar; Ardalan Zolfagharan
Abstract
Extended AbstractIntroductionProviding food security in scarcity conditions of water resources requires the optimal management of irrigation water. Estimation or determination of indices of water consumption management, such as water productivity in agricultural productions is one of the most important ...
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Extended AbstractIntroductionProviding food security in scarcity conditions of water resources requires the optimal management of irrigation water. Estimation or determination of indices of water consumption management, such as water productivity in agricultural productions is one of the most important key in macro-planning for the supply, allocation and consumption of water in different sections such as agricultural section. Therefore, conducting a research at the national level that can lead to the real water productivity in the horticultural production in Iran, is essential and important. According to the production (3.4 million tons), a significant amount of surface and groundwater resources are consumed for apple production. This research was conducted with the aim of determining the amount of consumed water in apple orchards in selected provinces under the management of gardeners at the national level. Findings of this study could assist to the decision on management of water and agriculture.MethodologyThe selected provinces were East Azarbaijan, West Azarbaijan, Ardabil, Isfahan, Tehran, Khorasan Razavi, Fars and Semnan. The water productivity in 145 sites was estimated, in addition to direct measurement of water consumption and crop yield. The factors such as irrigation systems, apple cultivars, gardeners' education, soil texture; and salinity of soil and irrigation water were also measured or recorded in apple orchards. The ANOVA was used to investigate the possible difference between the volume of consumed water, yield, and water productivity in apple production.Result and DiscussionThe results showed that the difference between the volume of water consumption, crop yield and water productivity was very significant in the orchards from provinces. The volume of consumed water and crop yield in apple orchards over the country averaged 9814 m3 ha-1 and 23.2 t ha-1, respectively. The water index was 2.73 kg m-3 in apple orchards over the country. The lowest and highest water productivity were obtained from the orchards of Fars and Semnan provinces. ConclusionsSome strategies have been proposed to optimize the consumption of water resources; and to improve apple yield and water productivity in the country's level. The results of the research in apple orchards of selected provinces in Iran revealed that average of water consumption in apple orchards were 9814 m3 ha-1 with the water productivity of 2.73 kg m-3. Application of high-efficiency and well-managed irrigation systems, and other appropriate improving methods of water productivity can lead to optimal use of water resources, improve yield and enhance water productivity in production.Result and DiscussionThe results showed that the difference between the volume of water consumption, crop yield and water productivity was very significant in the orchards from provinces. The volume of consumed water and crop yield in apple orchards over the country averaged 9814 m3 ha-1 and 23.2 t ha-1, respectively. The water index was 2.73 kg m-3 in apple orchards over the country. The lowest and highest water productivity were obtained from the orchards of Fars and Semnan provinces. ConclusionsSome strategies have been proposed to optimize the consumption of water resources; and to improve apple yield and water productivity in the country's level. The results of the research in apple orchards of selected provinces in Iran revealed that average of water consumption in apple orchards were 9814 m3 ha-1 with the water productivity of 2.73 kg m-3. Application of high-efficiency and well-managed irrigation systems, and other appropriate improving methods of water productivity can lead to optimal use of water resources, improve yield and enhance water productivity in production.Result and DiscussionThe results showed that the difference between the volume of water consumption, crop yield and water productivity was very significant in the orchards from provinces. The volume of consumed water and crop yield in apple orchards over the country averaged 9814 m3 ha-1 and 23.2 t ha-1, respectively. The water index was 2.73 kg m-3 in apple orchards over the country. The lowest and highest water productivity were obtained from the orchards of Fars and Semnan provinces. ConclusionsSome strategies have been proposed to optimize the consumption of water resources; and to improve apple yield and water productivity in the country's level. The results of the research in apple orchards of selected provinces in Iran revealed that average of water consumption in apple orchards were 9814 m3 ha-1 with the water productivity of 2.73 kg m-3. Application of high-efficiency and well-managed irrigation systems, and other appropriate improving methods of water productivity can lead to optimal use of water resources, improve yield and enhance water productivity in production.
Original Article
Irrigation network management
Mohammad Reza Shahraki; Mostafa Derakhshide
Abstract
Huge investments are being made in the development of water resources for the construction of water storage and transmission systems for agricultural irrigation networks. Since each project is unique in terms of region and geographical location, and potential unrecognized risks arise during project implementation, ...
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Huge investments are being made in the development of water resources for the construction of water storage and transmission systems for agricultural irrigation networks. Since each project is unique in terms of region and geographical location, and potential unrecognized risks arise during project implementation, a relatively accurate financial estimate cannot be calculated with certainty. The existence of these risks is a waste of investment. One of the effective measures that can be taken to reduce this depreciation is risk management. Risk management in PMBOK standard includes risk identification based on expert opinions and risk rating based on two criteria: probability of occurrence and severity of impact. Agricultural irrigation of Sistan plain, which uses different structures to store water and irrigate fields, has been studied in a case study in this study. In this research, the Delphi method is used to identify the risks and the hierarchical analysis process method is used to rank them. The risks of weather conditions and lack of commitment to perform accurate work on defined quality irrigation structures are assigned the highest score. have given. In order to prioritize several projects in Sistan region, taking into account the identified risks, Vickor method has been used, which shows the construction of first-class pressure irrigation structures, construction of pumping station and second-line transmission pipeline, construction of structures Irrigation greenhouses ranked third and irrigation structures of concrete canal ranked fourth for implementation with the lowest risk cost in this area.Introduction The return on investment in the construction of irrigation structures is achieved in the long run. These projects involve multiple stakeholders and their scope is influenced by many factors. The management of these projects is difficult and complex and requires multiple coordination to overcome these limitations [1]. Also, increasing investment in irrigation sectors, in addition to meeting basic needs, can have a positive impact on advancing strategic goals. [2] One of the most important issues in defining the types of irrigation structures is the uncertainty that they face due to the large size of the project or its uniqueness [3]. Existence of risk causes problems in project implementation, cost estimation, decline in quality and productivity of the project, as well as its delay [4]. Therefore, identifying uncertainties and analyzing risks play an important role in achieving the project's goals. Therefore, risks are performed according to the PMBOK standard and by probability-effect diagram, which is one of the pillars of risk management [5]. On the other hand, the impact of risks on structures is very important for their prioritization. Structural prioritization is also one of the most important factors of financial success for the Agricultural Jihad Organization [6]. For this purpose, multi-criteria decision-making strategy can be used to identify less risky structures [2]. Vickor method is one of the multi-criteria decision making tools that can determine the best and worst project with different criteria [7]. Since there is a kind of uncertainty in identifying and evaluating risks that includes personal comments or insufficient information in that field, the theory of rough number sets can be used to eliminate these types of uncertainties. [6] MethodologyExistence of various and influential factors has caused uncertainties in choosing the most appropriate irrigation structure and also one of the topics that is less practically used within organizations is risk management. Therefore, in this study, the identification and scientific evaluation of risks in the construction of irrigation structures has been done. Risk management is used to execute the project on time and to prevent the estimated price increase, as well as to prevent excessive losses. Then, in order to evaluate the risks in the studied irrigation structures, the risks were identified and their importance was determined by using the combinations of Delphi and AHP methods. Ruff number theory has also been used to incorporate uncertainty into problems. The results obtained from the Analytic Hierarchy Process (AHP) method indicated that the risks of weather conditions and lack of commitment to perform the exact work of the project with the defined quality have the highest score. In the following research, the risks are assigned to the irrigation structures of the studied organization with the help of VIKOR multi-criteria decision making method. The results obtained from VIKOR method include a list of ranking of irrigation structures based on the degree of risk impact on their construction performance. These rankings are as follows: construction of pressurized irrigation structures in the first place, construction of pumping station and pipeline in the second place, construction of greenhouse irrigation structures in the third place and concrete canal irrigation structures in the fourth place. This ranking can help to manage risks and select projects with less risk, and managers can also prioritize low-risk projects to build, and avoid high-risk projects. Keywords: Raff numbers, VIKOR method, AHP method, Delphi process, Risk management
Original Article
Pressurized Irrigation Systems
sefatollah rahmani
Abstract
Introduction:Water is a unique commodity and a very vital substance, and the limitations of this vital substance affect the capacities of other vital resources such as food, energy, fish and wildlife. One of the main concerns of human beings is water shortage, a shortage that is increasing every year. ...
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Introduction:Water is a unique commodity and a very vital substance, and the limitations of this vital substance affect the capacities of other vital resources such as food, energy, fish and wildlife. One of the main concerns of human beings is water shortage, a shortage that is increasing every year. Many people in developing countries now lack enough water to meet their basic needs. One of the most important signs of water scarcity is the drying up of rivers, which is now observed in a number of important rivers in the world.Of the world's total water, 97.4% is the brackish water of the seas and oceans, only 2.6% is the freshwater reserves. Most of it is in the form of ice in the poles of the earth and glaciers (1.98%) and groundwater (0.59%), which are not available. Globally, the average consumption of fresh water in the drinking and health sector is 10%, industrial, recreational and commercial activities and other cases is about 20% and agriculture alone 70%. In some countries, especially African countries, up to 90% of freshwater resources are spent on agriculture in the desert and coastal areas of Africa. In Iran, the share of the agricultural sector in water consumption is estimated at 93%.Including the strategic product of the agricultural sector; It is a wheat crop that produces a total of 712 million tons in the world, which is 28% of the world's grain. Iran is the 13th largest wheat producer in the world with a cultivated area of 7 million hectares (2.5 million hectares irrigated and 4.5 million hectares dryland) and a production of 15 million tons. In the production of which water is of great importance. Despite severe water resource constraints, the efficiency of using this input is low. Implementing proper management on the optimal use of water in farms and exploitation units in the form of policies and executive programs, is the most important action that is taken in the optimal use of water resources and combating water shortage and dehydration in different regions of the country.Among the measures taken to improve productivity and save agricultural water consumption is the development of pressurized irrigation systems. The present study was conducted with the aim of economic evaluation and estimating the efficiency of pressurized irrigation methods in wheat crop in Ardabil province.Methodology:In economic and social studies, usually two methodologies and mathematical program are used to achieve research objectives. In this study, for some reason, production function methodology has been used. This is a descriptive and applied research that uses the method of (questionnaires) to reach the top of the research. The study population is farmers in Ardabil province (in some crops, the Sprinkler method has been introduced and in others it has not been implemented).Results and Discussion:Estimates showed that the amount of water used in the Sprinkler irrigation method compared to the volume of water used in the traditional irrigation method has decreased by 17%. At the level of 5%, they have given meaning. But the volume of water used in the production method with Sprinkler irrigation is about 30% more than the water requirement of the plant (wheat). It is possible to reduce it by another 20%. In other words, by implementing the Sprinkler irrigation method, up to 37% of agricultural water consumption can be saved. If we consider productivity as the amount of product produced from each unit of input input, according to the estimates made in this study, per cubic meter of water used in the Sprinkler irrigation method has been produced 1.04 kg of wheat. Whereas in the traditional irrigation method, the amount of wheat produced per cubic meter of water is 0.62 kg.Conclusions and Acknowledgment:Comparison of these two numbers shows that water efficiency in Sprinkler irrigation method is more than 1.8 times compared to water efficiency in traditional irrigation method. In general, the estimated production function shows that the use of Sprinkler irrigation method has improved the composition of inputs and their proper and timely consumption. As a result, the amount of product produced has increased compared to the agricultural situation with traditional irrigation. And with the implementation of the new irrigation system, both the volume of water consumption has been reduced, and production costs have been reduced, and that wheat production has increased.
Original Article
Hydraulic
English Darvishi; Salah Kouchakzadeh
Abstract
IntroductionIn steady flow, the minimum specific energy and the specific force occur at critical depths. But will it be the same in the unsteady flow? In this research, using laboratory data of water surface profile, the correctness of these equations in unsteady flow and the location of critical flow, ...
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IntroductionIn steady flow, the minimum specific energy and the specific force occur at critical depths. But will it be the same in the unsteady flow? In this research, using laboratory data of water surface profile, the correctness of these equations in unsteady flow and the location of critical flow, minimum specific energy and specific force will be investigated. MethodologyLaboratory equipment The experiments were performed in a channel with a width of 0.37 m, a height of 0.6 m and a length of 3 m made of Plexiglas with a thickness of 2 cm located in the hydraulic laboratory of the Technical University of Vienna. Due to the importance of bed slope, especially in different water measurement structures, Darvishi et al. (2017) attempted to correct the Boussinesq equations Eq (6). Numerical model The numerical scheme used by Darvishi et al. (2015) to separate the derivative term of the variable f at point n from the distance of the four-point finite difference. The upstream boundary condition was considered as the flow discharge changes with time. This hydrograph was used as an upstream boundary condition in the unsteady flow. Results and DiscussionIn Figure 5, the position of the minimum specific force, initially has a displacement in the positive direction x, but over time, its position moves upward. While the position of the minimum specific energy and critical flow is constantly moving downstream to stabilize its position after reaching a steady flow. Therefore, determining the critical flow position to measure the flow in unsteady flow using the critical Froude number and minimum energy has a higher confidence than the minimum specific force. In order to investigate Equation 2 in the unsteady flow, the diagram of the changes of specific energy changes in the critical flow relative to the unit discharge is plotted in Figure 7. These two graphs are exactly the same, which means that Equation 2 in the unsteady flow also calculates the unit discharge correctly. These results are consistent with the results of Chanson and Wang 2013. A comparison of this chart with the chart provided by Castro-Orgaz and Chanson 2016 shows a significant difference. In their diagram, the unsteady flow line does not correspond to Equation 2 and for qc greater than 0.04 it deviates from Equation 2. The reason for this discrepancy can be related to the Saint-Vanant equations used by them to simulate unsteady flows. Figure 8 shows the changes in the depth slope at the critical depth (-hx)c relative to the product of the critical depth multiplied by the curvature of the bed hczbxx. Equation 4 is also plotted in the diagram. According to Castro-Orgaz and Chanson 2016 the relative error of estimation (-hx) c using Equation 4 varies from 8.5% to 17.5%. For unit discharge of 0.03559 m2/s in paper by Sivakumaran et al. 1983 is also plotted on the chart. As can be seen, at values -hczbxx less than 0.05, the data correspond to the graph of Equation 4, but with increasing this value, it moves away from this curve. In this case, the relative error is about 17%. So that the laboratory data does not match this curve. As Fenton and Darvishi (2016) have stated, Equation 4 often does not provide the right results. While Castro-Orgaz and Chanson 2016 have considered this Equation valid for values -hczbxx less than 0.15.ConclusionsThe position of the critical Froude number, the minimum specific energy, and the specific force on the trapezoidal broad-crest for the inlet incremental hydrograph to channel were investigated using the numerical solution of the modified Boussinesq equation and laboratory data. The results showed that the position of the minimum specific energy and the critical Froude number move in a short distance from each other and continuously in the direction of flow. While the position of the specific force, first moves in the forward direction and after a while in the opposite direction of the flow. The unit discharge is very close to each other in all three positions, and in the minimum specific energy and the critical Froude number are exactly the same. Specific energy was also plotted in critical flow versus unit discharge. This diagram is completely consistent with the specific energy relationship in the steady critical flow. In order to judge this relationship more accurately, it is necessary to examine hydrographs with different shapes. The singular point relationship for different beds in the steady flow was also investigated. This relationship has a good accuracy for values less than 0.05 times the product of the second order differential of the bed at critical depth on the studied beds. At values higher than this, there is a relative error of up to 18%.Keywords: Froude number, singular point, curved bed, minimum specific energy, minimum specific force.
Original Article
Hydraulic
Seyed Amin Asghari Pari; Mojtaba Kordnaeij
Abstract
Extended AbstractIntroductionStep chutes as a structure are commonly used in earth dams and weighted concrete dams (Chanson, 2001). The presence of a step in the spillway acts like a roughness compared to a smooth chute, which causes the amount of air to enter and as a result, the amount of energy dissipation ...
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Extended AbstractIntroductionStep chutes as a structure are commonly used in earth dams and weighted concrete dams (Chanson, 2001). The presence of a step in the spillway acts like a roughness compared to a smooth chute, which causes the amount of air to enter and as a result, the amount of energy dissipation in the direction of the spillway step increases. In recent decades, extensive research, often laboratory-oriented, has been conducted by researchers to identify the type of flow, the effect of step dimensions, the onset of aeration, and the mechanism of energy dissipation. Further research has attempted to place continuous and discontinuous obstacles and roughness at the bottom of the steps in Floors and edges of step with a variety of shapes and arrangements, deformation of steps, creating angles along the spillway, creating angles in the floor of the steps and edge obstacle, artificial aeration in the steps investigated the hydraulic conditions. In general, in some cases, depending on the height of the obstacle used, the slope of the spillway, the outlet flow, the type of obstacles and the location of the obstacle, the depreciation effect has been positive or negative. MethodologyThe flume used was direct, with a length of 10 m, a width of 1.2 m and a height of 1.2 m in the first 2 m, and 1 m in length of the flume with maximum flow rate 150 liters per second. Measurement of water depth in the tail-water and upstream was carried out using a point gage with an accuracy of ± 1 mm. The spillway have 8 steps, where the vertical length of step (h) is 10.9 cm, the horizontal length of step (L) is 31.3 cm, and the total height is 87 cm, while at a 1:2 slope, the length of step is 20.9 cm and the total height is 88 cm. The image was recorded by Sony FS5 camera with 240 frames per and second, along with 3 LED150 projectors. Results and Discussion In the 1: 3 slope in the transition regime, the obstacles used had a positive dissipation effect compared to the flat step. In this slope and flow regime, the porous obstacle (EP) has a greater dissipation effect than the porous screen (ES) and the full obstacle (EO), respectively, and in all three expressed arrangements (EO, ES, EP) in this regime the relative height of 0.38 had the highest dissipation rate. The superiority of the porous obstacle in this regime in energy dissipation is due to the three-dimensionality of the porous obstacle, which depletes the flow energy. Then in the procedure regime for 1: 3 slope, the results show that all three arrangements used have increased energy dissipation compared to the flat step, in this case, respectively, porous screen (ES), porous obstacle (EP) and full obstacle (EO), respectively. Had the highest energy consumption. For example, at the maximum flow rate, the flat steep energy dissipation rate is 46%, which is 55% for the porous screen (ES), 52% for the porous obstacle (EP) and 49% for the full obstacle (EO). ConclusionsThe present study compares the use of continuous obstacle, porous obstacle (3 dimensional) and screen obstacle (2 dimensional) with three heights at the edge of the step at two slopes of 1: 3 and 1: 2 in all three flows regime of nappe, transitional, and skimming.1- The placement of continuous obstacle with different shape (filled continuous, porous obstacle and screen obstacle) at the edge of spillway for both slopes of this research causes the onset of the flow regime shift to the flat step and start of the inception point of free aeration (IP) was transmitted to a lower step toward the downstream relative to flat step on both slopes of the present research.2- Based on the BIV results and a comparison of energy dissipation, it can be stated that continuous obstacles that can expand the mixing zones (including MZ and RF) increase energy dissipation. In fact, the recirculation zone has less dissipation effect than the mixing zone.3- The creation of a porous obstacle and a porous screen on both slopes has increased energy dissipation compared to the full obstacle in all three flow regimes. This effect will increase with increasing the relative height of the obstacle until it reaches the pool (RZp) on the steps.Keywords: Energy dissipation, BIV Technique, Step spillway, Screen obstacle, Continous obstacle, Porous obstacle.
