مجله هیدرولیک
سال هفدهم شماره 2 (تابستان 1401)

Transient currents occur when phenomena change with time, and ram impact is one of these phenomena. Since the ram impact phenomenon is a transient and damping phenomenon, it can therefore be called a non-continuous damping current, which occurs between two flow regimes. In this study, in order to investigate the ram impact phenomenon along with cavitation, a flow model in pipes in two-dimensional (quasi-two-dimensional) space has been developed. This numerical modeling has been done in a cylindrical coordinate system and the finite element numerical solution method has been used to solve the equations. This model has been used to calculate the shear stress between different layers of the flow, for each type of flow (quiet or turbulent) of its own relations. In this modeling, the continuity equation is explicitly solved and the momentum equation is implicitly solved. In order to find the best model, Araya laboratory conditions were modeled in both ANSYS and Fluent models and the output results were considered as the basis for selecting the best model. The output results indicate that the model built in Fluent is closest to the laboratory results. In the second stage, numerical modeling has been done in MATLAB software with the best model selected and laboratory conditions of Araya. At this stage, all three results were closely related.A numerical model of ram shock is the solution of simplified Navira-Stokes equations in the space of a tube and a cavitation model involves solving two-phase equations with shock and ram equations which are continuous. For numerical solution of both ram impact and cavitation models, the finite difference numerical solution method has been used. In these equations, the variable u is a function of r, x and t, while H is a function of t, x, so this model is a quasi-two-dimensional model. Wardi and Wang (1991) showed that for both slow and turbulent currents, the maximum radial velocity is between 10 and 20 μm / s. Along the pipe, the normal stress value at all points is assumed to be equal to the pressure head, so the values σr, σx and σθ are assumed to be equal to zero.Conclusion and selection of appropriate software for analyzing the water hammer impact phenomenon:In this section, three categories of results will be compared:1. Experimental data obtained from vote experiments2- Results of CDF 3. Results from UDF2.The quantities of steady state velocity, initial maximum pressure and the number of pressure wave oscillations generated during the seconds of recording the results have been selected as criteria for comparing these three groups of results. The values of these three quantities should be given in the table number table for the three groups of results. They have been compared. The values of these three quantities should be given in the table number for the three groups. The mentioned results have been compared. As can be seen, the results of UDF2 are not consistent with other results. Due to the inappropriate answers of UDF2, it can be concluded that this software has not modeled the water hammer impact phenomenon properly. As can be seen, the results of UDF2 are not consistent with other results. Considering the inappropriate answers of UDF2, it can be concluded that this software has not modeled the ram impact phenomenon properly.Transient conditions are created due to sudden changes in a hydraulic system. These changes are usually due to changes in flow by valves, turbines, etc. and cause sudden changes in pressure in pipelines. This increase or decrease in pressure can damage the pipes of hydraulic systems valves.two-dimensionality of the model and consequently segmentation of the pipe section.To different layers and separate calculation of each layer, the modeling is closer to the real state of the phenomenon and as a result the results are more realistic. The two-dimensionality of the model and as a result of dividing the pipe cross section into different layers and calculating each layer separately, has brought the modeling closer to the real state of the phenomenon (compared to one-dimensional models) and as a result the results are more realistic. Also, the performed modelings show that omitting the radial velocity component of the fluid in the pipes has no effect on the accuracy of the problem.Transient conditions are created due to sudden changes in a hydraulic system. These changes are usually due to changes made in the flow by valves, turbines, etc. and cause sudden changes in pressure in pipelines. This increase or decrease in pressure can damage the pipes of hydraulic systems valves.

It is necessary to perform the model calibration process to effectively use hydraulic models and improve the performance of water distribution networks (WDNs) in the design and operation stages. Several methods are proposed for the calibration of WDNs including 1) trial-and-error procedure models; 2) explicit models or hydraulic simulation models; and 3) implicit models or optimization models.Trial-and-error schemes were implemented to update unknown model parameters by solving the water network equations (Walski, 1983; Bhave, 1988). These models are only suitable for small problems due to the low convergence rate. Explicit models involve solving an extended set of continuity and head-loss equations in which the number of calibrated parameters are equal to the number of measurement parameters (Ormsbee and Wood, 1986; Boulos and Wood, 1990; Boulos and Ormsbee, 1991 and Ferreri et al., 1994). In implicit calibration methods, an objective function is formulated and solved by an optimization model. These methods have been investigated by a majority of the previous research (Kapelan et al., 2007; Dini and Tabesh, 2014; Do et al., 2016; Xie et al.; 2017). Recent and numerous studies indicate that evolutionary algorithms are efficient in solving complex and real-life WDNs.In this paper, five optimization algorithms, gray wolf optimization (GWO), invasive weed optimization (IWO), the genetic algorithm (GA), the imperialist competitive algorithm (ICA) and the simulated annealing algorithm (SA) are compared for the simultaneous calibration of pipe roughness coefficient and water demand coefficient in WDNs. For a closer look at the performance, these algorithms are evaluated in terms of two new criteria including, the success rate and the efficiency rate are used.

A brief description of each algorithm is presented. Evolutionary algorithms are combined with static and dynamic models of WDNs under EPANET software using a MATLAB code. The objective function is the minimization of the mean absolute percentage error (MAPE) between simulated nodal pressure and pipe flow and their corresponding measured values. The performance of these evolutionary algorithms are evaluated in terms of some criteria include statistical analysis, the optimum solution obtained, the number of objective function evaluations, the success rate, and the efficiency rate. The success rate represents the quality of the solution obtained for a specific problem and the efficiency rate indicates the performance of the algorithm and it is a neutral tool to compare the performance the different optimization algorithms applied to solve the same problem.These EAs are applied to three popular standard mathematical benchmark functions including Sphere, Rastrigin and Rosenbrock, a benchmark water distribution network and a real-life network located in the north of Iran.

The performance of five optimization algorithms was assessed by applying several mathematical test functions and a benchmark and real WDNs. The results of the application to mathematical test functions show that in most cases GWO has the best performance. After that, the five algorithms applied to benchmark WDN. Results show that GWO outperformed the other algorithms in both the success rate and the efficiency rate. The success rate for the GWO, IWO GA, ICA and SA were 60%, 20 %, 20%, 0% and 0%, respectively. The efficiency rate for the GWO, IWO, GA, ICA and SA were 16.93, 4.37, 10.27, 0 and 0, respectively.The GWO algorithm required fewer objective function evaluations to converge to the final solution. In contrast, the IWO algorithm required more objective function evaluations to reach the final solution.For the real WDN, the objective function (MAPE) obtained from the GWO algorithm improved by about 23% , 30%, 9% and 41% compared to the two GA, IWO, ICA and SA algorithms, respectively.The computational time is calculated by considering the average time for 10 computations. The comparison results indicated that the GWO had the least time consumption for all cases. This demonstrated the better performance of the GWO algorithm in searching all the problem space and its ability to avoid getting stuck in local optima. The results showed that early convergence in both GA, SA and IWO algorithms causes the optimization process to be incomplete.

Calibration of a water distribution network is beneficial for the operation and control of the water system. In this paper, simultaneous calibration of pipe roughness coefficient and water demand coefficient in WDNs was performed based on five evolutionary algorithms including The GWO, IWO, GA, ICA and SA. The performance of each algorithm is evaluated by using two new criteria including, the success rate and the efficiency rate. The success rate shows the quality of the solution obtained for a specific problem and the efficiency rate represents the performance of the algorithm. The results show that the GWO outperformed the other evolutionary algorithms in terms of the success rate, the efficiency rate, and the rapid convergence to the best solution.

Drain valves are usually constructed to control and drain flood, regulate flow, drain tank in critical cases, discharge sediment, and transfer current. Therefore, the study of their hydraulic conditions during design and operation should be considered by researchers and designers. As the height of the dam increases, the flow velocity in the semi-open valves of the dam also increases and as a result, the local pressure decreases, which consequently causes the cavitation phenomenon The presence of air near the rigid boundaries of the flow greatly reduces the destructive effect of cavitation and therefore the method of aeration and its effects and the percentage of air bubbles in the vicinity of these boundaries to prevent cavitation is one of the points to know the different types of aeration mechanism and bubble placement, and the type of valve according to the flow conditions. As mentioned, one of the phenomena that can endanger the safety of valves is cavitation. In these valves, the two-phase flow of air is transmitted at high speed. Due to the separation of the flow lines, a sharp drop in the downstream values of the valve occurs.

Siazakh rock dam is located in a place called Siazakh and at the junction of two tributaries of Ghezelozen river named Kaqli and Sheikh Haidar, 7 km from Divandere. The level of the dam on the riverbed is 1756 meters above sea level. The purpose of constructing this dam is to supply agricultural water, control and control river floods. In the middle of the duct, the control system is located, consists of an emergency sliding valve and a sliding service valve. The physical model of the valve includes a repair valve, a metal cover with a rectangular cross section, a duct inlet, a valve groove, a middle duct, an emergency valve, an emergency valve chamber, its grooves, a service valve, a vent between two valves and the entire downstream duct. In order to provide the required water height and required discharge, an open metal tank has been used. This tank is in the form of a cylinder with a diameter of 5 meters and a height of 6 meters.In order to measure the pressures on the valve, 8 piezometers are installed on the valve and all these piezometers are connected to the tightly connected hoses. The experiments were performed for four different heads. Two pumps and an outlet adjustment valve were used to adjust the head, so that only one pump was switched on at the lower heads and the output valve was bypassed to adjust the head. This time was chosen according to the turbulence of the air flow and minimizing its error by trial and error.

After adjusting the head, the service valve was placed in the pre-planned openings and the emergency valve was displaced so much that the most critical situation occurred. The criterion for detecting this critical state is the velocity of air suction from the aeration pipe between the two valves into the duct, which was measured by a hot wire. To measure the air velocity, the hot wire is placed inside the aeration tube in the center of the tube for one minute. After the desired time, the average inlet air velocity is recorded by the hot wire device. The results show that the most critical situation occurs when the jet passing under the emergency valve hits exactly the lower edge of the service valve. In this case, a severe disturbance occurs between the empty space of the two valves, which causes severe suction of air into the aeration pipe. According to observational experience, this condition is usually achieved when the percentage of emergency valve opening is up to about 5% less than the service valve opening.

The results of this study showed that when the emergency valve is broken in a certain opening and consequently the emergency valve enters the circuit, the most critical situation is when the amount of emergency valve opening is equal to the service valve. By measuring the amount of incoming air from the aeration tube in 24 different laboratory modes, and comparing them with different parameters, a relation was provided to determine the aeration coefficient which is a function of the landing number and includes a range between the lower and upper limits of the data. Also, by examining the amount of inlet air flow from the aeration tube for 24 different experiments, it was observed that this amount of air has a relative maximum at two points, the first maximum being related to low openings.

The safety of dams is directly related to the sufficiency of spillway capacity. Most dam failure occurs due to overtopping when the discharge capacity of the spillway was not sufficient. The safe operation of the spillway, under abnormal conditions, is an essential factor in the safety of dams. According to reports released by the International Committee on Large Dams, about one-third of dam failures stem from inadequate spillways. Owing to this sensitivity, the spillway must be designed and constructed as a strong, reliable, and highly productive structure that can be ready for operation at any time. Nonlinear weirs which can be seen in various forms in the plan are economical structures to increase the discharge capacity in a limited width. These weirs have a higher discharge capacity in the same hydraulic head and width. Due to the hydrodynamic complexities of the flow in nonlinear weirs, a general analytical method has not been developed yet in the literature to estimate the discharge capacity of this type of weirs. Usually, the discharge capacity of any nonlinear weir is obtained through various experimental investigations. In this research, a general method is presented for estimating the discharge capacity of nonlinear spillways.

The EDA method is based on nonlinear weir discharge analysis using energy and discharge equations for discrete elements of the solution domain (weir crest in the plan). On the other hand, due to the specific behaviors that occurred in nonlinear weirs (disturbed zone) which have a tangible effect on their discharge capacity, these effects have been taken into account. The geometry of the weir in the plan is the desired solution domain, which is divided into small elements and the corresponding equations in each element have been analyzed. The disturbed zone may also form at the junction of the weir crest to the sidewalls. This phenomenon reduces the discharge capacity, especially at high hydraulic heads. To apply the impact of this phenomenon on the discharge capacity of the affected elements, the relationships and results of the past works could be used. The system of differential equations for each element is solved following the discretization of the solution domain. Thus, the flow discharge past each element is found. Thereafter, the disturbed zones are identified and their reduction effects on the flow discharge of the elements are considered estimating the reduction factors of elements. Finally, the total discharge of non-linear weir will be obtained by integrating over the entire solution domain. To achieve this goal, a computer program is developed using the MATLAB programming language to code the above-mentioned steps.

This method is based on elementary analysis of nonlinear weirs, which calculates the discharge capacity of these weirs by solving energy and discharge equations for each element and correcting the effects of disturbed zones. For evaluating the performance of the proposed method, laboratory results performed on oblique and trapezoidal labyrinth weir have been used. Results show that the accuracy of the EDA model for calculating the discharge capacity has been in the error range of 12% and 20%, respectively. Also, the results of the laboratory model of the rehabilitation project of the Millsite dam spillway (arc labyrinth weir) have been used to investigate the performance of the proposed method in complex geometries. The EDA model with a maximum error of 15% had a satisfactory prediction of the discharge capacity of the Millsite dam weir.

Due to the unique characteristics and increasing application of nonlinear spillways in dams and other hydraulic structures, a general method for analyzing the discharge capacity of these structures can play an important role in design phases. One of the most important applications of nonlinear weirs is in dams where they are revised as rehabilitation projects to increase the capacity of the spillway overpass or increase the volume of the dam reservoir. Due to the hydrodynamic complexity of the flow in nonlinear weirs, no general method has been proposed for their discharge analyses and has often been investigated by laboratory models. In this research, a general method for analyzing nonlinear weirs discharge is presented. To ensure the performance of the EDA method, the laboratory model of oblique and trapezoidal labyrinth weir (at different scales) that studied has been used. The results show that the proposed method has good accuracy in estimating the discharge capacity of oblique and trapezoidal labyrinth weirs. The Millsite Dam spillway, which has one of the notable rehabilitation projects, was also investigated. The results show that the proposed method is relatively better in estimating the discharge capacity of the Millsite Dam spillway over other methods.

Channel bends are sometimes unavoidable due to project conditions or land topography. However, oblique cross waves are a distinct feature of supercritical flow in bends. These waves continue for a long distance downstream and increase the height of water considerably. Initially, the complex behavior of supercritical flow in bends was studied by hydraulic models in the laboratory. Later on, numerical models were found inexpensive tools to investigate flow patterns and explain features that may not even be possible to measure. In this article, the supercritical flow in a rectangular horizontal channel of 90º bend is studied with different ratios of radius to channel width (rc/b) using two- and three-dimensional numerical models. Water surface profiles are then compared with the data that were obtained from our experimental bend models. It is proved that three-dimensional models are more successful in predicting the flow profile, peak, and location of waves at the outer wall bend.

In this study, Flow3D was used for the three-dimensional simulation of flow patterns. This software had a wide variety of applications and capabilities. The user could enter information to select different models to provide a range of flow phenomena. Flow3D integrated the Navier-Stokes equations (N-S) with finite volume method (FVM), with different mesh configurations, suitable for complex geometries. The k-ε turbulence model was used to close the N-S partial differential equations. The volume of fluid (VOF) method was used to model the free surface boundary. Additional boundary conditions for supercritical flow in bends included constant depth and velocity at the inflow section and no-slip or zero velocity conditions at the floor and solid walls. The Roe2D model was used for the simulation of two-dimensional shallow water equations. This model was able to capture discontinuities such as shock waves in supercritical flow. A triangular mesh was used for the space discretization, and a minmod slope limiter was implemented to control oscillations. Experiments were performed in the curved channel of the hydraulic laboratory of Ferdowsi University of Mashhad. This rectangular channel was horizontal, 40 cm in width, and the walls and floor were made of transparent plexiglass sheets. A straight channel, 1.8 m length, was installed before the bend to ensure flow development length. At the end of this channel was the 90º channel bend with internal and external radii of 40 and 80 cm, respectively. The channel width could be changed by adding interior walls; thereby, the ratio of rc/b might be changed accordingly.

Several experiments were run in the curved channels with widths of 15, 20, 30, and 40 cm and different radius of curvature to channel width (rc/b). The flow rate and water depth were measured, and thereby, the approach Froude number Fro was calculated. New experimental equations were obtained to calculate the maximum flow depth and location of the first wave’s crest along the outer wall in terms of the approach Froud number and the geometric specification of the bend. For each experiment, the corresponding two- and three-dimensional computer models were performed too. The three-dimensional model was well able to estimate the behavior of the supercritical flow, including the depth and position of wave crest at the outer wall of the bend. As Fro increased or rc/b decreased, the wave peak increased and moved downstream. However, the two-dimensional model had acceptable accuracy only for low values of Fr0 < 3. the assumption of hydrostatic pressure in depth-averaged 2D models was not applicable to supercritical bend flows. For flows with low Fro, the vertical acceleration might be ignored; however, as Fro increased, it became significant within the bend, and its negligence led to large errors in computations. In flows with high Fro, the maximum vertical acceleration occurred at the beginning of the bend (minimum depth point), and the minimum occurred at the wave crest. At high Fro, the vertical acceleration was downward, causing the hydrodynamic pressure to become less than the corresponding hydrostatic pressure.

The three-dimensional model of Flow3D is a suitable tool for the simulation of high-velocity supercritical flows in bends in comparison with the two-dimensional depth-averaged model of shallow water equation of Roe2D. By examining the pressure distribution and vertical acceleration in numerical models, it may be concluded that the basic assumption in the extraction of shallow water equations, namely the hydrostatic pressure distribution, is not admissible, especially at high Froude numbers. Moreover, the effect of vertical acceleration of water particles has a great effect on the estimation of wave crest depth and its position in the bend. .

A spillway is a very important structure usually used to provide the controlled release of water from a dam or sometimes levee downstream, typically into the riverbed of the dammed river itself. Spillways ensure that water does not destroy parts of the structures not designed to convey water. many Energy-dissipating structures (such as ., hydraulic jump stilling basins, roller buckets, ski jump buckets) are usually located at the end of spillways discharge channels in order to dissipate the extra energy which comes from the water . Specifically, flip buckets are mainly placed at the end of f high dams in order to dissipate the energy with high-velocity flows . having said that these structures ( Flip buckets) are used when velocity of the water is larger than about 15-20 m/s. Energy dissipation controlling has always been one of the most significant and vital matter and concern of hydraulic scientists and researchers especially in tall dams. one of the most common method to dissipate energy is to discharge flow away from hydraulic structures and downstream by using Flip bucket spill way .The sky-jump spillway is an economical and effective solution to return water to a river . many years ago in the past various models of flip bucket spillways , like simple, splitter, and deflector, and so on have been built,but information about the ways of increasing energy dissipation and controlling the bad effects of the extra energy of the water are still limited and more studies are needed .in order to increase the efficiency of this dissipater structure some wedge shape deflectors were designed to decrease the effect of this destructive energy on down stream.in this regard the effect of deflector installation position on energy dissipation was experimentally investigated. The main result indicate that the increase of linear distance of deflectors from the bucket remarkably result in an increase in energy dissipation and a decrease in jet length..

To investigate the effect of deflector installation position on energy dissipation and the length of the jet a new experimental study was conducted in the Hydraulic laboratory of Shahid Chamran university of Ahvaz.3 wedged-shape structures with Hight of 10 cm ,,length of 6 cm and angle of 47 degree were made .40 experiments were performed at 4 different linear distance from the edge of the bucket and one deflector-free experiment was carried out as a compression to other experiments. It is worth mentioning that all experiments including deflector-free one ,were performed at 8 dimensionless parameter Yc/H . At each experiment the linear distance from the edge of bucket was increased and the depth of tailwater was read .In the end relative energy dissipation was concluded by measuring the total energy in the upstream and downstream. in addition to the energy dissipation , Jet length ( for each experiment )was determined by using Get data software and the photos taken during the study .

In general Data analysis demonstrated that the waged-shape structures resulted in a remarkable increase in the amount of energy dissipation and a major decrease in jet length ,due to the increase of water and air mixture compare to the deflector - free experiments .Indeed deflectors divide the incoming jet to two small different jets ,therefore the combination of these two small jets leads to the increase in water and air mixture and consequently the increase of relative energy dissipation .Moreover it has been shown that the energy dissipation increased by increasing the linear distance from the bucket. Furthermore the experimental study on jet length indicated a remarkable decrease in the jet length by the increasing of the linear distance.in other words the different installation position of deflector increase the Hight of jet trajectory .it directly increases the contact surface of jet and air and leads to increase of energy dissipation and consequently decrease of jet length.

In general the increase of linear distance from the edge of bucket ( in flip bucket spillway ) resulted in the increase in energy dissipation and the decrease in jet length .Maximum observed relative energy dissipation was 65.87 which occurred in the Yc/H = 0.027 and Lx/L = 7.3 and minimum observed relative energy dissipation was 57.54 ,which occurred in the Yc/H = 0.061 and Lx/L = 4.3. furthermore maximum observed jet length was105 cm, which occurred in Yc/H = 0.061 and its minimum was 35 cm, which occurred in Yc/H = 0.027. therefor according to the results of the all experiments using deflector in different possessions as a new way of controlling and increasing energy dissipation is highly recommended .

One of the vital parts of a dam is its energy dissipation structure. With the construction of a dam, the flow is conveyed downstream. The outlet flow from a dam has a lot of energy and to dissipate this energy the plunge pools are used. The impact of jet from a dam outlet to the river bed might cause a large scour hole, which is one of the most important topics in the field of river engineering. The scour phenomenon may lead to damages for the dam or adjacent structures. Therefore, accurate estimation of the depth and dimensions of the scour hole is necessary. Although, the symmetric crossing jets in the dam’s outlet structures are used as a solution for the energy dissipation, but the scour at downstream of these structures may also happen. Pagliara et al. (2011) studied the scour caused by two crossing jets. They used a uniform bed material with a diameter of d50=9.5mm. They observed that in the presence of high tailwater level, a significant decrease occurs in the scour depth at all the crossing angles. The continuation of studies in this field help to collect more information and findings. Therefore, the present research uses a different bed material size with d50=1.4mm. An attempt was also made to derive specific equations which includes the crossing angle as an independent variable to interpolate the scour value in different angles.

In this study, 54 experiments were conducted to investigate and analyze the scour caused by symmetric crossing jets, also 9 experiments with a single jet were performed as reference tests. The diameter of the equivalent single jet is equal to Deq=31.1 mm. A bed material with d50=1.4 mm and geometric standard deviation of σg=1.5 is used. The experiments were carried out in a 16 m long, 1 m wide and 0.8 m high canal at the hydraulic laboratory of the Semnan University. A hinged gate was used to adjust the tailwater level. To hold the jet pipes during the tests and change their height, a metal base was built. An electro pump with a maximum discharge of 10 lit/s was used. Accordingly, three discharge values (105, 91.5, 78 lit/min), three tailwater level (3, 6, 9 cm), two distances for the jets crossing point to the water surface (5, 10 cm) and three different crossing angles (30, 70, 110) were used. To predict the scour hole dimensions (the scour hole depth, the length and the width as well as the ending location of the downstream ridge), the linear and power regression models are also presented. The experiments performed systematically by changing the hydraulic parameters and the effect of each parameter was investigated on the scour hole dimensions. At the end of each experiment, the longitudinal and transverse profiles of the scour hole at the maximum depth section were measured using a laser measurer.

At the crossing angles of 70 and 110 with low tailwater level, the scour depth is more than that of the crossing angle of 30 and the single jet. It was also observed that at the crossing angles of 70 and 110 and low tailwater level the scour shape tends to be asymmetric. Increasing the tailwater level and the distance of the crossing point of the jets from tailwater increased the scour depth at the crossing angle of 30, but, at the angles of 70 and 110, on the contrary, the scour depth was decreased. Accordingly, it turns out that the use of crossing jets for the scour reduction is only effective in some hydraulic conditions. The linear and power equations obtained from the entire data collection were not able to estimate the scour hole dimensions accurately at all the crossing angles because of the complexity of the phenomenon. But, the power models obtained separately for each crossing angle were able to estimate the scour features satisfactorily. The longitudinal scour hole profiles are plotted and compared with each other at various crossing angles. To show the effect of each variable, the scour hole parameters are also plotted versus the independent variables.

The results of this research showed that the use of crossing jets necessarily does not reduce the scour, and at the same time this depends on different hydraulic factors, such as, the angle of the crossing jets, the tailwater level, and the distance of the crossing point of the jets from tailwater level. The results show that at low tailwater level, the amount of scour due to the crossing jets is more than that of the single jet at all the crossing angles.Keywords: symmetric crossing jets, scour hole dimensions, regression equations

The use of treated wastewater has been common in various countries around the world for a long time. With the increase in world population and the need for more water resources, the use of treated municipal wastewater for irrigation is expanding. One of the limitations of using treated wastewater for irrigation is the cost of transporting it to agricultural areas. In general, water conveyance line costs are estimated using pricing for constructed projects that may be similar in size, material, and depth. The water supply system for irrigation in the plains of Varamin and Pakdasht in the south of the capital has always been considered due to its size and socio-economic importance. The presence of a large treatment plant in the south of Tehran can be a reliable source of recycled water. This treatment plant with a capacity of 700,000 m3/day produces effluent of suitable quality for agriculture from the municipal wastewater treatment process. Part of this wastewater has been transferred to the irrigation network of Varamin through a 36 km long open canal for the last 30 years. The effluent extracted from the Tehran water treatment plant provides the conditions for the implementation of an efficient plan to solve the existing problems and provide safe water. Based on this, a 36 km transmission line with a water delivery structure to the downstream irrigation network was considered. After the implementation of the project, the transmission line with a discharge capacity of 9 cubic meters per second and the existing canal with a transfer capacity of 4 cubic meters per second, will perform the effluent transfer work with an integrated system. The existing canal will normally act as a substitute and complement, and in critical times and in the presence of rain and floods, it will enter the transmission circuit and operate with the main system.

The case study is the second line of wastewater transfer near the Tehran canal in the southeast of Tehran province. The Tehran canal, approximately 36 km long, starts from the southern Tehran treatment plant located in the south of the Shahre’Rey and joins the main canal of the Varamin irrigation network. Then it feeds the main canal (AB) of the Varamin irrigation network and secondary canals by a water dividing structure. In this section, different options of material and type of pipe for the second line of wastewater transmission, such as closed pipes (pipes and concrete boxes) or open canals are examined. The following is a brief description and economic estimate of the proposed options. In this study, by examining six different options and based on the material and type of transmission line and implementation feasibility, a suitable transmission line is selected technically, economically and environmentally. The considered options were as follows: building a new canal parallel to the existing canal, constructing two concrete boxes parallel to the existing canal, constructing a concrete twin box parallel to the existing canal (in one side of the Tehran canal) ), Compound cross-section option (correction of Tehran canal), re-lining the Tehran canal and using a pipeline parallel to it, and finally, implementing a transmission line parallel to the Tehran canal and maintaining the current operating conditions of the Tehran canal. To estimate the costs of executive operations, the proposed options are examined in detail. After selecting the appropriate option, which was to be implemented with thick polyethylene pipes, the production line of this type of pipes was imported to Iran by Mohammadian Oil and Gas Engineering and Development Company to produce pipe with a diameter of 3000 mm.

In this section, the transmission line flow was analyzed at different hours of the day and the design flow was obtained. Different materials were investigated for the transmission duct, the roughness coefficient proportional to the diameter and the material of the transmission pipe for the sewage was proposed, a hydraulic model was implemented to simulate the flow behavior in the duct and to determine the location of manholes. Finally, the economic analysis of the project was performed for different options and the sixth option was selected for implementation.

Open canal option in terms of environmental issues and sedimentation problems and maintenance and operation problems (especially because due to sewage, is prone to algae growth and needs regular and continuous attention, and given the short life cycle of the project) was not recommended. The cost of execution of concrete box in comparison with SRPE pipes does not show a significant difference and in terms of technical and operational issues, execution time, design safety (in terms of leakage), and difficulty of execution are not comparable to transfer using the pipe. Also, reinforced polyethylene pipe has a significant advantage over the concrete box. Therefore, the sixth option for the design was selected and implemented.