مجله هیدرولیک
سال شانزدهم شماره 3 (پاییز 1400)

In today's world, fresh water is known as a limited resource that all economic and social activities of human beings and more importantly human life and other organisms depend on this limited resource and this limited resource is decreasing day by day. At present, in most countries, desalination of the seas and oceans is the most important source of water supply near the coast. One of the products of desalination plants is saline effluent that is discharged into the sea environment. Improper discharge of this effluent causes damage to the environment and can cause irreparable damage to human life and other organisms. In this research, in a case study, the most optimal method of discharging the effluent of one of the Assaluyeh desalination plants is investigated in order to achieve the maximum amount of effluent dilution in the near and far fields. Also, the effect of increasing the number of dischargers on the dilution rate of effluent discharged from multi-port dischargers in the far field is investigated.

The most important environmental problem of desalination plants is the production of brine (containing high concentration of salt) that is discharged directly into the sea. In this research, using the VISJET integral model, the dilution of effluent from an Assaluyeh desalination plant is investigated. VISJET is an integral model that uses the Lagrangian method to solve equations and predict the amount of effluent dilution in the Water environment. VISJET has the ability to simulate a multilayer environment and simulates effluent with positive, neutral and negative buoyancy. VISJET does not consider effluent dilution in the remote field. Therefore, in this research, the CORMIX model is used to dilute the effluent in the far field. The CORMIX model has been developed to analyze and predict the discharge of effluents with positive, neutral and negative buoyancy into the water environment. Discharge of various types of industrial and toxic effluents in the form of single- port and multi- port submerged and surface discharge, as well as considering environmental conditions such as wind speed, speed and direction of ambient flow and land slope are among the features of this model. In addition to near-field effluent mixing, this model also predicts effluent mixing in the far field. CORMIX consists of three sub-models: CORMIX1 (discharge using single-channel discharge), CORMIX2 (discharge using multi-duct discharge) and CORMIX3 (surface discharge).

In this section, using the CORMIX model, the dilution of the effluent of Assaluyeh desalination plant is investigated. Then, using CORMIX and VISJET models, the submerged discharge scenario of this plant at different depths is investigated, with the aim of achieving the maximum amount of effluent dilution in near and far fields. At a distance of 200 meters from the discharge site of Assaluyeh desalination plant, the salinity of the ambient fluid increases by 16%. Therefore, Iranian environmental standards are not observed. This type of discharge (surface discharge) has the least dilution in the nearby field due to minimizing the contact of the effluent with the sea environment. In a submerged discharge, the height of the effluent in the plume condition increases with increasing discharge height from the ground. In this case, due to more contact of the effluent with the water environment and having more time for mixing, the dilution of the effluent increases. Using a mile discharge with a froude number of 27.4 at a depth of 9 meters is the best method for discharging the effluent of Assaluyeh desalination plant as a single port. In this case, the concentration of ambient fluid at a distance of 200 meters from the discharge site will increase by 1.5 percent, which is fully in accordance with Iranian environmental laws. Effluent dilution in a dynamic environment, in addition to the Froude number, discharge angle and ambient flow, also depends on the mass flux of the effluent. According to the results, increasing the number of outlets in multi-port dischargers (by keeping the froude number constant, ambient flow velocity and discharge angle for all dischargers) increases the dilution rate of effluent in near and far fields.

Surface discharge of Assaluyeh desalination plant effluent increases the concentration of the receiving fluid by 16% at a distance of 200 m from the discharge site. The use of a 60-degree multi-port discharger with 10 outlets and a Froude number of 27.4 at a depth of 3.8 meters to discharge the effluent of the Assaluyeh desalination plant increases the concentration of ambient fluid by 0.8% at a distance of 200 meters from the discharge site. This scenario is recommended for optimal discharge of effluent according to environmental standards.

The purpose of controlling hydraulic jump order to prevent damages caused by energy water in supercritical speeds of the research. To control the hydraulic jump and to prevent damage caused by water energy at supercritical speeds, at the end of structures such as spillways, special structures called energy dissipation are used which are built downstream. A further part of the research carried out by various researchers is expressed. Results show that the rough bed in comparison with the smooth bed, will decrease the jump relative depth in an average of 56.7 percent and the relative energy dissipation increases 69 percent and the shear modulus increases 2.6 percent. The goal of this study is reducing the hydraulic jump ̓s length to prevent the damage caused by the energy of water and reducing the length of the stilling basin, in the supercritical flow that passing the spillways.

The experiments had performed in a flume with a width of 0.3 m, a length of 10 m, its height that was 0.75 m at first 2.5 m of the flume and 0.45 m in its remaining flume length, and zero slopes in the hydraulic laboratory of Behbahan Khatam Al-Anbia University of Technology. In all experiments, hydraulic characteristics including jump length, rolling length, crossing discharge from the spillway, crossing discharge from the jet, second depth, tail water depth, water depth the back of the spillway, water height on the spillway, spillway water head recorded. The flow depth measured depth gauge with an accuracy of 0.1 mm at three fixed points and their average. In this research in order to determine the best model of energy dissipation and economization of the stilling basin with smaller dimensions for modeling the using several methods such as creating a slot in the spillway-body, on the floor of the stilling basin, and end of the stilling basin. In total 65 experiments with a Froude number of 4.56 to 10.18 were performed. In all experiments, the cross-section of the slot (jet) was constant and discharge was 16,12,8 L/s.

Four series of experiments with different landings were performed to determine the evaluation of different models to reduce the length of the hydraulic jump and select the best model. The first stage test (control test) will be used using a without jet spillway to determine the jet flow rate and compare the jump length with other models. The results of these experiments, similar to previous studies, show that with increasing discharge spillway, the Froude number decreases, and the length of the jump and the length of the roll increase. The experiment of the second series (slot in the body of the spillway) By creating a slot with an angle of 45 degrees in the body of the spillway, we came to the conclusion that the slot in the body of the spillway was able to reduce the jump length between 14.28 to 4.76 percent in different flows. Third stage experiment (slot in the floor) Comparison of the results of the tests of the effect of the slot in the floor spillway with the control experiments showed that the use of the slot in the floor of the spillway at all distances reduced the hydraulic jump length compared to the control experiments at similar discharges. Also, the effect of using a slot in the floor on reducing the length of the hydraulic jump has increased as the slot approaches the spillway. The best way to reduce the jump length is related to the slot attached to the spillway, which has reduced the jump length by 59 to 67% for different discharges of the spillway compared to without a jet mode. Third Stage Experiment (slot in floor) Comparison of the results of the stilling basin floor impact tests the free experiments showed that the use of the stilling basin floor slot at all distances reduced the hydraulic jump length compared to the free experiments at similar discharges. Also, the effect of using the slot in the floor on reducing the length of the hydraulic jump has increased with the slot approaching the spillway, so that the best way to reduce the jump length is related to the gap attached to the overflow, which is 59 to 67% for different discharges without jet reduced. Fourth Stage Experiment ( the jet at the end ) The jet at the end of the stilling basin at all distances experiments showed that the jet at the jump was submerged because the momentum caused by the discharge passing through the flow over the spillway caused it to push water. The spillway water a submerged jump mode has been created the jump energy has been depleted. The experiments showed all discharge inflow tested, the closer the jet is to the spillway, the best jump length. The best mode was to reduce the jump length of the jet attached to the spillway, which reduces the jump length by 80 to 88% in different discharges to the spillway compared to without a jet mode.

In these experiments, by examining the effect of the jet on different models, the results showed that using the jet at the end of the stilling basin at different distances and discharges has a better performance compared to other models. The jet at the end in the stilling basin had a jump length of maximum discharge 88% reduction, the slot jump length in the floor of the stilling basin 67.42% reduction and finally the slot jump length in the spillway body 14.28% reduction, which has the lowest reduction in jump length compared to other models of this research .In this study, the jet at the end of the stilling basin in different discharges reduces the level of the upstream water level, which in the maximum flow was able to reduce the upstream water level by 5.67%.

Water regulation and distribution structures are the main components of any irrigation network. If these structures fail, it has a direct impact on network performance and water loss. The type and shape of the regulation structure can be effective for better performance of the distribution structure. Studies show that one of the problems in irrigation networks is due to the mechanism of existing structures. At present, regulation structures with various shapes are used in the world. Rubicon Water has been working in Australia since 1995 to develop, build and install water regulation and distribution structures. The company's automated regulation structure, called FlumeGate, has been installed in different countries such as Australia, India, China and the United States. In the present study, the variable height whirling -VHW weir was introduced, designed, and constructed inspired by FlumeGate. The shape, mechanism and installation of this weir are relatively simple. The energy required to change its position is less than other gates. This is an overshot structure that has a better performance in the face of floating objects. Placing the weir crest at different heights is another advantage over fixed weirs. By determining the stage-discharge relationship at different angles, it can also be used as a flow measurement structure. The purpose of this study is to determine the stage-discharge relationship of the structure and its discharge coefficient at different openings.

The body of variable height whirling weir consists of two quarter circle sections on both sides and a rectangular section on the floor. At full opening, the rectangular section is placed horizontally and provides the maximum cross-sectional area for flow. By whirling the body, this structure acts like a weir and, while regulating the water level, also passes a specified discharge. A flume with a trapezoidal section with a length of 60.5 m was used to investigate the hydraulic behavior of VHW weir. The bottom width of this flume is 0.3 meters, the maximum depth is 0.25 meters, the side slope is 1:1 and the average slope is 0.0009. The VHW weir was installed at a distance of 44.5 meters from the beginning of the canal to create a uniform flow. To collect the required data, different weir openings were investigated in each specified discharge. Data including discharge, upstream water level of weir and angle of weir floor relative to the horizon were recorded. At each stage of the experiment, discharge was recorded by a flowmeter for two minutes and piezometer board was captured via digital photography. The recorded photos were digitized by Grapher software and the water depth in the all piezometers was determined. For determining the stage-discharge relationship of this structure in free flow condition, hydraulic, power and dimensional analysis methods were used.

In the hydraulic method, stage-discharge rating curves were plotted by the upstream water depth of the VHW weir and inlet discharge to the canal at different angles. Therefore, the discharge coefficient was determined for each opening. By obtaining the discharge coefficient for each opening, a relation can be written for the changes of the discharge coefficient versus the angle. Considering the relationship between the discharge coefficient and the angle, it can be seen that for angles larger than 35, the VHW weir had a different performance compared to smaller angles. the reason for changing the data trend can be attributed to increase the effect of the weir wall on the flow. In the power method by having the upstream water depth of the VHW weir and the inlet discharge to the canal, it is also possible to obtain a relation for the coefficient C and b versus the angle. In this method, the relationship trend changes at angle of 30 degrees. To generalize the results, the two dimensionless parameters which obtained from Buckingham theorem were plotted against each other. According to the graph and the data trend, the stage-discharge relationship can be divided into two parts. Data up to an angle of 35 degrees follows a trend, so it is best to use from one relation for angle of 7 to 35 degrees and another relation for angle of 35 to 50 degrees. Based on the statistical parameters, the obtained relationships based on dimensional analysis gave a better result.

discharge of VHW weir was obtained by three methods hydraulic, power and dimensional analysis. Comparison of the statistical parameters of these three methods shows that the relationship obtained from the dimensional analysis is most consistent with the data. The results show that the hydraulic behavior of the weir at angles larger than 35 degrees is different from smaller angles. The main reason for this difference is the effect of the structure body on the flow path.

By constructing a pipe containing fluids such as water and oil crosswise with the direction of the river, the pattern of river flow around the pipe changes. . These changes in the flow pattern around the pipe and an increase in shear stress on the substrate, which results in a scouring hole under the pipeline. Local scouring around pipelines across the river is one of the most important causes of their failure and destruction. Therefore, it is very important to study the mechanism of occurrence of this phenomenon around the pipelines and to evaluate the amount of scouring and the characteristics of the local scour hole around them. Wu and Chiew (2013) investigated the scour hole and the flow field around a pipeline under steady flow. The flow field in these experiments was measured by an acoustic Doppler velocimeter. The results of this study showed that the presence of vortices due to the pressure difference created upstream and downstream of the pipe causes the formation of a force for the movement and displacement of sediments. Also, the flow from under the pipe into the scour hole causes it to expand further. Zhao et al. (2015) performed laboratory and numerical study of scouring under two consecutive pipelines with different distances from each other. In moving bed conditions, it was observed that the depth of the scour hole under the upstream pipe is slightly greater than the scour hole under the single pipe, while the depth of the scour hole under the downstream pipe is much greater than the scour depth compared to the single pipe. Yan et al. (2020) numerically examined the local scour around the pipeline across the river under steady flow conditions. In their study, the CFD method and variable mesh technique were used to model the sediments transport and the results were compared with the results of the laboratory model. The results showed that the method used to model scour and sediment problems respond satisfactorily. The aim of this study was to investigate the effect of the installation depth of pipe across the river in steady flow on temporal changes in scour pattern and sedimentation around the pipeline were processed by recording video information during each experiment.

The present study was performed in the hydraulic laboratory of the Faculty of Water and Environmental Engineering, Shahid Chamran University of Ahvaz in a rectangular flume 10 m long, 0.74 m wide, and 0.6 m high. The walls of the flume were made of glass and the floor was made of steel. The flume had reservoirs at the beginning and end and a section to calm the flow. To investigate the scouring phenomenon around the pipe crossing the waterway, in the middle of the flume, in an area, 1.5 m long and 15 cm thick, uniform sediments with Medium size (d50) 0.7 mm, relative density (Sg) 2.65, and standard deviation (σg) 1.4 were poured. In this study, pipes with a diameter of 20, 40, and 60 mm at a quarter of the pipe diameter under the bed (e/D= -0.25), bed installation depth (e/D= 0), a quarter of the pipe diameter above the bed (e/D= 0.25), and half of the pipe diameter above the bed (e/D= 0.5) were used. The pipes were made of PVC and were installed perpendicular to the flow across the flume. The experiments were performed at a flow rate of 33 liters per second and a flow depth of 14 cm. The duration of all experiments was 120 minutes. The total number of experiments was 12. In these experiments, clear water conditions prevailed.

In most of the researches in this field, a comprehensive study has not been done on the temporal changes of the scour hole parameters and their focus has been mainly on the scour depth parameter when the pipe is placed on the bed. Comparing the present laboratory study with other studies related to the study of diameter and depth of installation, one of the most relevant studies is related to the laboratory estimation of scour under the pipeline by Ataieyan (2012). In which the scour under the pipeline is investigated with emphasis on the effect of installation depth. The maximum amount of scouring was observed at a depth of one-fourth of the pipe diameter at the top of the bed. The result of the experiments performed in the present study also confirms that at the depth of installation, e/D= 0.25, due to the narrowing of a certain distance between the sub-pipe and the surface of the sedimentary bed and The formation of vertical and horizontal vortices showed the highest maximum scour depth compared to other installation depths. The results related to the effect of installation depth for different modes are as follows, e/D= 0.25, e/D= 0, e/D= -0.25, e/D= 0.5 from maximum to minimum, respectively, they had the highest amount of scour depth. Another parameter studied for scouring is the distance between the maximum scouring depth and the center of the pipe. This parameter is indicated by Xds. the location of the maximum scouring depth at the beginning of the experiment was moving upstream of the pipe. At installation depth, e/D= 0.5, the highest rate of maximum scouring depth was observed downstream compared to all cases. In all experiments, about 80 to 90% of the height of the deposition ridge occurred in the first 10 to 20 minutes of each experiment.

The results of this study showed that at all installation depths, 80 to 90% of the scouring depth was performed in the first 40 minutes of each experiment. The depth of pipe installation was one of the most influential factors on the dimensions of the scour hole. In all experiments, sediment from erosion was deposited downstream of the pipe and formed a sediment ridge. The maximum and minimum deposition heights occurred at the installation depths of e/D= 0.5 and e/D= 0.25, respectively.

Resilience analysis of urban infrastructures such as sewerage systems due to different stressors is very crucial. Failure in these infrastructures may lead to economic, social, health and environmental consequences. The structural resilience of system can be analyzed in all failure levels based on global resilience analysis (GRA) method. To perform GRA under different scenarios of pipe collapse and blockage, it is required to evaluate the performance of the system in all possible link failure combinations which could take long time in real sewerage networks.Resilience is defined to evaluate system performance in exceptional conditions (Mugume and Butler 2016). Various conditions threaten sewer networks which some of them are unknown. Each event might have several different consequences or different events can lead to the same end states (Johnson et al. 2011). Accordingly, traditional risk analysis is not appropriate to investigate sewer networks, because it emphasizes on defining and evaluating the probability of an event besides its consequences. Therefore, the middle state analysis method is used to evaluate the system performance based on consequences caused by different and unknown threats. In this approach, the consequences of the events are investigated regardless of their type to represent all the potential modes of failure (Butler et al. 2014).Johnson (2011) presented a method for the global vulnerability analysis (GVA) of technical infrastructures and used it for an empirical analysis of the electrical distribution systems. Mugume et al. (2015) introduced global resilience analysis (GRA) in urban drainage network based on the middle state approach. In GRA, network performance is evaluated from zero to 100 percent failure levels and then the resilience is determined for different levels. This method has four steps. Firstly, the failure mode needs to be identified. In the second step, the system stress associated with the failure mode and the simulation manner are identified. Then, the system corresponding strain is detected and determined how to measure it. And finally, the failure mode strains are simulated under increasing stress magnitude up to 100 percent of maximum stress (Mugume et al. 2015).Mugume et al. (2015) used the sequential random link selections method for sewer networks in order to overcome GRA’s computational challenges. Diao et al. (2016) proposed a semi random selection method for GRA and applied it to water distribution systems. In their method, at each stress magnitude a fixed number of failure scenarios are generated randomly and 2⌊c-(c_f-1)⌋ number of failure scenarios are generated in a targeted manner, where c and c_f are total and failed components, respectively. Atashi et al (2020a) also used the same selection method as Diao et al. (2016) to determine the total number of scenarios in order to evaluate the resilience of water distribution systems based on location of isolation valves. In Diao et al. (2016), the total number of scenarios is directly related to the number of network’s links but Mugume et al. (2015) used a convergence analysis method to determine the required number of scenarios. This method is more generalizable to use in each network, because the effect of hydraulic properties is considered to determine the required number of scenarios. They showed that for an urban drainage system (UDS), by considering a sufficient number of random failure sequences the deviation percentage of GRA results are not significant, in all failure level. It means that, for one failure level if a sufficient number of scenarios are selected randomly, the average resilience for them is approximately equal to the average resilience of all scenarios of the failure level. So, to analyze global resilience with less time and computational cost it is necessary to use a scenario selection method which discover the extreme scenarios in different failure levels to obtain more accurate GRA results.

In this study, a scenario selection method is introduced based on roulette wheel to estimate GRA results without simulation all possible scenarios. In the proposed method, scenarios which lead to the minimum and maximum resilience at each failure level are identified as strategical scenarios and participated in generating (selecting) scenarios of the next failure level. In each failure level, the probability of a scenario being strategic is estimated by a Multi-Criteria Decision Making (MCDM) (Mardani et al. 2015). The scenarios with highest probabilities are selected to generating roulette wheel. Finally, scenarios of the next failure level are generated by selecting candidates from roulette wheel and adding a random link to the selected candidates.

The results of the simulations in the case study show that the minimum, mean and maximum resilience values was estimated by the proposed method with RMSE less than 0.025 and 0.022 comparing with simulating all possible scenarios, respectively. Also, the proposed method has been able to perform better than the random selection method in predicting the scenarios of the extreme points of the global resilience function.

In this article, a simple and rapid approach was presented for investigating structural resilience in sewer networks based on GRA. To properly cover the large space of failure scenarios that is a challenge in the real networks, a selection method is proposed based on the roulette wheel to identify the most strategical combination of failed pipes in each failure level.

In recent years, population growth and rapid economic development have exacerbated the problem of water shortage, especially in coastal areas, to the point that meeting freshwater demand has become a serious challenge for coastal communities (Herrera-Leon et al., 2018; Phan et al., 2018). This situation is further complicated by the irregular spatial and temporal distribution of freshwater resources in these areas. A coastal reservoir is defined as a water storage structure constructed at river estuary or other coastal area to store fresh water and control water resources. One of the obvious advantages of coastal reservoirs is providing additional fresh water storage capacity for water supply networks (Xu, 2001). In areas under water stress, coastal reservoirs, which are often the basis of local economic development, can help reduce water shortage (Li and Chen, 2005). Many coastal reservoirs have been constructed in China, South Korea, Hong Kong and Singapore (Yuan et al., 2007).Despite the importance of coastal reservoirs, there is little research on this issue in the literature and no studies have been conducted in this regard in Iran. In addition, there are many issues about the performance of these reservoirs that have attracted widespread attention worldwide. One of the most important issues is salinity changes in the coastal reservoir, which is the main focus of the present study. Accordingly, in this study, numerical simulation of flow and salinity transfer in a coastal reservoir along the Caspian Sea is developed as a case study.

Methodology:

Tajan river is one of the most important rivers in the Caspian Sea watershed, which originates from 3251 meters above the northern slope of the Alborz mountain range in the south of Sari city in the north of Iran. The flow in this river is influenced by hydraulic structures built at upstream of river, such as Shahid Rajaei Dam. In March 2016, due to heavy rains in the upstream basins, a large flood occurred in this river. Measurements showed that the peak discharge of flood was 880 m3/s and the maximum volume of flood was 3112560 m3. The return period of this flood was more than 1000 years.The modeling region in the present study is located between the estuary of Tajan river to the Caspian Sea and Neka river. The dimensions of the coastal reservoir in this study include 1 Km wide and 9 Km long (along the coastline) and the water supply to it is provided through a flood channel from the Tajan river. In the present study, MIKE3 which is a 3D numerical model was used. Two different models were developed and the results of each were studied. Model No. 1 where desalination of the coastal reservoir was considered by average monthly discharge of the Tajan river (Inflow boundary condition) and buttom outlets (Outflow boundary condition). The simulation period in this model was determined as 1 year. On the other hand, in Model No. 2 desalination of the coastal reservoir was considered by a 1000 year return period flood in Tajan river (Inflow) and an Ogee spillway (Outflow). Finally, similar to the water quality of the Caspian Sea, the initial salinity in the reservior was considered as 12 PSU.

Results and discussion:

  In this part, the results obtained from the both models No. 1 and No. 2 are presented and analyzed. The results of different models are also compared. Results in Model No. 1 showed that changes in water level and current speed were negligible with the maximum current speed of about 0.08 m/s. In addition, after 1000 hours from the start of the simulation, the salinity in the reservoir was about 8 PSU, and after 3000 hours it was about 3.5 PSU and after 8760 hours it was reached a maximum value of about 2 PSU. On the other hand, results in Model No. 2 showed that the current speed in the flood channel was about 7 m/s. However, the current speed inside the reservoir was low with a maximum value of about 0.2 m/s. This is about 10 times more than the current speed in Model No.1. Furthermore, result showed that at time step of the flood peak entry, significant decrease in salinity of the reservoir happened. Actually, the salinity of nearly half of the reservoir was less than 3 PSU in this time step. Finally, at the end of the simulation, the salinity of the reservoir was less than 1 PSU.

Conclusion:

A numerical study was carried out on the dynamic of salinity transfer and diffusion in a coastal reservoir under desalination condition. Two numerical models were developed. In Model No. 1, flow and salinity changes during one year simulation period with average monthly discharge of Tajan river were studied. In Model No. 2, changes in flow and salinity of the reservoir under a historical flood flow condition with peak discharge of nearly 200 times the average monthly discharge were studied. Salinity profiles in the depth of the reservoir and at different time steps showed that desalination occurred in the depth of the reservoir. In addition, the comparison of the two models showed that the salinity stratification in model No. 2 was more intense due to the rapid changes in the hydrograph flow. In both models, the salinity difference at the surface and depth of reservoir decreased over time from the beginning of modeling.

Floods are a natural disaster that threatens the lives of millions of people every year. Obtaining the flood zone and consequently obtaining the flood zone map for current with a specific return period for a desired basin is one of the important results obtained from different models. Therefore, extraction of flood zone is one of the basic needs in the design of water structures, a basic step for management and planning to reduce economic and social flood damage, use to determine the amount of insurance for residential areas along the river and also identify high risk areas of the river In terms of flood status and flood control measures. Evaluating the performance of the HAND model, which relies solely on topographic features, is one of the objectives of the present project.

In this study, the flood zone is determined using the HAND model with a calibrated coefficient of roughness. Seymareh River has been selected as a study area to challenge the performance of the model in relation to the observational data obtained from satellite images and also to evaluate it with the HEC-RAS hydraulic model. Also, the HAND model in low and high flows has been evaluated with a 1D and 2D hydraulic model to evaluate the performance of the model in different flow conditions.

In the first part, the HAND model was evaluated using satellite images, which show the very good performance of the model in determining the flood zone. Further sensitivity analysis of Manning roughness coefficient showed that increasing and decreasing it by 25% had no effect on improving the performance of the HAND model and the roughness coefficient was properly calibrated. Finally, the model was evaluated with 1D and 2D hydraulic model in low and high input flow conditions. The results showed that the HAND model still has a good capability in comparison with hydraulic models in different flow conditions.

The most important results can be summarized as follows:• The results obtained from the HAND model based on the calibration coefficient calibrated in Seimareh river indicate the proper performance of the model in obtaining flood zone. According to calculations, the rate of flood zone adaptation is higher than 92% compared to satellite images. Also, the average difference between the HAND model and satellite images for estimating flood zones during the study period of the river was about 8.5%. The occurrence of turbulence and rotational flows due to improper angle of connection between the channel and the freeway bridges in the future will have a significant impact on the hydraulic flow and sediment of the river, especially in the area of the bridges.• The results in Seimareh River show that increasing and decreasing the inlet flow does not change the performance results of the HAND model and also the model has a good capability compared to hydraulic models. According to calculations, the rate of adaptation of the flood zone in comparison with the hydraulic model in different discharges is always higher than 83%. Also, the average difference between the HAND model and hydraulic models for estimating flood zones during the study period of the river will be less than 13%. • Despite the very good performance of the HAND model in estimating the flood zone, in some intervals there are differences between the HAND model with satellite images and the hydraulic model, which can be done by using topographic maps with high resolution and river path inter Extraction of Rating-curves for each substrate greatly enhances the performance of the HAND model.• Hydraulic model has more error in estimating flood zone than HAND model. The main reason for this can be related to important factors such as: distance between cross sections, computational cell dimensions, numerical parameters used in the 2D hydraulic model (such as θ parameter and currant number), boundary conditions used in the hydraulic model Calibrate the time step and determine the Manning roughness coefficient for each cross section. In general, relatively more factors affect the performance of the hydraulic model and affect its output, while the HAND model experiences relatively better conditions in this regard, so that only by considering a coefficient of roughness for the whole The study interval and extraction of the Rating- curve can be used to obtain the flood zone. while the HAND model experiences relatively better conditions in this regard, so that only by considering a coefficient of roughness for the whole The study interval and extraction of the Rating- curve can be used to obtain the flood zone.

One of the phenomena that has been studied both theoretically and experimentally in hydraulic engineering is hydraulic jump. Hydraulic jump causes the flow to lose a considerable amount of energy due to the change in its regime from supercritical to subcritical. Since fluid flows in a conduit may be either of a free type (open-channels hydraulic) or of an under-pressure type (under pressure conduits hydraulic), the hydraulic jump can occur in both situations regarding the type and function of the system. Therefore, it can be said that hydraulic jump can occur in open channels as stilling basin. It can also occur in downward inclined pipes that contain a large air package. Additionally, since the present paper deals with pipelines, the following general statements can be mentioned about them. Pipelines are used to transfer fluids such as water, oil, gas, and wastewater offshore or onshore, either in the form of two-phase or multi-phase flows. The importance and function of the flows inside the pipeline must be studied. Export pipelines transfer fluids from platforms or FPSO (Floating Production, Storage, and Offloading) to the beach and they usually contain gas-condensate or oil with a little water. Infield pipelines transfer flows from the wells or manifolds to the platform or FPSO [Guo et al (2014)]. Offshore pipeline design includes structural, geometrical, and hydraulic designs. In structural design such matters as buckling and collapse during pipeline operation are considered, and several studies have been carried out regarding these matters. In geometrical design, diameter determination parameters (based on the flow capacity and precise analysis of the flow assurance in offshore pipelines), and wall thickness (according to the standards) are considered, each of which is somehow related to the flow hydraulics. Therefore, hydraulic design of pipeline is of utmost importance and problems related to this area must be examined precisely. However, it needs to be considered that most of the studies about hydraulic jump are carried out on channels, open conduits and stilling basin. Flows in open channels can shift from supercritical to subcritical. Such shifts happen very suddenly and appear due to hydraulic jump [Akan (2006), Lauchlan (2005) and Vasconcelos and Wright, (2009)]. Most of the studies about the hydraulic of pipelines that contain multi-phase liquid and gas flows concentrate on the function of flow regimes, pressure and sever slug. Therefore, it can be claimed that there is a lack in studying hydraulic jump in under pressure pipelines with multi-phase liquid-gas flows, because most of the studies are carried out on wastewater transfer lines and open conduits. The present paper, therefore, deals with the numerical analysis of hydraulic jump in pipelines with two phase water-air flows. To this aim, some experimental information has been taken from Pothof (2011) to verify the accuracy of findings and numerical modeling. It must be noted that Pothof has worked on wastewater pipelines that function gravitationally, while this study deals with under pressure pipelines in offshore conditions.

Regarding Pothof's experimental work (2011) which analyzes the occurrence of hydraulic jump, and using its data, the hydraulic jump is then numerically analyzed.In order to analyze the hydraulic jump numerically, roughness values, geometrical properties of the pipeline, and the angles are specified. General characteristics of the submerged pipe are also presented. Some other properties include: diameter=8in, water flowrate=128160kg/hr, air flowrate=32040kg/hr.Pressure loss in pipelines with multi-phase flows, includes frictional and hydrostatic pressure loss, is calculated based on mixture density and velocity. In hydrostatic pressure loss, it must be noted that since in horizontal pipelines ΔZ=0, the pressure loss istherefore zero, too. In upward inclined pipelines this value is positive (in line with increasing the total loss) and in downward inclined pipelines it is negative (in line with decreasing the total loss). In order to determine flow regimes semi-theoretically, Taitel and Dukler (1976) first modeled a stratified flow in a pipe, presupposing that the flow has been stable. Then, they determined how the flow regime was transferred from stratified to other flow regimes. The results of their analyses that are presented in a map for two-phase gas-liquid flow is used in this paper to determine flow regimes in two phase flow.

Hydraulic jump occurs in open water transfer structures and channels and its behavior and occurrence in such situations is studied precisely. Similarly, it is important to study it in pipelines, because it affects the behavior of the fluid inside the pipeline. When there is a pipeline containing a two-phase water-air flow, it can be assumed that the fluid inside the pipeline might face a hydraulic jump. Predicting such a phenomenon and its effects on pipeline during its working lifetime is a very important issue in the industries that deal with pipelines which transfer multi-phase fluids. Therefore, the present paper studies the occurrence of hydraulic jump in pipelines with two-phase water-air flows.

It can be concluded, based on the hydraulic gradient and the resulted losses, that hydraulic jump occurs when there is some air in the pipeline; and as the experimental researches showed, as the angle increases, the jump height increases, too. In all of the above- mentioned analyses except for the mode in which the angle is 30 degrees, flow regimes, according to Taitel and Dukler are annular mist for A-B, annular mist for B-C, and annular mist for B-D. Regarding what has been said, it can be stated that when total pressure loss in the negative direction (i.e., when the hydrostatic loss overcomes frictional loss) approaches zero, the flow regime might change.