JOURNAL OF HYDRAULICS
Year:2020 | Volume:15 | Issue:3|Papers Count:8

Introduction: Local scour is a main factor involved in the destruction of bridge piers in rivers before the life expectancy of these structures. One of the newest indirect methods for reducing the erosion and scour around the bridge piers is the air injection method based on counteracting with a downward flow to create conditions to prevent or reduce the flow impact on the bed and the destruction of bridge piers. Tipireddy and Barkdoll (2019) studied the effect of air injection on controlling bridge pier scour. The results of this study showed that the maximum scour depth decreased with increasing air injection rate until the ratio of air outflow velocity from the pores to flow velocity reached 57. 1 and then increased. Using air injection to reduce bridge pier scour has been explored in only one study, considering all parameters except for the constant air outflow rate. The main objective of this study was to investigate the effect of air injection on reducing bridge pier scour considering the number and the location of injection pipes. Methodology: Experiments were carried out at the Hydraulic Laboratory of the Faculty of Water Engineering, Shahid Chamran University of Ahvaz in a flume 10 m long and 0. 74 m wide and 0. 6 m deep. The bottom of the flume was covered by sediments with a mean diameter of 0. 7 mm with a standard deviation of 1. 21 indicating uniform sand. All experiments were done in four Froude numbers of 0. 18, 0. 2, 0. 22, and 0. 24 at a constant depth of 15 cm under clear-water conditions. To create these conditions, the flow depth was adjusted so that the ratio of flow velocity to the critical velocity could be less than 95%. In order to determine the appropriate time for the experiments, a 12-hour test at a Froude number of 0. 2 was performed and it was observed that about 90% of the scour occurred in the first 3 hours. In order to create an air injection system, porous pipes were selected with an internal diameter of 4 mm. Each pipe had 24 pores with a diameter of 2. 2 mm at fixed intervals mounted on the upstream half of the pier and the two ends were connected to the air compressor for injection. Experiments were carried out at an air injection rate of 100 lit/min and in 7 different numbers and positions of aeration pipes on the pier. The pipes were mounted in three general modes: one pipe, two pipes and three pipes. The installation level of the pipe on the pier was considered at three heights of 1/3h, 1/2h, and 2/3h from the bed. Results and Discussion: A number of four control experiments (without the air injection system) was first performed at four specified Froude numbers. A total number of 28 experiments were performed in the presence of the air injection system at the air injection rate of 100 lit/min. The aeration pipe at the upstream half of the pier provides some protection for the sediments against the horseshoe vortices. Effect of aeration pipe position on scour depth and scour development around bridge pier The transverse expansion of the scour hole for the bridge pier was plotted in two general modes using a single aeration pipe and two aeration pipes in four Froude numbers. In the single-pipe mode, a maximum decrease in the scour hole depth in front of the bridge pier (25. 5%) was observed at a pipe installation depth of 5 cm beneath the bed and for the Froude number of 0. 18. For the use of two pipes with the same injection rate and similar hydraulic conditions, the maximum decrease in scour depth of 11. 8% occurred when the pipes were installed at depths of 7. 5 and 10 cm beneath the bed. Effect of aeration pipe on scour depth in scour development around bridge pier In order to investigate the effect of the number of pipes on the scour depth, the transverse expansion of the scour hole around the bridge pier was plotted in three general modes: single pipe (three mode), two pipes (three modes) and three pipes (one mode). The results showed that a lowest efficiency was observed in the state of the three pipes and the efficiency is in the one state. Effect of Froude Number on Scour Depth and Scour Expansion around Bridge Pier The shape of the relative scour depth was plotted against the Froude number for the use of an aeration pipe. The results showed that there is a direct relationship between the scour hole depth and the Froude number and that the scour hole depth increases with the increasing Froude number. Conclusion: In this study, the effect of air injection system on the scour pattern and sedimentation around the bridge pier under clear-water conditions in a straight flume was experimentally investigated. All experiments were done with four Froude numbers of 0. 18, 0. 2, 0. 22, and 0. 24 and 7 different numbers and installation levels of the aeration pipe at the air injection rate of 100 lit/min. The results showed that aeration structure in the flume reduced the scour depth around the pier. The reduction of the scour depth at the front part of the pier in the single-pipe test was 25. 5% with an installation level of 5 cm, Froude number of 0. 18, and air injection rate of 100 lit/min. The results of comparisons aiming to investigate the effect of the number of aeration pipes on the pier showed that the three-pipe mode had the lowest efficiency. This system reduced the volume of scour hole around the pier. Therefore, it can be concluded that the application of this structure can be an appropriate alternative in comparison to the commonly used protective structures; therefore, further research is suggested with this respect.

Introduction: Flood is one of the most devastating natural hazards that causes significant losses and damages. Flood inundation maps represent the flood-prone areas over the catchment, which is initial requirements for integrated flood management plans. Over decades ago, surveyed topography maps and bathymetry data were utilized to construct the river terrain for flood inundation mapping accurately. However, in most developing countries, including Iran, such precious data is rare for the sake of the time-consuming and costly procedure of rivers surveying. Therefore, for tackling this challenging issue, DEMs as an accelerator and free of charge datasets, are widely used in flood modelling. Nevertheless, the reliability of the finer datasets, such as LiDAR, the limited coverage of world and the exorbitant price of provision has obliged experts to utilize coarser-resolution DEMs rather than these higher-resolution DEM sources. As a result, the accuracy of open-access and free of charge DEMs used in flood modelling in the data-scarce rivers should be studied broadly, unless the lower-resolution DEMs hinder flood modelling results by incorrectly reproducing river terrain. In this study, three sets of widely used open-access DEMs’ performance in flood inundation mapping and estimating hydraulic parameters of four various rivers are assessed thoroughly. Methodology: In this paper, three sets of free and accessible 30m resolution DEM resources (ALOS, SRTM, ASTER) of four various types of rivers in Iran will be utilized as HEC-RAS geometry input file. The procedure consists of 5 main steps: 1) Generating GDEMs from 1: 1000 or 1: 2000 topography maps; 2) Extracting the river geometry using HEC-GeoRAS; 3) Flood modelling 4) Assessment of DEMs’ performance in estimating hydraulic parameters; 5) Investigating the significance of morphological characteristics of four different Iran. Results and Discussion: From modelling of the study rivers with different morphology, these brief results are drawn. The river geometry derived from ALOS DEMs were more identical to surveyed cross-sections. Therefore, according to previous studies, the higher performance of this dataset in flood modelling is expected. However, all of these RS-based DEMs were unable to present the Gorganrud river geometry data. Apart from the better representation of river geometry, the ALOS dataset is superior to ASTER and SRTM DEMs datasets in terms of fairy prediction of hydraulic parameters (water extents and water surface elevation). For instance, ALOS had the least RMSE (2. 3-8. 6m) and the higher value of F statistics (nearly 80%) in predicting flood extents. Reversely, the RMSE of ASTER, the least accurate model, in flood extents estimation was from 2. 8 to 15m and with the F-statistics of 68% at most. The SRTM performance in generating flood inundation map was better than ASTER and less accurate compared to ALOS (maximum F-statistic value was 78%). The accuracy of DEMs in simulating WSE of the mountainous rivers was similar to each other, and it was higher than predicted WSE of flat rivers. Moreover, the estimated WSE using ALOS led to less disagreement with the benchmark values, whereas the operation of ASTER and SRTM for this purpose resulted in overestimating. Overall, despite the tremendous difference of these DEMs in predicting the flood extents, the performance of these DEMs was acceptable in the predicting WSE of the rivers (Mean Relative Error=1% within all cross-sections) save in Gorganrud river with the highest RE% (nearly 5%). Conclusion: The accuracy of flood inundation mapping is highly dependent upon the river geometry input files. Accordingly, it is critical to evaluate the influence of these DEMs on hydraulic outputs. Despite the significant impacts of river morphology characteristics in flood modelling, there is no viable reference indicating DEMs performance in various rivers with varying morphologies. The results of flood modelling in different types of Iran rivers revealed that the ALOS DEM dataset is superior to ASTER and SRTM DEM datasets in terms of a better representation of river geometry and fairy prediction of hydraulic parameters. For instance, the higher percentage of F statistics (approximately 80%) proves that this model presented the flood inundation map with the highest agreement. However, the maximum values of Fstatistics of SRTM and ASTER were nearly 78% and 68%, respectively, showing the flaws of these DEM sources in flood extents mapping. The efficiency of all DEMs datasets in estimating WSE of the rivers was excellent (under 1% within the cross-sections). Consequently, ALOS is particularly potent in accurately hydraulic modelling. Additionally, the remote-sensing based DEMs are more applicable in wide and (or) straight river reaches than narrow and meandering rivers. From Gorganrud river, we conclude the underperformance of DEMs in the prediction of the meandering rivers hydraulic parameters demonstrates that these DEMs are not appropriate for flood inundation mapping of free-meandering rivers.

Introduction: Time of concentration (TC) is the time in which a water parcel travels from a watershed divide to its outlet. Time of concentration is also the most important factor in selecting design discharge for an area since the most severe floods are those caused by rainfalls with durations equal to the concentration time of a watershed. Time of concentration is necessary for the studies of water resources management, flow volume and discharge estimation, design of spillways and hydraulic structures, development of flood predicting models, flood alert systems, river management, and drainage projects and many other water related studies. Currently, there are two main methods to evaluate the time of concentration; applying empirical formulas or applying graphical methods which require flood hydrograph and corresponding rainfall hyetographs. Due to the differences in the accuracy levels of empirical methods in different areas, along with the unavailability of graphical methods in most of the watersheds, this study aims to estimate TC, using the basic definition of time of concentration which is the travel time of a water parcel from basin divide to the outlet. The focus of this study is to simulate the water parcel to calculate the time of concentration with a two-dimensional hydraulic model (HEC-RAS 5. 0. 7). To the best knowledge of the authors, this method has never been applied for the estimation of time of concentration. Methodology: Two-dimensional HEC-RAS model was used to navigate the runoff flow in the main channel of a watershed from the farthest hydrological point to the outlet. Besides, 48 different empirical equations were gathered from the literature and used to estimate the time of concentration. To validate the numerical method and the empirical formulas, the actual concentration time of the flow was measured by salt solution tracking. Then, the comparison of the measured data with the results of the numerical and experimental methods was made, using the percent of error index. Ali Abad watershed located in Fars province was selected as a case study due to the appropriate data availability and the possibility of various measurements as described in the following sections. Results and discussion: Results showed that only five methods indicate relative errors less than 20%, of which four belong to the empirical formulas (8% of the total empirical methods) and one to the numerical simulation. The NRCS is also a well-known equation in which runoff flow in a watershed is divided into three parts: sheet flow, concentrated shallow flow, and open channel flow. Flow velocity is estimated by the Manning's equation in the reach according to this method. This method’ s accuracy is about 82%. In order to run the twodimensional model, DEM of the area with 10 meters’ spatial resolution was used to define the bathymetry. Manning roughness coefficient was also calibrated for model tuning. The best results were obtained from the hydraulic simulation of the case study, when applying bank-full discharge equal to 3. 53 cms so that the error of this method was limited to 3%. Hence, it might be reasonable to accept the computational costs of a two-dimensional hydraulic simulation to predict the time of concentration instead of empirical formulas in the case of utilizing the results for constructing costly hydraulic structures. Conclusion: Different methods of time of concentration estimations were evaluated and compared with the observed time of concentration obtained by salt solution tracing in Aliabad watershed located in Fars province. Two-Dimensional simulation of the water parcel (according to the definition of Tc) from the basin divide to the outlet was also performed by HEC-RAS 5. 0. 7. The results indicated that among empirical relations, the concentration time value obtained from the Simas and Hawkins equation (Azizian, A, 2018) is much closer to the actual value and is considered as the best empirical equation for Aliabad watershed. This equation involves river length and slope, watershed area and surface storage. Following Simas and Hawkins, equations developed by SCS, SCSlag, (Alizadeh, A, 2009) Yen and Chow (Azizian, A 2018), and NRCS (USDA Natural Resource Conservation Service, 2010) gave closest estimations to the actual concentration time, respectively. However, the results of hydraulic simulation show the most accuracy depending on water parcel definition. That is because, the two-dimensional model takes the topography, local slope, roughness and geometry of the water body into account and is a reliable technique to estimate the time of concentration in any desired location. Nevertheless, for empirical relations it is necessary to realize the limitations of each method and compare it with the study area. Hence, it is recommended to apply hydraulic simulation instead of empirical formulas to estimate the time of concentration. Also, with the measurement data, the results of this study can be used as a criterion for measuring concentration time in similar hydrological studies.

Introduction: Turbidity current plays the main role in the transfer and deposition of sediments in the dam reservoir, especially near the dam body at the site of its crucial structures, including bottom outlets and catchments; this is since the difference in the specific gravity or, indeed, the effect of the gravity acceleration on the difference in specific mass forms a density current. If the density difference is due to suspended materials, these currents are called turbidity. This study mainly aims to find a significant relationship between density current’ s hydraulic parameters, such as velocity, concentration, and thickness, understand the advance rate and the distribution of sedimentary currents, investigate the obstacle-shape (extended and local) effect in controlling turbidity current and its sedimentation pattern in the channel, and obtain a suitable dimensionless pattern of velocity and concentration of density current due to changes in the current hydraulic parameters. Methodology: The experiments are performed in a flume of 8 m long, 35 cm wide, and 60 cm high at Shiraz University. The flume is characterized by the bed slope. Using a flowmeter, the input density current enters the channel, and a clean water source is used to balance the water table. The flume has a positive and negative sloping capability. A 500-liter reservoir is used to enter the density current. Density current consists of a head, body, and a series of dense fluid formed by sinking a heavy fluid in clean water, forehead, or head; it grows as it progresses. Further, due to the bed friction, its tongue or ness rises from the ground. The body is located behind, and its depth is less than half of the current forehead. The screened rock powder (100% sieve passage) with a specific gravity of 2. 65 tm-3 is used as suspended sediments. In all experiments, the clean water has a density of 998. 2 kg-3, a slope of 1% and 3%, a discharge of 50 and 90 lmin-1, and a concentration of 1005 and 1008 kg-3. The inlet valve of the flume is devised for a density current of 1 cm. Samples were taken from 8 sections, started from 2. 5 m of the inlet valve, and divided with 50 cm intervals from each other. Results and Discussion: As the inlet discharge increases and the bed slope decreases, the profiles become more stable. Also, when the discharge of the input turbidity current is minimal, the profiles become more curved. An altitude with zero turbidity current’ s velocity represents the total thickness of the current; at higher altitudes, the velocity becomes negative to maintain current continuity, i. e., fluid above the current is not static and moves slowly upwards. In all experiments, the changes in the coefficient n are almost great and vary from 3. 027 to 5. 33 in different experiments. Such great changes in this coefficient can be due to the effect of bed shear on velocity profiles; an increase in the bed slope of the channel from 1% to 2% reduces the thickness of the turbidity current along the channel, increasing the current velocity. There are many changes in the wall region, and an increase in the concentration of the input turbidity current increases the drift current and the turbidity current’ s velocity. Furthermore, constriction causes the average velocity of density current to increase by 2. 26 times and the concentration of accumulated current behind obstacles by 1. 45 times. Conclusion: An increase in the concentration of the input turbidity current increases the maximum velocity (in the velocity profiles). An increase in the maximum velocity of the turbidity current is more evident in currents with higher inlet discharge rather than others. Dimensional velocity profiles at the upper edge of the current show more dispersion due to the current temporary behavior in this region. The maximum velocity of the density current in the wall region is higher than in the jet region. For the dimensionless profile of velocity at the wall region, the best coefficient n is equal to 3. 86, showing a high correlation of 0. 878, and also for the jet region, the best coefficient α and β are equal to 0. 412 and 1. 343, respectively, with a correlation coefficient of 0. 92. According to the results, local and extensive constriction increases the average velocity of the density current by 2. 26 times and also the concentration of the current sediments behind the obstacles by 1. 45 times; the trap efficiency of sediments is equal to 29. 8%.

Introduction: Weirs or spillways are the oldest and the most important hydraulic structures. They have several applications such as evacuation of excess water flow due to floods, control of water level in the reservoir, flow diversion, reduction of river erosion and flow measurement. The side weir is one of the various types of weir which is used to control flow level, diversion and flood damage prevention in dams and hydraulic systems. Also, the side weirs are divided into linear and non-linear crests. Non-linear weirs come in a variety of forms, such as labyrinth weir and piano key weir. These structures are used to increase the length of the crest and their discharge capacity where there is length limitation for the weir construction. Due to the importance of the discharge coefficients in the side weirs with the piano key and the labyrinth crest shapes, in the present work a vast range of experiments were performed on those types of weirs with different height and geometries. The results of experiments are then used to compare the piano key side weir with the labyrinth one. Methodology: The experiments were carried out on a 10 m flume at the Bu-Ali Sina University, civil engineering department. A simple rectangular cross section was selected with almost 10 m length, 0. 60 m width and 0. 60 m height. The rectangular labyrinth and piano key weirs experimental models are made using 5 mm plexiglass material in 3 cycles, and 4 heights of 5 cm, 10 cm, 15 cm and 20 cm. The side weirs models had 57 cm length and were fixed in the wall opening near the flume end. Since in this research the flow condition is the spatial varied flow, the De Marchi relationship and dimensional analysis have been used to investigate the discharge coefficients in the piano key weirs and the rectangular labyrinth weirs. Results and Discussion: This study generally shows that, with increasing value of Ht/P, the weir discharge capacity will be increasing. For example, in rectangular labyrinth weir with 20 cm height the discharge coefficient is almost 34%, 7. 3% and 14. 1% larger than that for weir with height of 5 cm, 10 cm and 15 cm respectively. Also, a comparison between the 5, 10 and 15cm weirs, with the 20 cm height weir, revealed that the weir efficiency has increased by 35%, 7. 8% and 14. 5%, respectively. Meanwhile, in the rectangular labyrinth weir with heights of 5 cm, 10 cm, 15 cm and 20 cm by increasing Ht/P from 0. 95, 0. 66, 0. 46 and 0. 32, respectively, the weir efficiency decreases significantly and its performance will be closer to the linear weirs. Compared to the piano key weirs with 5 cm, 10 cm and 20 cm heights, in the weir with 15 cm height, the averaged discharge coefficient increased by 9. 3%, 5. 5% and 9. 2%, respectively. The results of experiments on the piano key weir show that by choosing 15 cm as the weir height, the average weir efficiency increases by 9. 5%, 3. 5% and 9. 4% respectively (in comparison with 5 cm, 10 cm and 20 cm weir). Furthermore, according to the experimental results on the piano key weir with 5 cm, 10 cm, 15 cm and 20 cm height, by increasing the Ht/P ratio from 0. 88, 0. 6, 0. 44 and 0. 35 values, the weir performance also will be closer to linear weirs and the weir efficiency is reduced considerably. In rectangular labyrinth weir and piano key weir, the interference of the flow shedding blades causes a weir at the end of the outlet keys, which is the beginning of a significant decrease in the weir efficiency; and as the interference of these shedding blades increases, the weirs flow gradually deviates from its original function and acts as a linear weir. Conclusion: For the weir with a specific value of Ht/P, the smallest weir has the highest discharge coefficient and the lowest discharge capacity. Previous studies on the labyrinth and piano key weirs indicate that when the weir axis is perpendicular to the flow direction, the efficiency of the piano key weir is much more than that for the rectangular labyrinth weir. However, for side weirs where the weir axis is parallel to the flow direction the rectangular labyrinth weir shows better efficiency and performance compared with the piano key weir. The Type A piano key side weir performs better than the Type C piano key side weir.

Introduction: Human population growth and industrialization have led to an increase in freshwater demand all around the world, specifically in coastal areas. The conventional resources of freshwater (e. g., rain, rivers, lakes, etc. ) do not meet this demand; hence finding new resources of freshwater besides preserving and the optimal use of the available freshwater resources is strictly considered recently. During the last decades, the desalination of seawater by removing salt from the roughly unlimited supply of seawater has emerged as a new source of freshwater in coastal zones. One of the major by-products of desalination plants is the effluent with a higher salt concentration than the feeding water, called brines. Disposal of the produced brine into coastal bodies has raised serious concerns due to its potential to cause negative impacts on the marine environment, especially on the benthic communities. The disposal of brines is typically done through a single inclined nozzle or multiport diffuser that laid on the seafloor far enough from the coastline. So far, many different studies have been performed on dense jets to find the optimal angle of the inclination. The generally accepted design practice recommends a 60° angle as the optimal angle. However, the terminal rise height associated with this angle is relatively high. Consequently, smaller angles are more appropriate for shallow coastal waters. This paper studies geometrical and mixing characteristics of 30° inclined dense jets in free and proximate to bed conditions through simulating two numerical series. In the first series, nozzles are placed well above the bed in terms of 𝑦 0 𝑑 ⁄ to act like free jets. In the second series, the distance of nozzles to the lower boundary has reduced to observe the possible effect of proximity to bed on dense jets behavior. Methodology: The governing equations of the present problem are continuity, conservation of momentum, and tracer advection-diffusion equations. These governing equations are solved using an open-source finite volume model named OpenFOAM. The buoyant Boussinesq Pimple Foam solver, which is a transient solver for buoyant, turbulent flow of incompressible fluids, is modified within the OpenFOAM to solve the governing equations of the present problem. Moreover, the realizable 𝑘 − 𝜀 model and the Boussinesq approximation are employed for turbulent closure and buoyancy effects, respectively. Results and Discussion: The major geometrical characteristics of dense jets, including the centerline trajectory, the location of centerline peak, the terminal rise height, etc., are presented. The centerline trajectories are in acceptable agreement with previous analytical and experimental studies. They are generally symmetrical; however, a slight asymmetry was observed in the boundary-affected cases. The other geometrical characteristics in all cases are in good agreement with previous data. The mixing and dilution characteristics were also studied through cross-sectional concentration profiles. It is observed that the present simulations predict the dilution at the return point significantly conservative. The buoyant instabilities on the inner edge of flow are also evident in the mean concentration profiles. Conclusions: Ocean outfalls are the most widely used method for brines disposal. Therefore, predicting the flow behavior along the near field region (a short distance from the nozzle tip) is vital. The review of the previous studies showed that the literature is rich in this field. Several experimental and theoretical studies have been reported to predict the brine flow through surface and submerged discharges into both stagnant and flowing waters. There are also commercial models developed for this purpose, which work based on simplifying assumptions for the governing equations. Recently, thanks to the advancements in computer performance, the use of numerical methods to solve physical problems has become possible for engineering purposes. The discharge of brines, as with many other engineering flows, are physically complicated and fully turbulent, so requiring robust and accurate modeling. In the present paper, a numerical study was reported for inclined dense jets at the angle of 30° . Two series of simulations were performed. In the first series, the nozzles were placed far from the bed. While in the second series, the nozzles were placed in a close distance to the bed. The aim was to analyze the possible effects of proximity to bed on dense jets behavior. The locations of the terminal rise height and impact point as well as the dilution at the return point were determined. The simulations predict trajectory data in free jets with reasonable accuracy, but dilution predictions are conservative in comparison to previous analytical and experimental studies. Comparisons between two numerical series showed discharging 30° inclined dense jets in a close distance to the bed in the cases that in this study were examined had no appreciable effects on neither the geometrical characteristics nor mixing and dilution characteristics.

Introduction: Water distribution systems (WDS) are the crucial component of urban infrastructure that play a critical role in delivering sufficient water to users with acceptable pressure, volume and quality. Occurrence of a pipe failure may interrupt service, undermine system performance and ultimately lead to consumer dissatisfaction. Nowadays, the threat of accidental or man-made disruptions motivates water utilities to plan risk mitigation works and to improve the preparedness for extreme events. Pipe breaks increase with aging infrastructure, natural disasters such as earthquakes and man-made disruptions. Three criteria; reliability, resiliency and vulnerability have been used to assess the performance of the water distribution system (Hashimoto et al., 1982). The resilience capacities are absorptive, adaptive and restorative that a system needs to be able to respond to perceived or real shocks (Francis and Bekera, 2014). Butler et al. (2017) defined the resilience in WDSs as “ the degree to which the system minimizes level of service failure magnitude over its design life when subject to exceptional conditions” . Failure modes in WDSs can be broadly categorized into structural failure and functional failure (Mugume et al., 2015). Response to pipe failure can indicate system resilience to loss of structural connectivity (Butler et al., 2014). Todini (2000) proposed a technique based upon the definition of resilience index that emulate both reducing the cost and preserving a capability of the system to overcome failures while still satisfying demand and pressure at each node. Diao et al. (2016) proposed the Global Resilience Analysis (GRA) as a methodology that focusses on the response to system failure modes. Using GRA, the whole range of performance strains resulting from any stress magnitude can be evaluated. In GRA, the model of pipe failure mode (stress on the system) is modified by changing the pipe status to close for three hours during peak consumption (Diao et al., 2016). In this paper, the numerical code of the GRA method for NET3 network is evaluated and the resilience of water distribution network is examined separately from the main transmission lines. Then, the pressure-based algorithm for the above method is assessed. Then, the resilience of the real water distribution network in Iran is examined. Based on the inquiry from the water and wastewater company, and considering the diameter of the network pipes, the failure time of the pipes in the consumption peak (12-18) is considered to be an average of 6 hours. Finally, the critical network pipes are identified and the resilience analysis of the network is examined if these pipes are protected. Methodology: In this paper, the GRA approach is adopted to evaluate the system resilience under different pipe failure modes (Diao et al., 2016). The possible failure modes were modelled with increasing the stress magnitude and estimating the corresponding strains (Johansson, 2007). Different combinations of pipe failure are considered as stress magnitude and ratio of unsupplied demand to total demand is defined as strain magnitude. Due to huge number of possible combinations (i. e. a system with N component and m simultaneous failures has ∑ n! /m! (n-m)! potential failure scenarios), it is not possible to model every conceivable scenario for each system failure magnitude (Sweetapple et al., 2018). For any given stress magnitude, an appropriate affordable number of failure scenarios must be determined. Where the total number of scenarios (TNS) is determined as follows (Diao et al., 2016). As a demand-driven model, EPANET2 determines the nodal pressures by considering the specified demand at nodal points (Rossman, 2000). To illustrate actual supplied water to customers in abnormal conditions, the available nodal demand is expressed as a function (Eq. 2) of nodal pressure head (Wagner et al., 1988). Results and Discussion: Figure 4 shows the calibration of code with results (Diao et al., 2016) for the Net3 distribution network. The results of the code above 95% correspond to the results (Diao et al. 2016). In Fig. 5 the resilience of Net3 for two approaches (i. e., whole network (WN), and network without CRP (NWCRP)) are compared. The GRA showed that Net3 encountered complete failure due to simultaneous failure of the four main CRPs. Whereas excluding these pipes caused the failure of 12 pipes lead to the same results. The maximum and average network supply shortage were 36% and 12% higher than the whole network model. The supply shortage for all combinations of CRP failures in the peak demand period (18-20 pm) is presented in Fig. 7. In Fig. 8 the resilience of real water distribution network for three approaches (i. e., network without CRP1 (NWCRP1), and network without CRP2 (NWCRP2)) are compared. If the resilience of the main transmission lines is examined separately from the total distribution network, the resilience of the network will increase in three modes of maximum, average, and minimum by 72, 23, and 14%, respectively. The results showed that if ten critical pipes were protected, network resilience would increase by an average of 20 percent (Fig. 9). Conclusion: Resilience analysis is critical to the presentation of emergency schemes in distribution networks before a crisis occurs. One of the network components that is considered in resilience analysis is the failure of part or all of the different pipe combinations. In this study, after testing the resilience analysis model in the NET3 study network, the model was implemented for a real water network in Iran. Accordingly, by reinforcement of the main lines, the efficiency of the real network will increase by a maximum of 72%. Because this network has the only major source, with a single failure of the pipes, it reaches 100% of the water supply. The resilience analysis of other network pipes also shows that if the network's ten critical pipes are protected, the network's resilience will increase by an average of 20%.

Introduction: Non-linear Piano Key Weirs (PKW) enjoy not only a higher discharge but also a relatively simple and economic structure compared to linear weirs. Other advantages of the PKWs include the fact that they increase the discharge per unit width over the weir up to 100 𝑚 3 𝑠 ⁄ , the discharge over this type of weir is at least four times that over ordinary (linear) weirs, it increases the capacity of the reservoirs, and it is cost effective with lower maintenance expenses. This type of weir is utilized mainly with the aim of increasing its capacity over the available spillways and also as controlling structures on newly constructed spillways. Despite the research studies conducted in this regard, the scour downstream of the trapezoidal Piano key weirs has not yet been investigated, and there has been no comprehensive information on the properties of the scour profile downstream of these weirs. Hence, given the several advantages of the Piano key weir and lack of a comprehensive research on the amount of scour downstream of this type of weir, the need for investigation on the scour downstream of this weir under different hydraulic conditions is obvious. Methodology: Experiments were conducted in a rectangular channel with a width of 75 cm, metal bed, glass walls and a height of 80 cm in the hydraulic laboratory of water and hydraulic structural engineering of Tarbiat Modares University, Tehran. Water flow was supplied from an underground storage tank using a pump with a maximum discharge of 85 Lit/sec. A valve installed at the end of the channel was used to adjust the flow depth in the channel. The PKW was set up and sealed at a distance of 1 m from the channel end. All experiments on the weir were conducted under free flow conditions. A layer of uniform sediments with an average diameter of 1. 64 mm, a geometric standard deviation of 1. 24, a height of 42. 5 cm, and a length of 2 m was placed downstream of the weir. The type-A trapezoidal piano key weir made of thermoplastic (common PLA Filament) with a thickness of 1. 2 cm was utilized in this study. Weirs with 6 keys (3 inlet keys and 3 outlet keys), a width of 75 cm (the same as the channel), and the crest length (B) and a height (P) of respectively 50 and 20 cm were used. The experiments were conducted with three values of discharge 0. 03, 0. 04 and 0. 05 𝑚 3 𝑠 ⁄ and five tailwater depths varied from 0. 08 to 0. 18 m. Results and discussion: It is observed during the experiment that with the impact of the outlet flow from the weir with a downstream bed, the scour began and the process of erosion and sedimentation continuously occurred with development of the scour hole. Observations indicated that during the erosion stage, after the impact of the water jet with the bed and upon its dispersion, the scour of the bed material begins immediately and considerably. The material washed away from the bed is mostly transported downstream along with the flow and is deposited there. Generation of the scour hole entails circulation of flow inside the scour hole. Also, a portion of circulating flow inside the hole is deviated upward. A large body of sediments washed from the bed is transported downstream with the flow leaving the hole and a part of it rotates with the circulating flow inside the hole. A part of these sediments along with the circulating flow is deposited inside the scour hole and the other part is transported downstream by the flow leaving the scour hole. After the scour hole is generated, the jet entering the hole is divided into two parts at the deepest point of the scour hole. Such division is observable from the movements of sediments inside the hole so that some of the sediments are separated and transported downstream, leaving the scour hole, and the remaining sediments move and reside in the same zone as the circulating flow due to the backflow towards the weir foot. A sedimentary ridge is created downstream of the hole as a result of the eroded sediments concentration which have left the scour hole. As the scour hole is deepened, the sedimentary ridge is also enlarged. This trend continues until the flow is able to carry the particles out of the scour hole. These variations mainly occurred at the initial 20% of the test duration. It is also observable that the scour hole downstream of the weir is not symmetrical with the longitudinal axis of the channel, which is due to the effect of inlet and outlet keys on the direction of the outlet flow over the weir. However, the overall scour pattern is nearly the same under different conditions. Variations in the maximum scour depth downstream of the weir are approximately 5. 8 to 8. 8 times the water depth over the weir. The location of the maximum scour depth is also a function of discharge and tailwater depth, which was measured at a distance of 15 to 27 cm from the weir foot. Conclusions: This study has investigated the dimensions of the scour hole as well as variations of bed topography downstream of a trapezoidal piano key wer. It was found that with a 112% increase in the tailwater depth under a constant discharge of 30 L/s, the maximum scour depth is reduced by 37%. Increasing the discharge results in an increase in the dimensions of the scour hole, in such a way that a 66. 6% increase in discharge with a constant tailwater depth has increased the scour hole by 18. 5%. With an increase of the tailwater depth, the development of the scour hole downstream of the piano key weir is reduced. The minimum scour hole development in downstream direction was measured in tests with a discharge of 30 L/s and tailwater depths of 15 and 17 cm. 112 and 89. 5% increase in the tailwater depth for discharge values of 30 and 40 L/s reduces the area of the scour hole by approximately 46 and 25% respectively.