انجمن هیدرولیک ایراننشریه علمی هیدرولیک2345-423718420231222Optimal Estimation of Secondary Flow Coefficient in Compound Channels with Vegetated FloodplainsOptimal Estimation of Secondary Flow Coefficient in Compound Channels with Vegetated Floodplains11515465810.30482/jhyd.2022.344833.1608FAمرضیهمحسنیاستادیار گروه مهندسی عمران، دانشگاه صنعتی سیرجان، سیرجانامینهناصریمهندسی کامپیوتر، دانشگاه صنعتی سیرجانJournal Article20220607This study adopted the Shiono-Knight model (SKM) to estimate the lateral distribution of the depth-averaged velocity within rectangular and trapezoidal compound channels with emergent vegetation in floodplains. To implement the SKM, it was required to estimate the eddy viscosity coefficient, friction coefficient, and secondary flow coefficient. The present study estimated the friction coefficient using the Colebrook–White equation modified by Rameshwaran and Shiono for vegetated beds. An analysis of eddy viscosity models across compound channels indicated that the model was not sensitive to the eddy viscosity coefficient; thus, the eddy viscosity coefficient could be assumed constant across the channel. However, the negligence of the secondary flow in the model would lead to a significant error, and it was required to calibrate the secondary flow coefficient. Thus, this study used a genetic algorithm (GA) to develop equations for the secondary flow coefficient for different sections of the compound channel under two different approaches: (1) the approach of Abril and Knight (2004), who proposed constant values for the main channel and floodplains, and (2) the equations of Devi and Khatua (2017), which related the secondary flow coefficient to the relative depth and width ratio. It was found that the secondary flow coefficient was dependent on the relative depth and width ratio. As a result, the equation optimized based on the Devi-Khatua approach outperformed the Rameshwaran-Shiono technique in estimating the lateral distribution of the velocity, with a 10.2% lower error. <br />This paper employed SKM to estimate the depth-averaged velocity within three compound channels of rectangular and trapezoidal cross-sections with a vegetated floodplain at small and large scales. To solve the SKM, it was required to calculate the friction coefficient, eddy viscosity coefficient, and secondary flow coefficient. The friction coefficient was calculated using the modified Colebrook–White equation. Several eddy viscosity models were adopted to implement the SKM. It was found that the eddy viscosity coefficient had no significant effect on the performance of SKM. The present study focused on calibrating the secondary flow coefficient as it played a key role in the flow simulation of compound channels using SKM. Two approaches were adopted to calibrate the secondary flow coefficient: (1) the approach of Abril and Knight (2004) and (2) the approach of Devi and Khatua (2017). The latter defines the secondary flow coefficient as a function of the relative depth and width ratio. The optimal secondary flow coefficient was obtained using a GA and experimental data for different geometric and hydraulic conditions. A comparison of the predicted and observed velocities demonstrated that the Devi-Khatua calibration method improved the predictive accuracy of SKM by nearly 10.2%. The secondary flow coefficient was found to be dependent on the relative depth and width ratio. It was calculated to be positive in both the main channel and floodplain, suggesting clockwise secondary flows. The difference between the observed and predicted velocities was larger in the floodplain than in the main channel, which could have arisen from flow complexities around vegetation.This study adopted the Shiono-Knight model (SKM) to estimate the lateral distribution of the depth-averaged velocity within rectangular and trapezoidal compound channels with emergent vegetation in floodplains. To implement the SKM, it was required to estimate the eddy viscosity coefficient, friction coefficient, and secondary flow coefficient. The present study estimated the friction coefficient using the Colebrook–White equation modified by Rameshwaran and Shiono for vegetated beds. An analysis of eddy viscosity models across compound channels indicated that the model was not sensitive to the eddy viscosity coefficient; thus, the eddy viscosity coefficient could be assumed constant across the channel. However, the negligence of the secondary flow in the model would lead to a significant error, and it was required to calibrate the secondary flow coefficient. Thus, this study used a genetic algorithm (GA) to develop equations for the secondary flow coefficient for different sections of the compound channel under two different approaches: (1) the approach of Abril and Knight (2004), who proposed constant values for the main channel and floodplains, and (2) the equations of Devi and Khatua (2017), which related the secondary flow coefficient to the relative depth and width ratio. It was found that the secondary flow coefficient was dependent on the relative depth and width ratio. As a result, the equation optimized based on the Devi-Khatua approach outperformed the Rameshwaran-Shiono technique in estimating the lateral distribution of the velocity, with a 10.2% lower error.https://jhyd.iha.ir/article_154658_bedcdc1a66577509780be614e35fb4df.pdfانجمن هیدرولیک ایراننشریه علمی هیدرولیک2345-423718420231222Numerical Solution of the Discharge Coefficient of Trapezoidal Arced Labyrinth Weirs with Different Middle Cycles Using Flow 3D SoftwareNumerical Solution of the Discharge Coefficient of Trapezoidal Arced Labyrinth Weirs with Different Middle Cycles Using Flow 3D Software172517142710.30482/jhyd.2023.385080.1633FAجمالفیلیدانشجوی دکتری سازه های آبی - دانشگاه آزاد اسلامی واحد اهوازمحمدحیدرنژادعضو هیات علمی گروه سازه های آبی دانشگاه آزاد اسلامی واحد اهوازعلیرضامسجدیمدیر گروه سازه های آبی/دانشکده کشاورزی و منابع طبیعی، دانشگاه آزاد اسلامی، اهواز،ایرانمهدیاسدی لورعضو هیات علمی گروه هندسی آب واحد اهواز دانشگاه آزاد اسلامیJournal Article20230224In the present study, a three-dimensional hydraulic flow simulation was carried out on these weirs using Flow3D software and the modeling results were compared with the experimental results to study the discharge coefficient of trapezoidal arced labyrinth weirs. Moreover, these models were tested under laboratory conditions in a rectangular flume with a length of 12m, a width of 0.6m, and a height of 0.6m in clear water conditions. The results indicated that the numerical model data showed adequate conformity with the experimental model data. In general, the discharge coefficients in the results of the numerical model were 1.2 to 18.9% lower than the experimental model. The difference between the discharge coefficients in the numerical model and the experimental model increased with an increase in the arc radius. As a result, with the R/w1=5 and R/w1=15 radius ratios, the discharge coefficients of the numerical model were approximately 1.2% and 18.9% lower than the experimental model, respectively. <br />One of the pitfalls of the existing conventional linear weirs is their low discharge capacity due to the limited width of these weirs. The use of labyrinth weirs is considered an efficient and cost-effective solution for increasing the flow rate. These weirs provide a higher discharge capacity for the same hydraulic head than direct weirs due to the increase in the crest length in a given width. The flow running over the weirs within the peak flood hours has to flow within a short period of time. Therefore, it seems necessary to build a weir structure with a high discharge coefficient. Labyrinth weirs are used for this purpose because the amount of flow running through them is larger than linear weirs (Falvey 2003).<br />Labyrinth weirs are used as cost-effective technical solutions for controlling flow in different conditions such as in dam weirs. Labyrinth weirs may also be used to control discharge capacity, reduce channel water level slope, distribute water between irrigation channels, etc. (Neveen Sad and Fattouh Ehab 2017). The plans of labyrinth weirs are classified into three categories, namely the triangular, trapezoidal and rectangular plans. Most weirs are built with rectangular, trapezoidal, or isosceles plans to increase their performance and facilitate their construction (Crookston 2010). The discharge coefficient in these weirs is determined by various factors such as the weir water level, the walls angle, and the crest thickness and shape (Ghare et al. 2008). <br /><br />Dimensional analysis is among the basic methods for experimental research, which serves to determine the dimensionless ratios. In the first step of this method, the variables affecting the discharge of labyrinth weirs are identified and then the dimensionless parameters are determined based on Buckingham’s theory, . After determining the dimensionless parameters, their effect on the discharge of the weirs can be studied to obtain satisfactorily rational results.<br />The comparison of the experimental results with the results of the numerical model for the discharge coefficient of trapezoidal arced labyrinth weirs with different middle cycles and different arc ratios in Flow-3D software is presented in the following diagrams.<br />As seen in figures (5), (6) and (7), the discharge coefficient decreased with an increase in the hydraulic head. In other words, the results of the experimental model show higher discharge coefficient values than the numerical modeling results in Flow3D. In figures (5), (6) and (7), the trapezoidal labyrinth weir has a hydraulic head ratio of 0.1 to 0.7 in the adhesion and complete aeration phase and from 0.7 to 1 in the partial aeration and suffocation stage. Moreover, the arc radius ratio of 15 has the highest discharge coefficient values as compared to the 10 and 5 ratios. In other words, with an increase in the arc radius ratio, the hydraulic efficiency of the weir increases along with its hydraulic efficiency. As seen in figures 6 and 7, with an increase in the hydraulic head, the difference between the discharge coefficients in the numerical and experimental models decreased. Moreover, according to these diagrams, with an increase in the arc radius, the difference between the discharge coefficients in the numerical and experimental models increased, which could be attributed to an error in the numerical model in detecting the small variations in the arc radius. In other words, in the numerical model, the discharge coefficient did not differ significantly from the arc radius variations, whereas in the experimental model, the effect of the arc radius on the discharge coefficient was more significant. <br /><br />A comparison of labyrinth weir discharge coefficients resulting from the numerical and experimental models revealed that the discharge coefficients of the experimental values are higher than the numerical modeling results. Besides, the labyrinth weir properly completes the four hydraulic stages in the experimental and numerical conditions, reflecting the proper hydraulic performance of the weir. When the weir is in the full aeration state, the weir is in the maximum hydraulic efficiency state. It is worth stating that when the weir is in the partial aeration condition, its hydraulic efficiency starts to decline. Finally, if it reaches the suffocation stage, the weir loses its hydraulic efficiency, the energy is maximized, the entire length of the weir crest is fully submerged, and thus the weir functions as an obstacle in the flow path. The energy loss is maximized when the hydraulic head is maximized. As a result, the nappes collide in the weir outflow keys, resulting in a drastic energy loss. From the quantitative viewpoint, in the weir with a radius ratio of R/w1=5, the numerical and experimental results satisfactorily overlap, and for hd/p>0.2 in the two diagrams, they are fully in line. In the weir with the R/w1=10 radius ratio, the numerical model outflow discharge coefficient is 10.2 percent smaller than the experimental results on average. Besides, with the R/w1=15 radius ratio in the results of the numerical model, the discharge coefficients are approximately 18.9 percent lower than the experimental model. In general, with an increase in the weir arc radius, the difference between the flow coefficients in the numerical model and the experimental results increases.In the present study, a three-dimensional hydraulic flow simulation was carried out on Labyrinth weirs using Flow3D software and the modeling results were compared with the experimental results to Investigate the discharge coefficient of trapezoidal arced labyrinth weirs. Moreover, these models were tested under laboratory conditions in a rectangular flume with a length of 12m, a width of 0.6m, and a height of 0.6m in clear water conditions. The results indicated that the numerical solution data showed adequate conformity with the experimental model data. In general, the discharge coefficients in the results of the numerical solution were lower than the experimental model. The difference between the discharge coefficients in the numerical solution and the experimental model increased with an increase in the arc radius. As a result, with the R/w1=5 and R/w1=15 radius ratios, the discharge coefficients of the numerical solution were approximately 1.2% and 18.9% lower than the experimental model, respectively.https://jhyd.iha.ir/article_171427_f8109be1d26d7b8bf8e6ed34431c908f.pdfانجمن هیدرولیک ایراننشریه علمی هیدرولیک2345-423718420231222The inception point of flow aeration on a rough stepped spillwayThe inception point of flow aeration on a rough stepped spillway273317142810.30482/jhyd.2023.392329.1639FAعباسپارسائیدانشگاه شهید چمران اهواز0000-0001-7312-0634آرمانده مردهدانشگاه سیستان و بلوچستان، زاهدان، ایران0000-0003-0173-0139امیر حمزهحقی آبیدانشگاه لرستان0000-0001-9512-0360Journal Article20230409Stepped ogee spillways are one of the most widely used types of dams that are used in most dam construction projects, including small and large dams. The inception point of aeration on these spillways is an important place in determining the range of single-phase and two-phase flow, which characterize the areas at risk of cavitation. In this paper, the effect of roughness on the location of the inception point of flow aeration (IPFA) on the stepped Ogee spillways was investigated. For this purpose, the surface of the steps of a laboratory model was covered with gravel with specific granulation. The result indicated that by roughing the surface of steps, the displacement of IPFA moves towards the crest (upstream) and the length of non-aerated area on the stepped spillways is decreased by about 15 percent. The results declared that there is a direct exponentially relation between flow rate and displacement IPFA. At low flow rates, most of the flow turbulence is due to the roughness created by the geometry of the steps, hence the role of surface roughness is negligible, while with increasing flow rate, its role in increasing the flow turbulence increases, and its effect on displacement of IPFA becomes obvious. At a given flow, the length of the non-aerated is decreased with increasing roughness.<br />In this study, the effect of surface roughness of steps on the displacement of IFPA was investigated experimentally. To this end number of laboratory experiments were programmed. To investigate the objective of this study, a stepped ogee spillway in which its horizontal part of steps was covered by gravel with given grain size. The results declared that three factors including the flow rate, the roughness caused by steps dimension (ks), and the roughness of steps surface (ns) are effective in the displacement of IPFA. In this study, the change in the size of the steps and the longitudinal slope of the stepped chute on the displacement of IPFA has not been investigated because it has already been studied by other researchers. There is a direct exponential relationship between the discharge and the IPFA (length of the non-aerated area on the stepped ogee spillway). As the flow rate increases, the location of this point is transferred downstream exponentially. With the increase of flow, the role of roughness in IPFA displacement became clearer and the reason is the increase of its role in creating and increasing flow turbulence. On average, surface roughness can be about 15% effective in reducing the displacement of IPFA.Stepped spillways are used in hydraulic engineering projects such as small and large dams. The inception point of aeration on such hydraulic structures is essential in determining the zones of single and two-phase flow. In this study, the effect of the surface roughness of steps on the location of IFPA on a stepped spillway is investigated. This paper investigated the effect of the surface roughness of steps on the location of the inception point of flow aeration (IPFA). For this purpose, a laboratory model of Ogee-stepped spillway was designed based on the maximum energy dissipation guidelines and its steps were roughened with gravel (with a specific grain size). The experiments were conducted in a channel with a longitudinal slope of 0.001, length of 12m, width of 0.5m, and depth of 0.8m on a stepped spillway with a height of 0.6m that has 9 steps. The flow discharge ranged between 6 (l/s) and 16(l/s). It was found that aeration starts from about 12 times the critical depth and by doubling the critical depth, its distance from the crest increased up to 50 percent. Notably, roughing the step surface reduces the length of the non-aeration area by about 15%.https://jhyd.iha.ir/article_171428_5cf29901eb370f50d9fa06d616b05db9.pdfانجمن هیدرولیک ایراننشریه علمی هیدرولیک2345-423718420231222Design of Operation Strategy for Canal StructuresDesign of Operation Strategy for Canal Structures354817855010.30482/jhyd.2023.409407.1667FAکاظمشاهوردیدانشگاه بوعلی سینا0000-0001-8098-0931حسنملازینلیدانشگاه بوعلی سینا0000-0001-8098-0931صفرمعروفیدانشگاه بوعلی سینا0009-0009-1486-3636Journal Article20230804Simple operation strategies make the users capable of regulating standard gates, such as overshot and undershot gates. For complicated operation, a control algorithm must be used, almost always done by programming the control algorithm within a programming software and coupling it with a canal simulator. In this research, a new operation strategy was designed to regulate inline water structures in the Alborz canal in Mazandaran province (Iran). Simple operation strategies make the users capable of regulating standard gates, such as overshot and undershot gates. For complicated operation, a control algorithm must be used, almost always done by programming the control algorithm within a programming software and coupling it with a canal simulator. In this research, a new operation strategy was designed to regulate inline water structures in the Alborz canal in Mazandaran province (Iran). Simple operation strategies make the users capable of regulating standard gates, such as overshot and undershot gates. For complicated operation, a control algorithm must be used, almost always done by programming the control algorithm within a programming software and coupling it with a canal simulator. In this research, a new operation strategy was designed to regulate inline water structures in the Alborz canal in Mazandaran province (Iran). To this end, the classic proportional integral derivative controller was coded in the rules boundary condition, being called by HEC-RAS during the canal simulation. The HEC-RAS model of the canal was prepared designing a controller for each inline gate to regulate upstream water depth. Performance indicators and statistical indices were used for evaluation. The calibration results of the controller gains indicated that k_p is 5, 4.5, 3.5, and 5 for regulating gates 1-4, respectively. The k_i and k_d gains were also calibrated. The results showed that the designed model can simultaneously simulate the canal and regulate the gates successfully, obtaining maximum and average depth errors of 7.5% and about 1% which are quite acceptable. The adequacy was 1 in almost all cases, and the efficiency was more than 0.97 with equitable distribution.Simple operation strategies make the users capable of regulating standard gates, such as overshot and undershot gates. For complicated operation, a control algorithm must be used, almost always done by programming the control algorithm within a programming software and coupling it with a canal simulator. In this research, a new operation strategy was designed to regulate inline water structures in the Alborz canal in Mazandaran province (Iran). To this end, the simple and common classic proportional integral derivative controller was coded in the rule boundary condition, being called by HEC-RAS 5.0.7 during the canal simulation. The HEC-RAS model of the canal was prepared designing a controller for each inline gate to regulate upstream water depth. Performance indicators and statistical indices were used for evaluation. The tuning results of the controller gains indicated that the proportional gain of k_p is 5, 4.5, 3.5, and 5 for regulating gates 1-4, respectively. The k_i integral gain and k_d derivative gain were also tuned. The results showed that the designed model can simultaneously simulate the canal and regulate the gates successfully, obtaining a maximum and average depth errors of 7.5% and about 1% which are quite acceptable. The adequacy was 1 in almost all cases, and the efficiency was more than 0.97 with equitable distribution.https://jhyd.iha.ir/article_178550_9a135fe1b728bb0f5f999fc09923c12a.pdfانجمن هیدرولیک ایراننشریه علمی هیدرولیک2345-423718420231222An experimental examination of riprap effects on homogeneous embankment dams overtopping breachAn experimental examination of riprap effects on homogeneous embankment dams overtopping breach495918056810.30482/jhyd.2023.404272.1653FAمهدیابراهیمیدانشجوی دکتری مهندسی عمران (آب و سازههای هیدرولیکی)، دانشکده فنی و مهندسی، دانشگاه ارومیه0000-0002-6986-7388میرعلیمحمدیاستاد مهندسی عمران-هیدرولیک و مکانیک مهندسی رودخانه، دانشکده فنی و مهندسی دانشگاه ارومیه0000-0001-7194-9393سیدمحمدهادیمشکاتیعضو هیات علمی پژوهشکده هیدرولیک، موسسه تحقیقات آب0000-0002-2049-9676فرهادایمانشعارشرکت مدیریت منابع آب ایران0000-0003-0099-4474Journal Article20230626The overtopping phenomenon is the most common cause of embankment dams’ failure, and it includes a complicate process. In present research, a physical model of an earth dam covered by riprap was constructed, and its hydraulic outcomes were compared with a benchmark model by providing a three-scenario framework. The main results indicated that the breach process of physical models follows three stages including: initiation, development, and termination. Furthermore, the use of riprap has no significant effects on the peak flow discharge caused by the breach procedure. In the first scenario, without a filter layer, the breach process had the highest resemblance to the benchmark model. For the second scenario, by employing a composite system, the occurrence of 129% increase in the breach time and the longest duration of the end stage were recorded. For the third scenario, by employing a composite system at the downstream slope, 86% increase in breach time and no change in the terminal stage duration was observed. Besides, the mass of eroded material was calculated according to the achieved sedimentation pattern. In the second scenario, the maximum thickness of sediment was measured; it proved the transport influence of riprap at the downstream of laboratory channel. A relatively symmetrical sedimentation pattern was then observed. Moreover, more than 50% of riprap material was transported to the downstream. This paper comprises the simultaneous measurements of breach geometry, flow hydrograph, and ultimate sedimentation patterns may help researchers in this field of study, indeed. The overtopping phenomenon is the most common cause of embankment dams’ failure, and it includes a complicate process. In present research, a physical model of an earth dam covered by riprap was constructed, and its hydraulic outcomes were compared with a benchmark model by providing a three-scenario framework. The main results indicated that the breach process of physical models follows three stages including: initiation, development, and termination. Furthermore, the use of riprap has no significant effects on the peak flow discharge caused by the breach procedure. In the first scenario, without a filter layer, the breach process had the highest resemblance to the benchmark model. For the second scenario, by employing a composite system, the occurrence of 129% increase in the breach time and the longest duration of the end stage were recorded. For the third scenario, by employing a composite system at the downstream slope, 86% increase in breach time and no change in the terminal stage duration was observed. Besides, the mass of eroded material was calculated according to the achieved sedimentation pattern. In the second scenario, the maximum thickness of sediment was measured; it proved the transport influence of riprap at the downstream of laboratory channel. A relatively symmetrical sedimentation pattern was then observed. Moreover, more than 50% of riprap material was transported to the downstream. This paper comprises the simultaneous measurements of breach geometry, flow hydrograph, and ultimate sedimentation patterns may help researchers in this field of study, indeed.The overtopping phenomenon is the most common cause of embankment dams’ failure, and it includes a complicate process. In present research, a physical model of an earth dam covered by riprap was constructed, and its hydraulic outcomes were compared with a benchmark model by providing a three-scenario framework. The main results indicated that the breach process of physical models follows three stages including: initiation, development, and termination. Furthermore, the use of riprap has no significant effects on the peak flow discharge caused by the breach procedure. In the first scenario, without a filter layer, the breach process had the highest resemblance to the benchmark model. For the second scenario, by employing a composite system, the occurrence of 129% increase in the breach time and the longest duration of the end stage were recorded. For the third scenario, by employing a composite system at the downstream slope, 86% increase in breach time and no change in the terminal stage duration was observed. Besides, the mass of eroded material was calculated according to the achieved sedimentation pattern. In the second scenario, the maximum thickness of sediment was measured; it proved the transport influence of riprap at the downstream of laboratory channel. A relatively symmetrical sedimentation pattern was then observed. Moreover, more than 50% of riprap material was transported to the downstream. This paper comprises the simultaneous measurements of breach geometry, flow hydrograph, and ultimate sedimentation patterns may help researchers in this field of study, indeed.https://jhyd.iha.ir/article_180568_215febd26d24090f2071339251cb09df.pdfانجمن هیدرولیک ایراننشریه علمی هیدرولیک2345-423718420231222Effect of Slope on the Stability of Riverbanks with a Mobile Bed: An Experimental StudyEffect of Slope on the Stability of Riverbanks with a Mobile Bed: An Experimental Study616818241710.30482/jhyd.2023.409878.1675FAمحمدجامعگروه عمران، واحد شوشتر، دانشگاه آزاد اسلامی، شوشتر، ایران0009-0007-8026-1823محسنسلیمانی بابرصادمرکز تحقیقات علوم آب و محیط زیست، واحد شوشتر، دانشگاه آزاد اسلامی، شوشتر، ایران0000-0002-6676-0323محمدحسینپورمحمدیاستادیار گروه علوم آب، واحد شوشتر، دانشگاه آزاد اسلامی، شوشتر، ایران0000-0001-8828-8114حسینقربانی زاده خرازیاستادیار گروه علوم آب، واحد شوشتر، دانشگاه آزاد اسلامی، شوشتر، ایران0000-0002-6558-4508Journal Article20230910Introduction <br />In general, bank protection methods are divided into two groups: indirect protection methods and direct protection methods. Changes in river banks are used in direct protection methods. In what follows, national and international research on the protection and stability of river banks using direct and indirect methods is presented. Depending on the channel bed, bank slopes and water surface slope, the gravity and buoyancy forces can either cause resistance to or provocation of overturning. In previous studies, the effect of the moving bed has not been considered, and most attention has been paid to the sloped bank wall and riprap particles<br />Methodology <br />In this research, the effect of the riverbank wall slope and river hydraulics on the stability of the river wall in moving bed conditions has been investigated. For this purpose, the influencing parameters in the study should be extracted. After determining these parameters, effective relationships are determined using the techniques used in dimensional analysis. In order to carry out the experiments, a flume measuring 15 meters long, 90 cm wide and 60 cm high was built at the Sediment Research Center of Khuzestan Water and Power Organization, Ahvaz, Iran, with a closed system with the possibility of providing a flow rate of up to 80 liters per second. In addition, the flow rate was measured by an electromagnetic flow meter with an accuracy of ±0.02 liters/second at the entrance of the flume. In the first and last 3 meters of the flume, the floor and walls of the flume were stabilized with concrete mortar, and in the middle 8 meters, the floor and walls of the riverbank (wall with three different slopes) were filled with river sediments with a grain size of D50 = 0.2 and D90 = 0.3 mm.<br />Results and Discussion <br />In this research, a total of 21 experiments were conducted in the laboratory of the Sediment Research Center of Khuzestan Water and Power Organization on a river model with a moving bed in order to investigate the effect of the bank slope and flow rate on the stability of riverbanks with a moving bed. Most previous reports have focused on solid beds; however, in this research, a solid bed was not considered, and the bed conditions were the same, similar to the riverbank conditions. In this research, the scouring and bank destruction processes were very diverse, as in real rivers. The conditions were stable up to a certain limit (Frd=0.21 and U/U*=1), and no changes or destruction occurred with time (up to 10 hours). After this limit, the foot of the slope started to erode, and the riverside sediments slowly entered the erosion hole, where the sediments were washed downstream. Finally, after a while, the lateral slope started to overturn and collapse. At more than U/U*=1.70, the lateral slope completely disappeared and became level with the bed. According to the charts and graphs, the riverbank with a slope of 20 degrees is destroyed later than the other two slopes (25 and 30 degrees). As the Froude number increases above 0.2, all the bank slopes become unstable, although this instability occurs later for the bank with a lower slope than for the bank with a higher slope in terms of the time parameter. On the other hand, the results showed that with the increase in the Froude number of Frd particles, the failure time Tf decreases due to the distance from the motion threshold of bed and wall particles. As the flow speed increases, the instability increases, and bank destruction occurs in a shorter time.<br />Conclusion <br />The results showed that the riverbank with a slope of 20 degrees is destroyed later than the other two slopes (25 and 30 degrees). As the Froude number increases to 0.2, all riverbank slopes reach instability. However, this instability occurs later for the bank with a lower slope than for the bank with a higher slope in terms of the time parameter. Besides, with the increase in the Froude number of particles Frd and the flow depth, the collapse time Tf decreased due to going farther from the incipient motion of the bed and wall particles.The interaction of the river flow and riverbank wall particles leads to riverbank erosion and collapse in the long term. In the parts where riverbanks have fine-grained sediments and are subject to erosion and changes in water level, the possibility of bank collapse increases, and the creation of riprap or heavy protective structures might cause the riverbank to become more unstable. This research investigates the effect of changing the wall slope on the riverbank stability in mobile bed conditions. To this end, 21 experiments were conducted on three different slopes (20, 25 and 30 degrees) on river sediments at different stream depths. The results showed that the riverbank with a slope of 20 degrees is destroyed later than the other two slopes (25 and 30 degrees). As the Froude number increases to 0.2, all riverbank slopes reach instability. However, this instability occurs later for the bank with a lower slope than for the bank with a higher slope in terms of the time parameter. Besides, with the increase in the Froude number of particles Frd and the flow depth, the collapse time Tf decreased due to going farther from the incipient motion of the bed and wall particles. As the test are done under live bed condition the destruction is started faster than in clear water.https://jhyd.iha.ir/article_182417_379071b47172b96bcd75cf5f0cebece2.pdf