مجله هیدرولیک
سال هجدهم شماره 4 (Winter 2024)

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.

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.

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%.

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.

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 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.