نشریه تحقیقات مهندسی سازه های آبیاری و زهکشی
سال بیستم شماره 74 (بهار 1398)

Flow over side weirs has been the subject of many studies. Most of these studies related to sharp crested side weirs with rectangular cross section and less attention has been given to the discharge coefficient over the broad-crested side weirs with trapezoidal cross section. In this research a comprehensive laboratory study including 187 tests has been conducted to investigate the discharge coefficient over the broad-crested trapezoidal side weir under subcritical flow regime. Since a complete analytical solution of the governing equation for a side weir is not possible due to nonlinearity and the many variables involved, in this research water surface profile along the side weir is computed by using the fourth order Runge–Kutta method. By analyzing experimental data and using dimensional analysis as well as statistical analysis, some relationships in order to estimate the discharge coefficient were proposed. It was founded that the discharge coefficient of flow depends on the Froude number, the ratio of initial depth to crest width and the side slope of the weir. The mean absolute percentage error of proposed relationship is about 4% and indicates that the numerical method is very accurate.

Side weirs are hydraulic structures installing on the side walls of the channels to divert excess water of main channel. Labyrinth weirs are broken in their plans; so, they have more effective length and in some conditions have more discharge coefficient than that of simple ones. In this research, the effects of piles with different arrangements on discharge coefficient of semi-circular labyrinth side weir have been studied. The experiments were carried out in a rectangular channel with subcritical flow with Froude number range equal to 0.1-0.37. Three diameters were considered for semi-circular labyrinth side weirs with constant height. The piles used in the study were cylindrical and the same height of the side weir. The number of piles varied from 1 to 3, and fourteen arrangements were considered for them. First of all, the effects of dimensionless parameters, obtained from the Buckingham method, on side weir discharge coefficient were studied and then a relationship, with acceptable accuracy, between these parameters was obtained to predict the discharge coefficient of semi-circular labyrinth side weir with piles.. The results,  compared with semi-circular labyrinth side weir without piles, showed that semi-circular labyrinth side weir with arrangements of piles have higher discharge coefficient. In fact, piles proved an improvement in the performance of semi-circular side weirs, so that within the range of the studied Froude number, the discharge coefficient faced an increase up to 15% and specific energy changes faced a decrease up to 34%. The most increase in discharge coefficient and the most decrease in specific energy changes occurd when three piles were installed at the downstream end of weirs.

In this study, the roughness at downstream of ogee spillway has been simulated numerically for different flows, and the effects of roughness on the transformation of flow regime, the water surface profiles, and the energy losses also have been investigated. Hence, after solution domain generation, meshing, and specification of boundary conditions, the numerical simulation has been run by using k-e standard turbulence model, and in order to validation of the numerical results of the investigated ogee spillway, the experimental model of ogee spillway proposed by Chatila and Tabara (2004) has been used. Also, the effects of three types of roughness at downstream of this spillway were evaluated. The results indicated that by increasing the heigh of roughness, the energy loss increases up to 80 percent. The roughness types of 3 and 4, imposed the regime transformation and caused 70 to 50 percent, in average, energy losses respectively. Also, we found that increase in flow discharge affected directly the water surface profiles.  Results showed that if the design of stilling basin was considered, the roughness with a height of 0.6Hd had the ability of flow regime transformation and was evaluated as the most successful design.

This research was aimed to evaluate the available equations provided for non-Darcy flow in rockfill porous media, when there is a free surface flow, and when vertical pressure distribution is non-hydrostatic. Most of previous investigation about non-Darcy flow performed in permeameter that simulate one dimensional flow in porous media. Because of severe energy loss and considerable difference between upstream and downstream water surface elevations in rockfill porous media, a non-hydrostatic pressure distribution was expected. To carry out the research, a series of laboratory experiments have been conducted on rockfill materials with three differet diameters (1.68, 2.27 and 4.84 cm) and in a medium of 100cm in length, where water temperature varied between 10 and 29 °C. Results indicated that difference between water depth and piezometric pressure increased as water surface and water discharge increased.  Based on statistical analysis of existing experimental data, the most suitable model for energy loss in free surface flow in rockfill materials was introduced. Moreover, it was found that the introduced model had the lowest sensitivity to the variation of the input parameters, and the porosity, apparent velocity, median rockfill diameter and kinematic viscosity, respectively, had highest influence on head-loss results.

Flow water passing through spillways of dams has a high level of kinetic energy, which can lead to extensive damage to downstream facilities and bring about severe erosion of river beds. Energy dissipation would usually be accomplished by creating structures such as still basins at downstream of weirs, flip buckets, or steps in weirs. Stepped spillways are one of the common structures for energy dissipation, as well as reduction of the dimensions of still basins. The effects of labyrinths on total energy dissipation at downstream of the stepped spillways with slopes of 1:1, 1:2 and 1:3 was investigated; the height of labyrinths was 0.5 and 0.75 of the height of steps (h), working interspaces were equal to two times of the height of steps, and three roughness heights on the step face were 0.002, 0.004 and 0.006 m. The results showed that in first case, 1:1 slope of the stepped spillway, a labyrinth with height of 0.5h, working interspaces of 2h and equal length of the steps caused an increase of 12.7 percent in dissipation of relative energy. The comparison of results showed that for slope of stepped weir of 1:2, installation of a labyrinth with a height of 0.75h, interspaces of 2h and equal length to the height of the steps, the relative energy dissipation increased by 8.4 percent. When stepped weirs with slopes equal to1:3 were used, results indicated that installation sill with a length h, a height of 0.5h instead of labyrinths on steps, caused an increase of 4.7 percent in relative energy dissipation. Result showed that increase surface roughness of studied weirs reduced the relative energy dissipation by 3.6 percent.

Inefficient operational methods, in distribution of water within irrigation canals, call for applying more efficient ways such as using automation systems. This study assesses capabilities of the automatic operational systems, including centralized Model Predictive Control (MPC) and decentralized Proportional-Integral (PI) controller in enhancing the fairly water delivery throughout the Roodasht main irrigation canal. Existing canal’s operational condition was compared with operational status employing PI and MPC control systems. Comparison was conducted using water level error-based performance indicators of MAE and IAE, and equity indicator. Two operational scenarios including normal and severe inflow fluctuation were assigned. According to results of first scenario, upstream PI system resulting to better indicators of MAE and IAE values rather than other systems. MPC controller leading to better performance in comparison with upstream and downstream PI configurations. Application of MPC system resulted to 12% improvement in equity indicator. In the second scenario with sever inflow fluctuations at the headgate, the maximum IAE and MAE indices for MPC controller were 3.53% and 1.45%, respectively, while these indicators for decentralized systems exceeded 100%, demonstrating the inability of the decentralized systems to control the flow rate in severe water shortage conditions. Finally, calculated equity indicator in second scenario, for current operation, upstream and downstream PI and MPC, were 39.23%, 18.71%, 15.95%, and 4.33%, respectively. Results reveal that the application of centralized MPC controller has significantly improved the equity indicator by 35%.

Stepped spillways and stilling basins are the most important energy dissipation structures. Even though most part of energy would be dissipated by these two structure, the remaining part of energy of flow may be capable to grave the bed scour and to create the scour hole downstream of them. Structures could be destroyed if this part of energy is high. In this study, the effects of stilling basin slopes on bed scour at downstream of stepped spillway were investigated experimentally. Experiments were conducted in the laboratory of hydraulic structures at University of Kerman with six different discharges and five various stilling basin slopes. The following parameters were measured: maximum scour depth (ds), flow velocity (in three point), water depth in upstream and downstream stepped spillway and stilling basin, the distance from where  the maximum scour depth happened to sill (Ls), and the geometry of scour hole. Results showed 47 percent increase and 52.2 percent decrease in average of maximum relative scour depth when stilling basin slopes were 0.02 and -0.02, respectively. Also, it was shown that the distance between the point where maximum scour depth had happened to the end of stilling basin increased when Froude number increased and decreased when stilling basin slope decreased.

The estimation of hydraulic resistance of the flow in open channels has always faced a serious challenge because of presence of secondary currents and vortex viscosity. Determination of contribution of flow pipes in the bed and the wall is faced with error, due to effects of the walls on the maximum velocity position. In this study, the contribution of the flow pipes in the bed and the wall was approximated by using conformal mapping method and by plotting harmonic lines of current and potentials. Then, the shear stresses obtained from the weight of tube pipes in the bed and the walls were calculated by eliminating the effect of the velocity gradient factors in the simplified results of solving the conjugation and momentum equations. The rate of interaction of velocity gradient on shear stress results of the conformal mapping was determined by comparing the results of conformal mapping method with that of experimental results of direct shear stress measurement. Investigations have shown that the effect of the velocity gradient decreases with increasing aspect ratio, so that with increasing aspect ratio from 1 to 20, the effect of the velocity gradient on the shear stress of the bed has been reduced from 7 to 1 percent, and in the wall from 15 to 3 percent. Finally, measured values of shear stress in the bed and the wall were introduced by presenting some equations.

Determining the friction coefficient in erodible beds plays an important role in the design of alluvial canals. In most of the previous studies, an impact of the hydraulic parameters on the friction coefficient has been studied for non-erodible bed conditions. In this research, by performing a laboratory model in the erodible substrates, the effects of the bed slope parameters and bed load transfer rate on the bed friction coefficient were investigated. The experiments were carried out in the discharge rate of 0.90 to 4.75 l/s and the slopes of 2, 3 and 5 percent on the uniform non cohesive particles with the grain diameter of 1.7 and 3.29 mm. The roughness Reynolds number was in the range of 82 to 343, Froude numbers of these currents in the range of 0.93 to 1.51, and non-dimensional bed load transport rate was calculated in the range of 0.004-0.311. The experimental results showed that between the slopes of 3% to 5%, the bed friction coefficient and the roughness Reynolds number of the erodible bed increased significantly, while in the slope range of 2% to 3%, no significant increase was observed. Analyzing experimental results showed that by increasing the bed transport rate, the frictional resistance of flow (fc) decreased and subsequently, the bed loading movement resistance (fm) increased. Applying dimensional analysis, the effective parameters on fm were determined and an empirical equation to determine fm was designed and results were validated by laboratory outputs obtained by former researchers. Validation results have been proved acceptable.

The situation of water management was investigated in eight wheat fields in agricultural lands of Marzabad, Mousian and Patak district, within irrigation networks of Dehloran Doyraj Reservoir dam. The downstream conditions in all borders were open ended and the volume of inflow water and outflow runoff hydrograph were measured. The application efficiency parameters in those fields compared with that in simulated values using WinSRFR software. The minimum and maximum runoff in the fields were 18.9% and 33.1%, respectively, compared with that  in simulation mode that were 12% and 42%. In 75% of the fields, no deep percolation losses has been noticed. The average of minimum and maximum of application efficiency recorded as 60.3% and 80.5%, respectively, and in simulation mode 56% and 88%, respectively. The average of application efficiency measured in eight fields was 69.7%. Increase in efficiency of irrigation water can be attributed to mismanagement of unwanted low irrigation practices by farmers.