پیام خسروی نیا

The measurement of velocity in rivers confluences and open-channels junction is important in terms of hydraulic and environmental aspects. In this research, the performance of data driven models including ANN, ANFIS and GEP in estimating horizontal component of flow velocity in the open-channels junction was investigated using Khosravinia (2012) laboratory data. In the mentioned study, effects of a 45o side slope in the main channel on hydraulic characteristics of flow were investigated and compared with those at a 90o side slope. In this regard, the velocity field was measured for side slop angles of 45o and 90o using an ADV. For estimating the horizontal component of the flow velocity in the junction region, the discharge ratio and the dimensionless coordinates of measured points in three dimensional space of flow field were used. The performance of the models and comparison of their results were evaluated by coefficient of determination (R2) and root mean square error (RMSE). In addition to statistical indicators, for objective accuracy checking and performance of data driven models, scatterplot, box-plot, and Taylor diagram were used. Comparison of the results of different models using the best pattern indicates that the GEP model with the highest determination coefficient (R2 = 0.967), the lowest root mean square error (RMSE = 0.142) and the lowest mean absolute error (MAE = 0.094) in validation step has shown better performance than other models in (U/U0) estimation for the side slop angle of 45o. Similarly, the mentioned values were achieved 0.956, 0.184 and 0.128 using the GEP model for the side slop angle of 90o. This is while the ANFIS and ANN models ranked second and third. According to the scatterplots of the GEP model, nearly all the points are concentrated around the one-to-one line, which indicates the high level of predictive capability of this model in (U/U0) estimation for the both side slop angles. Also, according to the box plots, the statistical distribution of the GEP model in the lower and upper quartiles and median 50 percentile had a better performance than the other models, for the both side slop angles. The under and over estimation conditions of the ANFIS and ANN models were evident in these ranges. Moreover, according to the Taylor diagrams, the GEP model was closer to the observations and its superiority to the other models was tangible, with the lowest RMSE and the highest correlation coefficient for the both side slop angles. According to the results, GEP model as a powerful model can be used to replace the direct methods of velocity measurement in the junction region. In other words, using the mathematical equations derived from the GEP model in the present study, the longitudinal velocity field in the open-channels junction for side slopes of 45° and 90° can be predicted accurately.

Drought is one of the natural events that has a great impact on the environment. The severity and duration of drought are two important characteristics for the detection of drought and are usually derived from the weather data such as precipitation. In this study, two-dimensional copulas were used to construct bivariate distribution of drought characteristics for Sanandaj and Saqez stations located in the western part of Iran. Two important characteristics of drought including; duration and severity were derived from the standardized precipitation index (SPI) time series. In order to use copulas functions, Spearman’s rho and Kendall’s tau correlation coefficients were first calculated to assess correlation between variables of severity and duration of drought for both of considered stations. The results showed that there is a significant correlation between severity and duration of drought. After determining the best fitted marginal distributions on drought characteristics, the fittness of five different copulas for developing the bivariate distribution of severity and duration of drought was examined and the dependency parameter of each copula was calculated using the inference function for the margins technique (IFM). The results showed that for both stations (i.e. Sanandaj & Saqez) Frank copula function, due to having the highest log-likelihood (-328.9137 & -339.3758) and NSE (0.9393 & 0.9174), and the lowest values of RMSE (0.0655 & 0.0763) and AIC (695.8280 & 680.7516), is the most appropriate function for constructing the bivariate distribution of duration and severity of drought. Finally, the conditional probability of drought, joint and conditional returns periods of drought were calculated. The obtained results can provide useful information for planning and management of water resources over the studied area.

One of the most important issues in river engineering science is the river training in the bend of the rivers. Training operations are carried out to prevent changing the curvature in the bend of the rivers, protecting the external bank against erosion, and also controlling sedimentation in vicinity of the internal bank of the rivers. The use of submerged vanes is one of the practical methods used to train the rivers, stabilize the bank of the rivers and protect it against erosion. Submerged vanes are guidance stream structures that are installed at the river bed with an angle to the main flow and designed to adjacent flow pattern improvement. In this study, after dimensional analyzing and determining the effective dimensionless parameters, submerged vanes are placed in three lengths and three different angles in a channel with a mild sinuosity curvature and their performance was compared with each other. The results showed that by increasing the length and distance between submerged vanes in a constant Froude number, the maximum scour depths, increases, so that the maximum scour depth was observed for first vane in the angle of 110 degree and length of 2.66 H0. The most suitable and destructive angles for the establishment of submerged vanes are equal to 140 degree and 110 degree, respectively.

In this study, long-term memory and dynamic behavior of daily flow time-series of Khorramabad River, which its basin is mountainous and has urban land use, is investigated by Hurst exponent. The Hurst exponent of runoff signal of Khorramabad River during 1991-2014 period was obtained as 0.8. This value shows long-term memory and nonlinear, dynamic signal of this river’s runoff. By applying neural network and wavelet transforms, the rainfall-runoff time-series of this river was simulated. In this respect, by taking the time-series of rainfall and rainfall-runoff as input to the artificial neural network and wavelet-neural network hybrid, four models including: 1) rainfall, neural network, 2) rainfall-runoff, neural network, 3) rainfall, wavelet-neural network and 4) rainfall-runoff, wavelet-neural network were developed. In the hybrid models of wavelet-neural network, time-series of rainfall and runoff were decomposed to high-frequency and low-frequency sub-signals. Results of evaluating the accuracy and efficiency of the four models showed that the wavelet–neural network model correctly simulated the runoff behavior with the best efficiency at 99% confidence level. Comparison of the results of wavelet–neural network model to the neural network model, using Morgan-Granger-Newbold, showed significant superiority of the first model. Also, results of evaluating signal error of the four implemented models, using two tests of Von-Neumann and Buishand test, showed that there is a significant substitution point in the signal error of the neural network model and signal of rainfall-runoff model. Therefore, existence of very different monthly and periodical fluctuations in 1991-1998 and 1999-2014 in the behavior of rainfall-runoff leads to reduction of efficiency and precision coefficient of neural network model. While, in the hybrid model of wavelet-neural network, allocation of relative weight to each sub-signal, has effectively reduced the short-term, average and long-term fluctuations in modeling error.

Open channel junctions are so important in water conveyance networks. As a result, the researchers have been focusing on study of flow characteristics in these parts of water systems. Numerical simulation allows us to achieve the answer for engineering problems without encountering the experimental difficulty and with minimum cost. The aim of this study was, developing a 1D analytical model for simulating open channel junctions base on continuity, energy and momentum equations and some simple assumptions and comparing the experimental results in order to validation of analytical results. In experiments, side slope of main channel was 45 and 90 degrees. The studied variables were the ratio of depth at the junction. Investigation of results showed that increase of Froude number and inlet discharge ratio would lead to increase of turbulence which would decrease precision of analytical model. Also the increase of side slope of main channel caused less turbulence and more precision of the analytical model. In analytical model maximum reported error was about 15% for angle of 90 degrees, with relatively high discharge and depth in main inlet channel and minimum reported error was about 5% for angle of 45 degrees, with relatively low discharge and depth in main outlet channel

The study of hydraulic condition around the rivers confluence and open-channel is important in various aspects, including erosion, sedimentation and environmental considerations. One of the most important characteristics in the confluences is dimensions of separation zone. This zone immediately develops in the lower corner of the junction, as flow entrance of the lateral channel into the main channel. In this research, side slope effects of the main channel on dimensions of flow separation zone was studied. Experiments were conducted with four discharge ratios, four downstream Froude numbers and four side slope angles of 45°, 60°, 75° and 90°. Results showed that the separation zone enlarges by decreasing of side slope angle of the main channel wall. The results showed that on average, and for side slopes angels of 45°, 60° and 75°, the length of separation zone was increased 55.3%, 30.3% and 15.5% respectively in comparison of the vertical wall. The mentioned values were achieved 33.8%, 22.7% and 10.8% respectively, for the width of separation zone. On the other hand, the dimensions of separation zone increased by decreasing of the downstream Froude number and increasing of the discharge ratio. Also, increasing of side slope angle was accompanied with increment of separation zone shape index. For side slope angles of 45°, 60°, 75° and 90°, values of this index were obtained 0.144, 0.147, 0.150 and 0.156, respectively. Moreover, a regression equation was developed using dimensionless parameters for prediction of separation zone dimensions; it was compared with the equations presented by other researchers, for side slope angle of 90o.

Channel-river confluences are an important issue in open channel studies. Variation in quantity and direction of velocity and discharge value causes the erosion of the bed and banks near the confluence. Adequate knowledge about the process of forming a scour hole can be helpful to determine the proper distance of protective structure from channel confluence and river bank. The dynamic of river confluence is as a function of the momentum ratio of reaching flows and the geometry of the channels confluence location. By considering this fact that these conditions do not exist in nature and usually the banks of rivers are included. The slope of the banks causes the changes in three dimensional flow patterns in the place of confluence in relation to septum with 90 degrees that can be the reason of changing the pattern of scouring.
The main objective of this study is to investigate the effect of side slope of the channel on the maximum depth of the erosion at the confluence with a main channel. First by using the dimensional analysis, dimensionless parameters are derived. Then, by building a physical model, the effect of various parameters, including side slope of the channel (Z), discharge ratio (Qr), downstream densimetric Froude number, and downstream Froude number, on the maximum depth of bed erosion (ds) in a perpendicular confluence is investigated. The experimental tests were conducted in a main flume (6 m length, 80 cm width and 50 cm depth), a tributary flume (5 m length, 24 cm width, and 50 cm depth). The bed slope of two channels is considered as horizontal. Changes are made to form the false floor and movable bed, and also the width of the main channel is decreased from 80 to 50 centimeters to enhance the ability of turning the main channel wall to a sloping shape. Main and tributary channels with wooden platform with 14 centimeter height and the width that equal to width of main and tributary channels are raised. The space between these three false floors is connected as experimental region and then is filled with sediment. The side slope of the main channel is considered as 45, 60 75 and 90 degree. For all experiments, the input discharge of the flume was regulated as 15 lit/s. By considering four wall side slopes, four of discharge ratios and four different flow depths, four Froude numbers and four densimetric Froude numbers are applied. To regulate the water surface at the end of main channel, we used stop logs with one centimeter height and by omitting each stop log, one Froude number is produced. The experiment was ended when the equilibrium condition for erosion and scouring hole is created. By considering this fact that the most equilibrium time will take in the slope of 45 degrees in comparison with the other slopes. The experiments with the slope of 45 degrees were done at the most and least of ratio discharge and finally, after six hours, 90 percent of scouring was produced. Therefore, for all the experiments, the experiment time is considered equal to six hours.
Immediately after the experiments are started, because of contacting the tributary and main channel flow, two rounding vortices are made. These vortices moved in contrary to each other. It is the main factor to start the scouring of bed materials in the place of confluence. Rounding vortices that are nearer to the place of confluence, act stronger because of the contraction of flow. The bed material in downstream confluence is shouted to the surface of water and moved to the downstream of the channel. When the discharge ratio is going to be increased, because of the increasing of momentum of tributary channel, the tributary flow enter the main channel with an increasing intensity and this make the vortices and down-flow stronger and causes bed scouring especially in the first stages of the experiment. Bed materials that are shooting to the surface of the flow, after becoming nearer to the water surface, they lose their energy and when they are falling, the secondary flow transported them to the downstream confluence and by settling these particles, we could see little by little sediment bar.
The results indicate that the depth of scour at confluence increases with increasing the side slope of the channel, discharge ratio, densimetric Froude number, and Froude number, whereas it decreases as flow depth increase. The best performance in decreasing scour (equal to 46% in comparison with side slope of 90 degrees) belongs to side slope of 45 degrees and the discharge ratio of 0.2. The derived relationship for predicting the maximum depth of scour at the confluence shows that scour depth is more related to Froude number and downstream densimetric Froude number than the other parameters (i.e. discharge ratio, side slope of the channel and relative depth). The best performance in decreasing the scour was belong to side slope of 45 degrees and the discharge ratio of 0.2 which was equal to 46 percent. Since the side slope of 75 degrees is close to slope with 90 degrees, it doesnt show the appropriate operation, especially in high discharges ratio and it has 9 percent decreasing of scouring. In the present study a dimensionless equation was presented which can be applied for prediction of scour depth at river confluences with the variable side slope.

Existence of scour holes and depositional bar is directly related to flow pattern in river confluence zone. In channel junction zone، the flow pattern is very complex as a function of different parameters. In the current research، the effects of a 45- degree side slope in main channel on velocity distribution، water surface profile and dimension of separation zone at a 90- degree junction were investigated and compared with those at a 90- degree side slope. For this purpose، the experimental components of 3 dimensional (D) flows were measured and on the basis of them numerical Fluent model was calibrated. The Turbulence model including RNG was applied for numerical simulation. The results indicated that for a 45-degree side slope the length and width of the separation zone in comparison with a 90- degree side slope were smaller in bed and larger in water surface. For a 45- degree side slope، due to very small width of the separation zone near the bed، a region with high acceleration in downstream of junction was not formed and the rate of shear stress was reduced in this region. Also، the results showed that the water depth variations at the beginning and end of main channel for 45 and 90- degree side slopes were 2. 1 and 3. 3 percent، respectively.

Fluctuation of water level leads to variation of soil moisture regime around canal and cause destruction of the canal side slopes. In this study, stability of side slope of the earthen canal with two different slopes in presence of water table level was studied by using numerical and physical models. Then cut off is considered as a method for controlling failure. The results showed that the seepage surface and piezometric pressure near the side slope are two important factors in stability of side slope of earthen canals. In order to control the destruction of the earthen canal with steeper slope the sheet pile should be installed below the level of the bottom of the canal, but for milder slope the penetration depth of cut off up to the level of the bottom of the canal is adequate. The results showed that the numerical model had good agreement with experimental results in simulation of total pressure, discharge and phreatic line as the average error in estimating the total flow and pressure in the numerical model in comparison with experimental model were, 5.66% and 2.08%, respectively.

Abutments are used to protect erodible river banks. This structure is subjected to scouring due to flow convergence at the nose of structure. Therefore، countermeasure methods should be employed in order to prevent financial damages and life hazards. One of these methods is to use a slot. The main application of a slot is to deviate and change the down flow at the upstream region of an abutment. Also it reduces the power of vortices around the abutment. In this research، parameters such as depth، hole dimensions and time development of scoring process were measured around a vertical abutment. Operation of the slot was then evaluated at different height، depth، width and distance from the abutment nose and compared with unprotected abutment. The results showed that the models for which the slot was installed near the wall under the bed with the depth equal to the width of the abutment had the best performance. The amount of scour reduction for different models was 11. 8 to 43 percent.

Scour a very complicated process, is one of the main factors in abutment destruction. Complication of stream pattern around abutments, and the variation of effective factors on scour,have lead to the develop of innumerous empirical equations, which have many restrictions due to the limited experimental conditions. Applicability of multilayer pereceptron(MLD)networks to prediction of the maximum scour depth was evaluated for abutments having vertical, winged and semi-circural walls. The ANN results were compared with the calculated values by an empirical equation suggested by Barbhuya and Dey (2004). Eight scenarios were defined using effective parameters and several networks with different important parameters to predict scour depth. Comparison of the results of different scenarios showed that the one, which used only two parameters and to predict scour depth around abutments was the most efficient indoing so. Results of sensitivity analysis indicated that the two parameters, and, had the most effect on the scour depth prediction around abutments. A comparison of the obtained results using the ANN model, and the empirical equation with the experimental data revealed that the ANN model presented more precise results than the empirical equation for scour depth prediction around abutments. Moreover, the ANN model is more applicable to the scour depth prediction around the obutments wilk vertical walls than the other 2 types of walls.

Abutments are constructed to protect and control river banks. Studies show that methods of preventing and reducing scour are based on the scour mechanism. One of these methods is to set a collar around the abutment. Collars protect the bed against downward flow and vortex system developed due to the separation of flow at the upstream edge of the abutment and reduces the amount of scour. In this research, scour is considered around three types of abutments with 6, 8, 10 centimeters length. Trapezoidal collars with miscellaneous dimensions and fixing on bed surface under the clear water scouring conditions were also investigated and compared with the case of collars were not in use. The results obtained showed that increasing the collar width, improve the impact of collar on scour depth reduction and its time delay. The percentage of scour reduction for different collar width fluctuate from 15 to to 100.

Cylindrical weir is one of the broad-crested weirs used extensively due to steady state flow pattern and free passing of suspended materials over it. In this study, flow conditions over five physical models of cylindrical weir were tested and the effects of parameters such as weir diameter, hydraulic head at the upstream side and negative pressure on the weir were investigated. The flow was also simulated using turbulence model by Fluent software and the results were compared with those from the physical model. There was a rise in coefficient of discharge when the total head of flow and negative pressure over the weir were increased. The average relative errors of Fluent software in simulation of upstream flow depth, depth of flow over the weir and coefficient of discharge were 0.914%, 1.39% and 4.172%, respectively. By considering the hydraulic properties of flow over the cylindrical weir, a good agreement between the results of Fluent software and physical model was confirmed.