Editorial
Volume 21, Issue 78 , May 2020
Original Article
Mina Habibpanah; Mahdi Esmaeili Varaki; Maryam Navabian; Ramin behbodi; Mozhgan Farzin; Maryam saffari
Abstract
Introduction One of the important parameters of water quality is the high level of dissolved oxygen (DO) content that is essential for the survival of all aquatic organisms and water quality improvement. Aeration refers to the physical process of oxygen absorption from the atmosphere and enhancement ...
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Introduction One of the important parameters of water quality is the high level of dissolved oxygen (DO) content that is essential for the survival of all aquatic organisms and water quality improvement. Aeration refers to the physical process of oxygen absorption from the atmosphere and enhancement of the dissolved oxygen of water. Some hydraulic structures enhance the oxygen transfer by creating a great deal of turbulence and entering air bubbles. Stepped spillways are efficient in terms of air bubble entrainment. Advantages of stepped spillways include strong turbulent mixing, a large residence time and a substantial air bubble entrainment. Moreover, based on the laboratory data, some researchers have studied the aeration performance of labyrinth weirs in order to develop regression models for the prediction of aeration efficiency. The experimental results showed that the labyrinth weirs aerated significantly better than the normal weirs, especially at the lower drop heights. One of the methods to increase the content of dissolved oxygen is installation of structures that help increasing turbulence and entering small bubbles of air into water body. A falling jet of weirs is a specific case of creating turbulence in the water and increasing DO. Methodology Experimental measurements were conducted in the hydraulics modeling laboratory of University of Guilan, Iran in a flume with rectangular cross section having a 1.5 width, 1 m depth and 15 m length the experimental models consisted of five steps made of PVC panels. In this study three different slopes of spillway (1:1, 1:2 and 1:3 V: H) and one step height (h=0.10 m) were examined. In order to clarify the influence of labyrinth geometries on dissolved oxygen efficiency, intermediate blocks with different configurations were set in a zigzag pattern on every two steps. The height of labyrinths (H) was chosen 0.05 and 0.075 m, and the installed spacing between the labyrinths (L) along the width of channel were 0.1 and 0.2 m. In this study, the flow characteristics over the stepped weirs with intermediate labyrinths were compared with the pooled stepped ones which made by sill with height and thickness of 0.032 and 0.025 m, respectively. In order to investigate the aeration efficiency of stepped-labyrinth weirs, and in particular, to determine the effects of hydraulic and geometrical parameters, 572 tests were Experimental measurements were conducted in the hydraulics modeling laboratory of University of Guilan, Iran, in a flume with rectangular cross section having 1.5m width, 1m depth and 15m length the experimental models consisted of five steps made of PVC panels. In this study, three different slopes of spillway (1:1, 1:2 and 1:3 V:H) and one step height (h=0.10 m) were examined. In order to clarify the influences of labyrinth geometries on dissolved oxygen efficiency, intermediate blocks with different configurations were set in a zigzag pattern on every two steps. Two heights of labyrinths (H) were 0.05 and 0.075 m, and the installed spacing between the labyrinths (L) along the width of channel were 0.1 and 0.2 m. In this study, the flow characteristics over the stepped weirs with intermediate labyrinths were compared with that of pooled stepped ones which made by sill with height and thickness of 0.032 and 0.025 m, respectively. In order to investigate the aeration efficiency of stepped-labyrinth weirs, and in particular, to determine the effects of hydraulic and geometrical parameters, 572 tests were carried out. Moreover, the variation of DO concentration in water flowing over the weirs can be affected by a proportion of the upstream DO deficit. Therefore, in order to make the comparison as fair as possible, four different upstream DO concentrations (Cu) 2, 3, 4 and 5 (mg/l) were chosen to illustrate the effects of Cu value on the dissolved oxygen efficiency. The upstream DO concentrations were based on a range between minimum DO concentrations (2 mg/l) and dissolved oxygen saturation concentration (8-10 mg/l). Results and Discussion Comparison of results of DO concentrations (Cu) on aeration efficiency of the flat and stepped-labyrinth weirs with 1:1 slope under two tailwater conditions (dp=h and dp=2h) indicated that the S1H4L4b1 configuration had the highest DO efficiency. Thus, for upstream oxygen transfer efficiency (Eu) of 1.28, the concentration of dissolved oxygen associated with the stepped-labyrinth weirs was almost 48% higher than that for flat stepped weirs. For flat stepped weirs, since the upstream concentration of DObecame larger (Cu = 2, 3 and 4 mg/l), there was a decreasing tendency of Eu to 0.56, 0.42 and 0.27, respectively. However, corresponding Eu values for stepped-labyrinth weirs were 0.65, 0.45 and 0.33. As a consequence, for a given geometry and hydraulic condition, decreasing the upstream dissolved oxygen concentration increased the average DO efficiency of stepped weirs. For Cu=2 (mg/l), the S1H3L3b1 was the most efficient configuration due to providing the strong turbulent mixing and substantial air bubble entrainment which the average value of Eu in flat stepped weirs with S1 configuration, corresponding to the upstream dissolved oxygen concentration of 3, 4 and 5 (mg/l), was 0.55, 0.35 and 0.25, respectively (Fig. 12). However, intermediate labyrinths on the steps led to increase the air entrainment and the average value of Eu increased to 0.66, 0.42 and 0.33. for slope of 1:2, the S2H3L3b2configuration had the best performance in this slope. Hence, for Cu=2 (mg/l), this configuration increased the E20 and Eu up to 47% and 71%, respectively, compared to the flat stepped weirs. By reduction of stepped weir slope to 1:3, Cd of tested labyrinth weirs with the average E20 =0.44 and Eu =1.25 increased by 50%. The DO efficiency in the S3H3L3b2, S3H4L4b2, S3H6L6b1 and S3H7L7b1 configurations, which labyrinths were installed at the same edge as the steps, had better performance, compared with that of other tested geometries. Conclusion The air bubbles transfer and dispersion into water are governed by overflowing the jet, hydraulic jump and interaction of flow jet with receiving pool. The stepped-labyrinth weirs were shown to have an overall aeration advantage over the flat stepped weirs, largely because of the high turbulence and the high air bubble entrainment.The aeration advantages of the labyrinth-stepped weir become greater at smaller weir slopes. Conclusions revealed that for the slopes of 1:1, 1:2, 1:3 and tailwater of h, a labyrinth stepped weir with labyrinth height of 0.75h and labyrinth interspace of h, had 48%, 71% and 15% higher aeration efficiency than that of flat stepped weirs. However, with doubling of the tailwater depth, the dissolved oxygen efficiency increased by 77%, 51% and 15%, compared with the similar flat stepped weirs.
Original Article
minasadat seyedjavad; seyed Taghi Omidnaeeni; mojtaba saneie
Abstract
Introduction The flow passing through a side weir, one of the varieties of water diversion structures, is a variable flow with decreasing flow rate. Labyrinth weir is the basis for piano key weirs. They are often constructed with vertical walls and are much more efficient than the linear weirs. Nevertheless, ...
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Introduction The flow passing through a side weir, one of the varieties of water diversion structures, is a variable flow with decreasing flow rate. Labyrinth weir is the basis for piano key weirs. They are often constructed with vertical walls and are much more efficient than the linear weirs. Nevertheless, the flow, especially the bottom flow, enters this type of weirs and passes through two vertical walls of the side crests. Then it becomes squeezed and therefore the upstream and downstream crests come up with inappropriate hydraulic behavior. Also, the most outstanding disadvantage of this type of weirs is the large foundation area needed to be constructed on the concrete dams. The piano key weirs are a modern type of the nonlinear weirs which have been developed by Hydro Coop Institute of France and the Hydraulic and Environmental laboratory of the Biskara University of Algeria. In general, these weirs comprise of 4 different types, the differences of which lie in the presence or the absence of slopes created for them. Type A is sloped both upstream and downstream, Type B is sloped upstream, Type C is sloped downstream and Type D lacks any slope. The present study conducted show the effective geometrical parameters on the hydraulic performance and discharge coefficient (CM) of the trapezoidal piano key side weirs (TPKSW). The type of flow and its variations in a side weir can be considered as the C_M of the side weir, using simplifications and assumptions suggested by De-Marchi in 1934 to obtain suitable equivalents for side weirs. Methodology All tests have been conducted in a closed-loop rectangular Plexiglas flume in Soil Conservation and Watershed Management Research Institute (SCWMRI), Tehran, Iran. The study canal was10m long, 0.6m wide and 0.6m high. All tests have been carried out on the 0.6m wide canal. To prevent flow turbulence upstream of the canal, tranquilizing racks were used at the upstream. A calibrated triangular weir was also applied to measure the flow at upstream. Also, a calibrated rectangular sharp-crested weir was used downstream. The water surface profiles were measured longitudinally. For this purpose, a digital depth profiler with 0.1 mm precision was used. The profiler accuracy was valid for almost stable water surface but it could be decreased in highly turbulent flows. An electromagnetic velocity meter with 0.001 m/s precision was used to determine velocity components to obtain parallel (𝑉𝑥) and perpendicular (𝑉𝑌)to the side weir. The profiler and the velocity meter could move on a rail in both X and Y directions. Flow rates at the main and the collection canal were measured by a calibrated 90° V-notched and a rectangular weir, respectively. Figure 6 shows a general view of the laboratory. In this research, 16 models of Type-A trapezoidal weirs have been studied in two cases of 1 and 2. The weirs had 3mm thickness made of Plexiglas. The tests were carried out preventing the effects of viscosity and surface tension over the weir and considering the height of more than 3 cm. Results and Discussion In this research, for investigating the effects of a number of inlet cycles, the weirs were tested at two different directions of the side weirs located in the main canal. The results showed that the weirs with 15cm and 20cm had the highest discharge coefficient CM in dimensionless ratios of 0.2> H/P> 0.4 and H/P>0.5 respectively. Having reviewed previous studies, it could be concluded that the trapezoidal piano key side weir was capable of releasing a flow 1.2 times more than that of the linear trapezoidal labyrinth weir with 12 degrees angle and 1.87 times more than the one with 6 degrees angle, and 1.5 times more than that of the triangular labyrinth weir. Conclusions The result of the present study has shown that trapezoidal piano key weir can perform well on the side of trapezoidal and triangular labyrinth weir. In the comparisons made in this study, in comparison with the discharge coefficient of the side weir overflow, the trapezoidal piano key with the lateral overflow of the 12-degree Congress and the 6-degree trapezoidal labyrinth is equal to 1.2 and 1.87, respectively, and 1.5 times the lateral overflow of the triangular labyrinth weir. Although, the trapezoidal piano key weir in both lateral and direct modes is 1.55 times higher than the rectangular overflow of the direct piano key of the discharge coefficient. The trapezoidal piano key side weir in the dimensionless ratio of 0.4> H / P> 0.2 has the highest discharge coefficient flow. Keywords:Discharge, Flow, Water Diversion Structure
Original Article
Reza Moghanloo; Mohammad Zounemat-Kermani; Gholam-Abbas Barani; Amin Mahdavi-Meymand
Abstract
Introduction ...
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Introduction Dam reservoir sedimentation is known as one of the main serious problems that mainly affects the efficiency of dam's operation. Sedimentation may also block the conduits and it can destroy turbines, sluices, and valves. So it is necessary to find a way to solve this problem. In this regard, hydrosuction considered as a proper alternative and a potentially efficient method to remove the superficial deposited sediments from reservoirs. Hydrosuction system consists of a large pipeline working with an inlet suction tube lying on deposited sediments in the reservoir. In hydrosuction systems, the deposited sediments are withdrawn, as a mixture of sediments and water, from the reservoir and directed to downstream. The major advantage of using hydrosuction method is its economic aspects since the system doesn’t need extra energy for operation. Environment friendly method, hydrosuction can be used all over the reservoir, where the output and the volume of sediment removal could be under control. Researchers have tried to evaluate and improve the efficiency of this system. In this study, the effects of different shapes and forms of the suction mouth (tube inlet) on the efficiency of hydrosuction system in sediment removal were investigated. To achieve this goal, several experiments were carried out using different shapes of the suction mouth including the plain-type (circular) and wedge-shaped in the middle of the suction mouth. Methodology In the current work, the hydrosuction effective parameters were considered as the follow: water density (ρ), dynamic viscosity (μ), gravity acceleration (g), hydrosuction pipe diameter (Dp), diameter of sediment particles (D50), hydrosuction pipe velocity (V), length of pipeline (Lp), sediment density (ρs), the distance between inlet pipe and surface of sediment layer (Hp), the height of water on the sediments (Hw), the deference of height between water level and hydrosuction output (H), the angle between the head of the suction inlet and pipe (α), the shape of suction inlet (β), coefficient of particle shape (λ), sediment discharge (Qs), scour hole depth (L), scour hole diameter (R), scour hole volume (Λ), and time (t). Extracted dimensionless parameters by using Buckingham theorem are as follow: f(Q/VDp2,ρs/ρ, ρVDp/μ,D50/Dp,Lp/Dp,H/Dp,Q/VDp2,Hp/Dp,Hw/Dp,α,V2/Dpg,Vt/Dp,β,λ,Qs/VDp2,Λ/Dp3)=0 (1) Considering V, t, ρ, ρs, D50, Dp, Lp, and H as constants throughout the experiments, just two dimensionless parameters, Hp/ Dp and (Λ/Dp3), were evaluated in this study. The experiments were conducted in the hydraulic and water engineering laboratory of Water Engineering Department of Shahid Bahonar University, Kerman. The height, width and length of physical model tank (as the reservoir) were 70, 100 and 100 centimeters, respectively, and the diameter and length of hydrosuction pipeline were 3 and 250 cm respectively. Sediments samples were classified as sand with D50 = 0.51 mm. Before starting each experiment, the bottom of the model filled with a layer, 15 cm, of sediments . In this study, the effect of the suction mouth formation, as well as the effect of distance between the inlet pipe and the surface of sediments on the performance of hydrosuction system, were evaluated. The suction mouth formation included the plain-type (circular) and wedge-shaped in the middle of the suction mouth. The wedge-shaped type was considered with four angles of the pipe opening relative to the tube stretch ( =15, 30, 45, and 60 degrees). The values for were considered in three levels of 2cm above the surface of the sediment, on the sediments surface, and 2cm under the surface of the sediment. Results and Discussion The results of the experiments showed that with increasing the ratio of Hp/Dp , (Dp is the pipe diameter), the volume of sediment removal (Λ) decreased. Also, at α = 15o and 30o, the ratio of (Λ/Dp3) decreased, comparing to the reference test (plain-type, = 90 ), while at = 60 , the value of (Λ/Dp3) increased. By assuming a constant value for the ratio of Hp/Dp, the results implied that the ratio of (Λ/Dp3) and the concentration of the sediment outflow enhanced if the amount of α increased. By assuming a constant ratio value of Hp/Dp, just at α = 60 the ratio of (Λ/Dp3)increased compared to the reference test. Results revealed that a better performance of the hydrosuction system would occur by using a wedge-shaped suction mouth, α = 60 , and locating the suction tube two cm under the sediment surface. Conclusion In this study the hydrosuction process with 4 different angles of the pipe opening relative to the tube stretch (15, 30, 45 and 60), and 3 distances of the pipe inlet from the sediment level (above, tangent, and under the sediment level) were tested. Considering a constant wedge-shaped angle (α), the results indicated that by increasing the distance of the pipe inlet (Hp/Dp) from the sediment level, the amount of the extracted sediment will be decreased (ᴧ /Dp3). These results are in line with the results of Forutan-Eghlidi et al (2019). In general only at α=60 the wedge-shaped pipe have greater efficiency compared to normal pipe shape. In all conducted experiments, the middle wedge-shaped pipe with α=60 and Hp/Dp=-0.66 had the greatest performance in dredging the sediments.
Original Article
hadi Bali; Seyed Hossein Mohajeri; Amir Samadi
Abstract
Introduction In recent years, the advancement of computer science helped to examine digital elevation models (DEMs) that are produced in various methods. It is possible to study DEM at different scales. These scales are: 1-fine grain scale, 2-meso scale 3-reach scale, and 4-catchment scale. Determining ...
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Introduction In recent years, the advancement of computer science helped to examine digital elevation models (DEMs) that are produced in various methods. It is possible to study DEM at different scales. These scales are: 1-fine grain scale, 2-meso scale 3-reach scale, and 4-catchment scale. Determining and studying the digital elevation model of the bed in each of these scales is important. Today, the advances achieved in computer science and its combination with engineering sciences, including river engineering, have led to new approaches in this field. One of the most widely used devices is the Kinect. The use of the Kinect for scientific purposes was first introduced in 2013 by David Monkoff as a cheap, high-precision instrument to produce three-dimensional models that could be used in a wide range of scientific studies such as geology, geomorphology and bathymetry (Mankoff & Russo, 2012). In this study, the ability of Kinect device to determine the DEM of sand bed in the Kordan River, as a method for determining the roughness of natural riverbed, has been investigated by comparing the average and relative error of DEMs prepared by Kinect and theoretical models. Methodology In this study, the Microsoft Kinect Xbox 360 was used to produce a digital elevation model. This device costs about $100, with a frequency range of 9 to 30 Hz, the accuracy of spatial and elevation data in about a millimeter to a centimeter, and its best performance range between 50 centimeters to 5 meters. This device is capable of producing 3D information with high spatial (x, y) (2 to 20 mm) and high vertical accuracy (z) (error about 1 mm at 50 cm and error about 75 mm at 5 meters). The sensor angle of view is 57 and 43 degrees horizontal and vertical, respectively (Mankoff & Russo, 2012).The Kinect sensor is capable to capture simultaneously the color and depth images at a frame rate of more than 30 fps (30 frames per second). The incorporation of the depth and color data generates a cloud of color dots, about 300,000 dots per frame, which can consistently increase the density of dots or produce a full cloud of dots by sequential depth images. The minimum distance for Kinect is about 0.4 meters and the maximum varies between 4 to 5 meters (Khoshelham & Elbernik, 2012; Pagliari & Pinto, 2015). In this study, the kinect position was considered at 80 to 120 cm above the bed, so that all the boundaries of the bed were placed at the viewing angle of the kinect camera, achieving the lowest error rate. In order to investigate the ability of the Kinect device to determine the digital elevation model of the sandy river bed, two laboratory and field sections were defined. Two purposes of this segmentation were to compare the capability of a Kinect device in a laboratory-controlled environment with natural conditions, and to determine optimum conditions for the lab environment to be applied to the field. The results showed that the absolute error value and standard deviation related to detached cement hemispheres had been less than the figure for hemispheres joint together, however relative error was noticeably more. The results also showed that the error of the Kinect decreased with increasing size of the bed roughness elements. After having beds with regular geometric shapes been validated, the results of artificial sand beds consisting of natural aggregates with dense and non-dense arrangement were investigated. It has been observed that the error rate in the natural beds increased on average and the standard deviation of the results was twice as much as of the DEM with regular shape. It was obviously clear from the graphs that the digital elevation model developed by the Kinect device produced lower accuracy in lowlands than in upper elevations of the beds. Results and Discussion Having digital elevation models of artificial and natural beds been developed, the results were analyzed. At the beginning of laboratory investigations, the digital elevation model was examined on a regular basis. After beds with regular geometric shapes had been validated, the results of artificial sand beds consisting of natural aggregates with dense and non-dense arrangement were investigated. Conclusions To investigate the Kinect capability in determining the digital elevation model of sandy beds, its capability in artificial bed -consisting of small and large regular hemispheres and dense and non-dense sandstone aggregates- was first analyzed and the following results were obtained: 1. The results indicated that this device was capable to generate digital elevation models for determination of bed roughness using statistical analysis in laboratory environment. 2. Both infrared beams in outdoor spaces in sunlight and shadow in the open spaces among aggregates simply increased the error of the digital elevation model generated by the Kinect device in field studies. 3. Studies showed that the Kinect device could be a reliable replacement for outdated methods such as laser measurements and point gauges for digital elevation modeling of sand beds in laboratory.
Original Article
Saeedeh Malekzadeh; Ali Arman; Arash Azari
Abstract
Introduction Using hydrological information and physical and hydraulic characteristics of the river route for flood routing in different cross sections of the river, impact of forecasting on the occurrence and flow peak flow and successful implementation of flood alarm systems and forecasting flood volume ...
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Introduction Using hydrological information and physical and hydraulic characteristics of the river route for flood routing in different cross sections of the river, impact of forecasting on the occurrence and flow peak flow and successful implementation of flood alarm systems and forecasting flood volume downstream of the river. Given the importance of predicting flood hydrographs, especially in floodplain rivers, and the lack of sufficient information and statistics at some river basins, this may result in hydraulic methods in such rivers. This study aimed to compare the results of flood routing using the numerical model MIKE11 and the support vector machine method. This comparison was based on three parts: peak discharge, flood volume and baseline hydrograph time. Methodology In this study, based on physical and hydraulic information of the route, hydraulic routing of flood hydrographs between two hydrometric stations of Holeilan and Sazebon was conducted in a distance of 67 km from Semareh River in Ilam province, Iran. For this purpose, 365 cross-sections with an approximate distance of 200 m were considered for flow routing. The geometrical data of these sections and their physical characteristics in terms of their distance (in kilometers) were entered in the MIKE11 upstream interval. River bed gradiation curves were used to estimate the roughness coefficient in each section. These coefficients were optimized during model calibration and validation. In addition to the main river, discharge included two major sub-branches located along the river. The flow rate of these branches was defined as sub-flow of internal boundaries in the model. For upstream boundary conditions, hourly hydrograph data of Holeilan station and for downstream boundary conditions, flood hydrograph data and discharge values of rating-curve station at the last river crossing were entered. The SVM model was then used to predict the flood hydrograph at the output of the interval based on the input flood hydrograph data. Based on the delay time of flood passage between Holeilan and Sazebon stations, flood hydrograph data at Holeilan station located upstream of 0, 2, 4, 6, 8, 10, 12 and 14 hours delays as input layers and hydrograph discharge values at the location of the Sazebon station was considered as the output layer and the model was calibrated and validated using recorded hydrographs. Finally, the results of these two models were compared. Flood hydrographs were also upstream with different return periods and flood hydrographs were predicted at interval outflows with different return periods. Results and Discussion Based on the results of both calibration and validation, it was found that the support vector machine method predicted the peak discharge relatively better than that of the MIKE11 method, but with considering statistical indices, such as RMSE which calculated all hydrograph discharges, the results of the flood hydrograph prediction in MIKE11 model had relative advantages over the support vector machine model. This model also simulated the volume of floods more accurate. However, in order to compare the behavioral pattern of predicted flood hydrographs with different return periods, especially floods with the peak discharge more than the peak discharge hydrographs used in the calibration and validation phase, flood hydrograph values with period various returns as inputs to the study area were entered into each model at Holeilan station and flood hydrographs were predicted at the output of the interval and at the corresponding station location with the corresponding return period. Because the classification of data in the training phase is adjusted to discharges less than 25 years, the SVM model was able to predict only hydrographs with 2, 5 and 10 year return periods. But after the calibration and validation, the Mike11 model was able to predict the hydrograph well with the return periods of 2, 5, 10, 25, 50 and 100 years. Conclusions The results showed that the SVM model was somewhat better than the Mike11 model if the only criterion was to predict peak flow within the range of historical discharges. But this model was not accurate for predicting partial events with a return period of more than ten years. Given the statistical indices of RMSE, NRMSE, and NASH, which use all hydrograph discharges to evaluate results rather than using peak discharge, the Mike11 model provided better results than the SVM model. The Mike11 model performed better than the SVM model in predicting partial event hydrographs with different return periods. Acknowledgment The authors of the article extend their thanks reviewers for reviewing and improving the structure of the article, and also to the National Surveying Agency for providing the maps of the Seymareh River.
Original Article
Maryam Karimi; kourosh qaderi; Majid Rahimpour; Mohamad Mehdi Ahmadi
Abstract
Introduction Local scour around piers and bridge abutments is one of the reasons for instability and destruction of the bridges. Local scour of a bridge foundation is almost inevitable as far as rivers are concerned. There are generally three types of scours that affect the performance and safety ...
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Introduction Local scour around piers and bridge abutments is one of the reasons for instability and destruction of the bridges. Local scour of a bridge foundation is almost inevitable as far as rivers are concerned. There are generally three types of scours that affect the performance and safety of bridges: local scour, contraction scour, and degradational scour. During the last decades, different arrangements were proposed to protect bridges against local scour. The arrangements for local scour at bridge piers can be grouped in two categories: armoring devices and flow-altering devices. Flow altering devices that have been used to protect piers against local scour include protecting piles placed upstream of the pier, Iowa vanes, and flow deflectors attached to the pier, such as collars. This study addresses the effectiveness of collars on scouring reduction around abutments and pier bridges. Despite the availability of various studies about the effects of collar on scour at bridge pier and abutment (such as Laursen & Toch., 1956; Mashahir & Zarrati., 2002; Kayaturk, 2005 and Khozeymehnezhad et al., 2014), and due to importance of bridges structures, further laboratory investigations are needed to explain the different aspects of collars interactions with abutment and piers scouring phenomena. So the purpose of this study was to study the effects of different sizes of collars on a rectangular abutment and their location to the surface of the sedimentary abutment on bridge group piers scour reduction at the presence of debris. Methodology The experimental tests of this research were carried out at the Hydraulic and Water Structures laboratory of department of water engineering, Shahid Bahonar University of Kerman, on a laboratory flume with 8 m (length), 80 cm (width) and 60 cm (height), having glass walls and metal bottom. All experiments conducted in uniform flow with clear water, rectangular abutment and debris, rectangular collar and cylindrical piers, with non-cohesive particles of sediment with d50=0.91 and Q=51 L/s. The piers model used in the experimental test were steel cylindrical tubes with an effective diameter of three cm and a rectangular abutment in the form of (12×6 cm) made from galvanized sheet; debris model was rectangular shape, 19×7 cm dimensions. The arranangment of piers positions of were in the (2×2) piers group and debris was located on the front piers with a relative depth of 0.3.The dimensions of collars were considered to be 1.5-3 times the length of the abutment, and the experiments were designed in five different submergence ratios for each collar.Experiments on scour were in straight channel. Initially the bed surface was leveled, then inlet valve was opened slowly until discharge of water came to predetermined value so that no scour occurs at the mobile reaches of flume.The effects of four different size of collar in five different submerged ratios on protection of local scour around abutment and piers group with rectangular debris were investigated. Results and Discussion The results of the experiments were presented in two groups: without collars and in the presence of collars. To investigate the process of scoure in presence protective measure, at fierst it needed a series of experiments without any collar on the front piers and bridge abutment. The results indicated that collars caused decrease in the scour hole in all ranges of the present experiment and different submerged ratios.With increasing in dimensions of collar, in all submerged ratios of collar location, corresponding protective capacity of the collars improved leading to reducing the scour depth. Comparison of results indicated that the collar with dimension of 1.5 times the length of the abutment, had the lowest percentage reduction and the collar with dimension of 3 times the length of the abutment had the most percentage of scour reduction, 15% and 75% respectively.Also comparison of the effects of installation height of collars showed that collar reduced the local scour depth around the bridge piers and abutments. Results also indicated that collars installed under the riverbed had more influence on scour reduction than that installed upper riverbed, and collar exactly installed on riverbed had higher effect on scour reduction (nearly 75%). Conclusions In this research, scour around cylindrical piers and rectangular abutment and the effects of the collar dimension and different installation height on the scour protective effects were investigated by laboratory tests. Experimental investigations regarding local scour using collars on cylindrical piers and abutment in presence of debris were carried out. The protective efficiency of collars with different parameters, including collar installation height and collar dimension (size), were investigated and discussed.
Original Article
Ferdous Mirsalari; Mahmood Shafai-Bejestan
Abstract
Introduction In reservoir dams, high kinetic energy at downstream of their spillways can cause destruction of the spillway and its surrounding areas which results significant loss of life and financial loss, so it is necessary to investigate the performance of energy dissipation structures during its ...
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Introduction In reservoir dams, high kinetic energy at downstream of their spillways can cause destruction of the spillway and its surrounding areas which results significant loss of life and financial loss, so it is necessary to investigate the performance of energy dissipation structures during its operation. In this regard, the effects of the number of deflectors located just donsream of its chute on energy dissipation and its projectile length were investigated experimentally. Deflectors separate the incoming jet to few smaller jets, which pass through the slut between the deflectors or overflow above the deflectors. Therefore, more air mix with the jet flow and the separated jets hit each other, the results of which are increase in the amount of energy dissipation. On the other hand, the existence of deflectors reduces projectile length, makes smaller submerged ponds easier to maintain, and reduces costs. Methodology At the beginning of flume, a ski jump structure, with a height of 100 cm, a length of 90 cm and a radius of 14 cm was made by the galvanized sheet. Adjustment of the alignment and location of the hydraulic jump occurred by a slide gate located at the downstream of the flume. At each stage, the number of deflectors was deployed at the starting point of the jumper launcher such that the bottom side of the deflector was aligned to the horizon and the distance of the first deflector from the wall of the flume was halfway between the deflectors. Experiments were performed at four different ratios of critical depth to the total head (= 0.02, 0.035, 0.03 and 0.049) and three different tailwater depths. In these conditions, the deflector-free jumper launcher was tested using two, three and four deflectors. Relative energy dissipation was calculated by measuring the total energy in the upstream reservoir and downstream of the jetty overflow immediately after the ski jump, and projectile length was determined using projectile shooting and Get Data Graph Digitizer softwar. Results and Discussion Data analysis showed that for both cases, with deflector and without deflector, the relative energy dissipation rate decreased with increasing ratio of (Yc)/H , critical depth to the head, in each of the three adjoining depths. Because with increasing (Yc)/H as the discharge increases, the jet flows more rapidly mix with the air, which is less effective in resisting the jet launcher, mixing air and water. At a constant number of deflectors and at a constant (Yc) /H, the relative energy dissipation rate in the free hydraulic jump is greater than that int semi submerged jump and in the semi submerged jump more than that in full submerged jump, because by decreasing the projectile path, the air contact surface as a resisting agent of motion decreases. Also, at each of the three tailwater water depths, the relative energy dissipation rate increases as the number of deflectors at (Yc)/H increases. This is due to the mixing of jets with each other and the ambient air around the projectiles. In examining the effects of deflectors on the projectile length, the results showed that in both cases, without deflector and with deflector, the projectile length increased with (Yc)/H because with increasing (Yc)/H the flow rate increased, The greater depth of flow on steep slope, the greater slab thickness, the lower slab impact on slip velocity profile, and shear stress as a fluid impedance factor, and hence the more jet flows into the air and larger projectile lengths. At a constant (Yc)/H, the projectile length in the free jump was greater than that of the semi submerged hydraulic jump, and in the semi submerged jump was greater than that in full submerged jump because of increased depth of passage due to submerged hydraulic jump and failure to max. The possible path for the jet outlet from the jumper launcher was to shorten the projectile length. At each of the three steady depths at constant (Yc)/H, as the number of deflectors increased, the projectile length decreased because the path-based deflectors acted as bumpers and decreased the jet launch length and elongation. Conclusions The highest relative energy dissipation in four deflectors at (Yc)/H was 0.027 in free hydraulic jump, 65.87%, and the lowest in two deflectors at (Yc)/H of 0.049 in submerged full hydraulic jump of 6 52 /% and maximum projectile length in two deflectors, (Yc)/H = 0.049 was obtained to be 66.84 cm in free hydraulic jump for the caes of complete submerged was equal to 25.62cm. Based on triangular cross section deflector launcher performance in increasing energy dissipation and decreasing projectile length and saving running and maintenance costs, it is recomended, in terms of hydraulic and economical issues, to use deflector on the ski-jump with structural component.
Original Article
Ali Mokhtaran; Abdolali Gilani; Ali Akbar Ebadi; Mohammad Ali Shayan; khadijeh Sanei Dehkordi
Abstract
Introduction In Khuzestan province, waste water release from various sources, especially from agricultural farms, is a serious problem. The volume of drainage water resulting from irrigation and drainage networks of the Karun river basin is about two billion cubic meters per year, considering sugarcane ...
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Introduction In Khuzestan province, waste water release from various sources, especially from agricultural farms, is a serious problem. The volume of drainage water resulting from irrigation and drainage networks of the Karun river basin is about two billion cubic meters per year, considering sugarcane agro-industries and fish farming as the main sources of drainage water. Time-Averaged salinity of this drainage water, with source of sugarcane agro-industries, is about 6 dS/m which is valuable to irrigate salt-tolerant crops or aquaculture with saline water as part of the solutions for drainage water management and providing sustainable environment. This can also affect the amount of water allocated to irrigation networks and sugar cane industries. In this regard, reusing of agricultural drainage water to produce rice salinity resistant varieties and lines as a high-yielding strategy in Khuzestan, especially in the central and southern areas with high water demand, can be very useful. Methodology This study was conducted at farm code L08-20, in Mirza Koochak-Khan Agro-Industry Company, using split plot in a randomized complete block design with two factors and three replications. Irrigation interval with saline water daily, one-day and two-day alternations were main factors and three salinity-tolerant rice lines were sub factors. Subsequent selections from the International Treasury of rice cultivars, four salinity-tolerant breeding lines, one international control line and local cultivar were subplots. The amount of water applied to the plots was measured throughout the growing season and samples for determination of physical and chemical properties of soil and drainage water before planting until harvesting time for soil monitoring and soil salt balance analysis were collected. In this study, grain yield, biomass and harvest index were determined. Finally, water productivity was estimated as yield per cubic meter of water. Results and Discussion Due to the average salinity of irrigation water, 6 dS/m, the volume of water consumed during the growing season was estimated to be 30,000 m3/ha, based on water requirement calculations. Based on irrigation management, applied volume of water was estimated about 37500 m3/ha for treatment I0, 19500 m3/ha for treatment I1 and 13200 m3/ha for treatment I3. The average salinity of soil saturated extract was measured about 4 dS/m before cultivation. Except for the first 15 days, when irrigation was carried out with full irrigation for transplanting stage, the trend of soil salinity changes was decreasing, during the rest of the growing season until harvesting. Salinity of soil increased in all three irrigation managements. The rate of salinity changes varied from 50% in the daily irrigation round to 100% in the two-day irrigation round, compared to pre-cultivation soil salinity. During the crop growth from the transplanting, daily, one-day and two-day rounds irrigation managements caused enterance of 190, 99 and 66 tonnes of salt in the top 100 cm of soil profile. Increased salinity over growing time for daily, one-day and two-day round irrigation treatments, were 6, 6.5 and 7.2 dS/m respectively, according to soil salinity, 4 dS/m, before planting. Assuming the porosity of soil equal to 51%, it could be concluded that 7.6, 9 and 11 tonnes of salts stored in the upper 60 cm of soil profile for daily, one-day and two- day round irrigation management and the rest of the solutes extracted from soil profiles through underground drainage system. This behavior illustrated the importance of drainage, especially underground drainage system, in agricultural drainage reclamation and saline operations for soil conservation. The results showed significant decrease of farm applied water in daily irrigation water management relative to two-day and three-day intervals. Farm yield increased 6% from I0 with an average of 2139.3 to 2248 kg, I1 and then decreased by 30% in the three-day irrigation period. Conclusions The results showed that the highest and lowest water productivity were found in I2 and I0 irrigation treatments, respectively, with values of 0.128 and 0.057kg/m3. ESP monitoring showed that at the end of growing season, soil profile was not sodic and remained in saline condition for two irrigation regimes I0 and I1. However, in I2 irrigation regime, the soil profile status approached to the sodic state, with 17% increasing in ESP and 100% increasing in salinity relative to planting time. The reason for this behavoir was driness of land between two irrigation events which caused salinity moving upward to soil surface layers, so it could be addressed by considering the percentage of leaching at the end of the growing season. Acknowledgement The authors gratitude Mirza Koochak-Khan Agro-Industry Company, Khuzestan Water and Power Authority (KWPA), Agricultural Engineering Research Institute (AERI), Rice Research Institute of Iran )RRII), Khuzestan Agricultural and Natural Resources Research and Education Center for their overall supports to accomplish the study.
