جستجوی مقالات مرتبط با کلیدواژه « Physical model » در نشریات گروه « آب و خاک »

In the past, various methods have been proposed to control beach heel scouring.  For shallow rivers (such as mountain rivers), various types of overflows are used.  Therefore, the development of scour in cross-vane and w-weir structures for coastal protection was investigated in this study.  The results showed that by installing a w-weir structure in a 90-degree position compared to a 30 and 60-degree position, a 37.9% and 19.7% reduction of scouring was observed, respectively.  Also, by installing the cross vane structure in the 90-degree position compared to the 30 and 60-degree position, a 35.4% and 21.2% reduction of scouring was observed, respectively. With increasing width (L / B) (ratio of the width of structure to the width of flume), the w-weir structure decreased from 1.5 to 2, scour rate of 7.9%.  Also, with increasing width (L / B) (ratio of the width of structure to the width of flume), the cross-vane structure has decreased from 1.3 to 1.7, and the scour rate has decreased by 4.7%. The w-weir structure had an average of 7.3% less scouring than the cross-vane structure.

Among the problems faced by artificial feeding methods, we can mention low rainfall, limited water resources, high temperature and high evaporation, high sediment yield due to poor vegetation cover, etc. Artificial feeding methods in these areas should be designed in such a way that it has maximum efficiency from the available water resources. In this research, it has been tried to reduce the aforementioned problems by presenting a new method of artificial nutrition suitable for desert areas. In order to design a suitable method of artificial nutrition, sufficient information about the distribution of water flow in the soil is needed. On the other hand, research on the distribution of water flow in porous media without modeling the field conditions is time-consuming and expensive. In the current research, the issue of determining the infiltration capacity in the unsaturated environment was discussed using the integration of the infiltration trench and the permeable pipe in the laboratory environment.

For this purpose, a physical model was built in which water was injected into the unsaturated environment through a permeable pipe and a trench. The input flow to the model included 5 flow rates of 1, 1.5, 2, 2.5 and 3 liters per minute. With the beginning of the experiment, which was entered into the model with the mentioned flow rates, the amount of progress of the moisture front was determined every 5 minutes. This process continued until the moisture front reached the water level. At the same time as the water was removed from the model, the output flows were measured every 5 minutes. The way water moves in the unsaturated environment and the formation of the moisture front was photographed and the images were analyzed using Plot Digitize and AutoCAD software. In the next step, after creating a flow in the porous medium, the volume of passing water was measured in different conditions at a certain time. The amount of water output from the model depends on factors such as the flow rate entering the model, the dimensions of the model, the slope of the ponding surface, the distance between the bottom of the trench and the ponding surface, the texture of the soil, the length of the trench, the width of the trench, the height of the permeable pipe to the bottom of the trench, the average diameter of the permeable material, and the entry time. The water depends on the model until it reaches the stagnation level and the time it takes for the water to reach the stagnation level until the end of the test. In the experiments, the input flow to the model was variable and other factors were considered fixed. After the water reaches the stagnation level in time intervals of 5 minutes for 60 minutes (a fixed time, the duration of which is obtained according to reaching the peak output flow rate from the model and preliminary tests for the lowest flow rate) It was measured for all model inlet flow rates. Next, after the completion of 60 minutes, the amount of water output from the model was measured for another 30 minutes. In flow rates of 2.5 liters per minute and 3 liters per minute, due to the fact that the inlet flow rate was higher than the capacity of the model, the excess water volume overflowed from the model. Then the inlet was cut off and for another 120 minutes, the output flow rate from the model was measured in 5 minute intervals. Then, the volume of water entering the tank (V_in) and the volume of water leaving without calculating the base flow that was mentioned earlier was measured to simulate the static level, V_out=(V_B-V_A). V_A is the volume of water input to simulate the static surface and V_B is the volume of water output from the model. The performance of the model was calculated based on V_out in relation to the volume of water coming out of the model without calculating the base flow rate as maximum 〖(V〗_(out max)) and also V_out was calculated in relation to V_in.

The highest penetration capacity of the model was determined to be 2.049 liters per minute. The results showed the trend of changes in the output flow from the model, the time the moisture front reached from the trench to the reservoir surface, the average infiltration velocity, V_out, the time to reach the maximum output flow from the model, and the slope of the water discharge line from the model after approaching the flow rate proportional to the capacity. The influence of the model has decreased. The performance of the model was evaluated based on V_out during the duration of the experiment in two modes. The best performance of the model was related to the flow rate of 2 liters per minute, which is the closest flow rate to the flow rate corresponding to the infiltration capacity of the model. The results showed that the performance at a flow rate of 2 liters per minute in the case where V_out was measured in relation to V_(out max) (water entering the model is less than the infiltration capacity of the model), 96% and in the case where V_(out max) was compared to V_in was taken into consideration (water flow entering the model is greater than the infiltration capacity of the model), its performance was determined to be 98%. In the presented artificial feeding method, the inlet flow rate through the permeable pipe should be designed according to the infiltration capacity of the trench so that the maximum capacity of the trench is used and water loss is minimized.

Experimental investigation of embankment dams due to overtopping breach is a remarkable subject because it is the most possible failure reason, and it includes a complicated process. The mentioned phenomenon physical modeling has performed at energy ministry water research institute, hydraulics laboratory, and its hydraulic outputs compared with a benchmark model outcome in three scenarios framework. The results reveal that the breach process of physical models comprises three stages: i.e., initiation, development, and the end. Also, the development time is longer than that of the other stages. In first scenario, when shell gradation  varied from 0.5mm to 1.7mm, 26 percent of peak discharge increased and 14 percent of breach time decreased. In second scenario in which lake water level maintained at overtopping threshold for two hours (for more saturation), 15 percent of peak discharge and 14 percent of breach time declined. In third scenario where the primary breach groove did not excavate, the highest difference in comparison with benchmark model results occurred, when 34 percent of peak discharge grew and 24 percent of breach time reduced. Moreover, asymmetrical sedimentation pattern happened in the last scenario. The Calculation of eroded material volume and mass was sedimentation pattern determination harvest. Herein, the simultaneous measurements of breach geometry, flow hydrograph, and final sedimentation pattern are the research unique achievements. However, further acquired analysis would be influential for the embankment dam's failure phenomenon management.

Numerical Study on Vortices in Collision of Flow with Circular, Square, Triangular, and Pentagonal Barriers of Different DiametersStructures constructed on rivers induce downstream oscillating vortices. These vortices apply oscillating loads on the structure and harm its stability. This paper carried out numerical simulations in SOLIDWORKS to explore the effects of the barrier shape and size on the load applied by the vortex on structures constructed in water streams. It was found that a reduction in the barrier size diminished the vortices. The highest Strouhal number was calculated to be 5.2 at a Reynolds number of 5000 and a barrier diameter of 0.09. The maximum downstream vortices were induced by the triangular barrier, and the maximum Strouhal number occurred to be 7.8 at a velocity of 0.4 and a barrier diameter of 0.05. The maximum vortices induced by the square barrier occurred at a barrier diameter of 0.05. Keywords: Strouhal number, Reynolds number, Barrier, Physical model, Oscillation

In the sediment washing method under submersible flow, the volume of the discharged sediments depends on various parameters, which can be referred to the depth of the water inside the tank, the depth of the water inside the pond, the output flow from the lower discharger, the size and type of accumulated sediments inside the tank. did To check the mentioned parameters in this research, a physical model with a length of 1 meter, a width of 1 meter and a height of 1.10 meters and by performing various tests using 2 water heights inside the tank, 3 water heights inside the pond and with 3 types of sediment granulation (in total 18 experiments) were investigated and studied. The results of this research show that in sediment washing under pressure, when the lower discharger returns for sediment washing, a sediment washing cone is formed in front of it. The dimensions of the formed sediment washing cone depend on the discharge from the lower discharger, the height of the water inside the tank and the diameter of the sediments accumulated inside the tank, so that the measurement results show that in order to keep the height of submerged water constant, the height of water inside the tank increases. It increases the volume and length of the sediment washing cone. Also, for a fixed water height inside the tank, increasing the submerged water height increases the volume and length of the sediment washing cone.

Vegetation plays an essential role in modifying the flow characteristics of natural channels, such as rivers. Efficient hydraulic modeling of flow in compound channels with vegetated floodplains is necessary to understand and identify natural flow processes. In both natural and artificial channels, there are various types of vegetation with differing densities and heights. The main goal of this study is to investigate the effect of double-layered vegetation on flow characteristics in compound channels using the FLOW-3D model. The results of the numerical model have been calibrated and validated with the results of the physical model of the research of Takuya et al., 2014. Experiments were conducted in 2014 in the hydraulic laboratory of the Akashi National University of Technology in Japan, and in a straight trapezoidal channel with a length and width of 4.8 and 0.8 m respectively. During calibration, the model's estimation error for the depth-averaged velocity was within 4 to 6%, which was reduced to approximately 1.5% during validation. The average error in water depth estimation was around 3%. The numerical and physical models showed good agreement in simulating the flow pattern. The numerical model showed that, for larger floods when vegetation is submerged, the vertical profile of velocity in the floodplain is S-shaped. However, during smaller floods or when short and tall vegetation is emergent, the vertical velocity profile is relatively uniform or logarithmic. The resistance caused by the presence of vegetation in the floodplains leads to a decrease in the flow velocity in the floodplain area of the river and an increase in the capacity of flow transfer in the main channel.

Water diversion from river for agriculture or industry based on gravity is possible according to different methods where using porous media is one of its methods. It is necessary to study the water diversion in such flows because there is sediment in water flow in the nature. Different methods such as: porous media grain size, cohesive sediment density and various water discharging were studied in this research by making experimental model. The obtained results show that discharge coefficient in D50 = 16.5 mm in discharge 20.7 lit/s with 1.5, 3, 6.5 and 8 gr/lit density are 0.038, 0.035, 0.034 and 0.033 respectively. Reducing the flow velocity in porous media is because of increasing in density which is a reason of reducing in discharge coefficient. The discharge coefficient for 3 gr/lit density in discharge of 20.7 lit/s for the D50, 11.5, 16.5 and 25 mm are 0.025, 0.035 and 0.042. This is happened because of higher porosity in D50 = 25 mm than D50 = 16.5 mm and D50= 11.5 mm. it was observed that in lower discharges, discharge coefficient changes are more than inlet discharge but it is stable by increasing the inlet discharge. By analyzing the obtained data and using dimensional analyzing and multivariate regression, relationships to estimate discharge and discharge coefficient were proposed for this intake

Leaching modeling in the conditions of non-uniformity leaching in soil profile is desalination challenges. The final salinity in the soil profile has different values in two dimensions of soil depth and distance from the drainage pipe. Therefore, estimation the salinity values in the soil profile requires two-dimensional modeling of leaching. In this research, the data required for modeling were prepared by soil profile leaching in a physical model with dimensions (height × width × length) of 1×0.5×2 m. In this model, soil drainage conditions were created for half the distance between the two drains. The target of this study was to compare the relationships of one-dimensional (in soil depth) and two-dimensional (in soil depth and distance from drain) in leaching modeling. Regression models included linear, exponential, logarithmic, polynomial and power functions. The results showed that in one-dimensional modeling, the coefficientR^2 for linear, exponential, logarithmic, polynomial and power functions were equal to 0.392, 0.557, 0.404, 0.406 and 0.562, respectively. But in two-dimensional modeling, it was equal to 0.796, 0.94, 0.55, 0.614 and 0.587, respectively. Therefore, increasing the coefficient R^2 in two-dimensional modeling, showed an increase in validity in leaching modeling. In evaluating two-dimensional models by terms of ME, RMSE,R^2,R_adj^2and EF, were selected exponential and linear models as the optimal model, respectively. For leaching modeling in the soil profile between two drains, using the two-dimensional model had better performance than the one-dimensional model.

It has been documented that the assumption of capillary movement of water in a bundle of cylindrical tubes often leads to systematically underestimation of soil unsaturated hydraulic conductivity at low potentials which is due to ignoring the contribution of adsorptive forces and liquid films. In this study, the performance of two physical models of (Tuller-Or) and (Lebeau-Konrad) that take into account the contribution of both adsorptive and capillary forces and the well-known capillary-based model of (Van Genuchten-Mualem) for modeling the soil-water retention curve and estimation of the unsaturated hydraulic conductivity were evaluated. To that end, experimental data gathered from literature including six soils that cover a broad range of texture and hydraulic behavior. The results showed the superiority of the two capillary-adsorption models over the capillary-based Van Genuchten-Mualem model in estimating the soil-water characteristic curve and unsaturated hydraulic conductivity. Among the two physically capillary-adsorption based models, the Lebeau-Konrad model performed better. The results showed that the Lebeau-Konrad model underestimates the hydraulic conductivity of clayey soils in the near saturation range and the best performance of the Tuller-Or model was shown to be for loamy soils. Because the Tuller-Or model is the most comprehensive and physics-based model for modeling the unsaturated hydraulic conductivity up to date, future studies should be devoted to improving the flexibility of this model via extending the model to other pore size distribution than the original Gamma distribution, such as lognormal, incomplete gamma and Weibull distributions.

The phenomenon of mixing saline and fresh water in aquifers near the sea coasts and the margin of salt marshland, limits the application of high-quality groundwater resources. On the other hand, by increasing concentration of saline water in aquifer due to evaporation from the soil surface and also decreasing pressure head in freshwater aquifers as a result of groundwater over exploitation, lead the mixing front advances toward the freshwater aquifer. In this study, by making a physical model, mixing area and salt distribution in both saturated and non-saturated zone of porous media has been studied. Four different hydraulic scenarios have been performed, including equal water table of fresh and saline water, higher freshwater level and two higher saline levels (10 and 15 centimetres). The concentration of saline water and freshwater were 20 and 0.98 dS/m, respectively. The physical model size was 4×1×1 meter. The results showed that the water table shape is an important factor for distribution and scattering of salinity in both saturated and non-saturated areas. By decreasing the water level in the freshwater reservoir by 10 and 15 centimetres, the boundary between the fresh and saline zone below the water table progressed 55 and 96 cm respectively, and by increasing the water level in the freshwater reservoir by 5 cm, the same zone has had a recession to 28 cm.

The combined weir-gate structure has various applications in hydraulic engineering and can eliminate some of the shortcomings of each individual application. The combined weir-gate structure, with the ability of simultaneous passage of the material to be deposited through the gate section and that of the suspended material from the weir, prevents the accumulation of the sediments and the suspended materials behind the weir and helps increase the measurement accuracy and flow passing. Some studies conducted on the labyrinth gates are related to triangular and trapezoidal labyrinth weirs. However, regarding the performance, the rectangular labyrinth gates could be built and run better in some areas. Moreover, in the studies carried out in the field of combined simultaneous flow above the weir and below the gate, the combined weir models with sliding gates have been rarely addressed. One of the significant issues in the combined rectangular labyrinth weir-gate structure is the position of the gate which has not been investigated yet. Therefore, this study aims to investigate the effect of the gate position on the discharge coefficient of the rectangular labyrinth weir-gate and that of increasing the weir height on the discharge coefficient of the rectangular labyrinth weir-gate in different gate positions. This study investigates the effect of gate position on the discharge coefficient using physical models of rectangular labyrinth weir-gate, made of Plexiglas with 15 and 20 cm heights in 15 positions of gates in different situations. All experiments in this research were conducted in a glass rectangular channel with the length of 12, width of 0.5, height of 0.7 meters, and longitudinal slope of zero degrees. The discharge varied from 10 to 50 liter per second. To measure the depth of water at the upstream weir and the triangular weir, a depth-measuring device with the precision of 0/1 millimeter was used. Considering the width of the laboratory flume and the decreasing effect of walls surface tension of the rectangular labyrinth gate-weir, two cycles were selected for the weir. The weirs with the crest of 90 ° (straight) and thickness of 10 mm were made of 1, 2, 3, and 4 sliding gates. The models were mounted on a four-meter upstream channel. In general, 390 experiments were conducted in this study. To investigate the effect of gate position on the flow discharge coefficient, experiments were done using 1, 2, 3, and 4 gates in different positions. For weir models with heights of 15 and 20 cm and a gate, when the gate is located in the forehead of the upstream weir (model 4), the discharge coefficient was more than those of two other models (2 and 3) due to the gate’s perpendicular position to the flow direction. For the two-gate mode in model 6 in both weirs with heights of 15 and 20 centimeters, the discharge coefficient was higher than other 3 models, due to both gates’ perpendicular positions to the flow direction. Models 10 and 14, with 3 and 4 gates had a higher discharge coefficient. In these cases, when the number of the gates’ perpendicular positions to the flow direction increased, they had a greater effect on the discharge coefficient than other states did. The results showed that the discharge in the combined weir-gate structure was more than that in weirs with no gates; that in fact, showed the effect of the gate in a rectangular labyrinth weir on the discharge increased. According to the results, the discharge coefficient in the rectangular labyrinth weir gate was more than that in the rectangular labyrinth weir with no gate. In other words, the gate effect on the discharge coefficient increased in a rectangular labyrinth weir. However, considering the results, the discharge coefficient increase in the low current range (less H/P) was greater than that in the high current range (higher H/P). In fact, the result revealed that the gate in the rectangular labyrinth weir-gate in the low current range (less H/P) had more impact on the discharge coefficient increase and, consequently, on the transit of discharge increase. Given that the reduction of the discharge coefficient with the increase in the H/P ratio results from the increase in water jets interference in adjacent cycles and the increase in local weir submergence, the flow below the gate also caused additional, new interference within the flow of water at the bottom of the structure and, consequently, reduced the discharge coefficient. The highest efficiency of the combined rectangular labyrinth weir-gate model in less H/P is recommended. According to the obtained results to achieve the highest efficiency, the maximum water ratio (H/P) was recommended to be less than 0.5 and 0.7, respectively for weirs with the height of 20 and 15 cm. This issue almost corresponds to Lux’s results who suggested the maximum water ratio (H/P) for a trapezoidal labyrinth of 0.45-0.5. This study investigated the effect of gate position on the discharge coefficient in the combined rectangular labyrinth weir-gate structure. According to the results in the studied states, when gates were located perpendicular to the flow direction, they had higher impact on the discharge coefficient. Moreover, the discharge and discharge coefficient in the rectangular labyrinth weir-gate were more than those in their counterpart with no gates. In fact, the gate in a rectangular labyrinth weir led to an increase in discharge and discharge coefficient.

In this research work, besides analyzing the scour hole at the downstream of the siphon spillway physical model, some equations have been presented to predict scour hole developing. A physical model of siphon spillway along with three flip buckets of angle 30°, 45° and 60° for three types of sedimentary materials of mean size 1.8, 3.5 and 1.4 (mm) were used to study scour hole formation process. Geometric characteristics of the scour hole were collected for four flow discharges of 39.2, 42.12, 42.12, 49.76 (lit/s) and five tail-water depths of 15, 20, 25, 30 and 35 (cm) using a mesh grid size of 10 (cm) ×10 (cm). Three dimensionless parameters were extracted for analyzing experimental results using dimensional analysis. Of all scour hole dimensions, scour depth (ds), scour length (Ls) and distance of downstream hill up to bucket lip (L6) were adjusted for numerical modeling. Results showed that increasing flow rate causes growth and developing of scour hole geometric properties simultaneously. Increasing the particle size showed an inverse relationship with three dimensions of the scour hole. Also, the reduction of the bucket's angle led to a reduction in ds, Ls and L6. The maximum correlation coefficient obtained between ds, Ls and L6 with particle size, flip bucket angle and discharge/tailwater, respectively. Finally, predictors were presented to describe above-mentioned dimensions of scour hole dimensions.

Many factors affect runoff and erosion. However, rainfall and soil characteristics are the two main factors affecting runoff and soil erosion. Among the rainfall characteristics, intensity and duration of precipitation are the two dominant factors that control the hydrological responses. Changes in rainfall intensity have major effects on soil erosion. In this study, thirty minute rainfall intensity (I30) is considered as a rain erodible index based on the kinetic energy of rainfall intensity, which is a well-known indicator in different parts of Iran. Soil hydrophobicity (SWR) is a soil feature that affects the hydraulics and hydrologic features of soils. When soil particles are coated with hydrophobic materials, water penetration is severely delayed, which reduces soil moisture capability. Studies have shown that under conditions of soil hydrophobicity, infiltration and runoff production time will be shorter. In the case of high rainfall, the effect of SWR will also be intensified. According to the studies, it cannot be concluded that there is less sediment or more sediment in hydrophobic soils. Considering Iran's location in arid and semi-arid climates and the importance of studying hydrological phenomena in this climate, simulating the effect of different probability of precipitation intensity on volume and coefficient of runoff and sedimentation directly using physical model and also effect. These probabilities on hydrophilic agricultural soils and different degrees of hydrophobic soils are essential both in research and practical projects. To create the homogeneous hydrophobic conditions in the soil with definite physical specifications, the soil is made hydrophobic artificially by the use of stearic acid. The texture of the tested soil was sandy loam. The soil hydrophobicity is done in 5 degrees (hydrophilic as the control sample, slight repellency, strong repellency, severe repellency, and extreme repellency). The amount of the required stearic acid estimated for different hydrophobic levels was determined by WPDT empirical test, together with trial and error considerations. Using a physical model the amount of sediment and runoff was simulated on five soil treatments under five rainfall intensities with a probability of occurrence of 0 (probability of occurrence), ±10% and ±20% relative to the 30-minute rainfall with a return period of 1000 year of Shahr-e-Kord rain gauge station (base rainfall intensity: 1.41 mm / min) . The physical model of a special equipment is named “Advanced Hydrological Investigations”. The driving force of the equipment includes an electric pump with the power equal to 0.55 KW. There are eight nozzles that provide sprinkler irrigation with square spraying pattern. The spraying flow is adjusted up to max. 1500 l. /hr., by a rotameter underneath the equipment. The required water for spraying is stored in a 220-Litre tank. Working with the equipment is easy. The equipment consists of a soil tray with 2 m length, 1.2 m width, and 20 cm depth. Due to the 20-cm depth of the tray, the upper 5 cm is considered as the free board space. Five cm of the bottom of the tray was filled by sand in order to facilitate and accelerate the drainage of water. A galvanized mesh is placed on the sand. The upper 5 cm of the 10-cm of soil was considered as the surface soil. Runoff was volumetrically measured and sampled continuously for sediment concentration. The sediment concentration was determined as the ratio of the dry sediment mass to the sampled runoff volume. In control treatment, the rainfall duration depends only on the rainfall intensity and the maximum rainfall time is 53 minutes (related to the lowest rainfall level (-20% Probability of the base rainfall) and the minimum rainfall time is also 47 minutes (related to the highest rainfall level (+ 20% Probability of the base rainfall). In the hydrophilic soil treatments in addition to rainfall intensity, the degree of soil hydrophobicity affects also the rainfall time. Since the water absorption is negligible, the rainfall duration is shorter than the control sample. The higher the water hydrophobicity, the less rainfall duration. The less hydrophobicity degree, the less runoff generated. In hydrophobic treatment, due to water repellency, the runoff occurs rapidly, and (hydrophilic soil). The highest observed runoff was 7000cc in severe repellency treatment and the rainfall with +20% Probability, means 120lph. However, the minimum volume of runoff observed in control sample in probability level of -20%, 720 cc. On the other hand, the higher hydrophobicity level, the higher runoff coefficient was observed. Runoff coefficient has been observed in hydrophilic soil from 0.000 to 0.0011 and in hydrophobic treatments 0.05 to 0.94. Severe and extremely severe hydrophobic treatments worked quite imperviously. The rate of sedimentation exited along with runoff is decreases by increasing the hydrophobic level. The highest observed sedimentation was 12gr in hydrophilic treatment and the rainfall with +20% Probability. However, the minimum volume of sedimentation is 2 gr which is observed in extreme soil repellency treatment in probability level of -20%. The observed deep percolation in the control treatment (hydrophilic soil) is 17.5 to 23.8 liters. The deep percolation amount was observed only in low and moderate hydrophilic levels (380 to 950 cubic centimeters). No significant deep percolation, was observed in severe and extreme severe hydrophobic treatments.

Shohada diversion dam was constructed on the border of agricultural lands of Behbahan plain (Khuzestan province, Iran) to divert the water of the Maroun River. This dam has a concrete-soil composite. The concrete part consists of an ogee spillway, a stilling basin, and two intake channels and sediments on the right and left sides. The height of the dam is 12.2 meters and its spillway length is 150 meters. The dam has a sloping basin and its capacity is 22 m3/sec. The longitudinal slope of this basin is 1 to 5 (vertical: horizon). The studies have shown that parts of downstream of the stilling basin are being eroded and scoured. Unless controlled properly, this will continue and might lead to the destruction of the basin or the main structure of the dam. Most of the stilling or apron basins used in the previous studies are horizontal and smooth, and no research has been conducted on scouring downstream of sloping basins so far. Therefore, the purpose of this research is to explore the causes of scouring downstream of the Shohada dam's stilling basin and its controlling factors to finally provide an appropriate strategy to prevent its spread.

Scouring is one of the main reasons for the failure of bridges in the United States and the world. The flow characteristics, the base shape and the angle of its deposition relative to the flow and characteristics of the sediments are all factors that interfere with the complexity of the scouring problem of bridge bridges. It should be noted that the final scour depth created near the bridge base is equal to the total erosion depth due to local, general, and narrowing of the flow width. Determining the depth of erosion within the range of bases requires knowledge of the displacement of sedimentary materials in the river bed. The bases disrupt the normal flow of the river, and the turbulence and disturbances resulting from it erode sedimentary materials around the base. Since the propagation of the scour hole threatens the stability of bridge structure, a common engineering practice in the field of river engineering involves the prediction of scour depth to take necessary controlling measures. Accordingly, this study aimed at investigating the effect of air foil lattice collars on airfoil bridge piers. According to the results, scouring decreased further with increasing collar length. By installing lattice collars with a length (L/D) of 6, 8, and 10 at a relative depth (Z/D) of 0.1, scouring reduced by 16.6, 22.3 and 24.7%, respectively, compared with a collarless bridge pier. By installing lattice collars with a length (L/D) of 6, 8, and 10 at a relative depth (Z/D) of 0.5, scouring reduced by 35.2, 37.4 and 38.4%, respectively, compared with a collarless bridge pier. By installing lattice collars with a length (L/D) of 6, 8, and 10 at a relative depth (Z/D) of 1, scouring reduced by 27.7, 31.6 and 31.4%, respectively, compared with a collarless bridge pier. Scouring increased by 113.8% on average by increasing the relative velocity (V/Vc) from 0.54 to 0.95. By installing the collar at a relative depth (Z / D) of 0.1, 0.5 and 1, we see 16.6, 35.2 and 27.7 percent lower scouring than the collar less base. Also, by increasing the depth of the lattice aerodynamic collars (Z / D) from 0.1 to 0.5, the scour reduction decreased by 22.3% and also with increasing the depth of the lattice aerodynamic collars (Z / D) from 0.5 to 1, increasing the scour 11.6 percent. In this way, it can be seen that the best depth of the collar is about half the diameter of the base of the bridge. Also, simulation with the Flow-3D math model is close to the physical model, with an average of only 5.4% error, which is acceptable.

A ‘spillway’ is a structure used to provide the controlled release of flood water from upstream into downstream area of a dam. As an important component of every dam, a spillway should be constructed strongly, reliably and efficiently to be used at any moment. Labyrinth and stepped spillways are presented as appropriate modifications to those spillways hardly capable of managing the maximum potential discharge. Owing to their nonlinear crests for a given width, labyrinth and stepped spillways have a larger discharge rate than linear- crest spillways at an identical height. Compared to other energy dissipaters, the combination of stepped and labyrinth spillways is known as a very strong energy dissipater. In the following part, the combination of these two structures and their dimensional change for increasing the water- energy dissipation are addressed. To conduct this study, an experimental flume with a 90- degree bend in the Islamic Azad University of Ahwaz was used. In total, 90 experiments were conducted on three different labyrinth- shape stepped spillway models with two different lengths, three different widths, and five different discharges. Analysis of the results showed a greater energy loss reduction in triangular rather than rectangular or trapezoidal labyrinth- shape stepped spillways. In addition, energy loss was greater in labyrinth spillways with two cycles than those with one cycle. Energy loss was increased by raising the Froude number from 0.05 to 0.1; in contrast, energy loss was decreased with increasing the Froude number from 0.1 to 1.0, which was due to the submergence of steps, a decrease in the roughness of steps and an increase in the intensity of aeration.

Piano key weir (PKW) is a hydraulic structure that can be installed at dams and canals for regulating the flow surface and discharge. The main feature of this weir is the ability to pass a large flow of water over a small head.Regarding its geometrical properties, this weir is classified into four types of A, B, C and D. PKW with symmetrical upstream and downstream overhangs is classified as Type A, one with only upstream overhangs as Type B, one with only downstream overhangs as Type C, and one without overhangs as Type D.Despite various studies on piano key weirs (some of which were mentioned in the text), the flow behaiviour over these structures is very complex, unpredictable and three-dimensional.So further laboratory investigations on PKWs are needed. In the present study, the effect of the width of the inlet and outlet keys on the hydraulic characteristics of these weirs is investigated. In addition, the occurrence of undular flow on these types of weirs is reported for the first time. To achieve the aims of this study, more than 300 experiments were conducted at a laboratory flume.

The experimental tests of this research were conducted in the hydraulic & water structures laboratory of 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.The flow discharge was adjusted in a range of 5 to 60 liters per second by a valve. In total, 16 physical models of PKW-A and PKW-D weirs were constructed to investigate the effect of width of inlet and outlet keys on the hydraulic characteristics of flow over such weirs. Seven discharges were tested for each model of weirs, and experiments were repeated three times for each discharge.

The results demonstrated that at low water loads (Ht <3cm), both types of weirs have almost the same performance. But as the water load increases, the performance of PKW-A weir deviates from the type PKW-D weir, i.e. it was able to pass larger discharges for an identical flow head. The superiority of PKW-A weir was more evident in small inlet-to-outlet ratios of keys.For low flow heads, the performance of weirs with different Wi/Wo ratios in terms of discharge capacity is almost similar. Anderson and Tullis (2013) found similar results in their experiments.At higher flow heads, the PKW-A1.66, compared to other models, had the largest discharge capacity in same flow heads, indicating its better performance. At maximum flow head (5.5cm), this weir was able to discharge 52 liters per second, which is 24% more than PKW-A0.6 weir. Similar trend exists for D-type piano key weirs.It was observed that undular flow is formed on D-type piano key weirs. Although, this phenomenon was previously observed on rectangular broad-crested weirs (Chanson, 1976; Madadi et al, 2013), but for the piano key weirs, this is the first report on formation of undular weir flow above D-type PKW.

According to the results of this study, the ratio of the width of the inlet keys to the width of the outlet keys is a very effective parameter in the discharge capacity of the piano key weirs, and the presence of a forehead can also play a role in enhancing the performance of the weir.Also, the results indicated that for a given head, not only the A-type PKW has more discharge capacity comparing to D-type weir, but also due to its special geometry, the undular flow phenomenon cannot be formed above such weir. Furthermore, the PKW weir with inlet to outlet key width ratio of 1.66 demonstrated 30% higher performance comparing to the other investigated models.

After Hamidieh Diversion Dam near the city of Hamidieh, Karkheh River is divided into two streams known as Hufel and Nissan. At the lower flow rates, Nissan makes up a greater share than Hufel due to the steeper slope of the former. This study attempted to construct a hydraulic structure to appropriately divide water flow in Hufel. In a laboratory experiment, a flume with a 90-degree bend was used at Islamic Azad University of Ahvaz. Various experiments were conducted at different widths and heights. Furthermore, this model was simulated through CCHE2D, the results of which were compared against those of physical and mathematical models. The results indicated that the weir height increased the deviation flow percentage to the Hufel stream due to rising water level. Moreover, the deviation flow percentage to Hufel was declined as the weir width was increased due to falling water level. At Hufel, the installation of rectangular weir in different dimensions yielded the minimum of 34.3% and the maximum of 61.5% increase in the flow rate. In the normal mode without any weirs installed, however, there would be an increase in the flow rate, as compared to the mode where a weir has been installed. This can be associated with the flow controlled by the weir. On average, the deviation flow rate was increased by 2.8% in the weir mode and 7.7% in the weir-less one. An increase in the Froude number from 0.21 to 0.38 led to a lower average deviation flow rate by 19.3%. Moreover, the results of the simulation through CCHE2D were demonstrated to be largely similar to those of physical model experiments. However, an increase in the Froude number did not lead to a decline in the deviation flow rate (i.e. it remained constant). This trend was inconsistent with the results of the physical model.

The ogee spillway with a curve axis has a longer crest length than the spillway with linear crest. Therefore, in a specific reservoir water level, it can discharge higher flow rate compared to a straight one and due to this reason is preferred in applicable plans. In this study, physical model of Germi-Chai spillway which include an ogee crest with a curve axis and converging training walls was constructed in scale of 1:50. The SCWMRI Soil Conservation and Watershed Management Research Institute, has led a research effort on it. For each of the convergence angles, including 60 and 90 ̊ in both symmetrical and asymmetrical situations, flow characteristics such as discharge, water surfaces, depths and distributions of pressure were investigated in the downstream channel of the spillway. Experiments conducted in varying flow discharge from 30% to 177% of  design discharge. Based on visual observation, at the toe and the end of straight portions of the spillway face, due to converging training walls, interference streamlines occurred which led to generate a rooster tail phenomenon. It was observed that in the convergence angle of 90°, rooster tail had been witnessed up to slightly more than 118% Qd. However, it saw nearly 147% Qd in 60° convergences. Moreover, it should be emphasized that due to asymmetric angles, closest wall to the rooster tail had more static pressure.

Hydraulic characteristics of wide channels differ from narrow channels due to the higher ratios of width to depth, b/h. In this research, using a physical model of a rigid boundary channel having 60m length, 1.5m width and a bed slope of 0.001 with b/h ratio of 12 to 56, hydraulic characteristics of wide channels including: stage-discharge relationship, velocity and shear stress distributions were experimentally considered. The results indicate that the maximum velocity in the wide channel was occurred nearby the water surface. Investigation of the vertical velocity distribution reveals that the flow velocity follows the well-known logarithm distribution law. The also results show that the shear stress was maximized in the centerline of channel section, and the dimensionless shear stress was increased by increasing the ratio of b/h. In ratios of b/h less than 30, the dimensionless bed shear stress value is less than 0.9 and in case of b/h greater than 30, it is greater than 0.9. A comparison of the results for wide channels and channels with an optimal width of b/h=2, reveals that the relationship between b/h and shear stress in narrow channels is linear, while in wide channels a power relationship is governing. Moreover, in wide channel sections, the percentage of shear force on the walls (%SFW), due to the low depth of flow which is less than 10 and negligible, so that to contribute the walls to the shear stress can be ignored for design purposes.