flow

Coastal aquifers are groundwater aquifers located by the sea. The water quality of these aquifers has always been considered and one of the main concerns, in this case, is the infiltration of salt water into the aquifer. The effectiveness of aquifer water depends on the flow of groundwater as well as the concentration of salt contaminants. On the other hand, the amount of salinity is dependent on factors such as agricultural and human activities, climate change and so on. Today, due to the scarcity of water resources, the use of groundwater resources has increased, so the study of saline water intrusion is considered necessary, which is studied in this study. In this research, diffusion equations including flow and transport equations have been used. To solve the above equations, the meshless local Petrov-Galerkin method has been used. The Henry standard problem was solved to validate the results of the equations. To evaluate the results, the Henry problem was solved with FEFLOW software and compared with the proposed model and it was observed that the results of the meshless local Petrov-Galerkin method are close to the results of the FEFLOW finite element model, which indicates the acceptable accuracy of this model.

Water management in water basins requires information of some facts and full acquaintance of basin conditions, which is problematic due to the deficiency of data collection stations in the country. One of the most suitable methods for flow simulation is the use of hydrological models. In this study, in order to simulate runoff caused by precipitation and to investigate the apparatus of runoff formation and outflow at the outlet of Shahid Rajaei Dam basin located in Sari, the HBV-Light model was used. The purpose of evaluating the stochastic method is to estimate the model parameters and reduce the uncertainty. The length of the daily statistical period was the variables of temperature, precipitation, runoff and evaporation from 1981 to 2015. The Monte Carlo random method was used to estimate the appropriate parameters for the study area. For a consistent assortment, the values of the parameters with a relatively good coefficient of determination were used in the validation section. Finally, the results show the good aptitude of the model in simulating runoff in the study basin. The values of coefficient of determination 0.87, Nash coefficient (NS) equal to 0.66 in the range of good evaluation and RMSE equal to 0.26 in the validation period indicate this issue. In the analysis of uncertainty caused by model parameters, K1, K2 and UZL parameters were identified as the most sensitive in the model reaction subroutine. Therefore, the results showed the importance of accurate determination of water and soil parameters affecting subsurface runoff.

Surface runoff and water flow in rivers cause soil erosion and carry sediment materials. Knowledge of how erosion and the ability to carry sediment in rivers and waterways should be considered in every engineering plan. One of the most important factors in disrupting the hydraulic balance of the river is the indiscriminate removal of sediments from the river bed. Today, the materials obtained from rivers are very vital in human life, especially in civil and industrial activities, and are of great importance. Indiscriminate and out-of-capacity harvesting of sand causes changes in the morphology of rivers, which results in the river's reaction to establish a new balance. The study of past research indicates that sand harvesting has caused different changes in the hydraulic pattern of rivers, changes in morphology, and changes in the sediment balance of rivers. The extraction of sand from the country's river beds has increased in recent years. Due to the complexity of hydraulic and sediment problems in rivers, it is not possible to solve the equations analytically, hence numerical methods are usually used. Various studies have been conducted using the HEC-RAS model to investigate the flow of hydraulics in the river. Various researchers in the country have also used this model to investigate sediment transfer in rivers and reservoirs of dams.

In this research, a part of the Khara River located in Khandab City, which is subject to excessive sand harvesting, was investigated. In this study, HEC-RAS 5.3 model was used to simulate sediment flow. For Joshirvan hydrometric station, discharge was calculated with a return period of 2, 5, 25, 50, and 100 years and used for hydraulic simulation of the river. To use the HEC-RAS model for hydraulic simulation of flow and sediment, river information including geometric data, hydraulic data, and sediment data was used. In the geometric section, the general plan of the river along with cross sections was introduced to the model. Using the topographical map of the river course in two time periods before sand and sand harvesting (2015) and after sand and sand harvesting (2017), a digital elevation model of the Kurkhane river course with a scale of 1:2000 was prepared for both periods. Then, a TIN was made from the prepared digital elevation model, and 200 sections were extracted in the HEC-GeoRAS add-on package in the Arc Map software along the length of 3.5 km of the river. After preparing cross-sections and measuring the distances of the left and right banks of the main channel of the river, the relevant information was connected to the HEC-RAS model in the form of a GIS file to introduce the geometry of the river. Finally, the changes made in the geometry and morphology of the river were compared by examining the parameters before and after harvesting the materials and field investigations in the periods when this operation was carried out.

By comparing the longitudinal profile of the bed in the post-harvest conditions compared to the pre-harvest conditions, it was found that in the first half of the studied interval from the upstream side (section 1-98) a sedimentation phenomenon occurred with a shallow depth, while in the middle half of the studied interval study (section 100-150) there has been an uplift of the river bottom. The results showed that the amount of erosion and sedimentation in the first 1.5 km and the last 1 km is almost low, and the materials in this area are not very removable. The best area for collecting materials in this interval from 1.5 to 2.5 km is almost in the middle of the interval. According to the changes in the river bed, the maximum change is about 1.2 meters and the average changes are about 0.5 meters along the river path.

Results showed that the rate of erosion and sedimentation in the first 1.5 km and the last 1 km almost decreased in the sedimentation state and the materials in this area are not very harvestable. The best area for harvesting materials in this range is from 1.5 to 2.5 km approximately in the middle of the range. Due to the slope and cross-sectional shape, the flow velocity has decreased and sedimentation with an average depth of 1.2 meters has been done. Calculations showed that the amount of sediment that can be removed from the river in this period is about 200 tons per year.

Poor management of agricultural waste is one of the sources of water pollution. In this study, the surface water quality of Jiroft Dam watershed was modeled using the QSWAT model. The study area is located at the upstream of Jiroft Dam watershed with the total area of 783446.81 hectares in Kerman province. The rainfall-runoff model was simulated over the 21 years from 2000 to 2020 for a monthly time step. Data from Konaroye hydrometric station was used as observed flow data. The meteorological data was collected from Baft synoptic station. The model was calibrated and validated using the SUFI-2 automated algorithm in SWAT-CUP software for periods (2011-2019) and (2008-2010), respectively. The final results of determination and Nash-Sutcliffe coefficients from calibration and validation processes obtained 0.79, 0.77, 0.81 and 0.82, respectively. Sensitivity analysis was performed for 12 calibration parameters. The results show that base-flow alpha factor is the most sensitive parameter. After modeling of the flow rates in watershed, in next step surface water quality was modeled in QSWAT by considering Urea as fertilizer which is mostly used on the area under cultivation of Jiroft Dam watershed. The results for Nitrate load show that model prediction is in good agreement with the experimental data. The results of this study show that QSWAT model can be used as an effective and efficient method in order to predict surface water quality and managing of water resources.

Probabilistic designation is a powerful tool in hydraulic engineering. The uncertainty caused by random phenomenon in hydraulic design may be important. Uncertainty can be expressed in terms of probability density function, confidence interval, or statistical torques such as standard deviation or coefficient of variation of random parameters. Controlling cavitation occurrence is one of the most important factors in chute spillways designing due to the flow’s high velocity and the negative pressure (Azhdary Moghaddam & Hasanalipour Shahrabadi, 2020). By increasing dam’s height, overflow velocity increases on the weir and threats the structure and it may cause structural failure due to cavitation (Chanson, 2013). Cavitation occurs when the fluid pressure reaches its vapor pressure. Since high velocity and low pressure can cause cavitation, aeration has been recognized as one of the best ways to deal with cavitation (Pettersson, 2012). This study, considering the extracted results from the Flow-3D numerical model of the chute spillway of Darian dam, investigates the probability of cavitation occurrence and examines its reliability. Hydraulic uncertainty in the design of this hydraulic structure can be attributed to the uncertainty of the hydraulic performance analysis. Therefore, knowing about the uncertainty characteristics of hydraulic engineering systems for assessing their reliability seems necessary (Yen et al., 1993). Hence, designation and operation of hydraulic engineering systems are always subject to uncertainties and probable failures. The reliability, ps, of a hydraulic engineering system is defined as the probability of safety in which the resistance, R, of the system exceeds the load, L, as follows (Chen, 2015): p_s=P(L≤R) (1) Where P(0) is probability. The failure probability, p_f, is a reliability complement and is expressed as follows: p_f=P[(L>R)]=1- p_s (2) Reliability development based on analytical methods of engineering applications has come in many references (Tung & Mays, 1980 and Yen & Tung, 1993). Therefore, based on reliability, in a control method, the probability of cavitation occurrence in the chute spillway can be investigated. In reliability analysis, the probabilistic calculations must be expressed in terms of a limited conditional function, W(X)=W(X_L ,X_R)as follows: p_s=P[W(X_L ,X_R)≥0]= P[W(X)≥0] (3) Where X is the vector of basic random variables in load and resistance functions. In the reliability analysis, if W(X)> 0, the system will be secure and in the W(X) <0 system will fail. Accordingly, the eliability index, β, is used, which is defined as the ratio of the mean value, μ_W, to standard deviation, σ_W, the limited conditional function W(X) is defined as follows (Cornell, 1969): β=μ_W/σ_W (4) The present study was carried out using the obtained results from the model developed by 1:50 scale plexiglass at the Water Research Institute of Iran. In this laboratory model, which consists of an inlet channel and a convergent thrower chute spillway, two aerators in the form of deflector were used at the intervals of 211 and 270 at the beginning of chute, in order to cope with cavitation phenomenon during the chute. An air duct was also used for air inlet on the left and right walls of the spillway. To measure the effective parameters in cavitation, seven discharges have been passed through spillway. As the pressure and average velocity are determined, the values of the cavitation index are calculated and compared with the values of the critical cavitation index, σ_cr. At any point when σ≤σ_cr, there is a danger of corrosion in that range (Chanson, 1993). In order to obtain uncertainty and calculate the reliability index of cavitation occurrence during a chute, it is needed to extract the limited conditional function. Therefore, for a constant flow between two points of flow, there would be the Bernoulli (energy) relation as follows (Falvey, 1990): σ= ( P_atm/γ- P_V/γ+h cos⁡θ )/(〖V_0〗^2/2g) (5) Where P_atm is the atmospheric pressure, γ is the unit weight of the water volume, θ is the angle of the ramp to the horizon, r is the curvature radius of the vertical arc, and h cos⁡θ is the flow depth perpendicular to the floor. Therefore, the limited conditional function can be written as follows: W(X)=(P_atm/γ- P_V/γ+h cos⁡θ )/(〖V_0〗^2/2g) -σ_cr (6) Flow-3D is a powerful software in fluid dynamics. One of the major capabilities of this software is to model free-surface flows using finite volume method for hydraulic analysis. The spillway was modeled in three modes, without using aerator, ramp aerator, and ramp combination with aeration duct as detailed in Flow-3D software. For each of the mentioned modes, seven discharges were tested. According to Equation (6), velocity and pressure play a decisive and important role in the cavitation occurrence phenomenon. Therefore, the reliability should be evaluated with FORM (First Order Reliable Method) based on the probability distribution functions For this purpose, the most suitable probability distribution function of random variables of velocity and pressure on a laboratory model was extracted in different sections using Easy fit software. Probability distribution function is also considered normal for the other variables in the limited conditional function. These values are estimated for the constant gravity at altitudes of 500 to 7000 m above the sea level for the unit weight, and vapor pressure at 5 to 35° C. For the critical cavitation index variable, the standard deviation is considered as 0.01. According to the conducted tests, for the velocity random variable, GEV (Generalized Extreme Value) distribution function, and for the pressure random variable, Burr (4P) distribution function were presented as the best distribution function. The important point is to not follow the normal distribution above the random variables. Therefore, in order to evaluate the reliability with the FORM method, according to the above distributions, they should be converted into normal variables based on the existing methods. To this end, the non-normal distributions are transformed into the normal distribution by the method of Rackwitz and Fiiessler so that the value of the cumulative distribution function is equivalent to the original abnormal distribution at the design point of x_(i*). This point has the least distance from the origin in the standardized space of the boundary plane or the same limited conditional function. The reliability index will be equal to 0.4204 before installing the aerator. As a result, reliability, p_s, and failure probability, p_f, are 0.6629 and 0.3371, respectively. This number indicates a high percentage for cavitation occurrence. Therefore, the use of aerator is inevitable to prevent imminent damage from cavitation. To deal with cavitation as planned in the laboratory, two aerators with listed specifications are embedded in a location where the cavitation index is critical. In order to analyze the reliability of cavitation occurrence after the aerator installation, the steps of the Hasofer-Lind algorithm are repeated. The modeling of ramps was performed separately in Flow-3D software in order to compare the performance of aeration ducts as well as the probability of failure between aeration by ramp and the combination of ramps and aeration ducts. Installing an aerator in combination with a ramp and aerator duct greatly reduces the probability of cavitation occurrence. By installing aerator, the probability of cavitation occurrence will decrease in to about 4 %. However, in the case of aeration only through the ramp, the risk of failure is equal to 10%.

 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.  

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.  

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. 

The results of the present study showed that these types of weirs could have a better lateral performance than other weirs. In addition to this research, other researchers can conduct detailed studies on sedimentation and sediment control in this type of weir.   Keywords:Discharge, Flow, Water Diversion Structure

Weirs are always one of the most important components of water transmission networks, due to its simple structure and function. These components play an important role in the hydraulic structures by regulating the water surface, measuring the flow discharge and increasing the water level. And as a result, provide water heights needed to divert the desired flow into the lateral channels. Also, these structures are used as flow measuring devices of the important applications of overflows, the secure flow of floods behind the dams. The purpose of this study is to investigate the investigation the effect of positive Variation of weir in cross section on discharge coefficient of triangle weirs structures and provide a relationship for estimating the discharge coefficient based on geometrical hydraulic parameters. The discharge coefficient was defined as a function of Froude number (Fr), angle of vertex, ratio of water head to height of weir (H/P) and ratio of water head to effective length (H/Le). To achieve this aim, several experiments were done in the water and sediment laboratory, located in Gorgan agricultural sciences and natural resources university . The experiments were accomplished by 4 different angles of vertexes and 3 different slopes. Then, an equation was set by using Gene Expression Programming (GEP) to estimate the discharge coefficient by more accuracy. The findings showed that the discharge coefficient would decrease by increasing trend in the side slopes in the constant Froude number. Also, by increasing the ratio of H/P a decreasing and increasing trend in the discharge coefficient was seen, respectively. The results show that GEP predicted the coefficient of triangle weirs structures with R2 of 0.9676 and 0.8591 and RMSE of 0.0706 and 0.0247 for training and testing stages, respectively. This model gave better results compared by regression equation with R2 of 0.9253 and 0.8029 and RMSE of 0.0467 and 0.084 for training and testing parts, respectively. In the other words, the error of coefficient triangle weirs structures prediction was decreased about 47.10% using GEP approach. The results show that GEP intelligence approach is an adequate model to coefficient triangle weirs structures. Also, the results of traditional regression equations were improved using this method. In the other words, these results indicated that GEP is reliable to evaluate the coefficient discharge of triangle weirs structures by more accurate estimation. So; use of this way is suggested in future studies related to this topic.

Recent human activities have raised average temperature of the Earth’s surface. This increase will also influence climate variables and will result in climate change. With changing climate variables such as temperature and precipitation, the hydrologic regime of the rivers, and consequently flood frequency and magnitude, will also change (IPCC, 2001; Khazaei at al., 2012). For active adaptation strategy, it is necessary to assess impacts of climate change on floods. It is frequently mentioned in the literature that one of the potential impacts of climate change is the change on floods, however limited studies aimed at investigation of the change of flood regime due to CC. Generally, climate change impact assessment on floods comprises two main steps: preparing future climate data and hydrological simulation of river-flow. For hydrological simulation of flood flows, hydrologic models can be classified in two main classes, including single-event models and continuous models. In some studies, single-event rainfall-runoff models have been used (e.g. Roy et al., 2001; Muzik, 2002). In such studies, the reason for using these models was simplicity. In spite of the ease in using single-event models, the initial soil moisture condition in the future changed condition is unknown. Due to high sensitivity of simulated floods to initial condition of soil moisture, application of single-event models deals with great uncertainty (Roy et al., 2001). So, for assessment of climate change impact on floods, continuous models are required (Prudhomme et al., 2002). For climate change impact assessment on floods using continuous hydrologic models, normally, watershed-scale time series with fine time step for future climate are needed (Prudhomme et al., 2003). The most common tools to simulate future climate scenarios are GCMs. However, since resolution of GCM outputs is course, it is necessary that GCM outputs be downscaled. At least, rainfall and temperature data should be downscaled for continuous hydrologic simulation, throughout it is important to preserve the correlation between the downscaled variables (Fowler et al., 2007). Among downscaling methods, Change Factors (CFs), Weather Generators (WGs), and RCMs preserve the correlation between downscaled variables. In general, RCMs and WGs cannot accurately reproduce extremes. So in most previous studies CFs method have been used (e.g. Reynard et al., 2001; Prudhomme et al., 2002, 2003; Mareuil et al, 2007; and Kay et al., 2009).
In this paper, the climate change impacts on floods were assessed in one of the main sub-basins of the Karun basin. Rainfall-runoff process of the basin was simulated using ARNO semi-distributed continuous rainfall-runoff model (Todini 1988). The main phenomena which represented in the ARNO model are: snow melt, water losses through evapotranspiration, soil moisture balance, groundwater flow, overland and channel flow routing. The rainfall-runoff model was calibrated and validated for the basin using eight years of high-quality daily data of stream-flow at the outlet, and daily precipitation, Tmax, and Tmin at Yasuj meteorological station, close to the centroid of the basin. For future climate scenarios, projections of the CGCM3 model under A2, A1B and B1 emission scenarios were used for both control (1974–2000) and future (2067–2093) periods. The climate scenarios were downscaled for the basin using the Change Factors (CFs) method. In CFs method, the differences between means of GCM outputs for control and future periods are applied to every baseline observed data series, either as summation (for temperature) or multiplication (for precipitation).
As result of rainfall- runoff modeling, the Efficiency Criterion (EC) of calibration and validation stages were turned out to be 0.87 and 0.83, respectively, also determination coefficients (R2) were 0.85 and 0.88, respectively; while the flood values were simulated closely. In comparison with other studies, Zhang and Savenije (2005) adopted acceptable calibration when EC is greater than 0.6. Meanwhile, Kamali et al. (2007) accepted EC values of greater than 0.7. Thus, the performance of the model in overall the hydrograph is very good. In order to produce future climate series, the CGCM3 projections for each of the A2, B1 and A1B scenarios were downscaled for the basin. With the future climate data and the rainfall-runoff model, daily stream-flow series at the future period were generated. Annual maxima daily floods were extracted from the daily stream-flow series and climate change impacts assessed on annual maximum floods distribution. Based on the results, the magnitude of the floods will increase in the changed future climate. For instance, under these scenarios, flood magnitude with a return period of 25 years will increase between 50% and 120% for period of 2067–2093, in comparison to 1974–2000 historic period. Also, flood magnitude with a return period of 100 years will increase between 54% and 126%, under B1, A1B, A2 scenarios. It is concluded that despite the magnitude of the change, which is upon the choice of the emission scenario, the climate change will impose considerable increase on floods under all the regarded scenarios.

Cylindrical weir is one of the most common structures for measuring flow rate in open channels. Cylindrical weir is one type of broad-crested weirs that has extensive application due to its stable flow pattern and ease of passing suspended solids. Therefore, in this article, flow over a 7.5 cm diameter cylindrical weir in the rectangular channel was simulated using k-ε turbulence model in three-dimensional flow3D model. Validation was performed with experimental results. The obtained root mean square error of comparison between numerical discharge coefficient and physical values was 0.3427, which represents a good agreement of hydraulic characteristics obtained from numerical and physical models. It was also observed that discharge coefficient value of cylindrical weir was greater than 1.0. Dimensionless ratio of hydraulic head to crest radius was an effective parameter on discharge coefficient, such that its 100% increase enhances discharge coefficient more than 100%. In the numerical model of cylindrical weir, such parameters as velocity, pressure, flow depth and kinetic energy and turbulence were analyzed and compared in some sections of the channel with respect to the weir. Results showed that depth and pressure in the upstream have larger amounts than in the downstream. But, results of velocity were opposite the pressure and hydraulic head. Finally, a relationship was provided for determination of kinetic energy of the flow over the cylindrical weir.

Labyrinth weir is one of the nonlinear hydraulic structures that its geometrical shape increases the discharge coefficient of flow over the weir. In this study, a labyrinth weir, located in a 14.6 m long channel, was simulated and verified using an experimental model with 6 different discharges (15

One of the highest losses due to natural disasters is bank erosion. Rivers affected by erosion and sedimentation are subject to various changes such as change of direction, movement in transverse and longitudinal directions, bed level changes and transformation of geometric features. There are several methods to protect the bank in the outer arc, spur dikes are one of thebest and most economical methods used in most parts of the world. In this study, flow and sedimentpatterns in a 90 degree mild bendwith and without spur dikes by changing the position and length of the spur dikes with Configurations 15%, 20% and 25% of the flume width was examined using numerical model CCHE2D and by considering the hydraulic performance of spur dikes the optimum combination of parameters, length and position of spur dike in the bend were investigated.
The bend used in the numerical simulation in this study isa 90 degree mild bend flume with 70 cm width in hydraulic laboratory of Shahid Chamran University. In order to simulate the flow and sedimentpattern the numerical model CCHE2D was used in this study. This model is a two-dimensional hydrodynamic model which has been prepared and developed at theInternational Science and hydraulic center of Mississippi School of Computational Engineering in America.
Hydraulic and sedimentary results were verified by comparing the simulated results by model with experimental results. The results indicatethe numerical models high capability in simulating the flow and sediment pattern in the bend. Comparison of the model and experimental velocity results indicates an accuracy of more than 94 percent. The sediment validation also indicated that the models accuracy in estimating the sediment erosion and deposition is over 90%.
The results show that by increasing the length of the spur dikes, the maximum velocity and depth of erosion and sedimentation also increases. For example, the maximum scour depth of spur dikes with length equal to 15 and 20 percent of flume width compared to spur dikes with 25 percent of flume width length decreases 44% and 33% respectively. Also the maximum velocity of spur dikes with 15 and 20 percent of flume width length decreases 9% and 16% respectively compared to spur dikeswith 25 percent of flume width length. The results show that the erosion and sedimentation pattern of spur dikes with length equal to 20% of flume width is preferred. Because, firstly they divert the flow to the center of the main channel with causing the least changes in the channel bed. Secondly, the spur dikes with 15% and 25% of the channel width length cause a massive volume of sedimentation in the inner arc of bend.

In this research the spreading coefficient of dense flow under the jet hydraulic in the surrounding fluids of clean water and at the accepting environment with the low depth and high depth has been analyzed. The analyzed parameters are included of discharge injection, density of contaminating fluid, diameter and angle of the contraction of jet nozzle and shallow and deep water ambient fluid.
These tests are being conducted in the flume laboratory. The results obtained from the tests show that the circulation coefficient is a function of contaminating density and the depth of the accepting environment, such that with increase in the density, the accepting environment depth coefficient will an increase and circulation and coefficient dispersal with the densities of 15, 30, 50, 200 g/lit, are 0/121, 0/135, 0/153, and 0/196 respectively. On the one hand, in the accepting environment depth it has been shown that increase in the Froude density number up to 30 causes decreases in the circulation and coefficient dispersal and then this coefficient will be used in the constant amount of 0/1.
Results showed that the profiles taken by the GOSEN distribution function and also coordinate the direction taken compliance with about 8/9% errors. Therefore the amount of dispersion of drained stream with accepted error and the use of accepted axial- radial coordinate have been extracted. The most speed has been taken place in the central line and getting further from the center reduces the speed. On the one hand, along the moving path the limits of Jet reduce which is surrounding conditions. On the other hand, considering the continuity coordination in different places from the jet, and reduction of speed, the dispersion width increases. And also according to the analysis conducted it is clear that speed profiles measured is consistent with Gussein distribution. Generally the flow of the sank jets, which are located at an accepting running flow such as rivers or seas, consisted of two areas, with different equations. These two areas are consisting of area (field) close to the jet and area (field) far from jet. When two fluids with different consistencies interfere with each other, it produces a floating jet. In this phenomenon the effective power consisted of composition of floating powers and the amount of movement. Now, if the injected fluid is heavier than the acceptant fluid, the jet will have a negative floating condition and if it is lighter, the jet will have positive floating condition. Ls are the space between an acceptance static fluid and a homogenous fluid and the amount of momentum is more than the floating charge. If the flow of acceptor fluid and jet are not in the same direction, it shows the jet penetration in the fluid, but if both are in the same direction, in this case Ls shows the limitation of the jet. The power and ability of the jet depend directly on the Frode density number. Since in the Frood number, higher density causes stronger jet with the initial momentum. Since the distribution of coefficient after the Frode density number densimetric 30 will be used at the constant amount, it can be said that the amount before this is the "jet near field and the amount more than this is jet far field. The amounts for diagonals 5, 8.15 mm are 141/9, 225/90, 423/57 mm respectably. Results show that in the acceptor environment with low depth, development of the moving borders is nonlinear with second degree equations. In this condition maximum disposal coefficient is equal to 0/28 and its minimum is 0/095. In a low depth environment it has been seen that in a relatively constant depth increase in the Frode density from 52 to 120 the amount of coefficient dispersal decreases up to 2/7 times. This is when for a constant Frode density, the average increase in the relative depth from 5 to 15 the amount of coefficient dispersal is about 16.5%. Increase in the Frood density number causes decrease in the coefficient dispersal. This decrease is due to increase in the speed of fluid entrance in the jet and more energy drop due to more friction with the fluid jet borders. In the other words, increase in the amount of momentum coefficient dispersal will be reduced. At the constant hydraulic conditions, with increase in the relative depth, acceptor environment coefficient dispersal increases which is due to decrease in the adhesion condition and decrease of the depth. Acceptor environment with low depth initial entering speed increases which is due to increase in the Frode density number in one constant length which causes decrease in the floating parameters. On the one hand, increase in the entering speed the amount of friction with the border and therefore the amount of energy drop increases and cause disturbance in the flow with the moving jet borders.
In the low depth acceptor environment with a relative constant depth, the amount of percentage of increase in the density of Frode number decreases. Considering the tests conducted it has been shown that the coefficient of dispersal in the acceptor environment low and high depth are opposite to the Frode density number, which means that with an increase in the density of Frode number, the coefficient dispersal decreases. It is also shown that increase in the depth, causes increase in the coefficient dispersal until it reaches a constant amount. Dependency of coefficient dispersal in relation to Densimetric Frode number and convergence angle show increase in the effect of density of Frode number in the convergence angle.

Bridge failures due to scour at bridge abutments clarify importance of flow field around them. Scope of this study is the comparison between experimental results and numerical simulation of bed shear stress around bridge abutment in a compound channel by Flow-3D model. In order to calculate the experimental bed shear stress, flow velocity was measured by a 3D electromagnetic velocimeter in different levels of flow depth of floodplain. For estimation of Reynolds stresses of u w¢ ,u¢v¢ and v¢w¢ , in low flow depth of floodplain, extrapolations of these values to the bed were used. Experimental results showed that maximum bed shear stress occurred at the upstream corner of the abutment. After mesh generation, hydraulic simulation of flow with Flow-3D model was run in 5 turbulent models of Prandtl mixing-length model, one equation turbulent energy model, k-ɛ model, renormalized group (RNG) model and large eddy simulation model. Comparison between models showed that the results achieved by the RNG model had a better agreement with experimental observations and the pattern of shear stress around the bridge abutment was well predicted by this model. Bed shear stress at the upstream corner of the abutment was determined by experimental results and RNG model giving 3.84 and 4.6 N/m2, respectively.

Scour generation and its development around bridge piers are the main causes of bridges damage and failure. Understanding the scour mechanism is essential to predict the scour and equilibrium scour hole status around bridge piers. In the recent decades, the use of compound bridge piers instead of the simple piers in construction of bridges, has been developed. In this study, using the FLOW-3D software, process of the formation and development of the scour around bridge pier with compound geometry has been investigated. Numerical results obtained from this model were compared with available experimental data. The results showed that this model had the capability to predict the threedimensional flow field and could effectively provide a better understanding of the experimental studies. The results also indicated the complexity of turbulent flow near pile cap so that these flows were deflected in all directions. On contrary to the simple pier, in which the positive maximum velocity occurred in the sides of pier, in the case of piers with compound geometry this velocity occurred in the center of the pier and downstream of the pile cap.

Weirs have widely been used for the flood flow, flow measurement, flow diversion and control of water levels in dams, rivers and open channels. This study was curried out to investigate the hydraulic characteristics of flow over the sharp-crested triangular plan form weirs for different apex angles. Three-dimensional flow field over the weirs 30, 60, 150 and 180 degrees was numerically simulated based on the RNG turbulence model using the software Flow-3D version 10.0.1. The results showed as the apex angle increases, the interference of the longitudinal and lateral falling flows decreases and in turn leads to less disturbance and vortex flow. Also, in downstream, the flow surface knob of the longitudinal profile and height difference between the transverse cross-section profile becomes less and velocity and Froude number increase, whereas the pressure on downstream bottom decreases. The results show that the RNG turbulence model for determining water surface profiles along the channel downstream of the weir of appropriate accuracy.

The flow-duration curve, has a great importance in design of dams, hydroelectric powers plants, watershed operations, drought risk assessment and checking the river ecosystems health, so it is better to be employed in the rivers hydrological plans. The aim of this study is to evaluate the efficiency of flow duration curves for verification of the Soil Moisture Accounting (SMA) model, in different time scales such as annual, semi-annual, seasonal and monthly modes to determine the effect of soil moisture on runoff generation in the Zola-Chay watershed. In this study, after the Zola-Chay watershed geometrical modeling using HEC-GeoHMS, soil moisture accounting model parameters were estimated and then rainfall-runoff simulation was done in different time scales. By examining flow-duration curves in different time scales with SMA model, it could be concluded that the flow-duration curves in the monthly time scale, were more accurate than the annual, semi-annual and seasonal time scales. These results endorsed the more accurate performance of monthly time scale compared with other time scales in rainfall–runoff simulation.

Examining the properties and behavior of the flow in the rivers and its associated structures is one of complex phenomena that make the use of software inevitable. First, the results of laboratory test carried out by Duan et al. (2009) in Minnesota university, are used verification and comparison of numerical simulations of FLOW-3D(version 9.3). The vertical spur dike was first simulated to verify the model results and the inclined spur dike with 60° and 30° to the flow direction was then considered. The simulation performed with FLOW-3D, for 650 seconds using turbulence models (k-ɛ, RNG, LES). By comparing different turbulence models with experimental results, the maximum scour depth at the tip of the spur dike was 8.82 cm. Then the maximum scour depth calculated by FLOW-3D in the turbulence models of (k-ɛ, RNG, LES) was 9.1, 8.9, 9.1 cm. So the error in RNG turbulence model is about 9 %, compare to the turbulence model k-ɛ, and of LES shows more agreement. In the simulation, the maximum scour depth at the tip of the spur dike 60° and 30° was 8.75 and 6.5 cm respectively.

One of the important purposes of river engineering science is to protect river banks from erosion phenomenon and to prevent shifting of the main channel path. Spur dike is a hydraulic structure which has a lot of applications for stabilizing river banks and increasing water depth. According to widespread use of this structure, it is important to understand the flow pattern around it. Since flow pattern around a spur dike is complex and fully 3D, 3D simulation was done in this study. FLOW-3D software was employed to simulate the flow around a submerged spur dike. VOF method was used for free surface simulation and RNG k-ε model was used for turbulence modeling. Based on comparison of numerical and experimental results for stream wise velocity component and flow depth, it was concluded that numerical model could simulate the flow parameters with relatively high accuracy. In following, the effect of discharge increase on velocity profiles and flow free surface was investigated. According to obtained results, maximum longitudinal velocity Infront of the spur dike nose and flow depth at the upstream of spur dike increased with discharge increase. In lower discharges, the changes rate was more and vice versa. Also, the ratio of the flow depth at the upstream and the flow depth at the downstream increased with discharge increase.

Most rivers have bend routs that the quite complex flow pattern is dominated on them. It is necessary to study the behavior of a river, the flow pattern is well known that the dominant bend. Numerical models as a powerful instrument for the prediction of such areas can provide a good understanding of them. In the present study using three-dimensional numerical model Flow-3D, Parameters of U/Uc the flow pattern at a 90 degree arc of the moving bed is placed. The results were compared with experimental data.Analysis of results relevant to flow pattern in cross sections and different plans are among other points introduced in this paper.

Cohesive sediments have large specific surfaces which enable them to absorb other cohesive sediments and polar particles such as mud and sodium. Floccules form by joining these particles. The behavior of cohesive sediments in aquatic environments is completely different from that of granular sediments. Under certain value of shear stress, the structure formed from cohesive sediments is divided into smaller particles, which can be eroded easily. Up to now, researchers have proposed empirical formulas which correlate the rate of erosion to the bed shear stress and the rheological characteristics of cohesive sediments. In this study, the calibration and verification tests are performed on Mike21 software to attain the results more adjusted with the experimental data. Afterwards, the data are developed by the model and converted to the dimensionless form. Finally, an exponential function is proposed for the erosion rate in cohesive sediments. It is found that the coefficient of determination is 0.99