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Introduction: There is a number of evidence for the construction of weirs and diversion dams in river bends, and sometimes building water intakes on both sides of the river bend are needed. However, this encounters problems in terms of asymmetry of flow distribution into the intake structures. Most recent studies have been conducted for clear water flow conditions. The main purpose of this study was to investigate the uniformity of sediment transporting flows into bilateral intakes on both sides of a spillway in a channel bend. FLOW-3D numerical model was used to test the effects of intake angle, intake sill and sluice way on the uniformity of flow and sediment load entering the intakes and the distribution of sediment deposits in the intake area. The numerical model was calibrated and confirmed based on the information of the physical model for clear water flow conditions. Then, the numerical model for sediment transport flow was validated and adjusted, and it was implemented for seven scenarios of the arrangement of the weir and its related structures in the channel bend. The results showed that the most of the sediment deposition is towards the inner-bend intake. Without the intake sill and sluiceway, the ratio of outer to inner intake for five intake angles of zero, 30, 50, 60 and 90 degrees is about 2.1, 3.8, 5.0, 4.17 and 2.4, respectively. Using a 90-degree intake is more efficient due to less sediment entry and uniform inflow distribution to both bilateral intakes. Inclusion of sill and sluiceway in the intake system results in the reduction of the ratio of outer to inner intake to be reduced to 1.1 and 1.3 for the two intake angles of zero and 90 degrees, respectively. The results show that it is necessary to use the intake sill and the sluice way to control the sediments entering to the intakes, especially in inner intake. Methodology: In this study, FLOW-3D numerical model was used to simulate sediment transport flow into bilateral intakes on both sides of a diversion dam in a channel bend. The geometric conditions of modeling are considered based on the laboratory study (FarhadiBansuleh and Yasi, 2019). The laboratory channel is a rectangular channel with a 90o bend. Numerical model based on physical model information (Farhadi-Bansuleh and Yasi, 2019) for clear water flow conditions, calibration and validation; and validated and adjusted for sediment transport flow. In reality, dewatering from diversion dams takes place at different angles, therefore, in this research, an attempt has been made to investigate the effect of different intake angles on the uniformity of water distribution and the entry of sediments into intakes, so there are seven scenarios to test the effects of intake angles, intake sill, and sluice way, in checking the flow pattern and deposition of sediments in the area of intakes, and the distribution of flow and sediment load to outer and inner intakes. Results and Discussion: In the modeling of sediment transport flow, the results show that the uniformity of water distribution is better in intakes with a zero degree angle. So that the rate of sediment into the outer and inner intakes is 9 and 14 times higher than the 90o intakes, respectively. The rate of sediment into 90o intakes is 6, 4.4 and 3 times lower for the outer intake, and 18, 17 and 15 times lower for the inner intake than at 30, 50 and 60 degrees. Inclusion of sill and sluice way in the intake system results, the uniformity of water distribution in intakes with zero and 90 degrees angle is improved by 47 and 45 percent, respectively. In the zero-degree intakes, the sediment load into the outer intake does not change significantly compared to the condition without a intake sill and sluice way; But this amount decreases by about 65 percent in the inner intake. These results are also true for the 90 degree intakes, so that the sediments load into the outer intake does not change, but in the inner intake it decreases by about 71 percent compared to the condition without intake sill and sluice way. Conclusion: The results showed that the most of the sediment deposition is towards the innerbend intake. Without the intake sill and sluiceway, the ratio of outer to inner intake for five intake angles of zero, 30, 50, 60 and 90 degrees is about 2.1, 3.8, 5.0, 4.17 and 2.4, respectively. Using a 90-degree intake is more efficient due to less sediment entry and uniform inflow distribution to both bilateral intakes. Inclusion of sill and sluiceway in the intake system results in the reduction of the ratio of outer to inner intake to be reduced to 1.1 and 1.3 for the two intake angles of zero and 90 degrees, respectively. [ABSTRACT FROM AUTHOR]

The volume of sediment transport rate during floods is one of the important issues in river engineering. This volume of sediments has caused countless damages to the hydraulic structures which are built along the rivers, every year. The purpose of this study was to investigate the effects of hydrograph unsteadiness parameter on bedload transport rate. For this purpose, a real unsteady flow hydrograph was created inside a 15 m long tilting flume by installing an interface board between the computer and the pump inverter. 20 cases of hydrographs with different unsteadiness parameters were tested and the scour rate was obtained during the hydrograph time. The results indicate that the maximum scouring rate always occurs near the peak of the flood hydrograph and the time lag between them was positive. For hydrographs with the same peak and different base time, the maximum scouring rate occurs in the hydrograph with more unsteadiness. The maximum scouring rate of the bed has a direct relationship with the unsteadiness parameter, and it can be said that an 88% decrease in the flow unsteadiness parameter leads to a 76% decrease in the maximum bedload rate. Also, the scour rate in the ascending limb of the hydrograph is higher than the descending limb, which by reducing the unsteadiness parameter, the distance between the limbs in the sediment hysteresis diagram decreases.

The formation of bed form in alluvial rivers due to sediment transport has a significant effect on the hydraulic parameters of the flow such as bed shear stress. The formation of the bed form and its shape and geometry depends on the bed shear stress. Therefore, the relationship between bed form and flow parameters (such as bed shear stress) is complicated. In the present study; the effect of dune bed forms with different heights on bed shear stress has been investigated. Artificial dunes made by sand-cement mortar with a length of 25 cm and heights of 1, 2, 3, and 4 cm were used. In the tests of this research, flow discharge of 10, 15, 20, 25, and 30 l/s and bed slopes of 0, 0.0001, 0.0005, 0.001, and 0.0015 were used. The results showed that with increasing the relative submergence and Δ/λ, the bed shear stress increased in dune-covered beds. The formation of the dune bed form and the increase in its height leads to an increase in the bed shear stress. The bed shear stress in dunes with a height of 1, 2, 3, and 4 cm was, on average, 39, 80, 141, and 146% more than in plane beds, respectively. Moreover, form shear stress for dunes with a height of 1, 2, 3, and 4 cm was, on average, 27.37, 43, 57.11, and 58.74% of the total shear stress, respectively.

Natural rivers experience significant sediment transport rates during floods. The purpose of this study was to investigate the effects of flood hydrograph intensity parameter on the amount of bed sediment transport rate. For this purpose, a real unsteady flow hydrograph was created inside a 15 meters long tilting flume by installing an interface board between the computer and the pump inverter. Sediments with a d50 of 2.69 mm have been put uniformly on the bottom of the channel and the flood hydrograph has been applied on it after saturation. 20 cases of hydrographs with different intensity parameters were tested and the erosion rate was obtained during the hydrograph time. The results show that the maximum erosion rate always occurs near the peak of the flood hydrograph and the time delay between the peak of the flood hydrograph and the peak of the sediment hydrograph is mostly positive. The erosion rate in the rising limb of the hydrograph is higher than the falling limb, and the distance between them decreases in the hysteresis diagram as the flow intensity parameter decreases. The changes of bedload transport rate (qb) in terms of flow rate (Q) are clockwise hysteresis. By decreasing the hydrograph intensity parameter by 32, 57, 75 and 87%, the total volume of transferred sediments decreases by 27, 51, 78 and 90%, respectively. A 50% decrease in the base time of the hydrograph under the same conditions has caused a 46% decrease in the total volume of transported sediments. [ABSTRACT FROM AUTHOR]

Flood zoning maps are among the basic and important sources of information for studying development projects in the world. In the conventional method of determining flood zoning maps, calculations are performed on the basis of a steady flow, assuming a fixed bed (without considering sediment transport). This study aimed to investigate the impact of river erosion and sediment transport on river flood zoning. So, the flood zoning calculations of Ajichai River were done using HEC-RAS model and the conventional method of steady flow with a fixed bed. In the next step, flood zoning calculations were performed using quasi-steady flow with moving bed and compared with the results of the previous step to determine the impacts of sediment transport on flood zoning. Comparison between the results obtained from steady flow (fixed bed) and quasisteady flow with moving bed showed that in sedimentation sections, the width of the water surface increases in the flow mode with moving bed. The maximum rate of this increase in width is 19%. In other words, in the mentioned river, the width of flood zoning is less in the conventional method. This issue confirms the necessity of studying the river conditions in terms of erosion and sedimentation so that the amount of flood zone could be determined more accurately while the river is sedimentary. The increase of flood zone in sedimentation sections is due to the accumulation of sediments and consequently the increase of flow level and width of flood zonation. Therefore, it is suggested that in sedimentary rivers, a quasi-steady flow model (mobile bed) be used to prepare flood zoning maps for providing more safety. [ABSTRACT FROM AUTHOR]

The formation of bed form in alluvial rivers due to sediment transport has a significant effect on the hydraulic parameters of the flow such as bed shear stress. The formation of the bed form and its shape and geometry depends on the bed shear stress. Therefore, the relationship between bed form and flow parameters (such as bed shear stress) is complicated. In the present study; the effect of dune bed forms with different heights on bed shear stress has been investigated. Artificial dunes made by sand-cement mortar with a length of 25 cm and heights of 1, 2, 3, and 4 cm were used. In the tests of this research, flow discharge of 10, 15, 20, 25, and 30 l/s and bed slopes of 0, 0.0001, 0.0005, 0.001, and 0.0015 were used. The results showed that with increasing the relative submergence and Δ/λ, the bed shear stress increased in dune-covered beds. The formation of the dune bed form and the increase in its height leads to an increase in the bed shear stress. The bed shear stress in dunes with a height of 1, 2, 3, and 4 cm was, on average, 39, 80, 141, and 146% more than in plane beds, respectively. Moreover, form shear stress for dunes with a height of 1, 2, 3, and 4 cm was, on average, 27.37, 43, 57.11, and 58.74% of the total shear stress, respectively. [ABSTRACT FROM AUTHOR]

Coarse particle motion behavior plays a crucial role in sediment and hydraulic engineering, though its physics is still not fully understood. Disregarding the inherently stochastic nature of the sediment transport leads to various equations for bedload transport which are now being challenged due to their poor results. By applying sensors, like accelerometers and gyroscopes, particle transport physics could be carried out in a more scrutinized approach. In this study, an instrumented synthetic particle ("so-called" the smart particle) was designed and applied (with different densities) in sets of laboratory experiments that covered a hydraulics domain between low transport regime (near- and above-threshold) and higher transport regime (above threshold with a relatively high Reynolds number) conditions. Using the instrumented particle (smart-particle) could bring opportunities to learn more about the physics of the bed particle transport in rivers for different regimes and could bring data in hand for instantaneous particle changes throughout time (hear 0.004 seconds used for data sampling). Therefore, the kinetic energy as a parameter that delivers the behavior of particle energy interaction between the exposed particle and its surroundings (flow and the bed particles) was chosen to be studied. Since the dynamic features of the particle in transport are stochastic, the probability distribution functions, which could describe the particle behavior, were selected (Weibull, Lognormal, Normal, and Gamma distributions). In this case, it was shown that the Weibull distribution best described the particle kinetic energy in lower transport regimes, while for a higher transport regime, the Log-normal distribution worked better. Furthermore, the energy signals of the particle moving throughout the flume for different transport regimes were derived, and it was shown that the average energy gain and loss of the particle decreased exponentially as the particle Reynolds number increased. The presented results here could also be applied in similar hydraulic conditions in eco-hydraulic topics, specifically macro-plastic movement as bedload in river courses and the Aeolian research.

Laboratory experiments were carried out to investigate the hydraulics, turbulence structure, and sediment removal capacity of bridge pier with different adjusted roughness. Four experimental models of the roughness were employed to measure the effect of the geometry of the roughness on the scour hole formation and depth. The effects of roughness geometry on the turbulence structure and local erosion through the bridges were studied for one sand sediment size. The three-dimensional velocity profiles and turbulence characteristics of flow downstream and upstream of the bridge pier were measured by Acoustic Doppler velocimetry (ADV) technique due to different adjusted roughnesses. After filtration process by WinADV software, the contour plots of the turbulence kinetic energy were depicted due to triangular roughness. The maximum longitudinal eroded section, which is commonly located by bridge pier corners, was measured through the experiments. The results of the scour hole measurements indicate that due to increasing the length of the roughness, the scour hole depth values decreased; however, increasing the vertical distance has the same effect on the scour hole formation. Furthermore, different geometries of the employed roughness illustrate that the triangular roughness has less scour hole depth than other experimental models with the same hydraulic condition. The detailed information of the magnitude, distribution, and probability of turbulence structures was extracted from time-series data using power spectra. The turbulence data were compared with the topography of upstream erosion. Analysis of the power spectrum density function indicated that the discontinuous adjusted roughness remarkably reduced the downward energy level of vortexes at the upstream of bridge pier, which is supposed that the gap opening through the roughness can increase downward jets impact. It appears that this condition reduces the turbulence kinetic energy near the bed elevation at the upstream face of squire bridge pier.

The authors unanimously wish to retract this paper because of several incorrect statements and erroneous presentation and copyrights issues of primary data.

Water supply at a desired rate at any time to meet the water requirements regardless of river discharge must be considered in the general design of intakes provided that the needs do not exceed the river flow. Due to the lack of necessary information in this field and the importance of sediment transport to the lateral intakes at river bends, this study aimed at understanding the mechanism of this phenomenon. To this end, the combined effect of convergence and divergence in lateral intakes on the sediment transport was investigated. According to the results, the diversion discharge to the intake was increased by converging the laboratory flume. By narrowing and converging the end of the flume, the diversion discharge was increased further, so that as the flume was converged to the size (b/B) of 0.75 and 0.5, the diversion discharge to the intake was increased by 13.6% and 75%, respectively. This could be connected to narrowing, flow obstruction and backflow to the intake. In contrast, different results were found by diverging the flume. In other words, the inflow to the intake was decreased by diverging the flume. As the flume end was diverged, the diversion discharge was decreased further. By diverging the flume to the size (b/B) of 0.75 and 0.5, the diversion discharge to the intake was decreased by 21.9 and 31.8%, respectively. The average diversion discharge to the intake at 30, 60 and 90º was 13.2, 15.2 and 11.5%, respectively. By converting the flume to the size (b/B) of 0.75 and 0.5, the diversion sediment to the intake was increased by 18.5 and 71.4%. In contrast, by diverging the flume to the size (b/B) of 0.75 and 0.5, the diversion sediment to the intake was decreased by 35.4 and 49.9%, respectively.

Water supply at a desired rate at any time to meet the water requirements regardless of river discharge must be considered in the general design of intakes provided that the needs do not exceed the river flow. Due to the lack of necessary information in this field and the importance of sediment transport to the lateral intakes at river bends, this study aimed at understanding the mechanism of this phenomenon. To this end, the combined effect of convergence and divergence in lateral intakes on the sediment transport was investigated. According to the results, the diversion discharge to the intake was increased by converging the laboratory flume. By narrowing and converging the end of the flume, the diversion discharge was increased further, so that as the flume was converged to the size (b/B) of 0.75 and 0.5, the diversion discharge to the intake was increased by 13.6% and 75%, respectively. This could be connected to narrowing, flow obstruction and backflow to the intake. In contrast, different results were found by diverging the flume. In other words, the inflow to the intake was decreased by diverging the flume. As the flume end was diverged, the diversion discharge was decreased further. By diverging the flume to the size (b/B) of 0.75 and 0.5, the diversion discharge to the intake was decreased by 21.9 and 31.8%, respectively. The average diversion discharge to the intake at 30, 60 and 90º was 13.2, 15.2 and 11.5%, respectively. By converting the flume to the size (b/B) of 0.75 and 0.5, the diversion sediment to the intake was increased by 18.5 and 71.4%. In contrast, by diverging the flume to the size (b/B) of 0.75 and 0.5, the diversion sediment to the intake was decreased by 35.4 and 49.9%, respectively. [ABSTRACT FROM AUTHOR]

Investigation of channel capability for sediment transport is an important factor in sanitary sewer and urban runoff drainage system design. This is because of the undesirable effects arising from the reduced channel hydraulic capacity due to the deposition of sediment particles. Self-cleansing channel designs minimize sediment deposition and, thereby, prevent reduced channel hydraulic capacity. Our literature review revealed no previous report on self-cleansing models yet proposed for channels with trapezoidal sections. An experimental study was conducted using a trapezoidal channel and a non-deposited bed to investigate the self-cleansing process with four different sediment particle sizes under various slopes and discharge rates. The experimental data were exploited to develop a bed load self-cleansing model for the trapezoidal channel considering the specific flow, fluid, sediment, channel, and sediment characteristics. The proposed model was then compared with those reported in the literature for circular and rectangular channels. It was found that channel section geometry is a decisive factor in channel self-cleansing rate. Comparisons revealed that circular and rectangular self-cleansing models produce an error of approximately 15% when employed for designing channels with trapezoidal sections. Hence, the model developed in this study is recommended for designing channels with trapezoidal sections

In general, rivers are one of the best and most accessible water resources at the disposal of mankind. So, given the effect of the force of water and changes on the flow patterns and consequently, on river morphology changes, the analysis of the flow in the river is important and necessary to organize projects, flood control and water supply structures downstream. In this study, by using numerical models CCHE2D hydraulic conditions Dimeh River Bridge between Oregon Bridge Sudjan was investigated. CCHE Model is a mathematical model capable of simulating the flow patterns and sediment transport in rivers and canals laboratory network. The numerical model in 1998, based on the calculations by the National Centre for Water Science and Engineering, University of Mississippi (NCCHE), was developed and has been applied in many research projects related to water engineering. At the outset, the input data required model provides and numerical model was implemented. In the next step, the results of the model were calibrated and validated using field data measurements; eventually, they were extracted and their model results were compared; it was confirmed that CCHE model could still simulate the flow pattern. [ABSTRACT FROM AUTHOR]

1- Introduction The reduction of biomass in arid, semi- arid and semi- humid ecosystems is called desertification. In recent years, processes of desertification have created many unrepairable damages. Desertification in developing countries and in countries with the high potential of decortications is more severe. Then, control of this phenomenon, spatially in these countries is more useful. To present the strategies and suitable methods for management in this background, understanding of effective parameters in desertification is very important and virtual that it should be investigated. Many researches for investigating the condition of desertification have been done by some researchers in the world such as Harasheh et al (2000), Ladisa et al (2002), Lira (2004), Monia Santini et al (2010), Faiz nia et al (2000), Abrisham (2004), Khosravi (2004), Fallah mehne (2004), Sepehr (2005), Ahmadi (2006), Zehtabian et al (2006), Chaman pira et al (2006), Abdi (2007), Tabatabaei (2010). 2-Methology The general aim of this research is to investigate the condition of desertification in the study area by measuring the soil erosivity and determining their effective factors and critical areas for controlling the desertification. For doing that the IMDPA model has been used as this model is the result of integrated plan of indices and criterion of desertification in Iran. This model is the first one that has presented for quantification of effective indices of desertification in biomes of Iran. In this research, for investigating the condition of desertification and presenting its map the IMDPA model has been used and indices of water and wind erosion have been investigated. Land desertification was studied in map unit and under arid climatic condition. For criteria of water erosion, four indices (water erosion density and type, land use, vegetation density) were investigated and their data layers were created in GIS system environment. After that by laying each pair of data layers, the final score of water erosion criteria was obtained in each unit by equation 1. I= equation (1) 1I=i ΠIi 1 ≤i≤ 3Where I: the final score of index of desertification potential based on water erosion criteria in each unit. Ii: the score of each index in each unit. For wind erosion criteria, their indices (appearance of erosion, density of non- alive cover and the numbers of dusty days) were measured by laying these digital layers, the final score of wind erosion criteria in each unit was obtained. I= equation (2) 1I=i ΠIi 1 ≤i≤ 3 I: final score of index of desertification potential based on wind erosion criteria in each unit Ii: the score of each index in each unit. Finally, the intensity map of desertification based on criteria of wind and water erosion was provided separately. 3-Discussion The obtained results show that surface cover has important role in desertification phenomenon from viewpoint of water erosion (vegetation index) and also from viewpoint of wind erosion criteria (density of non alive and vegetation). Some parts of this problem is due to the climatic condition of study area such as arid climate, less rainfall, high evapotranspiration, have been created sever condition. This point, following the intensitive drought in recent years, has been made the reduction of quantity and quality of vegetation. Moreover, railway, and other communicational roads (like Bafgh- chadormaloo) has been effective in degradation of vegetation. With respect to the obtained results, the important factors in erosion (wind and water) and desertification phenomena can be introduced as follows: • Intensive and erosive winds that leads to the moisture reduction, degradation of vegetation and finally detachment and transport of windy sediments. • Daring water erosion in sensitive formations in mountains of study area, fine sediments hare been scattered on the surface and finally these sediments can be moved by wind erosion. Moreover, inappropriate activities by some organizations (such as embankment dams) have been lead to severity of wind erosion. • Dominant of dry climate, less precipitation and high evapotranspiration, has been created hard conditions in the study area. This point following the sever droughts in recent years have increased the wind erosion in study area. • Release of agricultural lands, especially near the Shour river of Bahabad. • Constructions of many roads have also been created water and wind erosion. • Digging the deep wells for agricultural and industrial activities • Transgression to riversides and water ways and non scientific planting (especially around the Shour River in Bahabad). Overall, it can be stated that although the natural factors have been affected in desertification, but human parameters have also created desertification directly (land degradation) and indirectly (as a factor on intensification of degradation of natural factors). This point is also accordance with the results of sepehr (2005) in regarding to the effects of desertification in south of Fars province and Chamanpira (2006) for desertification in kouh- Dasht watershed. 4-Conclusion IMDPA model is integrated and complete method that has been calibrated with Iran conditions, then this method has less error. Moreover, existing the sufficient numbers of indices (coinciding with the area condition) has been made to obtain the good estimation from desertification condition. In the other hand, to access the results it is essential to investigate the other criterion of IMDPA model such as climate, geology, geomorphology, soil, vegetation, agriculture, water, social- economical problems and technology of city development. Finally and witch respect to the results of this research that surface cover is important factor in intensification of wind and water erosion, than it is essential to change the sight of people and users to natural resources. Therefore, considering the environmental problems and land logistic rules for each project in the study area is essential. Moreover, instruction the local communities and increasing the level of information and knowledge of decision makers and users can improved the sustainable development and lead to the control of desertification. [ABSTRACT FROM AUTHOR]

Construction of ports and coastal structures actually affects the coastal flow pattern and results in the changing of the sedimentation pattern. The research carried out in this paper, aims to simulate sedimentation process following the construction of the Bandar-e Anzali New Breakwaters at the site, using Iranian developed PMO hydrodynamics and well known MIKE21 modeling package developed by DHI. These two models utilize different mesh technique to solve the governing flow hydrodynamics and transport equations. So to compare the results obtained from these two models, sensitivity analysis and calibration procedures using field data were undertaken firstly. Then wave propagation pattern of waves with heights of 0.5, 1 and 1.5 m in the spectral wave module (SW), long shore currents in the hydrodynamic module (HD) and sediment transport simulation in the sediment transport module (SD) have been considered using both models. Various statistical parameters were obtained and the results showed good agreement between the two mentioned models with at least 90% correlation coefficient in all cases. Furthermore, the study showed acceptable results can be obtained by center point mesh-type technique using PMO Dynamics model with much easier calculation procedures that reduces the computation time significantly even by a factor of 4.

The current and sediment transport patterns are important factors affecting coastline morphology. Subsequently, these factors are influenced by waves and currents. Currents are generated by waves breaking on the coastal area. A simultaneous presence of a long shore and tidal currents makes the inlet. A complex hydrodynamic area. The effects of tidal currents on sediment transport pattern and sedimentary features of inlets were studied by numerical modeling. The junction of a small bay to an open sea was modeled using the MIKE21 software. Different conditions of tide amplitudes (0.5, 1.5, 2.5 meters) were investigated. The results clearly indicated the formation of two vortexes during transformation from flow to ebb tide and vice versa. These vortexes, in association with the tidal flow and ebb currents, produce some shallow areas at the sides of the inlet. The radius of the tidal vortexes, and the width of sedimentation area, are directly dependent on the tide amplitude. Using an analysis of Keulegan, when tide amplitudes were 1.5 and 2.5 meters, there was flow dominance in sediment transport capability (i.e. net bay-ward transport).when the tide amplitude was 0.5 meter, there was the ebb dominance of sediment transport capability.

A main source of sediment transport in damreservoir and lakes are density currents. A main parameters in densitycurrents, is sediment entrainment in the body. In this study the effectiveparameters of sediment entrainment was studied. Experiments were conducted inhydraulic modeling laboratory of hydraulic engineering department, ShahidChamran University of Ahwaz. The measuring section includes a flume withadjustable slope, 9.25 mlong 0.5 mwidth and 0.75 mdepth. Results show that, by increasing shear velocity and concentration ofinflow, sediment entrainment coefficient of body will increase. Normally,sediment concentration in the body of the current will decrease due tosedimentation but in the currents with sediment concentration less thantransport capacity, sedimentation are not occurred. Finally, two equations areproposed for estimating sediment entrainment coefficient of the body ofturbidity currents.

Density currents are the main cause for sediment transport in dams reservoirs and seas deltas. One of the problem solution is to reduce or eliminate the effect of them using completely block the density current and as a result the sediment settle far away from the dam in strolling of density current, some experiment were carried out on a flume in water Sciences Engineering Laboratory, Shahid Chamran University of Ahwaz. In this research density current were provided using sediments with d50 of 28.9 µm and passing flow from obstacle was investigated under different bed slopes and discharges. The obtained results show that the effect of obstacle for sub-critical flow is more than supercritical flow. However it was found that even for supercritical flow obstacles are considerably effective on preventing of density current flow.