Sedimentation by gravity is a common, highly applicable separation method for the suspended solid particles of water and wastewater. Sedimentation basin is an important component of every water treatment process. Due to high maintenance costs of these basins, up to about 30% of all costs in a water treatment plant, optimum performance of settling basin is very significant. In order to improve the efficiency of the basin, engineers have proposed various methods, among which, “ changing the geometry along with installation of baffle in the basin” is economic and has attracted the attention of researchers. In the present paper, numerical simulation was made by using Flow3D software and RNG k-ε turbulence model for a flow consisting of settlement particles in the rectangular settlement basin by a finite volume method (FVM). This study aims at numerical simulation of the hydraulic flow in settling basins with various baffle configurations, and finally, obtaining the best geometry for the baffle. Considering the relative consistency of the numerical model results and the experimental data, the numerical simulation results were validated using the Flow3D model. The results showed that the flow in the settling basin is severely affected by the baffle. According to the studied models, it is clear that the baffles installed with lower height and closer to the basin inlet and baffles with high height and far away from the basin inlet have the most effective case on the settlement efficiency.

Estimation of reservoir sedimentation volume is necessary for design and hydraulic structure management purposes where different empirical and mathematical methods are employed in this regard. Due to different factors effecting sedimentation process and their stochastic process, uncertainties arise which cause failure and may force designers to consider safety factors in their designs. Therefore, uncertainty analysis may introduce a better understanding of the effect of different input parameters and their separate contributions to the whole output error. In this research, the sediment discharge rate was estimated by employing different methods such as USBR, average of classes, and the FAO modification coefficient. In these methods data collected from Yalfan hydrometry and Shakhe Dovom SAD stations were used. To calculate the trap efficiency the Brown method, and for specific weight Lane & Koelzer and Miller methods were used. The results of the FAO modification coefficient on average of classes and specific weight of Miller method compared to other corresponding methods show better agreement with the measured ones. In this research, Mont Carlo Simulation and Har's methods were investigated. Calculation of The Mont Carlo method and the uncertainty contribution of each parameter were conducted by a FORTRAN computer program introduced by the author. The results show that the sediment discharge rate and the flow rate introduce the highest contribution to the whole uncertainty of sedimentation volume, respectively. Also, Har's method show less uncertainty value compared to the Mont Carlo method.

Calculated factors such as level, shape, slope, drainage network and calculated and delineate curves hypsometric and curves undimension hypsometric constructed after analysis erosion and sedimentation in Watershed Ladiz have been done. Physiographical properties subwatershed in Geographical Information System (GIS) environment is obtained indicating equilibrium between the mountains and plains of the Saadabad subwatershed. Mianrud and Siahjangal subwatershed and young areas and their heights is highly exposed to erosion. Comparison of the extent, shape, slope and curves hypsometric subwatershed indicate the extent and severity of erosion under the mianrud area than other areas under more. General watershed areas Ladiz young and active can be considered as more than 3/2 level of the mountains is at risk of erosion and shall not establish the equilibrium.

Flood flow in rivers is often of density current type. Hence, recognizing and exploring these currents can solve some problems of sedimentation. In this study, the effect of porosity and the angle of permeable obstacles on the control and trapping of density current have been investigated in the laboratory. For this purpose, an expanded polystyrene (EPS) polymer was used with 1. 135 g/L density and average diameter of 1. 15 mm. The experiments were carried out with two concentrations (10 and 20%) and 5 porosity and 4 angles. The obstacles were made of palsy glass plates and two types of groove and cavity with 8. 2 mm width of the groove and the diameter of the cavity. The results showed that, with an increase in porosity ratio, the amount of trapping to optimum porosity decreases and then increases. The optimal porosity of the cavity and groove is 22 % and 19%, respectively. In experiments, the cavity trapping was observed more than the groove, in the concentrations of 10. 20% it was 0. 13 and 0. 14%, respectively. In addition, with the increase of the angle, the amount of trapping has reduced and its value was observed in the groove more than the cavity. The correlation coefficient in the grooves and cavities was 0. 996 and 0. 937, respectively. The major effect of obstacles, reducing velocity and slowing flow were identified as the average velocity in the cavity was 62. 3% higher than the groove. Accordingly, in the same conditions, the cavity obstacles have better performance than the groove obstacles.

Variability analysis of river sediment transport in different temporal and hydrological conditions is important in hydraulics and hydrological science and engineering. Otherwise, behavior analyzing of the riverian systems at the different temporal conditions is necessary in managerial decisions to control and reduce sediment transport. However, knowledge about the type and amount of sediment in watersheds in various temporal and hydrological conditions is limited. Therefore, this study aimed to investigate the variability of bed and suspended load and bed to suspended load ratio. The 6-years period (1998-2003) data of bed and suspended load (g l-1) and discharge (m3 s-1) were collected from Yazdekan station of Qotour Chay River. The analyses also were carried out in Excel 2007 software. The results indicate that discharge increasing caused that the suspended load was increased and the bed to suspended load ratio was decreased at all seasons. As well, the lowest and highest bed and suspended load transport were occurred at the winter and spring, respectively. Amounts of minimum, maximum and median bed to suspended load ratio at spring, summer, autumn and winter were 5.02, 563.99 and 27.34%; and 0.075, 2034.91 and 135.80%; and 28.31, 659.15 and 184.94%; and 28.96, 457.61 and 169%, respectively. Also, during the study period the bed to suspended load ratio was varied about 0.7 up to 2034%. Therefore, using indirect methods to estimate sediment is not accurate because of complex behavior of sediment particularly bed load and bed to suspended load ratio with discharge. By and large, it is necessary that daily bed load measuring in sediment gauges.