Eroded sediments from catchment areas transport by streams and deposit in downstream less steep areas. Despite reducing the useful life of various hydraulic structures including reservoir dams, flood walls, and bridges, this phenomenon changes the main river hydraulic conditions and increases the flood prone farms in the riverbank area. Check dams are among the structures that can prevent form such phenomenon. In addition to the technical performance, hydraulic structures including dams can provide beautiful view in the areas that have the potential to attract tourists. Stepped Slit Check Dams are combination of stepped and slit check dams. The present study investigated the effects of slope, discharge, gradation type, and check dam geometry on the sediment-trapping coefficient of the dam. Finally, a relation for prediction of the sediment-trapping coefficient in the reservoir of Stepped Slit check dams was presented. پرونده مقاله

Downfall flows from different outlet hydraulic structures such as culverts and jetsthrowingtothe erodible downstream bed cause scour hole and changes in the downstream bed topography. Therefore,by performing some physical modeling tests on culvert jet flow under different angles, changes in the downstream bed topography under the effect of different parameters such as flow rate, depth of the tail water and the important factor of falling jet angle of the culvert were studiedin this paper.Water jet was modeledusing a plastic pipe with a circular section throwing on a Silica bed material with a uniform grading in three different culvert angles of80, 90 and 100 degreesrelative to the vertical axis. The results showed that by increasing thejet angle from 80 to 100 degrees,depth of the scour hole increasedand the place where the maximum scour holedepth occurs changed. Besides, by usingthe Non-dimensional Analysis, a relationship for measuring the maximum depth ofthe scour hole and maximum height of the scour mound was presented in this paper. پرونده مقاله

Transfer of debris flow caused by floods in the river downstream of the mountains leads to several damages every year. Numerous researches have been carried out on the Mountain Rivers the results of which show the importance of performing more researches to control debris flows in the floodplain because of various effective hydraulic-geometric parameters.For this purpose, AbNik Mountain River located in Jajrood basin, northern Iran was selected to evaluate the effect of geometric and hydraulic parameters on moving and controlling the debris flows. Therefore, a length of 200 meters of the steep mountain river length was chosen for which velocity values were measured at different times and at different levels. In 28 selected sections, bed materials were sampled and mapped. Using the analytical methods for field data measurement and geometric properties of the composite trapezoidal channels and hydraulic equations such as Manning, sensitivity analysis of different geometric- hydraulic parameters was performed. In this analysis, using Manning equation in the composite trapezoidal channels, a multivariate equation was obtained by which the flow depth is obtained using trial and error analysis method (Newton-Raphson equation), i. e. variations of each parameter with respect to flow depth in the flood plain are obtained by keeping the other parameters constant at the minimum value. Changes of the geometric and hydraulic parameters were plotted versus flow depth. Results were obtained by investigating the resulted diagrams and equations. Analysis of the results showed that the longitudinal slope of the channel and width of the channel floorhad the greatest effects on the flow depth in the flood plain of the Mountain Rivers. پرونده مقاله

Pre-sedimentation basins are among the most important elements of the conventional water treatment process. In pre-sedimentation basins, due to different velocity gradients, secondary and rotational flows are formed that will create short paths and increase dead and still flow zones as well as changes in the flow mixing. This will prevent laminar flow conditions for sedimentation and will reduce the basin efficiency. The first step in optimization of the pre-sedimentation basins is the correct calculation of the velocity field and rotating zones volume. In this study, flow in a rectangular basin was simulated numerically and continuity and Novier-Stokes equations were solved using the Finite Volume method. 3-D flow simulation was performed using standard k-ε turbulence model and flow velocity profiles at different sections of the pre-sedimentation basin were compared with the experimental results and the results were in good agreement. Then, in order to investigate the sedimentation pattern in pre-sedimentation basin, convection-diffusion equation of the sediment concentration was simultaneously solved with the governing equations of the flow hydraulics. Finally, vertical distribution of sediment concentration at different basin sections was compared with the experimental and numerical results of other researchers. The results indicated a good agreement between the numerical and experimental results as well as the model ability to predict sediment distribution profiles in pre-sedimentation basins. پرونده مقاله