Sedimentation basin is an important component of every water treatment process. In order to improve the sedimentation efficiency (SE) of rectangular sedimentation basins, many researchers have proposed various methods. Among the suggested methods, the change of the geometry with installation of baffle in the basin floor is simple and completely economic. In this research, the hydraulic characteristics of the flow with various baffle configurations in the basin floor have been evaluated and the best geometry of the baffle has been presented. The agreement between numerical and experimental results was good. The results showed that the flow in the sedimentation basin is strongly influenced by the baffle. Also, the baffles installed with lower height and closer to the basin inlet and baffles with high height and far from the basin inlet have the greatest effect on the SE.
Hydraulic characteristics of the flow and sediment transport conditions are among the most important issues in design of the lateral intakes in order to minimize the flow loss. In this study, a 3D numerical model has been employed in a parametric study to study the performance of a lateral pipe intake. Observations indicated that the flow was affected by the pipe intake so that the recirculation area was close to the wall of the main channel, the wall of the lateral pipe intake and back of the lateral pipe intake. The pipe intake in vertical direction to the main channel showed the highest performance, although sedimentation behind the pipe intake in this diversion angle was higher. In addition, pipe intake showed a quite acceptable performance for almost 40% intrusion to the main channel width. Relationships for the coefficient of discharge were also developed.
Karstic rocks exist in different areas of the world having by case useful/ harmful structural and environmental impacts. These rocks like gypsum and salt are dissolved against water. In the current research, gypsum solubility is investigated by collecting outcomes of several experiments on crushed gypsums. During the tests, rates of gypsum solubility were measured and appraised through application of various parameters such as compaction quantity, period of water flow inside specimen as well as diameter of the initial trial hole increase. The initial trial holes’ diameters were 0 (in the specimen without hole), 5, 8, 10 and 12 millimeters. Two compaction cases were comprised; with and without compaction. Furthermore it should be mentioned that flow of water was continued inside the specimens for a period of 3, 10, 20 and 30 days in the separate experiments in order to assess the time factor on the solubility quantity of the gypsum. Solution rate respectively for crushed gypsum were computed 2.49 cm/year. These experiments indicate that progress of solution phenomena does not have a particular trend.
Karstic rocks (soluble rocks) exist in different areas of the world having useful/harmful structural and environmental impacts. One of the useful aspect is availability of rich water resources in some regions. An important defect of this kind of rocks is their low strength against water flows. These rocks usually dissolve in acidic water and as a result abundant caverns are created inside them. The gypsum and salt present in these rocks dissolve even in non-acidic water. Presence of these rocks in different foundations and reservoirs especially in dams could be potentially dangerous and cause enormous problems. If dams are located above soluble rocks like limestone, dolomite or gypsum they are endangered by karstification. Karstification is a dynamic process resulting in voids within the rocks due to dissolution. This dissolution leads to the formation of a pipe system within the sub-surface In the physical modeling, effects of cut-off wall height within gypsum layer were examined and monitored. Then with GeoStudio and Flac software, results of physical modeling are analyzed. In each experiment, cut-off wall height was changed. The result of the experiments indicated that as the gypsum Karst is very weak against water, cut-off wall must continue completely within the gypsum layer, as a complete positive cut-off wall.
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