Experimental and numerical investigation of the effect of submerged walls on sediment trapping efficiency in settling basins of diversion dams

One of the most important and essential parts in the set of water transfer structures is settling basin in water transfer networks. Settling basins are among the essential structures that are constructed to separate sediments along the inflow, after the reservoir and at the beginning of water transfer canals. Since the presence of excess sediments is especially harmful for agriculture and aquaculture and reduces the efficiency of related productivity, the importance of these structures increases.

In the present study, the effect of placing a wall perpendicular to the flow path in the settling basin on the sediment trapping efficiency, in both walled and plain modes (without wall or control), was investigated. For this purpose, 5 physical models of sediment basins in simple (without wall or control) and walled, with height ratios of 1/3 and 1/2 to the height of the sediment basin, and with three and five walls of the compressed plastic material were made. Experiments were conducted by entering sediment particles with diameter less than 0.1mm and constant mass of 2.8kg into the rectangular concrete canal in the hydraulics laboratory of Sari Agricultural Sciences and Natural Resources University. After ending of each experiment on models the deposited sediments were collected, dried and finally weighed. In these experiments, the number and height of walls placed in the settling basin changed and their effect on the efficiency of trapping was investigated. At the end, the results of the experiments were verified using a numerical model using FLUENT software and a statistical test using SPSS software.

Experimental results showed that the presence of walls in the flow path in the settling basin significantly increased the sediment trapping rate. Increasing the number of walls from three to five, in the ratios of heights 1/3 and 1/2 to the settling basin wall, causes an increase of 5.9 and 7.65 percent on sediment trapping efficiency, respectively. The results of this study also showed that the simultaneous effect of both height parameters and the number of walls caused a 10 to 27% increase in sediment trapping efficiency. Statistical results showed a significant difference between the presence and absence of a wall on the efficiency of trapping. The results of numerical simulation also show the effect of the presence of walls on changing the flow pattern and show that increasing the number of walls has increased the amount of sediment in the settling basin.

In general, it can be concluded that the use of the wall in the passage of the stream containing sediment from the settling basin, reduces the turbulence of the inlet flow and reduces the flow velocity in the basin. It can be stated that increasing the length of the flow path and spreading the incoming sediments across the pond increases the amount of settling and trapping efficiency.