Document Type : Original Article
Authors
1 Ph.D. student, Department of Water Engineering and Management, Faculty of Agriculture, the University of Tarbiat Modares, Tehran, Iran.
2 Professor Department of Water Engineering and Management, Tarbiat Modares University, Tehran, Iran.
Abstract
Extended Abstract
Introduction
Sediment accumulation is a persistent challenge in the operation of diversion dams, which are critical infrastructures for water diversion and flow management. Sediments tend to deposit in front of intake structures, obstructing water flow and impairing operational efficiency. Sediment flushing, achieved through sluiceways equipped with control gates, is an effective approach to alleviate these deposits. However, one of the key design parameters the gate opening-to-width ratio (a/b) significantly influences flushing efficiency, though no standardized guideline for optimizing this ratio currently exists. This study investigates how the gate opening-to-width ratio (a/b) and sluiceway width (Ws) affect sediment flushing performance using the FLOW-3D computational fluid dynamics (CFD) model. Simulations under controlled flood conditions provide insights into optimal design parameters to enhance sediment flushing efficiency, aiming to inform best practices in hydraulic design.
Methodology
This study employs FLOW-3D, a high-resolution CFD software that solves the Navier-Stokes equations for incompressible, turbulent flow. The model integrates the RNG k-ε turbulence model, which accurately captures complex shear flows and turbulent interactions, making it ideal for studying sediment transport in hydraulic structures.
Simulations were conducted under constant flood inflow conditions, with variations in the gate opening-to-width ratio (a/b) for each sluiceway width (Ws). To ensure model accuracy, results were validated against experimental data from prior research, confirming the model's ability to reproduce sediment flushing patterns. The study examined sluiceway widths from 0.58 to 1.83 times the intake channel width (Wi), assessing how each width and its corresponding a/b ratio affected flushing performance. Key parameters such as Froude number (Fr), gate dimensions, and sluiceway configurations were analyzed to determine their impact on sediment removal efficiency.
Results and Discussion
Results indicated that a Froude number between 0.16 and 0.3 produced the best flushing efficiency, providing sufficient flow energy to mobilize and transport sediments while minimizing turbulence and backflow. Analysis of sluiceway widths showed that as the width increased, flushing efficiency declined due to reduced flow velocities. A narrower sluiceway width of 0.58Wi exhibited high sediment removal rates, but this aggressive flushing risked destabilizing upstream structures due to increased erosive forces. Conversely, a wider sluiceway (1.83Wi) promoted sediment deposition, as lower flow energy led to ineffective flushing and potential blockages.
An optimal range for sluiceway width between 1.0 and 1.15 times the intake width (Wi) was identified. This range provided adequate flow velocity and shear stress to minimize sediment deposition within the sluiceway and control downstream sediment transport without risking erosion of upstream structures.
Regarding the gate opening-to-width ratio (a/b), simulations showed that an a/b ratio of 0.5 consistently enhanced flushing efficiency across different sluiceway widths. Lower ratios (<0.5) resulted in reduced flushing due to insufficient flow energy, while higher ratios (>0.5) created localized turbulence and erosion, compromising overall system stability. Optimizing the a/b ratio at 0.5 balanced sediment mobilization with flow stability, achieving efficient flushing without excessive backflow or structural impacts.
The study further evaluated sediment transport length, or the effective flushing range, within the sluiceway. With an a/b ratio of 0.5, the effective sediment transport distance reached approximately 60% of the sluiceway length for narrower configurations, though this range decreased with increased sluiceway widths. These results underscore the need to balance sluiceway width and gate ratio to maintain effective sediment transport along the sluiceway length.
Conclusion
This research presents essential guidelines for enhancing sediment flushing in diversion dams through optimized sluiceway design. A Froude number between 0.16 and 0.3, combined with an a/b ratio of 0.5, was found to maximize sediment removal efficiency. An optimal sluiceway width between 1.0 and 1.15 times the intake width (Wi) further improved sediment transport, achieving efficient flushing with controlled downstream flow and minimizing upstream erosion.
Keywords
Main Subjects
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