Browsing by Author "Mc Leod, Claudia"
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- ItemOptimisation of sand trap and settler designs for efficient deposition of suspended sediment(Stellenbosch : Stellenbosch University, 2024-03) Mc Leod, Claudia; Bosman, Adèle; Smit, G.J.F; Stellenbosch University. Faculty of Engineering. Dept. of Civil Engineering.ENGLISH ABSTRACT: Sand traps and settlers are used at river abstraction or diversion works for the control of sediment loads for potable, irrigation and hydropower usage. The performance of a sand trap and settler is judged by its capability to sufficiently deposit suspended sediment particles and its flushing capability of bed load sediment. The design properties of a canal type sediment trap, such as the depth of flow, total length, cross-section, slope and inlet position, mainly determine its hydraulic efficiency. One of the main objectives of this study was to develop hydraulic design guidelines for sand traps and settlers for river conditions that have high loads of fine non-cohesive sand. This study investigates design considerations (dimensions, slope, cross-section, type of intake locations, and sediment intake concentration as well as inlet designs) of sediment traps by using an existing fully three-dimensional Computational Fluid Dynamics (CFD) model coupled in terms of hydrodynamics and sediment transport developed by Sawadogo (2015). The hydraulic performance of an existing sand trap and settler in Southern Africa was also investigated to identify hydraulic design aspects that could be improved. This was achieved by performing field measurements, analysing the field results of sediment deposition and velocities within the traps, and numerically investigating the case studies to recommend possible design upgrades to improve the efficiency of the traps. This study also investigates the innovative “Split-and-Settle” sand trap concept, initially proposed by Støle in 1993, by means of a three-dimensional CFD model as a second main objective. The “split-and-settle” approach directly refers to dividing the flow in a sand trap into sediment-free and sediment-laden water and then removing the sediment from the water. As sediment-laden water traverses a canal, the suspended sediment concentration increases near the bottom along the length of the canal as sediment tends to deposit. The split-and-settle concept leverages this sediment concentration gradient by dividing the flow into upper and lower parts. The concept was investigated by conducting physical modelling to generate data in a controlled environment to calibrate a numerical model. To calibrate and evaluate the sensitivity of the numerical model, appropriate parameters were adjusted until a good agreement was reached between the physical and numerical model results for the suspended sediment concentration. The parameters included the convection-diffusion equation’s turbulent Schmidt number, mesh configuration for capturing the split plate boundary and turbulent intensities. The principal contribution from this work is the calibrated and validated numerical model which could be further used to propose design guidelines for the split-and-settle sand trap. Additional benefits of the Split-and-Settle sand trap design include that it reduces the required length of sand traps and therefore are more economical whilst being hydraulically efficient, sustained operational capacity for handling substantial volumes of sediment-laden water, and minimal maintenance demand due to continuous flushing. Moreover, it operates without the inherent risk of scour holes that can become blocked or clogged and reduce efficiency. Ultimately, this research underscores the potential of the Split-and-Settle sand trap as a valuable tool in sediment management and hydraulic engineering.