Optimisation of sand trap and settler designs for efficient deposition of suspended sediment

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dc.contributor.advisorBosman, Adèleen_ZA
dc.contributor.advisorSmit, G.J.Fen_ZA
dc.contributor.authorMc Leod, Claudiaen_ZA
dc.contributor.otherStellenbosch University. Faculty of Engineering. Dept. of Civil Engineering.en_ZA
dc.date.accessioned2024-02-26T11:48:15Zen_ZA
dc.date.accessioned2024-04-26T14:48:45Zen_ZA
dc.date.available2024-02-26T11:48:15Zen_ZA
dc.date.available2024-04-26T14:48:45Zen_ZA
dc.date.issued2024-03en_ZA
dc.descriptionThesis (PhD)--Stellenbosch University, 2024.en_ZA
dc.description.abstractENGLISH 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.en_ZA
dc.description.abstractAFRIKAANSE OPSOMMING: Sandvanger en setlaars word by rivieronttrekkings- of afleidingswerke vir die beheer van sedimentladings vir drinkwater-, besproeiings- en hidrokragverbruik, gebruik. Die prestasie van 'n sandvanger en setlaar word aan die hand van hul vermoë om voldoende gesuspendeerde sedimentdeeltjies te laat uitsak asook hul uitspoelvermoë van gedeponeerde sediment, beoordeel. Die ontwerpseienskappe van 'n kanaal tipe sedimentval, soos die vloeidiepte, totale lengte, dwarssnit, helling en inlaatposisie, bepaal hoofsaaklik sy hidroliese doeltreffendheid.Een van die belangrikste doelstellings van hierdie studie was om hidroliese ontwerpsriglyne vir sandvanger en setlaars vir rivieromstandighede wat ‘n hoë las van fyn nie-kohesiewe sand het, te ontwikkel. Hierdie studie ondersoek ontwerpsriglyne (afmetings, helling, dwarssnit, tipe inlaatplekke, en sediment inlaat-konsentrasie sowel as inlaatontwerpe) van sedimentvalle deur van 'n bestaande, volledig driedimensionele Rekenkundigevloeidinamika (RVD) model, gekoppel in terme van hidrodinamika en sedimentvervoer, ontwikkel deur Sawadogo (2015), gebruik te maak. Die hidroliese prestasie van 'n bestaande sandvanger en setlaar in Suid-Afrika is ook ondersoek om hidroliese ontwerpaspekte te identifiseer wat verbeter kan word. Dit is bereik deur veldmetings uit te voer, die veldresultate van sedimentneerslag en snelhede binne die valle te analiseer, en die gevallestudies numeries te ondersoek om moontlike ontwerpaanpassings voor te stel om sodoende die doeltreffendheid van die valle te verbeter. Hierdie studie ondersoek ook die innoverende "Verdeel-en-Uitsak" sandvanger-konsep, aanvanklik voorgestel deur Støle in 1993, deur middel van 'n driedimensionele numeriese ondersoek as 'n tweede hoofdoel. Die verdeel-en-uitval benadering verwys direk na die verdeling van die vloei in 'n sandvanger in sedimentvrye en sedimentbelaaide water en die verwydering van die sediment uit die watervloei. Terwyl sedimentbelaaide water deur 'n kanaal vloei, neem die gesuspendeerde sedimentkonsentrasie naby die bodem langs die lengte van die kanaal toe omdat sediment neig om uit te sak. Die verdeel-en-uitval konsep maak gebruik van hierdie sedimentkonsentrasiegradiënt deur die vloei in bo- en onderdele te verdeel. Die konsep is deur fisiese eksperimente om data in 'n gekontroleerde omgewing te genereer om 'n numeriese model te kalibreer, ondersoek. Om die numeriese model te kalibreer en die sensitiwiteit daarvan te evalueer, is toepaslike parameters aangepas totdat 'n goeie ooreenkoms tussen die fisiese en numeriese modelresultate vir die gesuspendeerde sedimentkonsentrasie bereik is. Die parameters het die turbulente Schmidt-getal van die konveksie-diffusievergelyking, die matriksopstelling vir die vaslegging van die verdeelplaatgrens en turbulente intensiteite ingesluit. Die belangrikste bydrae van hierdie werk is die gekalibreerde en gevalideerde numeriese model wat verder gebruik kan word om ontwerpsriglyne vir die verdeel-en-uitsak sandvanger voor te stel. Addisionele voordele van die verdeel-en-uitsak sandvangerontwerp sluit in dat dit die benodigde lengte van sandvanger verminder en dus meer ekonomies is terwyl dit hidrolies doeltreffend is, aanhoudende bedryfskapasiteit vir die hantering van aansienlike hoeveelhede sedimentbelaaide water bied, en minimale instandhoudingseise het as gevolg van aanhoudende spoelwerk. Daarbenewens werk dit sonder die inherente risiko van uitskuringsgate wat geblokkeer of verstop kan raak en die doeltreffendheid kan verminder. Uiteindelik beklemtoon hierdie navorsing die potensiaal van die verdeel-en-uitsak sandvanger as 'n waardevolle instrument in sedimentbestuur en hidroliese ingenieurswese.en_ZA
dc.description.versionDoctorateen_ZA
dc.format.extentxix, 224 pages : illustrations.en_ZA
dc.identifier.urihttps://scholar.sun.ac.za/handle/10019.1/130361en_ZA
dc.language.isoen_ZAen_ZA
dc.language.isoen_ZAen_ZA
dc.publisherStellenbosch : Stellenbosch Universityen_ZA
dc.rights.holderStellenbosch Universityen_ZA
dc.subject.lcshSand trap -- Design and constructionen_ZA
dc.subject.lcshSuspended sedimentsen_ZA
dc.subject.lcshComputational fluid dynamicsen_ZA
dc.subject.lcshHydrodynamicsen_ZA
dc.subject.lcshSediment transporten_ZA
dc.titleOptimisation of sand trap and settler designs for efficient deposition of suspended sedimenten_ZA
dc.typeThesis en_ZA
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