Bend diversion to minimise sediment intake

[摘要] ENGLISH ABSTRACT: The primary aim of the research was to determine the optimum diversion location in acurved channel to minimise the abstraction of sediment. The secondary aim was todetermine the optimum diversion angle for a diversion channel located on the outsideof a bend at the optimum diversion location.The velocity distribution in the curved channel was investigated to try obtain a betterunderstanding of curvilinear flow. The scour patterns in the channel were monitoredin order to compare them with the measured velocity distributions.Simulations were carried out with the DELFT 3D (hydrodynamics) and Mike21C(sediment dynamics) modelling programmes and compared with the results obtainedfrom laboratory experiments and with existing empirical formulas.The optimum diversion location was found to be located on the outside of the bend inthe downstream section of the bend. Three main scour zones were identified with thethird scour zone at the location of the maximum velocity. The location of themaximum velocity was found to be relatively constant with varying Froude numbers,but moving in the downstream direction with increasing radius of curvature-to-widthratio. The velocity distributions in the horizontal and vertical planes are well definedand correspond to descriptions in the literature.It is evident that the diverted discharge ratio increases with an increase in thediversion angle while it decreases with an increase in Froude number. Higher Froudenumbers in the curved channel lead to more favourable conditions for the diversion ofwater. The diversion does not influence the secondary flow patterns (for the range ofDiversion Discharge Ratio's tested) and that the maximum velocity zone stayed in thesame location as in the tests without a diversion.The hydrodynamics of the laboratory experiments were well simulated with theDELFT 3D hydrodynamic model, using three-dimensional and two-dimensionalformulations. Mike21C was used to simulate the sediment dynamics of some of thelaboratory experiments that gave relatively good agreement with experimental data.A two-dimensional depth averaged model could therefore be used with reliability tosimulate field conditions in relatively shallow rivers, and is preferred to empiricalmethods to predict maximum scour that were calibrated under very specific hydraulicconditions.

[发布机构] Stellenbosch University