Experimental study of sediment transport and mechanism of sediment entry to a lateral intake in a 180 degree channel bend using sediment injection on rigid bed

Sediment transport by a fluid flow is one of the most important two phase flows in the nature.
Predicting river behavior at bends is important since rivers rarely run on straight paths in nature, and most rivers have meandering forms. In a river bend the presence of centrifugal force leads to the formation of secondary flow. As a result water particles near the surface are driven outward and the flow at the bed of a channel is directed toward the inner bank. Therefore locating the intake at outer bank of bend is one of the ways to reduce sediment intern to the lateral intake.
Due to the existence of secondary current in channel bends, the mechanism of flow and sediment transport is much complex whereas locating lateral intake at outer bank of the bends decreases this complexity.
Lateral intakes are hydraulic structures, used for water conveyance for domestic, agricultural and industrial purposes, characterized by a very complex three-dimensional morphodynamic behavior: since streamlines near the lateral intake are deflected, some vortices are formed; also, the pressure gradient, shear and centrifugal forces at the intake generate the flow separation and a secondary movement responsible for local scour and sediment deposition.
Knowing the mechanisms of sediment transport in the channel bends with lateral intake and the manner in which sediments can enter the diversion can help engineers in the better design of these hydraulic structures.
In this paper, sediment transport phenomena and mechanisms of sediment entry to the lateral intake were carried out in a 180 degree channel bend using injection of sediment on rigid bed. In this order, a sediment injection device with uniform and adjustable rate were designed and made. The intake were installed in position 115 degree of bend with 45 degree diversion angle according to previous research suggestion. The sediment injection device were fixed at upstream of the bend and dried sediment with the rate of equal to the capacity of the channel upstream of the bend were injected.
In order to analyzing the results, three components of flow velocity were measured using 3D Acoustic Doppler Velocimeter (Vectrino). Moreover, the sediment movement path in different times and diverted sediment ratio to intake are measured.
In this research, effect of Froude Number and diversion discharge ratio on sediment transport in the bend and mechanism of sediment entry to the intake were considered. The results showed that in different Froud number and diversion discharge rate, after equilibrium time, a sediment accumulation occurred in section 45 degree of bend and another sediment accumulation occurred in section 135 degree of bend near inner bend. The reduction of Froud number caused development of bed forms and their heights. Also the results showed the mechanism of sediment entry to the lateral intake is affected by diversion discharge ratio. In Qr=40% (and Fr=0.38), the mechanism of sediment entry were consisting of continues entrance from downstream edge of intake and periodic entrance from upstream of the intake but in Qr=25% (and Fr=0.38), the mechanism of sediment entry were only consisting of continues entrance from downstream edge of intake.