Experimental study on velocity distribution and bed load transport in compound channels: Effect of the floodplain’s wall parallel with the meandering main channel

Abstract

In this study, the effect of the floodplain’s parallel wall with a compound meandering main channel over the hydraulics flow has been analyzed experimentally. A constant sinuosity factor of 1.3 and relative flow depths of 0.3 to 0.55 were considered to illustrate the effect of the hydraulic parameters on the variations of the velocity components. Velocity components were measured by ADV velocimeter at seven cross sections with angles of zero, 30, and 60 degrees and mesh size of 2 cm × 2 cm. Furthermore, a laser meter measured the topographies of the sediment bed in the 33 cross-sections with an angle difference of 5 degrees to the bend apex. The results showed that in lower relative depths, due to vortexes and high turbulence intensity, the ability of flood damage will be more eminent. The CS04 section with the least longitudinal and transverse changes in the water level is the best position for hydraulic investigation of the meandering rivers. The left bank in sections CS03 to CS07 will be the place of deposit of sediment in nature with the formation of the stagnation area. The velocity of (Ud(fp-inner)) is 3 to 5 times higher than (Ud(fp-outer)). For this cause, the flow in the outer bank, unlike the inner bank, has a reduced effect on the flow velocity in the main channel. Increasing the relative depth, the ratio (Ud(mc)/Ud(T)) and (Ud(fp)/Ud(T)) decreased and increased, respectively. Therefore, the average velocity values in the main channel and the floodplains reached the average velocity of the whole section. The flow velocity in the main channel is always higher than in the floodplains, and the ratio (Ud(fp)/Ud(mc)) is less than one. The variation trend in the average values of bed shear stress, turbulence kinetic energy (TKE) and average kinetic energy (MKE) was decreased with increasing relative flow depth. Both factors of relative depth and Froude number will affect the location of the occurrence of the maximum values of velocity, bed shear stress, maximum depth hole and the peak of the sedimentary hill.