Journal of Irrigation and Drainage Engineering

Suspended sediment concentration is critical for many aspects of water resources management, such as sedimentation prevention in irrigation channels. Samplers from the Federal Interagency Sedimentation Project (FISP) are widely used for suspended sediment measurement. There is a need to evaluate their accuracy. This paper reports the use of a three-dimensional (3D) computational fluid dynamics (CFD) model to make such evaluation. Two selected depth-integrating samplers, D95 and D96, were studied, with the focus on the intrusion effect of the samplers. Suspended sediment transport was simulated to capture the entrainment, transport and deposition processes. The turbulence was simulated using a Reynolds-averaged Navier-Stokes (RANS) $k\text{-}\omega$ model. The samplers were placed at three different vertical locations in an open channel. The simulation results showed that the surrounding flow was disturbed by the sediment samplers. However, regardless of the vertical location of the samplers, they had a negligible effect on the sediment concentration at the inlet nozzle. The main reason is that the inlet nozzles of both samplers had enough protrusion upstream such that the intake was not affected by the sampler bodies. The results did not show significant vorticity at the inlet nozzle either, which in the past was suspected of imparting centrifugal force on sediment particles and thus having selective sampling efficiency depending on sediment sizes.

When designing trickle irrigation systems in sloped fields, the use of pressure-compensating (PC) emitters is generally preferred to ensure the emitter distribution uniformity regardless of the land topography and the variable operating pressures. However, the cost of PC emitters is generally higher than non-pressure-compensating (NPC) ones; moreover, the compensating membrane installed inside the emitters can lose elasticity due to the exposition to solar radiation, water quality, and chemical applications. Recently, the irrigation laboratory (IRRILAB) version 1.0 software application was developed to design microirrigation systems for rectangular and planar sectors when using NPC emitters under any field slope and by neglecting the local losses due to the emitter connections. The objective of this work is to demonstrate that even in sloped fields and neglecting the local losses, it is possible to use NPC emitters by maintaining acceptable values of field distribution uniformity. In addition, the influence of local losses caused by the emitters installed in the laterals is also investigated to assess their role in the examined applications. The IRRILAB software was initially used to design a microirrigation sector, to suggest the optimal operating pressure, and to simulate the operating pressure heads and flow rates. The latter values were compared with the corresponding values measured in the field. The software was additionally assessed based on a second experimental campaign, after limiting the length of the laterals to account for local losses. For both experimental campaigns, the values of the commonly used uniformity coefficients were deemed acceptable according to the American Society of Agricultural Engineering (ASAE). However, the introduction of minor losses in the hydraulic design showed an improvement in terms of the emitters’ flow rate distribution in the whole sector and uniformity coefficients.

Vortex-settling basins (VSBs) have been constructed with support columns under the deflector to enhance the structural stability of the deflector. This paper presents a retrofit for such columned VSBs by installing vanes at the bottom of the support columns to reduce the sediment deposition on the basin floor. Experiments were conducted for VSBs both with and without vanes, where the thickness and mass of sediment deposition, sediment trapping efficiency, and water abstraction ratio of the VSBs were measured and compared. The VSB with vanes exhibited a similar sediment trapping efficiency and water abstraction ratio to the original columned VSB. When the inflow is equal to or greater than the design discharge, the vanes showed a significant effect on reducing the mass of sediment deposition by an average of 11.71% and 22.25%, respectively, and the formed sandwave on the basin floor was smaller. When the inflow is less than the design discharge, the effect of the vanes was limited, with the mass of sediment deposition slightly reduced by 5.25% on average.