Journal of Irrigation and Drainage Engineering

In this study, the hydrodynamics of rectangular broad-crested porous weirs were numerically simulated using a nonlinear model between the pressure gradient and flow velocity through the porous medium. Computational fluid dynamics (CFD) analysis has been performed and renormalized group (RNG) $\mathrm{k}\text{-}ϵ$ model is used as the turbulence closure for Reynolds-averaged Navier-Stokes (RANS) equations. Solid and porous weirs with various properties were examined, and the drag coefficients of the porous weirs in the nonlinear flow resistance model were determined using sensitivity analysis. A logarithmic equation to determine the drag coefficient directly as a function of the hydraulic permeability is presented. By performing three-dimensional (3D) numerical simulations for a wide range of the approach discharge for different porous weir models, the discharge coefficient is described as a piecewise function of related parameters, such as head over the weir, porosity, and the grain diameter of the porous weir. Moreover, for the simulated scenarios, ratios of water passing through and over the weir are determined; consequently, new equations for the discharge ratio are developed. Finally, complex flow features over and through the different porous weirs have been expounded using developed discharge ratio curves.

The present study is concerned with the analysis of moisture flow in the crop root zone and estimation of soil hydraulic and root water uptake parameters from soil moisture depletion data using the inverse procedure. The parameter estimation is formulated as a least-squares minimization problem in which the parameters are estimated by minimizing the deviations between model-predicted and field-observed soil moisture data in the root zone. A parameter estimation code is developed by coupling a numerical model simulating one-dimensional vertical moisture flow (Richards equation) in the root zone with a genetic algorithm. The root water uptake is accounted for as a sink term in the Richards equation. Identifiability of soil hydraulic and root water uptake parameters from the inverse procedure are studied by generating synthetic soil moisture depletion data. It is observed that with soil moisture data alone, it is not possible to estimate both soil hydraulic and root water uptake parameters uniquely. This is evidenced by the presence of local minima in the parametric space involving root water uptake as one of the parameters. Field experiments were also conducted on two major Indian crops: wheat and berseem. The inverse procedure is applied to estimate the root water uptake parameter for these crops. Using optimized values of root water uptake parameter of the two crops, the percentage soil moisture depletion at discrete irrigation intervals are compared with observed data. The results indicate a fair agreement between the computed and observed percentage soil moisture depletion values.

Weirs, orifices, baffle sluice gates, and sluice gates are widely used in irrigation networks for distributing water from the source to irrigated areas. Side orifices are generally placed in the side of a channel for diverting some of the source channel flow. Prediction of the discharge rate through side orifices of different shapes is important in irrigation and hydraulic engineering. The hydraulic behavior of side triangular orifices (Δ-shape orifices) has not been studied either experimentally or theoretically. In this study, sharp-crested side triangular orifices are studied experimentally and analytically. Several models are derived for the discharge coefficient based on Buckingham’s theorem of dimensional analysis. A series of laboratory experiments (570 runs) were performed to investigate the flow discharge through side triangular orifices located in horizontal rectangular channels under free flow conditions. Using the collected data in the present work, proposed models were calibrated. One model that includes the approach Froude number has an average error of 2.1%, while a second model that does not include the approach Froude number has an average error about 3.3%. Therefore, actual discharge through the side triangular orifices can be accurately estimated using the proposed models.

An innovative measurement system using submerged ultrasonic Doppler velocimetry (SUDV) has been adopted by the Lower Neches Valley Authority (LNVA) in Texas to measure flow velocity in corrugated metal pipes of an irrigation turnout. However, a 20% error in flow rate has been found due to the corrugation feature of the pipe. The objective of this study is to determine the correction coefficient by comparing the measured flow velocity with that measured using SUDV under full pipe flow conditions. The physical model is set up with inflow controlled by a sluice gate, passing through three chambers in series with two combinations of pipe sizes (61, 76, and 61 cm, and 91, 76, and 61 cm), which then flows through the last chamber and discharges water over a weir into a channel. Experimental results show an average velocity correction coefficient of 0.824 is satisfied for all pipe sizes evaluated in the experiment, with $R^2=0.9898$. The SUDVs in LNVA irrigation turnouts have been programmed with the correction coefficient to improve flow measurement accuracy for better water use management planning.