Journal of Irrigation and Drainage Engineering

A numerical method is developed for the identification of bed resistance and infiltration parameters in surface irrigation based on global procedures. The method is characterized by global convergence—a unique solution from any feasible set of initial parameter estimates, which is not possible for standard variable metric methods. The algorithm is applied to border irrigation described by the zero-inertia model and is used to produce three-dimensional maps of the convergence history of some well-known field observations. Additional enhancements regarding parameter scaling, gradient modification, and combination with a Gauss-Newton method yield a robust and efficient algorithm that can be applied to a variety of practical problems.

A numerical model is developed for the simulation of vertical unsteady-state, two-phase reactive solute-transport through the unsaturated zone. Advective transport is simulated using the method of characteristics, whereas diffusive-dispersive transport and interphase lateral diffusion are accounted for by an implicit finite-difference scheme. The soil moisture and flux distribution required for solving the solute-transport equation is obtained by solving Richards' equation. The model is verified by comparing model-simulated solute-transport with the results of an existing analytical solution. A good agreement is obtained for different sets of parameters. Also for very small dispersivity values no numerical dispersion is present. The proposed model is also used to simulate reported experimental data of a field experiment and shows adequate agreement.

Real-time measurement of velocities in porous media is desirable for engineers engaged in ground-water remediation, monitoring projects, drainage studies, etc. This paper investigates the theory supporting the heat sense flowmeter and introduces a finite difference conduction-convection-dispersion model to convert instrument response to Darcy velocity. The model was tested under laboratory conditions and demonstrated good agreement with the empirical data. Results showed a noticeable attenuation of the heat pulse amplitude for high velocities. This suggests that for high velocities, correlating the Darcy velocity with amplitude gives more accurate readings than correlating Darcy velocity with time to peak.

The most common types of weirs are the broad-crested weir, the sharp-crested weir, the circular-crested weir, and nowadays, the ogee crest weir. Advantages of the cylindrical weir shape include the stable overflow pattern, the ease to pass floating debris, the simplicity of design compared to ogee crest design, and the associated lower costs. In this study, the writers describe new experiments of circular weir overflows, with eight cylinder sizes, for several weir heights and for five types of inflow conditions: partially developed inflow, fully developed inflow, upstream ramp, upstream undular hydraulic jump, and upstream (breaking) hydraulic jump. Within the range of the experiments, the cylinder size, the weir height D/R and the presence of an upstream ramp had no effect on the discharge coefficient, flow depth at crest, and energy dissipation. But the inflow conditions had substantial effects on the discharge characteristics and flow properties at the crest. Practically, the results indicate that discharge measurements with circular weirs are significantly affected by the upstream flow conditions.

Side-weirs located on straight channels have attracted considerable interest and research effort. The same, however, is not true for side-weirs on curved channels. The existing studies deal mainly with sediment transport problems and lateral intake structures. The present study focuses on the investigation of the hydraulic behavior of a rectangular sharp crested weir at various locations along a 180° bend. The flow resulting from the effects of the bend and the side-weir was investigated experimentally. Velocity measurements were carried out both for the bend with and without active overflow conditions while surface profiles were determined only for the former case. Velocity measurements were made over the depth at several cross sections along the bend. Observations indicated that a stagnation zone existed at the side-weir section along the inner side of the bend, and that standing waves were present downstream of the side-weir even under subcritical flow conditions. Both phenomena were found to be highly dependent on the upstream Froude number. The side-weir discharge coefficient was determined at one section along the approach to the bend and at five stations along the bend for a number of different side-weir dimensions. The side-weir discharge coefficient along the bend was found to depend on the upstream Froude number, the dimensionless weir height, p/h₁, and the dimensionless weir length, L/b. The variation of the discharge coefficient along the bend as a function of the Froude number and the dimensionless weir length was found to exhibit a parabolic relationship.

The subject of investigation in this experimental study is discharge estimation in flow measurement flumes of rectangular compound cross sections with different geometries. General equations for C_v and C_d have been found as a function of relevant parameters. By using these general equations, one can estimate the flow discharge of a flume when the head value over the crest elevation is given with an absolute error of 5%.