Journal of Irrigation and Drainage Engineering

Two low energy precision application (LEPA) sprinkler methods (double-ended socks and bubblers) and two spray sprinkler methods (low-elevation spray application and overhead spray) were used to irrigate corn, grain sorghum, and winter wheat in the Southern High Plains. For full or 100% irrigation, sufficient 25-mm applications were applied to maintain soil water at non-yield-limiting levels determined in earlier research with the three crops. Deficit-irrigated treatments were irrigated on the same days as the control treatment in 25 or 33% increments of the fully irrigated amount. Irrigation water was applied to or above alternate furrows with a three-span lateral move irrigation system. Corn and sorghum were grown on beds and furrows with all furrows diked, and wheat was flat-planted without basin tillage. Grain yields increased significantly with irrigation amount (p ≤ 0.05) for all crops during all years. With full irrigation, grain yields varied little among the sprinkler methods, and yields averaged 13.5, 8.9, and 4.6 Mg/ha for corn, sorghum, and wheat, respectively. With the 25 and 50% deficit irrigation amounts, sorghum yields with LEPA irrigation were 1.1 Mg/ha larger than with the two spray methods. For 75% irrigation of sorghum and for deficit irrigation of the other two crops, there was little yield difference between the LEPA and spray sprinkler methods. Grain yields were significantly correlated with seasonal water use with regression coefficients of 2.89, 1.84, and 0.915 kg/m³ for corn, sorghum, and wheat, respectively.

A semiempirical equation for cumulative infiltration in a furrow irrigation system was developed using an empirical wetting front advance equation and a volume balance technique. This equation was verified using the field data obtained in a Yolo loam soil (Typic Xerorthents) planted with a furrow irrigated tomato crop. Two distinct cases were considered: (1) furrows with deposional crusts at the bottom (uncultivated); and (2) furrows in which a crust breaking device was used to remove the deposional crust (cultivated). The semiempirical equation for cumulative infiltration correlated to the measured cumulative infiltration very well for both the calibration and the prediction data set. The coefficient of multiple determination was 0.997 for the cultivated furrows and 0.998 for the uncultivated furrows. Simulation studies were conducted to determine the possible use of this equation in furrow irrigation management.

Automated open- and closed-loop control systems can enhance the performance of irrigation delivery systems. This paper examines the response of the canal test cases developed by the ASCE task committee on canal automation algorithms to a particular anticipatory open-loop control technique, gate stroking. The performance of the ideal gate-stroking solution is compared with the performance of an approximate gate-stroking schedule that was generated by imposing practical constraints on the frequency and magnitude of the gate adjustments. Also analyzed were the performance of a nonanticipatory open-loop control scheme and the effect of model parameter uncertainties on the effectiveness of the control. For the test cases, the approximate gate-stroking schedules performed similarly to the ideal schedules. For two of the test cases, delivery performance was similar with and without anticipation, but was substantially different for the other two tests. The quality of the control degraded as a result of errors in model parameters, particularly in cases with incorrect check gate calibrations and submerged gate flows. Results point out the importance of combining open- and closed-loop control measures to improve the overall effectiveness of the control.

A simple water level controller for irrigation and drainage canals is proposed; the proposed controller has a master-slave structure where the slaves control the flow rates through the control structures. The master controller consists of PI-based controllers for feedback, and a decoupler and feedforward controller that are based on the inversion of a simple dynamic model of the canal system. The applicability of the controller is demonstrated in field experiments.

A general solution scheme for determining ground-water levels for channel/group-water systems with recharge is developed and verified. The analytical solution uses the Laplace transform method to solve a linearized form of the Boussinesq equation. Unlike other solutions, this scheme allows for both boundaries and sources/sinks to vary as a function of time and space. To verify the analytical scheme, three one-dimensional case studies of flow between two line sources in an unconfined aquifer were explored through a base run and a set of sensitivity analyses. These runs involved comparisons to MODFLOW and changes in the boundary conditions and dimensions. As noted, the flow equations were linearized about a point called the representative flow depth. A value of havg, defined as the average water depth between the initial and steady flow conditions, was used as the representative flow depth. Results of the proposed method matched very well with MODFLOW solutions for all times and locations using an optimal linearization point. In addition, using havg improved the solutions compared to those obtained previously.

Hydrological studies were conducted in a lateritic hillslope watershed of Kerala, a humid tropical region in India. The watershed characteristics, soil moisture properties, and hydrological processes were evaluated. The prominent mechanisms of runoff generation were identified as saturated through flow and saturated source areas. A 2D lateral saturated flow model linked with a vertical column model was developed to simulate these hydrological processes. The model with calibrated effective values of hydraulic conductivity and specific yield was found to be capable of predicting the hillslope hydrological processes.

The sorption behavior of atrazine (2-chloro-4-ethylamino-6-isopropylamino-s-triazine), a commonly used herbicide for corn, on intact soil columns was studied by incorporating a new two-stage sorption mechanism into PESTFADE, a pesticide fate and transport model. This mechanism takes into account intraparticle diffusion of pesticide into the soil matrix (also sometimes known as bound residues), the sorption capacity of soil, and a variable pesticide distribution coefficient K_d. The modified model's performance was verified by comparing simulated values with those obtained from an intact column study in the laboratory. The two-stage mechanism was also compared and contrasted with the conventional adsorption approach based on a constant K_d. Simulations with the two-stage mechanism indicated a closer agreement with measured values (deviations in the range of 5–65%) than that of the conventional adsorption approach (deviations in the range of 10–700%). Furthermore, it was found that simulated values were particularly sensitive to soil tortuosity τ, soil bulk density ρ, soil moisture content θ_w, labile sorption capacity θ_c, and intraparticle diffusion parameters.

Irrigation wells frequently discharge directly into canals. Upstream elbows, the pump head, or other pipe fittings may produce a distorted flow profile that is detrimental to the proper installation and operation of commonly available pipe meters. Before attempts to condition the flow with longer discharge piping or straightening vanes, it is desirable to know how distorted the flow profile really is. If this information can be provided, the meter technician can determine whether a correction in the meter coefficient will suffice, or if flow conditioning equipment is needed, or whether flow conditioning equipment, if already installed, is working effectively. An economical method of field evaluating the result of an installed meter in this compromised situation is described. The method uses a conveniently fashioned pitot-tube system that can be clamped to the pump discharge pipe. It is used to quickly detect the velocity at several points across the pipe diameter. Distorted profiles can be detected and measured. Pitot-tube systems have long been used in pipe flows. Most require that special taps be drilled in the outflow pipe of the well. Some use special double-tube constructions that are difficult to build using simple machine-shop procedures. This pitot impact tube, with its static pressure companion tube, can be constructed using common shop techniques and standard small pipe fittings.