Journal of Irrigation and Drainage Engineering

In this paper an experimental investigation was carried out to deduce an evaluating procedure of local losses due to the protrusion of emitter barbs into the flow in drip-irrigation lines. Local losses corresponding to different pipe-on line emitter systems were measured for different Reynolds number values. Each pipe-emitter system was characterized by an obstruction index (OI) summarizing the reduction of cross-sectional area of the pipe due to the emitter connection. A power relationship between a characteristic value of the α coefficient, expressing the local losses amount as a fraction of the kinetic height, and the corresponding OI index was deduced. Two evaluating procedures of OI were also compared: an analysis of photographs of the connections obtained by dissecting the pipe at the emitters and the use of a caliper to measure emitter protrusion dimensions. Only the first procedure makes it possible to obtain an estimating criterion of the α coefficient because it takes into account both the characteristics of the emitter connection and the deformation of the pipe surrounding the stem.

A procedure was developed to determine the maximum surface runoff volume (MSR) employing the constant rate of infiltration after prolonged wetting of the soil (f_c). This procedure can also be employed to determine a factor (H), which, associated with the land topography and the soil conservation system characteristics, is used to calculate the depth of the stored water in level terrace channels. This procedure is applicable to places where the rainfall intensity-duration-frequency relationship is known. Hence, it has been applied to the typical conditions of Cascavel, state of Paraná, Brazil. Graphs and equations relating the MSR and the H factor with the f_c are presented. The calculated values using this procedure were compared with those obtained by the U.S. Soil Conservation Service—USDA curve number method. The effects of f_c and of the return period on MSR values were analyzed.

A reliability problem in irrigation canal systems where the water demand fluctuates stochastically is examined. A flow model of open channel with control structures is developed to include the lateral withdrawal, in which the flow rate is suddenly changeable temporally and spatially. Discussion is focussed on the propriety of a steady flow surface profile for an averaged water demand pattern. Assuming that the temporal evolution of unsteady flow surface profile is a Markov process, the theory of statistics is applied. Since the probability density function is governed by the Fokker-Planck partial differential equation, evaluating the reliability that the disturbance of surface profile around the steady state is small enough, is reduced to solving the heat equation deduced from a geometrical consideration. The acquired concept is applied to the design problem of a reliable steady surface profile. Computations are performed through roughly two stages, i.e., the approximation of the diffusion tensor that constitutes the coefficient matrix of the governing equation using the flow model and the diagonalization of the diffusion tensor.

Discharge measurement in partially filled pipes, as occurs in sewage and drainage engineering, is considered with an improved device. The so-called pipe flume is suited for mobile discharge measurement either for a single discharge reading or for the determination of daily or weekly hydrographs. It can easily be mounted in commercially fabricated pipes, and sediment transport does not detract from its accuracy. The device has been extensively tested in a hydraulics lab and the device has an accuracy of ±5% in optimum field conditions. Simplifications compared to the original design include the head determination in the cylindrical container, by which surface fluctuations are practically removed, and effects of pipe slope are eliminated. A discharge-head equation is established for pipe flumes having a diameter larger than 200 mm, where effects of scale are negligible. The discharge-head equation accounts for the pipe filling and the constriction rate, as well as for the position relative to the pipe outlet section.

Simple, analytical approximations to the solution of the one-dimensional Boussinesq equation are obtained using a weighted residual method. The approach can be applied to both the recharging and the dewatering of an unconfined, homogeneous aquifer from a fully penetrating trench. Estimates for recharge, discharge, and the elevation of the water table are given by explicit algebraic expressions. Comparison with numerical solutions illustrates the accuracy of these new formulas.

Curve numbers (CNs) are developed from measured rainfall (P) and runoff (Q) data, yet there is no standard method for determining CN. The original method of CN determination used maximum annual events. Subsequent development treated measured P and Q data as frequency distributions. In this paper, derived frequency distributions are evaluated as another method for determining watershed CNs from measured data, treating P and Q data as separate frequency distributions. A Monte Carlo simulation showed the derived-distribution method gave fewer variable estimates of CN for a wide range of sample sizes than two other methods for CN estimation. CN estimates using measured data with the derived-distribution method agreed well with CN estimated by the asymptotic method for the watershed types tested. The derived-distribution and asymptotic methods were in agreement, and the other methods gave lower CN estimates for the “violent” watershed type. CN was indeterminate for the derived-distribution and asymptotic methods for “complacent” watersheds. The derived-distribution method has a potential for determining CNs when there are limited P and Q data.

An integrated irrigation-drainage design and management system is developed and applied to a hypothetical farm representative of the field conditions of the San Joaquin Valley (SJV), Calif. through computer simulations. The system is a departure from the traditional ways in which irrigation-drainage systems are designed and managed to satisfy not only the traditional agricultural objective (i.e., crop productivity), but also water-quality protection. The strategy is composed of a series of no-drainage and drainage cycles in which the former is an extended period in which drains are not operated; the latter is a limited period in which drains are allowed to release drainage water. The results of the computer simulations show that the integrated system can sustain crop productivity while reducing drainage water by 50–58% over a simulated eight-year period. It also leads to the overall improvement of the efficiency of the drains to intercept salt, thereby preserving current salt balance of traditional systems. A cost-benefit analysis has shown that the integrated system is economically more attractive than the traditional system.

The predictive canal operation method (PCOM) provides optimal real-time control of irrigation canals with incorporation of current and forecasted demands. PCOM utilizes an efficient, nonlinear, optimal control algorithm interacting with a fully dynamic, unsteady-flow hydraulic model. Optimal predictive controls are determined for all check structures and demand points along the canal, as well as the intake pump station, if one is present. Optimal control is performed with consideration of hydraulic conditions along the entire canal, as modeled by a Preissman-type implicit scheme for the complete St. Venant equations. The algorithm generates predictive control policies (anticipatory control) and system-wide feedback control under complex hydraulic conditions, including zero flow and closed gates. Equable distribution of shortages is achieved in cases of water supply deficiencies. PCOM is applied to Main Canal 3 of the Formoso H project, Bahia, Brazil, as a case study, and performs well under severe operational constraints. The computational efficiency of the algorithm allows implementation on microcomputer controllers for real-time use.

Alluvial channels, in the context of this paper, are unlined man-made channels with predetermined bed slopes used to convey water that carries sediment. An extremal hypothesis is presented, namely, an alluvial channel attains a stable width when the rate of change of unit stream power with respect to its width is a minimum. An easy-to-use width control parameter is presented and compared with a form of Lacey's silt factor. The hypothesis is tested on data from canals located in the Punjab and Sind provinces of Pakistan.

Research was conducted to estimate grass consumptive use and return flow (deep percolation) in urban lawn water use. Two types of small lysimeters were used—a drainage-type lysimeter of 40 cm diameter and 60 cm depth and a weighing-type lysimeter of 30 cm diameter and 60 cm depth. A large hydraulic weighing-type lysimeter of 1 m² surface area and 1.3 m depth was used as the reference for comparison. The amount of water application, deep percolation, and change in soil moisture content were measured for the 1992–1994 summer seasons, and evapotranspiration (ET) was calculated using a volume balance equation. The results suggest that the small lysimeters are of acceptable accuracy compared to large lysimeters for estimating evapotranspiration. The weighing-type small lysimeters appeared to be more consistent but underestimated evapotranspiration compared to the drainage-type lysimeters. The results for estimating deep percolation with the small lysimeters are not conclusive yet.